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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K

(Mark One)

For the fiscal year ended December 31, 2003

OR

For the transition period from             to            

Commission file number:  000-31615

DURECT CORPORATION

(Exact name of registrant as specified in its charter)

10240 Bubb Road

Cupertino, CA 95014

(Address of principal executive offices, including zip code)

Registrant’s telephone number, including area code:  (408) 777-1417

Securities registered pursuant to Section 12(b) of the Act:

None

Securities registered pursuant to Section 12(g) of the Act:

Common Stock, $0.0001 par value

(Title of Class)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period than the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    YES  x    NO  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    ¨

Indicate by check mark whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Act).     YES  x    NO  ¨

The aggregate market value of the voting stock held by non-affiliates of the registrant was approximately $84,845,570 as of June 30, 2003 based upon the closing sale price on the Nasdaq National Market reported for such date. Shares of Common Stock held by each officer and director and by each person who may be deemed to be an affiliate have been excluded. This determination of affiliate status is not necessarily a conclusive determination for other purposes.

There were 51,175,284 shares of the registrant’s Common Stock issued and outstanding as of February 27, 2004.

DOCUMENTS INCORPORATED BY REFERENCE

Part III incorporates information by reference from the definitive Proxy Statement for the 2004 annual meeting of stockholders, which is expected to be filed not later than 120 days after the Registrant’s fiscal year ended December 31, 2003.

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DURECT CORPORATION

ANNUAL REPORT ON FORM 10-K

FOR THE FISCAL YEAR ENDED DECEMBER 31, 2003

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PART I

Item 1.    Business.

Overview

We are pioneering the treatment of chronic diseases and conditions by developing and commercializing pharmaceutical systems to deliver the right drug to the right place in the right amount at the right time. Our pharmaceutical systems combine engineering innovations and delivery technology from the drug delivery and medical device industries with our proprietary pharmaceutical and biotechnology drug formulations. By integrating these technologies, we are able to control the rate and duration of drug administration as well as target the delivery of the drug to its intended site of action, allowing our pharmaceutical systems to meet the special challenges associated with treating chronic diseases or conditions. Our pharmaceutical systems can enable new drug therapies or optimize existing therapies based on a broad range of compounds, including small molecule pharmaceuticals as well as biotechnology molecules such as proteins, peptides and genes.

Our pharmaceutical systems are suitable for providing long-term drug therapy because they store highly concentrated, stabilized drugs in a small volume and can protect the drug from degradation by the body. This, in combination with our ability to continuously deliver precise and accurate doses of a drug, allows us to extend the therapeutic value of a wide variety of drugs, including those which would otherwise be ineffective, too unstable, too potent or cause adverse side effects. In some cases, delivering the drug directly to the intended site of action can improve efficacy while minimizing unwanted side effects elsewhere in the body, which often limit the long-term use of many drugs. Our pharmaceutical systems can thus provide better therapy for chronic diseases or conditions by replacing multiple injection therapy or oral dosing, improving drug efficacy, reducing side effects and ensuring dosing compliance. Our pharmaceutical systems can improve patients’ quality of life by eliminating more repetitive treatments, reducing dependence on caregivers and allowing patients to lead more independent lives.

Our lead product, the CHRONOGESIC^® (sufentanil) Pain Therapy System, intended for treatment of chronic pain, combines the DUROS^® technology, a proven and patented drug delivery platform we licensed for specified fields of use from ALZA Corporation (ALZA), a Johnson & Johnson company, with a proprietary formulation of sufentanil, a potent opioid currently used in hospitals as an analgesic. As of December 31, 2003, we have completed an initial Phase I trial, a Phase II clinical trial, a pilot Phase III clinical trial and a pharmacokinetic trial for this product. We do not currently have any on-going clinical trials with respect to this product and are engaged in implementing some necessary design and manufacturing enhancements to the CHRONOGESIC product. We anticipate that we will again re-start clinical trials to support regulatory approval of the product in the U.S. and other countries of the world commencing in the second half of 2004 after we have implemented the required design and manufacturing enhancements to the product. This product is aimed at the approximately $3 billion opioid market for the treatment of chronic pain and will compete with oral opioids, analgesic patches and external and implantable infusion pumps.

We are also developing a sustained release injectible product intended to treat post-operative pain which uses our SABER^™ delivery system and a local anesthetic. This product is designed to be administered around a surgical site after surgery to provide local analgesia for up to three days, which we believe coincides with the time period of the greatest need for post surgical pain control in most patients. Bupivacaine, the active agent for the product, is currently FDA-approved for use in hospitals as a local anesthetic. In 2003, we successfully completed a Phase I clinical trial for our post-operative pain product. The clinical trial was conducted in Europe

NOTE: CHRONOGESIC^®, IntraEAR^®, ALZET^®, SABER^™, DURIN^™ and MICRODUR^™ are trademarks of DURECT Corporation. LACTEL^® is a trademark of Absorbable Polymers International Corporation (formerly Birmingham Polymers, Inc.), a wholly owned subsidiary of DURECT Corporation. DUROS^® is a trademark of ALZA Corporation, a Johnson & Johnson company. Other trademarks referred to belong to their respective owners.

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and enrolled 12 normal, healthy subjects. The objectives of the clinical study were to determine the safety and tolerability of the SABER delivery system and the SABER-bupivacaine combination and to evaluate the pharmacokinetics of our SABER product versus current treatment methods.

We are also currently researching and developing pharmaceutical systems in a variety of therapeutic areas, including chronic pain, local post-operative pain, central nervous system disorders, cardiovascular disease and cancer based on our proprietary SABER^™, DURIN^™ and MICRODUR^™ drug delivery platform technologies, as well as based on the DUROS technology. Our SABER Delivery System is a patented controlled-release technology that can be formulated for systemic or local administration of active agents such as proteins and small molecules via the parenteral (i.e., non-oral) route. The potential advantages of the SABER system over other available injectable controlled release technologies include less burst upon injection, higher drug loading and greater ease of administration and manufacturing. In addition, we are exploring the use of our SABER system as the core vehicle for controlled release oral pharmaceutical products. Our DURIN technology consists of a polymer-based biodegradeable implant that enables parenteral delivery of drugs from several weeks to six months or more. Our MICRODUR technology consists of a biodegradable microparticulate controlled release injectable which can provide sustained release of drug from a few days to many months. The DUROS technology is a miniature drug dispensing pump that releases minute quantities of concentrated drug formulations in a continuous, consistent flow over months or years using an osmotic engine. The miniature pump, made out of titanium, can be as small as a wooden matchstick and can be implanted under the skin. We intend to continue to develop and acquire additional pharmaceutical systems technologies consistent with our objective of delivering the right drug to the right place in the right amount at the right time.

Industry Background

Chronic Diseases and Conditions

Although the pharmaceutical, biotechnology and medical device industries have played key roles in increasing life expectancy and improving health, many chronic, debilitating diseases continue to be inadequately addressed with current drugs or medical devices. Cardiovascular disease, cancer, neurodegenerative diseases, diabetes, arthritis, epilepsy and other chronic diseases claim the lives of millions of Americans each year. These illnesses are prolonged, are rarely cured completely, and pose a significant societal burden in mortality, morbidity and cost. The Centers for Disease Control estimates that the major chronic diseases are responsible for approximately 70% of all deaths in the U.S., and medical care costs for these conditions totaled more than $400 billion annually. Currently, more than 60% of total health care spending in the U.S. is devoted to the treatment of chronic diseases. Demographic trends suggest that, as the U.S. population ages, the cost of treating chronic diseases as a proportion of total health care spending will increase.

Current Approaches to Treatment

Drugs are available to treat many chronic diseases, but harmful side effects can limit prolonged treatment. In addition, patients with chronic diseases commonly take multiple medications, often several times a day, for the remainder of their lives. If patients fail to take drugs as prescribed, they often do not receive the intended benefits or may experience side effects, which are harmful or decrease quality of life. These problems become more common as the number of drugs being taken increases, the regimen of dosing becomes more complicated, or the patient ages or becomes cognitively impaired. It is estimated that only half of prescribed medicines are taken correctly.

The Pharmaceutical Industry.    The pharmaceutical industry has traditionally focused on the chemical structure of small molecules to create drugs that can treat diseases and medical conditions. The ability to use these molecules as drugs is based on their potency, safety and efficacy. Therapeutic outcome and ultimately the suitability of a molecule as a drug depends to a large extent on how it gets into the body, distributes throughout the body, reacts with its intended site of action and is eliminated from the body. However, small molecules can act in diverse tissues throughout the body resulting in unwanted side effects.

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Most drugs require a minimum level in blood and tissues to have significant therapeutic effects. Above a maximum level, however, the drug becomes toxic or has some unwanted side effects. These two levels define the therapeutic range of the drug. With conventional oral dosing and injections, typically a large quantity of drug is administered to the patient at one time, which results in high blood levels of drug immediately after dosing. Because of these high levels, the patient can be over-medicated during the period immediately following dosing, resulting in wasted drug and possible side effects. Due to distribution processes and drug clearance, the blood level of drug falls as time elapses from the last dose. For some duration, the patient is within the desired therapeutic range of blood levels. Eventually, the blood level of drug falls sufficiently such that the patient becomes under-medicated and experiences little or no drug effect until the next dose is administered.

When drugs are administered orally, transdermally or by injection, they are absorbed into the systemic circulation and distributed throughout the body. Because the drug is dispersed throughout the body, relatively large quantities are necessary to create the desired effect at the intended site of action. In addition, systemic administration of drugs in this fashion may result in unwanted side effects, because the drug has access to many tissues and organs in the body other than the intended site of action.

The Biotechnology Industry.    Over the past twenty years, the biotechnology revolution and the expanding field of genomics have led to the discovery of huge numbers of proteins and genes. Tremendous resources have been committed in the hope of developing drug therapies that would better mimic the body’s own processes and allow for greater therapeutic specificity than is possible with small molecule drugs. Unfortunately, this huge effort has led to only a limited number of therapeutic products. The proteins and genes identified by the biotechnology industry are large, complex, intricate molecules, and many are unsuitable as drugs. If these molecules are given orally, they are often digested before they can have an effect; if given by injection, they may be destroyed by the body’s natural processes before they can reach their intended sites of action. The body’s natural elimination processes require frequent, high dose injections that may result in unwanted side effects. As a result, the development of biotechnology molecules for the treatment of human diseases has been limited.

The Drug Delivery Industry.    In the last thirty years, a multibillion dollar drug delivery industry has developed on the basis that medicine can be improved by delivering drugs to patients in a precise, controlled fashion. Several commercially successful oral controlled release products, transdermal controlled release patches, and injectable controlled release formulations have been developed. These products demonstrate that the delivery system can be as important to the ultimate therapeutic value of a pharmaceutical product as the drug itself. However, to date, most drug delivery products deliver drug systemically and do not target delivery to the intended site of action. In addition, drug delivery products are generally limited to durations of one day for oral products and a maximum of one week for transdermal products and therefore may be less desirable for treating chronic diseases. Furthermore, oral and transdermal products are generally not capable of administering biotechnology agents such as proteins, peptides and genes.

The Medical Device Industry.    Advances in the field of medical device technology have dramatically improved device miniaturization and sophistication and allowed minimally invasive surgical access to remote locations within the body. For example, a coronary bypass patient can be treated with a stent in a procedure with a relatively short recovery, rather than with major surgery. Most devices, however, apply only mechanical solutions, rather than delivering chemical or biological agents.

The DURECT Solution: Pharmaceutical Systems

We are pioneering the treatment of chronic diseases and conditions by developing and commercializing pharmaceutical systems that will deliver the right drug to the right place in the right amount at the right time. By integrating chemistry and engineering advancements, we can achieve what drugs or devices alone cannot. Our pharmaceutical systems enable optimized therapy for a given disease or patient population by controlling the rate and duration of drug administration. In addition, if advantageous for the therapy, our pharmaceutical systems can target the delivery of the drug to its intended site of action.

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DURECT Pharmaceutical Systems Technology

DURECT’s pharmaceutical systems combine technology innovations from the drug delivery and medical device industries with proprietary pharmaceutical and biotechnology drug formulations. These capabilities can enable new drug therapies or optimize existing therapies based on a broad range of compounds, including small molecule pharmaceuticals as well as biotechnology molecules such as proteins, peptides and genes. We currently have four major technology platforms:

DUROS Technology

The technological foundation of our lead product, CHRONOGESIC, is the DUROS implant technology. The DUROS system is a miniature drug-dispensing pump made out of titanium which can be as small as a wooden matchstick. We have licensed the DUROS technology for specified fields of use from ALZA. The potential of the DUROS technology as a platform for providing drug therapy was demonstrated by the Food and Drug Administration’s approval in March 2000 of ALZA’s VIADUR^® product (leuprolide acetate implant), a once-yearly implant for the palliative treatment of prostate cancer, the first approved product to incorporate the DUROS implant technology. By leveraging this proven technology, we believe we can reduce our development risk and more rapidly introduce new products to the market.

The DUROS pump operates like a miniature syringe. Through osmosis, water from the body is slowly drawn through a semi-permeable membrane into the pump by salt residing in the engine compartment. This water fills the engine compartment and slowly and continuously pushes a piston to dispense minute amounts of drug formulation from the drug reservoir. The osmotic engine does not require batteries, switches or other electromechanical parts in order to operate. The amount of drug delivered by the system is regulated by the semi-permeable membrane’s control of the rate of body water entering the engine compartment and the concentration of the drug formulation.

The DUROS system has performance characteristics that cannot be matched by drug delivery pumps on the market today. First, the engine can generate sufficient pressure to deliver highly concentrated and viscous

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formulations. Second, the system can be engineered to deliver a drug formulation at the desired dosing rate with a high degree of precision, to less than 1/100th of a drop per day on a continuous basis. The titanium shell of the DUROS system protects the drug formulation from degradation by enzymes and clearance processes within the body. As a result, the DUROS system can store drugs for up to one year as they are being released into the body.

The DUROS system can be used for therapies requiring systemic or site-specific administration of drug. To deliver drugs systemically as in our CHRONOGESIC product, the DUROS system is placed just under the skin, for example in the upper arm, in an outpatient procedure that is completed in just a few minutes using local anesthetic. Removal or replacement of the product is also a simple and quick procedure completed in the doctor’s office.

To deliver drug to a specific site, we are developing proprietary miniaturized catheter technology that can be attached to the DUROS system to direct the flow of drug directly to a target organ, tissue or synthetic medical structure, such as a graft. Site specific delivery enables a therapeutic concentration of a drug to be present at the desired target without exposing the entire body of the patient to a similar dose. The precision, size and performance characteristics of the DUROS system will allow for continuous site-specific delivery to a variety of precise locations within the body.

By concentrating drug in proprietary formulations, we can store enough drug in our pharmaceutical systems to dose a patient for extended periods of time, for up to one year. Our proprietary formulations of traditional small molecule drugs are much more concentrated than those currently available on the market. Concentrated formulations allow our pharmaceutical systems to be significantly smaller than alternative drug delivery systems available today. We also believe that we can keep these formulations chemically and physically stable for extended periods of time at body temperature. Our formulation expertise, combined with the protection provided by the reservoir of the DUROS system, may allow for the stable storage and delivery of proteins, peptides, and other large molecule agents in a long-term continuous fashion, thus enabling the full therapeutic potential of a wide range of biotechnology compounds.

The SABER Delivery System

Controlled Release Injectable Dosage Forms

The SABER system is a patented controlled-release technology that can be formulated for systemic or local administration of active agents via the parenteral or oral route. We are researching and developing a variety of controlled-release products based on the SABER technology. These include injectable controlled release products for systemic and local delivery and oral products.

We believe that our SABER system can provide the basis for the development of a state-of-the-art biodegradable, controlled-release injectable. The SABER system uses a high-viscosity base component, such as sucrose acetate isobutyrate (SAIB), to provide controlled release of the drug. When the high viscosity SAIB is formulated with drug, a biocompatible solvent and other additives, the resulting formulation is liquid enough to inject easily with standard syringes and needles. After injection of a SABER formulation, the solvent diffuses away, leaving a viscous depot. Depending on how it is formulated, the SABER system can successfully deliver therapeutic levels of a wide spectrum of drugs from 1 day to 3 months from a single injection. Based on research and development work to date, our SABER technology has shown the following advantages:

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In 2003 we successfully completed a Phase I clinical trial of our most advanced injectable product based on the SABER Technology. In this clinical study, SABER formulations were safe and well-tolerated, and no significant side effects or adverse events were reported.

SABER Oral Dosage Forms

We also believe that the SABER technology can be used as the basis for controlled release oral technology, which can transform short-acting oral capsule dosage forms into controlled release oral products. Oral dosage forms based on the SABER technology may also have the added benefit of being less prone to abuse than other controlled release dosage forms on the market today.

In December 2002, we entered into an agreement with Pain Therapeutics Inc. under which we granted Pain Therapeutics, Inc. the exclusive right to develop and commercialize selected long-acting oral opioid products using the SABER system. The first product being developed under the collaboration is Remoxy^™, a novel long-acting oral formulation of the opioid oxycodone that utilizes our SABER technology and which is targeted to decrease the potential for oxycodone abuse. In January 2004, our partner Pain Therapeutics, Inc. began Phase I clinical testing of the Remoxy product.

The DURIN Biodegradeable Implant Technology

Our DURIN technology is a proprietary biodegradable implant that enables parenteral delivery of drugs from several weeks to six months or more using our Lactel^® brand polymers and co-polymers of lactic and glycolic acid. The DURIN technology can deliver a wide variety of drugs including small and large molecule compounds. Our proprietary implant design allows for a variety of possible delivery profiles including constant rate delivery. Because DURIN implants are biodegradable, at the end of its delivery life, what remains of the DURIN implant is absorbed by the body. DURECT is researching and developing products based on the DURIN technology for a variety of chronic disease applications.

The MICRODUR Biodegradable Microparticulate Technology

Our MICRODUR technology is a patented biodegradable microparticulate depot injectable. We have experience in microencapsulation of a broad spectrum of drugs using our Lactel^® brand polymers and co-polymers of lactic and glycolic acid. In our MICRODUR process, both standard and proprietary polymers are

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used to entrap an active agent in solid matrices or capsules comprising particles generally between 10 and 125 microns in diameter. Through suitable choice of polymers and processing, sustained release from a few days to many months can be achieved. As with the DURIN technology, MICRODUR particles degrade fully in the body after the active agent is released. Our range of experience extends from manufacture of the polymer raw material to process and product development, scale up and cGMP manufacture.

DURECT Strategy

Our objective is to develop and commercialize pharmaceutical systems that address significant medical needs and improve patients’ quality of life. To achieve this objective, our strategy includes the following key elements:

Focus on Chronic Debilitating Medical Conditions.    Many of the diseases that present the greatest challenges to medicine are chronic, debilitating diseases such as chronic pain, central nervous system disorders, cardiovascular disorders, cancer and degenerative neurological diseases. Our initial efforts will focus on using our versatile drug delivery platform technologies to develop products that address these diseases.

Minimize Product Development Risk and Speed Time-to-Market.    Initially, we intend to minimize product development risk and speed time-to-market by using our drug delivery platform technologies to administer drugs for which medical data on efficacy and safety are available. This strategy reduces much of the development risk that is inherent in traditional pharmaceutical product discovery. We anticipate that we can expand the medical usefulness of existing well-characterized drugs in several ways:

We anticipate that our products can be more rapidly developed at lower cost than comparable products that are developed purely based on chemical solutions to the problems of efficacy, side effects, stability and delivery of the active agent. We believe that our ability to innovate more rapidly will allow us to respond more quickly to market feedback to optimize our existing products or develop line extensions that address new market needs.

Enable the Development of Pharmaceutical Systems Based on Biotechnology and Other New Compounds.    We believe there is a significant opportunity for pharmaceutical systems to add value to therapeutic medicine by administering biotechnology products, such as proteins, peptides and genes. We believe our technologies will improve the specificity, potency, convenience and cost-effectiveness of proteins, genes and other newly discovered drugs. Our systems can enable these compounds to be effectively administered, thus allowing them to become viable medicines. We can address the stability and storage needs of these compounds through our advanced formulation technology and package them in a suitable pharmaceutical system for optimum delivery. Through continuous administration, the DUROS, SABER, MICRODUR and DURIN technology platforms may eliminate the need for multiple injections of these drugs. In addition, through the use of our proprietary miniature catheter technology or by precise placement of our proprietary biodegradable drug formulations, proteins and genes can be delivered to specific tissues for extended periods of time, thus ensuring that large molecule agents are present at the desired site of action and minimizing the potential for adverse side effects elsewhere in the body.

Expand Our Technology Platforms.    Beyond our four core technology platforms, we will continue to develop, license and acquire other technologies consistent with our objective of delivering the right drug to the right place in the right amount at the right time. For example, through our April 2001 acquisition of Southern

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BioSystems, Inc. (SBS), we acquired an experienced team of specialists and patented technologies in the field of controlled release injectables, implants, microspheres and biodegradable polymers. This acquisition, along with our internal development activities, has increased the breadth and depth of our technology platforms. We expect to continue to license or acquire technology that will complement our core capabilities.

Enable Product Development Through Strategic Partnerships.    We believe that selective partnering of our product development programs can enhance the success of our product development and commercialization, diversify our product portfolio and enable us to better manage our operating costs. We currently have the following product collaborations with third party companies:

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We expect to continue to partner select product development activities when it is advantageous to DURECT from a financial and risk management perspective.

Product Research and Development Programs

Our development efforts are focused on the application of our pharmaceutical systems technologies to potential products in a variety of chronic disease areas including pain, cardiovascular disease, CNS disorders and other chronic diseases. Our ongoing product research and development efforts in these areas are set forth in the following table:

Chronic Pain (Systemic)

Market Opportunity.    Chronic pain, defined as pain lasting 6 months or longer, is a significant problem associated with chronic diseases, including cancer and various neurological and skeletal disorders. Chronic nonmalignant pain affects as many as 34 million Americans annually. In addition, the National Cancer Institute estimates that 8.4 million Americans alive today have a history of cancer. About 1.2 million new cancer cases are expected to be diagnosed annually, and about 50%-70% of cancer patients experience chronic pain during the course of the disease. Sales of opioids for the treatment of malignant and nonmalignant pain exceed $3.0 billion.

Development Strategy.    We are developing the CHRONOGESIC (sufentanil) Pain Therapy System, a subcutaneous, implantable DUROS-based system that delivers sufentanil systemically at a constant rate for 3 months. This product is intended for patients with chronic pain that is stable and opioid responsive and results from a variety of causes. Sufentanil is an off-patent, highly potent opioid that is currently used in hospitals as an analgesic. If approved for marketing and sale, this product will provide an alternative to current therapies for the treatment of chronic pain such as pills and patches, as well as ensuring improved patient compliance and

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convenience. We will develop a family of dosage strengths, tailored to meet market needs. We have completed an initial Phase I clinical trial, a Phase II clinical trial, a pilot Phase III clinical trial and a pharmacokinetic trial for our CHRONOGESIC product.

We initiated our first pivotal Phase III clinical trial for the CHRONOGESIC product in June 2002. In August 2002, the FDA requested that we delay enrolling new patients in our Phase III clinical trial initiated in June 2002 until the clinical trial protocol is revised and approved by the FDA to provide for additional patient monitoring and data collection. These requested protocol changes were not in response to any observed patient safety or adverse event. We subsequently discontinued all patients from the clinical trial at our discretion in September 2002. Independently from the FDA’s request for protocol changes, in October 2002, we started to implement manufacturing process enhancements to the CHRONOGESIC product to permit terminal sterilization of the product and system design enhancements to prevent a premature shutdown in the delivery of drug prior to the end of the intended 3-month delivery period which was observed in a number of units utilizing the previous system design. We have stopped all clinical trials for the CHRONOGESIC product until the system design is completed. We anticipate that we will again re-start clinical trials to support regulatory approval of the product in the U.S. and other countries of the world commencing in the second half of 2004 after we have implemented the system enhancements to the product.

In November 2002, we entered into a development, commercialization and supply license agreement with Endo Pharmaceuticals Holdings Inc. (Endo) under which the companies will collaborate on the development and commercialization of our CHRONOGESIC product for the U.S. and Canada. In January 2004, we amended the agreement to take into account the delay in the CHRONOGESIC development program due to DURECT’s implementation of necessary design and manufacturing enhancements to the product. In connection with the execution of the agreement, Endo purchased 1,533,742 shares of newly issued common stock of DURECT at an aggregate purchase price of approximately $5.0 million. Under the terms of the agreement, as amended, we will be responsible for the CHRONOGESIC product’s design and development. For the period commencing January 1, 2004 until the earlier of January 1, 2005 or the commencement of a specified clinical trial, Endo will fund 25% of the ongoing development costs for the CHRONOGESIC product in the U.S. and Canada excluding system redesign costs and pharmacokinetic trials necessitated by any system redesign up to an aggregate amount of $250,000 for the period. Commencing on January 1, 2005 or, if earlier, the commencement of a specified clinical trial, Endo will fund 50% of the ongoing development costs and will reimburse us for a portion of our prior development costs for the product upon the achievement of certain milestones. Development-based milestone payments made by Endo under this agreement could total up to $52 million. In addition, under the agreement, Endo has licensed exclusive promotional rights to the CHRONOGESIC product in the U.S. and Canada. Endo will be responsible for marketing, sales and distribution, including providing specialty sales representatives dedicated to supplying technical and training support for CHRONOGESIC therapy and will pay for product launch costs. We will be responsible for the manufacture of the CHRONOGESIC product. We will share profits from the commercialization of the product in the U.S. and Canada with Endo based on the financial performance of the CHRONOGESIC product. Based on our projected financial performance of the product in the U.S. and Canada, we anticipate that our share of such profits from commercialization of the product will be approximately 50%.

In addition to our development efforts on the CHRONOGESIC product, in December 2002, we entered into an exclusive agreement with Pain Therapeutics Inc. (Pain Therapeutics) to develop and commercialize on a worldwide basis selected long-acting oral opioid products using the SABER system. The agreement also provides Pain Therapeutics with the exclusive right to commercialize products developed under the agreement on a world-wide basis. In connection with the execution of the agreement, Pain Therapeutics paid us an upfront fee. We will receive payments upon the achievement of certain development and regulatory milestones, payments for research and development expenditures, as well as royalties based on product sales. The first product being developed under the collaboration is Remoxy^™, a novel long-acting oral formulation of the opioid oxycodone that utilizes our SABER technology and which is targeted to decrease the potential for oxycodone abuse. In January 2004, our partner Pain Therapeutics, Inc. began Phase I clinical testing of the Remoxy product.

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Local Post-Operative Pain

Market Opportunity.    More than 60% of patients who undergo surgery experience moderate to extreme-post operative pain. In the United States, over 25 million patients are afflicted with post surgical pain annually. The current standard of care for post surgical pain includes oral opiate and non-opiate analgesics, transdermal opiate patches and muscle relaxants. While oral analgesics can effectively control post surgical pain, they commonly cause side effects such as drowsiness, constipation and cognitive impairment. Effective pain management can be compromised if patients fail to adhere to recommended dosing regimens because they are sleeping or disoriented. The majority of post surgical pain can be localized to the incision site. Post surgical pain can be treated effectively with local anesthetics; however, the usefulness of these medications is limited by their short duration of action. In general, post-operative pain is either undertreated or poorly treated.

Development Strategy.    We are developing a sustained-release formulation of a local anesthetic using our SABER delivery system for the treatment of post surgical pain. The physician would administer this product at the time of surgery. Placed in the tissues immediately adjacent to the surgical site, this formulation is designed to provide sustained regional analgesia from a single dose. We believe that by delivering effective amounts of a potent analgesic to the location from which the pain originates, adequate pain control can be achieved with minimal exposure to the remainder of the body, and hence minimal side effects. The duration of local delivery of the anesthetic by the product is expected to be a few days, which coincides with the typical timeline by which post surgical pain resolves in most patients. We are currently conducting preclinical studies on this product.

In 2003 we successfully completed a Phase I clinical trial for our post-operative pain product. The clinical trial was conducted in Europe and enrolled 12 normal, healthy subjects. The objectives of the clinical study were to determine the safety and tolerability of the SABER delivery system and the SABER-bupivacaine combination and to evaluate the pharmacokinetics of our SABER product versus current treatment methods. Additional clinical and pre-clinical studies are planned in 2004.

Alzheimer’s Disease

Market Opportunity.    Alzheimer’s disease is an incurable, neurodegenerative disorder that affects over 4 million Americans. This disease typically leads to progressive memory loss, impairments in behavior and language, and physical deterioration. The market potential for Alzheimer’s disease treatments is estimated to be in excess of $10 billion.

Development Strategy.    In July 2002, we entered into a development and commercialization agreement with Voyager Pharmaceutical Corporation (Voyager). Under the terms of the agreement, we will collaborate with Voyager to develop a product using our DURIN technology to provide a sustained release therapy based on Voyager’s patented method of treatment of Alzheimer’s disease. The agreement also provides Voyager with the right to commercialize the product on a worldwide basis. We will receive payments upon the achievement of certain development and regulatory milestones, payments for research and development expenditures, as well as royalties based on product sales.

Central Nervous System Disorders

Market Opportunity.    Millions of people suffer from chronic diseases and disorders of the central nervous system (CNS), including brain and spinal cord tumors, chronic pain, psychosis, epilepsy, spasticity, spinal meningitis, Parkinson’s disease, and multiple sclerosis. The following are some therapeutic opportunities that we are pursuing in this area:

It is estimated that 180,000 new brain tumors are diagnosed in the United States every year. In addition, approximately 350,000 patients are living with primary brain tumors, of which, about 25% are malignant. Current treatments for CNS tumors include radiation, resection and chemotherapy. Treatment success rates vary

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by tumor type, but are generally low, and the risk of side effects or disability is high. It is generally recognized that improvements in treating primary metastatic brain tumors are needed, particularly for those which are inoperable.

Schizophrenia, a disease of the brain that manifests itself through multiple signs and symptoms involving thought, perception and behavior, is another CNS disorder estimated to affect about 2.5 million patients in the U.S.; worldwide, the incidence is about 250 million. Patients typically begin exhibiting symptoms early in life and the illness is usually severe and long lasting, requiring lifelong treatment. Adherence to prescribed drug regimens is recognized as a significant treatment obstacle in the schizophrenic population. Although it is estimated that 50% of patients in the U.S. are either untreated or under treated, the aggregated sales of antipyschotic medications in 2002 exceeded $5.7 billion. Opportunities exist to apply our pharmaceutical systems for treatment of these and other CNS disorders.

Development Strategy.    We are developing the DUROS platform technology in combination with various catheter systems for targeted treatment of select CNS disorders. We are also developing our biodegradable platform technologies for systemic and targeted delivery of drugs to treat select CNS disorders.

We also currently have a collaboration with the Johns Hopkins University, Department of Neurology/Neurosurgery, exploring the feasibility of treating tumors of the brain stem by site specific delivery of a chemotherapeutic agent directly to the tumor via a DUROS system attached to a catheter. The program is currently in preclinical development studies in primates. We view this development program as a proof-of-concept application of the DUROS and catheter technologies to treat CNS disorders. Once we have demonstrated proof-of-concept, our long-term plan is to use the DUROS platform with other therapeutic agents to develop products for a broader range of CNS disorders.

In addition, we are conducting preclinical research on a SABER-based injectable controlled release product to deliver a potent antipsychotic agent in a controlled fashion, with a goal to deliver medication for 30 days from a single injection.

Cardiovascular Disease

Market Opportunity.    Cardiovascular disease, principally heart disease and stroke, accounts for 40% of all deaths, or 960,000 fatalities, annually in the U.S. About 58 million Americans, roughly 25% of the population, are currently living with some form of cardiovascular disease. The aggregate annual cost of cardiovascular disease in the U.S., including treatment and lost productivity, is estimated at $274 billion.

Ischemic heart disease, one of the major forms of cardiovascular disease, is the leading cause of death worldwide. Existing treatments for ischemia, or insufficient blood flow to the heart muscle, include cardiovascular bypass, angioplasty and the use of cardiovascular stents and similar medical devices. While effective, these treatments are invasive, and in roughly 40% of patients, ischemia returns within 2 years. There is a need for less invasive and more long lasting treatments for ischemic heart disease.

Development Strategy.    In collaboration with the University of Maastricht in The Netherlands, we are working to develop methods for treating ischemic heart disease and other chronic cardiovascular diseases through continuous delivery of drugs to the pericardial sac of the heart, a thin membrane that envelops the heart. To date, our research in animal models suggests that ischemic heart disease may be treated by the induction of new blood vessel growth as a way of regenerating normal blood flow to the heart and thereby restoring function to the diseased heart. Our research data showed that the delivery of a proprietary angiogenic factor directly to the pericardial sac of a test animal resulted in the growth of new blood vessels and increased bloodflow in the heart. Should we choose to develop and commercialize a product using such proprietary angiogenic factor or other proprietary agent, we may be required to obtain a license to use such agent in our product. Any required licenses may not be available to us on acceptable terms, if at all. See “Factors that May Affect Future Results—We may be required to obtain rights to certain drugs.”

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Asthma/Allergic Rhinitis

Market Opportunity.    Asthma is a serious, chronic, potentially life-threatening condition that affects approximately 20 million people in the U.S.. Allergic rhinitis (seasonal allergies) is the fifth most common chronic disease in the U.S., and affects as many as 40 million people in the U.S.. Sales of asthma and allergic rhinitis treatments exceeded $5 billion in 2000.

Development Strategy.    We are researching and developing a product for the treatment of asthma and allergic rhinitis utilizing one of our proprietary drug delivery platforms. Cromolyn sodium, a non-steroidal anti-allergy medication, is an FDA-approved drug for the management of mild-to-moderate persistent asthma and is recommended for early intervention and daily anti-inflammatory therapy. Cromolyn sodium has an excellent safety profile, and its position in asthma therapy is well-established. In 2002, we completed an initial clinical feasibility study where we infused the drug intravenously to test the efficacy of delivery of cromolyn sodium when delivered parenterally (i.e., not by inhalation as the drug is conventionally administered). We anticipate that we will be pursuing additional clinical testing of this product concept.

ALZET Business

We currently make and sell the ALZET^® product on a worldwide basis. We market the ALZET product through a direct sales force in the U.S. and through a network of distributors outside the U.S.

The ALZET product is a miniature, implantable osmotic pump used for experimental research in mice, rats and other laboratory animals. These pumps are neither approved nor intended for human use. ALZET pumps continuously deliver drugs, hormones and other test agents at controlled rates from one day to four weeks without the need for external connections, frequent handling or repeated dosing. In laboratory research, these infusion pumps can be used for systemic administration when implanted under the skin or in the body. They can be attached to a catheter for intravenous, intracerebral, or intra-arterial infusion or for targeted delivery, where the effects of a drug or test agent are localized in a particular tissue or organ.

We acquired the ALZET product and assets used primarily in the manufacture, sale and distribution of this product from ALZA in April 2000. We believe that the ALZET business provides us with innovative design and application opportunities for potential new products.

Absorbable Polymers International Corporation (API)

Absorbable Polymers International Corporation (API), formerly known as Birmingham Polymers Inc., an Alabama corporation, is a wholly-owned subsidiary of DURECT that designs, develops and manufactures for pharmaceutical and medical device clients a wide range of standard and custom polymers based on lactide, glycolide and caprolactone under the Lactel^® brand. These materials are manufactured and sold by API directly from its facilities in Birmingham and Pelham, Alabama and are used by DURECT and other API customers for a variety of controlled-release and medical-device applications, including several FDA-approved commercial products. After the acquisition of Absorbable Polymers Technologies, Inc (APT) in August 2003, Birmingham Polymers, Inc. (BPI) changed its name to API. BPI was a wholly-owned subsidiary of SBS when we acquired SBS on April 30, 2001. BPI became a wholly-owned subsidiary of DURECT when SBS was merged with and into DURECT on December 31, 2002.

API has approximately 10 employees and operates from a leased facility located in Pelham, Alabama.

Marketing and Sales

In general, we intend to establish strategic distribution and marketing alliances for our pharmaceutical systems. We recognize that pharmaceutical companies have established sales organizations in markets we are

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targeting. We plan to leverage these sales organizations to achieve greater market penetration for our products than we could on our own. Because our first products combine drugs for which medical data on efficacy and safety are available with a proven technology platform, we believe we have the flexibility to enter into these alliances at a later stage of clinical development, when the product development risk is diminished, in order to retain greater economic participation. We may also establish our own sales force when strategically or economically advantageous.

We market and sell our ALZET product in the U.S. through a direct sales force, and we have a network of distributors for this product outside of the U.S.

Customers

A substantial portion of our product revenues is derived from sale of the ALZET product line. Until such time that we are able to bring our pharmaceutical systems to market, if at all, we expect this trend to continue. Since our acquisition of the ALZET product line in April 2000, one customer accounted for 8%, 11% and 11% of our total revenue in 2003, 2002 and 2001, respectively. We also receive revenue from collaborative research and development arrangements with our strategic partners.

Manufacturing

The process for manufacturing our pharmaceutical systems is technically complex, requires special skills, and must be performed in a qualified facility. For our CHRONOGESIC product, we subcontract to third parties the manufacture of components of the DUROS system, which we then assemble. In 2001, we completed the construction of a flexible manufacturing facility to produce product for our clinical trials required for regulatory approval and market launch of our CHRONOGESIC product and to serve as a pilot facility for additional DUROS-based products under development. In 2002, we completed qualification and validation of this facility and used it to make clinical supplies for the Phase III trial that was initiated in June 2002 and subsequently discontinued. In addition, we are evaluating alternative strategies to meet our long-term commercial manufacturing needs.

We manufacture our ALZET product in a leased facility located in Vacavill