2. TDF Litigation

TDF Litigation Before the California Supreme Court

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This is intended for US audiences only.


Plaintiffs’ lawyers have brought lawsuits in California state court seeking to impose the following new legal obligation on a manufacturer selling a beneficial, non-defective product: to continue researching and developing a completely different product if that new product would be an improvement over the existing product.

The California Supreme Court has agreed to determine whether such a legal obligation actually exists under California law. On May 1, 2024, it granted Gilead’s petition asking it to review an earlier decision by the California Court of Appeal, which would have imposed this new legal obligation across all fields of innovation and manufacturing. The importance of this case to innovation, public health, and the ability to serve people has been underscored by a wide range of groups—from patient advocacy organizations to technology and other innovation-based businesses—that have filed amicus letters and briefs urging the California court to reject this new theory of liability.

Plaintiffs’ counsel represents individuals who took medications made with tenofovir disoproxil fumarate (TDF) to treat HIV. Plaintiffs acknowledge that these medicines are not defective. But, they nevertheless argue that the TDF medicines caused bone, kidney, and/or tooth injuries. Plaintiffs do not criticize Gilead for not properly warning of these side effects; all agree that these potential side effects were fully and properly disclosed. Rather, plaintiffs claim that Gilead had a legal obligation to continue researching and developing a different drug—tenofovir alafenamide (TAF)—and market it sooner than it did based on the theory that TAF-based medicines are less likely to cause these same side effects.

The underlying merits of plaintiffs’ allegations, which Gilead continues to dispute vigorously, are not at issue in this appeal. Gilead received FDA approval for its first TDF-based medicines in 2001. Around the same time, Gilead obtained FDA approval to begin testing TAF in humans. In 2004, Gilead stopped TAF development because it had not distinguished itself from TDF, which had already been on the market for years and had a proven safety and effectiveness profile. Gilead instead focused its resources on developing combination medicines itself to be effective, safe, and well tolerated. Gilead instead focused its resources on developing combination medicines containing TDF so that people living with HIV could take a single, once-a-day pill rather than the complex and complicated cocktail of numerous different medicines they had previously been required to take. Plaintiffs allege that Gilead “knew” TAF was safer than TDF in 2004 and should be liable for stopping its development. However, the evidence shows that the long-term safety of TAF was unknown and impossible to predict in 2004, when Gilead stopped TAF development in favor of further developing TDF-based medications. Gilead started looking into TAF again in 2010, and, after five years of additional research and development and clinical trials, received FDA approval to market TAF-based medicines in 2015.

Gilead is proud that, today, both TDF- and TAF-containing medicines remain approved by the FDA, are recommended in the U.S. Department of Health & Human Services HIV treatment guidelines, and help treat and prevent HIV in millions of people. Gilead is committed to continue driving innovation to meet patient needs and, ultimately, help end the HIV epidemic.

The products at issue here are two classes of lifesaving, FDA-approved medicines that, in combination with other medicines, can be used for treating HIV and other diseases — tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF) —both manufactured by Gilead Sciences.

Gilead researched, developed, and satisfied the rigorous FDA approval process to bring five separate TDF-based medicines to market between 2001 and 2012.

With regard to TAF-based medicines, Gilead started looking into TAF in the late 1990s, but stopped that research in 2004. The only study of TAF in humans at that time involved 20 patients taking TAF for two weeks, which found no safety improvement over TDF. When Gilead stopped TAF development, TDF was already approved both by itself and in a combination tablet together with another HIV medicine (emtricitabine/TDF), for the treatment of HIV in combination with other antiretrovirals. Since then, consistent with FDA guidance and requests from the patient community at the time, Gilead has developed additional TDF-based medicines for HIV treatment, including TDF-based complete single tablet regimens.

In 2010, Gilead started studying TAF again as a possible additional treatment option for the aging population of individuals taking HIV medicines. It took five more years of clinical trials and additional research to demonstrate the safety and effectiveness profile of TAF at treating HIV and to receive FDA approval to start selling TAF-based medicines. To be clear, the evidence shows that the long-term safety of TAF was unknown and impossible to predict in 2004, when Gilead stopped TAF development in favor of further developing TDF-based medications.

If not overturned, the Court of Appeal’s decision could have widespread, negative ramifications across all fields of innovation and manufacturing. It could disincentivize innovation and discourage manufacturers from investigating and developing ways to improve products. As with Gilead’s early research into TAF, this work could form the basis for lawsuits targeting their earlier, non-defective products.

If the California Supreme Court affirms the lower court’s decision, the new liability rule could undermine the way in which companies develop new products and discourage them from looking for ways to improve existing products.

The California Supreme Court granted Gilead’s petition for review in May 2024.

Briefing for the California Supreme Court began in July 2024 and is expected to continue into late 2024.

The Court will then set a date for oral argument; there is no set timeframe for the Court to do so.

Given the potential widespread effects of this new legal theory, the case has drawn attention from other companies, legal scholars, the pharmaceutical industry, health policy experts, and patient advocates—all of whom are concerned about the negative impact this new legal obligation would have on innovation, public health and the ability to serve people and patients.

In November 2024, in support of Gilead’s briefing on this matter before the California Supreme Court, 12 separate amicus briefs representing 67 signatories, were filed:

Companies (across industries):

Trade & Civil Justice Groups:

Academics/Experts:

In March 2024, in support of Gilead’s petition for review by the California Supreme Court, 14 separate amicus letters, representing 50 signatories, were filed.

Over the course of the litigation, editorial boards, legal scholars and public health experts have weighed in on the adverse implications of this new legal theory. These include:

This page is intended to share information on the TDF litigation only and is not for product promotion.
For full Prescribing Information for Gilead medicines, please see www.gilead.com/medicines.