New & experimental HIV treatments

Maraviroc approval delayed in the US

Edwin J. Bernard
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US Food and Drug Administration (FDA) approval for Pfizer’s maraviroc (Celsentri) has been delayed due to “outstanding questions”, according to a Pfizer press release. Maraviroc was expected to have received full approval from the FDA on June 20th following a unanimous recommendation by a key advisory committee to grant accelerated approval.

Maraviroc is still expected to become the first licensed drug from a novel class of antiretrovirals known as CCR5 inhibitors that prevent HIV’s entry into CD4 cells by blocking the CCR5 co-receptor on the cell’s surface.

However, instead of approval, the FDA yesterday issued an ‘approvable letter’. This usually means that although the FDA believes that a drug is worthy of approval, it requires additional information in order to approve it.

Glossary

Food and Drug Administration (FDA)

Regulatory agency that evaluates and approves medicines and medical devices for safety and efficacy in the United States. The FDA regulates over-the-counter and prescription drugs, including generic drugs. The European Medicines Agency performs a similar role in the European Union.

CCR5

A protein on the surface of certain immune system cells, including CD4 cells. CCR5 can act as a co-receptor (a second receptor binding site) for HIV when the virus enters a host cell. A CCR5 inhibitor is an antiretroviral medication that blocks the CCR5 co-receptor and prevents HIV from entering the cell.

receptor

In cell biology, a structure on the surface of a cell (or inside a cell) that selectively receives and binds to a specific substance. There are many receptors. CD4 T cells are called that way because they have a protein called CD4 on their surface. Before entering (infecting) a CD4 T cell (that will become a “host” cell), HIV binds to the CD4 receptor and its coreceptor. 

CD4 cells

The primary white blood cells of the immune system, which signal to other immune system cells how and when to fight infections. HIV preferentially infects and destroys CD4 cells, which are also known as CD4+ T cells or T helper cells.

The Pfizer press release provided little information on what additional information is required by the FDA, or the timeline required to address the outstanding issues: “We continue our discussions with the FDA to address outstanding questions and finalize the product labeling as soon as possible,” it said.

However, a Pfizer spokesperson told aidsmap.com that although “we cannot comment specifically on our discussions with the FDA...we are working quickly to resolve outstanding questions in order to obtain approval. Although we can't speculate on exact timings we are committed to finalising the product labelling as quickly as possible.”

Maraviroc has been available in 30 countries via an expanded access program (EAP) since early 2007. In addition, more than 2,000 individuals worldwide have received or are currently receiving treatment with maraviroc through clinical trials.

The Pfizer spokesperson noted that the US delay is unlikely to affect approval elsewhere, including the European Union. “Pfizer is currently in the process of submitting marketing applications around the world to make maraviroc available. Regulatory agencies are independent bodies, and decisions made by the US FDA should not impact ongoing marketing applications outside of the US,” she added.

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