Abacavir Struggles to Carve Out Niche
Studies of abacavir suggest no distinguishing benefit for abacavir compared to other currently available marketed therapies. The drug is clearly active against HIV in a variety of different patient groups; however, no evidence suggests clinically greater utility than existing nucleoside analogue combinations -- especially in nucleoside pre-treated patients. Approval of abacavir will offer patients another "choice" in antiretroviral therapy, but data so far suggest that the choice offered is not a functionally important one; rather, it is more like the choice between a blue pill and a red one. Furthermore, use of abacavir has been associated with a potentially serious hypersensitivity response which seems to resolve rapidly with permanent treatment discontinuation.
Although Glaxo has conducted a number of studies of abacavir, two key groups of studies stand out: studies that compare the combination of AZT+3TC to the combination of AZT+3TC+abacavir (Guess what? Three Glaxo drugs are better than two!) and studies that evaluate the virologic effects of abacavir in combination with amprenavir, Glaxo's protease-in-development. Additional on-going boutique-style studies are evaluating the quadruple combination of AZT+3TC+abacavir+amprenavir. If Glaxo's goal is to establish simultaneous administration of four Glaxo products as the standard-of-care for HIV infection, then approval of abacavir at this point could well be regarded by the company as the next step toward that aim. But until the quadruple-combination is thoroughly evaluated, patients have little reason to use abacavir following the drug's approval.
All this raises questions about on-going regulatory policies regarding approval of new drugs. While Glaxo has technically met the accelerated approval requirement that its drug demonstrate "preliminary evidence of efficacy," the regulations also require that drugs receiving accelerated approval demonstrate properties that existing therapies do not have. Abacavir has not met this standard. Consequently, advocates for people with HIV should think long and hard about the wisdom of bringing "me too" drugs to the market under reduced standards of safety and efficacy. It is worth asking whether the benefit of having an unremarkable drug like abacavir on the market outweighs the increased risks to patients of marketing a drug whose safety and efficacy have not been well-characterized. Ultimately, this may be a case in which it is best to let the market sort out available therapies. But in doing so, physicians and patients should be aware that existing double-nucleoside combinations may be just as useful as abacavir, and at substantially lower prices.