The FDA acted after issuing a draft guidance document in May 2004 encouraging manufacturers to develop co-formulated regimens. Specifically they were responding to a controversy about the co-formulated pills produced by several Indian generic drug makers that are widely used in treatment programs in the developing world. These medications have been evaluated and "prequalified" by the World Health Organization (WHO) for purchase by private and government sponsored treatment programs. The generic all-in-one pills (nevirapine, AZT and d4T is one common combo) are preferred by programs operating in resource-poor regions because adherence is better, education and dispensing is simplified, and procurement problems are minimized. Also, the generics typically cost only about a tenth what their branded counterparts do. But representatives of the multi-national pharmaceutical industry, perceiving a threat to their markets, have been fostering the impression that these drugs are of inferior quality and have convinced the U.S. government to only buy drugs that have received FDA approval. With $15 billion promised by President Bush for his international AIDS program, known as PEPFAR (President's Emergency Plan for AIDS Relief), the drug companies have a powerful motivation to keep the generic makers out of the loop. But the practical result of their obstruction will be far fewer people receiving treatment and suboptimal outcomes for those who do benefit from the U.S.-sponsored programs.
The FDA, to its credit, stepped into the middle of this argument and has offered a fast track for generic makers to receive FDA review of their products, even if they are not approvable in the U.S. due to patent issues. While many feel that the WHO prequalification process is sufficiently stringent and that FDA review is superfluous, given the political climate and the power of the pharmaceutical lobby, it is unlikely that U.S. dollars will become available without this extra step. Even so, the flap over prequalification of generics may prove to have been a feint, and the U.S. will simply continue to funnel money to the multi-national companies.
The company also says it is working on a new, more stable formulation of ritonavir that will not require refrigeration. The new process is said to employ Abbott's proprietary melt-extrusion (Meltrex) technology, whereby drug molecules are stabilized in a solid dispersion within a special polymer that dissolves at a controlled rate. This could overcome one of the biggest limitations to using Kaletra in resource-poor settings, which has been the need for a cold distribution chain. But don't expect this new product very soon. Typically, pharmaceutical companies start to introduce new formulations only when their patent protections begin to sunset. This allows them extend the market life of their branded products. Abbott's Kaletra patents don't begin to expire until 2012.
One dark cloud over the potential for using Kaletra in other parts of the world: a recent report found resistance to Kaletra developing fairly rapidly in a treatment-naive woman in South Africa who had Subtype C HIV.
Now Trimeris has announced that it is beginning studies of a needle-free injection system for the current generation of Fuzeon, and is moving forward with studies using the drug in a once-a-day regimen, although these improvements may not become generally available until 2006 or after. Trimeris is also pressing forward with the search for second-generation fusion inhibitors with better resistance profiles and more convenient dosing (possibly once a week) and says it may be able to announce a drug candidate by the end of 2004.
The company doesn't believe that the coming wave of oral CCR5 inhibitors will make Fuzeon obsolete. Since up to 40 percent of people with advanced HIV disease will have an X4-using virus that will not be susceptible to the new drugs, Trimeris thinks there will continue to be a place for fusion inhibitors in this population. They cite in vitro studies that show dramatic synergy between Fuzeon and other entry inhibitors when used in combination, and suggest that viral suppression could be achieved with only one tenth of the current dose of the drugs when used individually -- at one tenth the cost. One needle-free shot, once a week, costing only $40 may be just the thing to turn Trimeris' fortunes around.
One fallback position (though it will likely slow enrollment) may be to require Fuzeon for every trial participant as a "safety net" to catch any virus that achieves coreceptor binding. A bonus to this is suggested by a bit of recently reported data that found Fuzeon may also block X4 coreceptor usage, in addition to mucking up fusion.
Also, BI has announced that a clinical trial with alovudine (MIV-310), an NRTI targeting multiresistant HIV has recently begun. Continuing BI's foray into salvage therapy, alovudine (say it with a Cockney accent) was licensed from Medivir in July 2003. The trial has been designed to evaluate short-term antiviral activity and safety in patients with HIV resistant to multiple NRTIs. The trial is a dose finding study in patients infected with HIV resistant to multiple NRTIs and with detectable viral load. They will be treated for one month with alovudine added to their standard regimens.
Now Gilead is working on a prodrug concept that goes one -- if not two or three -- steps further. The company's scientists have invented a chemical modification that specifically targets a drug to lymphocytes -- precisely the kind of cells that HIV infects. The prodrug modification is clipped by an enzyme specific to these cells and only turns into its active form once it is in or around lymphatic tissue. Details of the enzyme involved and how all this works have not yet been published. So far Gilead has tested its prodrug concept with a modified form of tenofovir (Viread), which, in a short term clinical trial, effectively lowered viral loads with only a fraction of the usual dose required.
Gilead is also developing a new protease inhibitor that uses the prodrug trick. The chemical modification is tailored to let the prodrug be easily absorbed in the gut, and also let it dodge premature clearance by the CYP 3A4 enzyme system in the liver, so no boosting should be required. The active form of the drug would only get down to business after it is modified in its target cells, where it would be trapped. If this all pans out -- and the PI version has yet to be tested in people with HIV -- protease inhibitor therapy may take a quantum leap in terms of activity, tolerability and pill burden. The inherent efficiency of the prodrug system means that much smaller dosages are required, which could open the door for a three-in-one, PI-based, single pill regimen. The specificity for lymphocytes might mean that collateral toxicity to other cell types could be greatly reduced. In lab tests, the PI appears to have a similar resistance profile to that of tipranavir, which is active against many HIV strains that are multi-PI resistant. It is yet to be determined if the prodrug will reach infected cells in reservoirs or sanctuary sites in the body. Despite the exciting potential, it may be another year before we know if this prodrug technology will survive the boot camp of Phase I trials, and then another year or two until it becomes available, most likely in a tenofovir version first.
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