Anti-HIV Drug Updates -- Three Drugs on the Near Horizon
The most significant new information about anti-HIV drugs offered in Barcelona concerned those drugs that are either already available or which will soon be available. This includes new information about T-20 (now called enfuvirtide or Fuzeon) and atazanavir -- two drugs which will likely be approved within the next six months. Another new drug likely to be approved soon is FTC (Coviracil), a close relative of 3TC (lamivudine, Epivir), though its importance is less certain than that of enfuvirtide and atazanavir. Important new information was also released about tenofovir (Viread), a drug approved by the FDA late in 2001 (see article). Equally important were new observations about some older drugs, particularly the combination of ddI and d4T (see article). Many comparative studies of different drug combinations were also reported, offering new information about the relative value of a number of treatment strategies.
Since enfuvirtide represents the first of an entirely new class of drugs, it is of great interest to people who have developed resistance to all or most other classes of drugs. It will, of course, work best when combined with two or more drugs that are still active, but it has shown that it can help even when people are already resistant to most other anti-HIV therapies. Enfuvirtide's main limitation is that it cannot be made into a pill and therefore must be taken by injection twice daily. Using the drug properly is complex, as it comes in a powder that must be mixed with sterile water and then injected. The principle side effect of the drug is injection site reactions, which are seen in virtually all people taking it (though not to a degree that prevents them from using the drug). As the drug becomes more widely available, the manufacturer is providing training sessions for doctors throughout the country. The current expanded access program for the drug requires that doctors be trained before the drug is shipped. It is likely that some form of training will be required when the drug is approved by the Food and Drug Administration (FDA).
In the main studies submitted to the FDA, enfuvirtide was used in people who had previously developed resistance to all three classes of drugs and were in need of "salvage" treatment. At Barcelona, researchers reported on two such studies, called Toro 1 and Toro 2. All volunteers were given an "optimized" regimen composed of five to eight anti-HIV drugs and half were also given enfuvirtide. The "optimized regimen" was chosen individually for each person based on expert evaluation of resistance tests and prior anti-HIV drug history. Patient advocates applauded the study design because it closely approximated the real-world choices that people with advanced disease must face.
The main side effect reported in both studies was injection site reactions, which to some degree affected nearly 98 percent of the study volunteers. Not all such reactions, however, were serious. These reactions, while very unpleasant, caused only a small number people to drop out of the study. The study underlined the importance of careful training for both doctors and users in order to minimize such reactions and to maximize benefits.
While the results of Toro 1 and Toro 2 differ slightly, the basic picture is the same. In both, volunteers who received enfuvirtide on top of an optimized regimen fared much better than those receiving only the optimized regimen. In many if not most people, the drug was very likely the only fully active anti-HIV therapy in the mix. Still, the results are impressive, considering the challenge such "salvage" situations present. It is fair to say that enfuvirtide represents an important advance in the treatment of advanced HIV disease.
A small expanded access program for enfuvirtide is currently underway for people who have failed previous therapies. The program will provide drug for only about 600 people in the US. To sign up, doctors must fill out an application form over the internet and if accepted they will be required to take part in training as noted above. Although all currently available slots in the program were quickly taken, more may open up if drug supply increases. Also, not every person who gets accepted into the program actually goes on to use the drug. Therefore, some slots may become available between October 2002 and the expected approval date in mid-March of 2003. Applications for access are still being taken at www.T20EAP.com.
The small size of the program is also something of a warning that the company might be unable to meet the initial demand for the drug when it is approved. If so, there will likely be a staged rollout of the drug, focusing first on people with the most advanced disease.
Atazanavir is the newest member of the protease inhibitor class. It is expected to get FDA approval early in 2003 and is currently available in a large expanded access program. There are two main differences between atazanavir and other protease inhibitors. First, it is designed for once-daily dosing, making it easier to create a once-daily regimen that uses a protease inhibitor. Perhaps more importantly, it is the first protease inhibitor that does not appear to have a potentially harmful effect on cholesterol levels. In studies comparing atazanavir to nelfinavir (Viracept) in an otherwise common combination with d4T (stavudine, Zerit) and 3TC (lamivudine, Epivir), the group receiving atazanavir experienced no significant increase in cholesterol or triglyceride levels over 48 weeks of follow-up. Also, it appeared to at least equal the effectiveness of nelfinavir in suppressing HIV. While nelfinavir is generally considered to be among the less active PIs, it has commonly been used in comparison studies.
Another important study asked whether switching to atazanavir from another protease inhibitor would reverse the cholesterol changes caused by the other protease inhibitors. The study followed 346 people (217 men, 129 women) who had been in the earlier atazanavir vs. nelfinavir comparative study. Of the people who had previously used nelfinavir, 63 were changed to receive 400 mg of atazanavir (the lower of the two doses of atazanavir used in the prior study). People who had previously been assigned to receive either 400 mg of atazanavir were allowed to switch to 600 mg (still once daily). All volunteers continued to receive d4T and 3TC.
Twelve weeks after the 63 people were switched from nelfinavir to atazanavir, their cholesterol levels were measured again and compared to previous levels. Changing to atazanavir obviously had the desired effect of reducing cholesterol and triglyceride levels as shown in the table above. This indicates that, at least for the first 12 weeks, switching to atazanavir has a positive effect on cholesterol. Volunteers who either stayed on 400 mg atazanavir or switched to 600 mg experience no significant change in these measurements.
Unless other unforeseen side effects appear later in the study of atazanavir, the drug appears to represent an important advance in field of protease inhibitors. Only time will tell if long-term switching to atazanavir will help correct some of the fat redistribution problems experienced by people on protease inhibitors and nucleoside analogue drugs.
The expanded access program for atazanavir is quite liberal, requiring only evidence of failure on existing protease inhibitors or the presence of fat distribution problems. To apply for the program, have your doctor call 1-877-726-7327.
Emtricitabine is a new drug considered to be similar to 3TC. The drug's development has been painfully slow but has finally reached completion. The company making FTC, Triangle Pharmaceuticals, has submitted data to the FDA seeking accelerated approval for the drug.
While there is not much excitement about FTC because it so closely resembles 3TC, regulators and advocates alike must give the drug a fair hearing. Its one clear distinction from 3TC is that it is intended to be used once a day, which is an attractive feature for many people. If FTC is otherwise just a "me too" copy of 3TC, it is unclear whether it warrants either accelerated approval or expanded access. Triangle asserts that there are other important differences between FTC and 3TC, differences that they believe warrant more interest than the drug has been given.
In the earliest studies, people receiving FTC as single agent therapy (monotherapy) for 2 weeks achieved an average 2 log reduction in viral load. Although this finding comes from a small and uncontrolled study, it is still impressive, one that rivals any protease inhibitor and appears somewhat superior to 3TC. In laboratory studies, the drug appears to be 4 to 10 times more potent, by weight, than 3TC and more importantly, seems to be slower to develop resistance than 3TC. Rapid development of resistance is 3TC's Achilles heel.
One FTC study presented at the Barcelona conference followed the experiences of 468 people receiving treatment for the first time. They received either FTC or 3TC, along with d4T and either nevirapine (Viramune) or efavirenz (Sustiva). The main study endpoint was virologic failure, defined as either failing to achieve a viral load below 400 copies, or a return of viral load above 400 copies. Both groups had similar levels of virologic failure. The main benefit seen for FTC was that fewer of the people with virologic failure while on the drug had developed resistance to FTC, compared to those on 3TC who became resistant to that drug. This suggests that more of the failures could be attributed to the other drugs in the mix and that FTC was less likely to develop resistance. It is not clear whether this difference was statistically significant, nor is it clear whether it matters much since the overall failure rate on the two treatment regimens was the same.
In two well-controlled studies comparing FTC to 3TC, study authors concluded that the drug is equivalent to 3TC in terms of anti-HIV effectiveness.
In late September of 2002, the manufacturer announced interim results from a new study comparing a once-daily combination of FTC, efavirenz (Sustiva), and ddI-EC (Videx EC) against once-daily efavirenz and ddI-EC plus twice-daily d4T (Zerit). The study, which includes 571 people (85 percent male), is scheduled to run for 52 weeks, but the initial analysis looked at a mix of 24- and 52-week data accumulated to date.
The big picture seems to be that FTC is better proven in once-daily use and that it may be slower to develop resistance than 3TC, even though the failure rates of combinations using the drug are the same as when using 3TC. Larger or longer studies will be needed to determine whether FTC offers any practical advantage over 3TC. Whether all of this, taken together, warrants a special place for FTC, or expanded early access, is a decision that will have to be made by the FDA.
As PIP 35 goes to press, Gilead Sciences, maker of tenofovir, announced that it had purchased Triangle Pharmaceuticals, maker of FTC; Gilead also announced that it planned to create a new formulation of tenofovir that included FTC and tenofovir in a single pill.
This article was provided by Project Inform. It is a part of the publication Project Inform Perspective. Visit Project Inform's website to find out more about their activities, publications and services.