Scientists are developing an anti-AIDS pill that can be taken before sex and prevent transmission of the deadly disease.
The successful development of such a treatment would be controversial because it raises ethical questions about the circumstances in which the pill should be taken.
Experts in the disease, which claimed two million lives last year, are involved in scientific trials on antiretroviral drugs that already used to prevent transmission of AIDS from infected mothers to their babies during birth.
Scientists are hopeful that similar protection can be offered during sex.
Three trials of antiretroviral drugs are underway around the world. A report published in the Lancet claims they are “showing great promise” as experts meet in Mexico City for the International Conference on AIDS.
More research has to be done on the side-effects of the pill and the development of resistant strains of HIV before it is made available.
Controversy is bound to arise over who should take the pill and for what reasons. Globally, use would probably have to be restricted to those at greatest risk from AIDS such as sex workers or injecting drug users.
The pill could also have a major impact on the lifestyles at a time when experts have observed that promiscuity is on the rise.
“The party scene involving multiple sexual partners is definitely back in London and probably in most European cities,” said Sheena MCormack, a specialist in HIV prevention and reader in clinical epidemiology at Imperial College London, said.
“There is metrosexual mixing involving gay, bisexual and some heterosexual cases. We estimate new HIV infections in gay men are running at three per cent a year.”
She added: “People could pop a pill on a Friday night and be covered for a whole weekend.”
The trials involve 2,400 drug injectors in Thailand, 1,200 heterosexual men and women in Botswana and 3,000 homosexual men in America, Africa and Asia.
Experiments on primates suggest that the drugs are effective and can prevent the disease being passed. But their success in humans has yet to be proved, the Lancet report by Nancy Padian of Women’s Global Heath Imperative, San Francisco, said.
The trials use tenofovir, a drug currently used to treat AIDS, with a combination of other drugs.
Tenofovir (Trade name Viread) is an anti-HIV drug approved by the FDA (In October of 2001) to be used in combination with other HIV fighting medications. Viread belongs to a new class of drugs called Nucleotide Reverse Transcriptase Inhibitors (NtRTI). These are related to Nucleoside Reverse Transcriptase Inhibitors (NRTI) like zidovudine (AZT, Retrovir). The body converts Viread into a chemical that prevent HIV from reproducing in uninfected cells, but it does not help cells that have already been infected with the virus. As people with HIV lose CD4 cells - one of the immune system’s main defenses - they become more likely to get infections and illnesses.
Currently available anti-HIV drugs like AZT need three separate chemical steps before they are active. Viread needs only two chemical reactions (phosphorylation) to occur before it can start working. Partly due to this unique chemical feature, Viread also carries a “negative charge”, allowing it to stay in the cells where it is active for a longer period. As a result, Viread only needs to be taken once a day.
Viread was approved based on two clinical trials involving 736 people with an average CD4 cell count of about 400. These volunteers had taken anti-HIV medications for an average of five years. They were having difficulty suppressing HIV with their current combination therapies. Based on genotypic resistance test results, about 94% of the volunteers had at least one NRTI (like AZT) resistant strain of HIV.
Volunteers in Trial 902 had an average of 5012 viral load (range 52-575,000) at the start of the trial. Viread was added to existing combination therapies using variously: didanosine (DDI, Videx), lamivudine (3TC, Epivir), indinavir (Crixivan), efavirenz (Sustiva), and lopinavir/ ritonavir (Kaleatra). After 24 weeks, 19% of the volunteers were able to get their viral load below 400. 11% were able to lower it to less than 50.
In Trial 907, participants started off with a lower average viral load of 2340 (range 50-75,900). After 24 weeks, 40% of the volunteers were able to get their viral load below 400. 19% were able to lower it to less than 50. At the end of both trials, Volunteers had an average increase of 11 CD4 cells.
Even though these results have shown Viread’s ability to lower and suppress HIV levels in the blood, it has not been shown to significantly increase CD4 cell levels. This might be due to the fact that these trials were conducted with people who had been on combination therapy for a while and had fewer CD4 cells to work with.
Since the drug’s approval, other trials involving people who have not previously taken anti-HIV medications have demonstrated that Viread is also effective as a first line treatment.
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