"In most trials where HIV drugs go head to head, they usually end with one being as equally effective as the other. This is the first time that one protease inhibitor drug combination has been found to work better than another in patients who haven't received treatment before," says Dr. Sharon Walmsley, associate professor of medicine at U of T and senior scientist at Toronto General Hospital, University Health Network. Walmsley is lead author of a paper to appear in the June 27 issue of The New England Journal of Medicine. "The new drug combination is superior in inhibiting the virus and it's easier for patients to take. We also found that patients did not develop resistance to the drug, a major factor in HIV treatment."
The human immunodefficiency virus is a type of retrovirus that attacks the body's immune system. An enzyme called the protease enables the HIV virus to mature and replicate itself. One class of anti-retroviral drugs used to treat HIV is protease inhibitors, which work by blocking the protease thereby halting the replication process. They are typically used in combination with another class of anti-retroviral agents called reverse transcriptase inhibitors that hamper an earlier stage of HIV replication.
In the double-blind trial, the researchers tested 653 HIV-infected adults from 13 countries who had not previously received anti-retroviral therapy. Walmsley and her colleagues tested the new drug (a lopinavir-ritonavir combination, which is essentially two protease inhibitors in one) against nelfinavir (the most common protease inhibitor used in Canada). Both sets of patients also received two other anti-HIV agents generally taken with protease inhibitors.
At the end of the 24- and 48-week periods, more patients using the new lopinavir-ritonavir combination were able to suppress the amount of virus in their blood to under 50 copies per millilitre, a level that doctors and researchers aim for when starting therapy, says Walmsley.
"Ritonavir is being used as what we call a 'booster,'" she explains. "Ritonavir slows lopinavir from being metabolized in the body and, as a result, increases the amount of lopinavir in the blood stream many times higher. Getting the levels higher makes the drug far more potent and prolongs its effectiveness. This boosting of protease inhibitors is a whole new concept in HIV therapy."
For current non-boosted protease inhibitors on the market, patients must be extremely regimented about taking their medication on a regular schedule because the levels of drug in the body are barely above those needed to kill the virus. If patients do not take their drugs right on schedule - for example, three pills three times a day every eight hours - the drug level could decrease, thereby allowing the virus to grow and resistance to the drug could occur. In contrast, the lopinavir-ritonavir combination boosts drug levels and prolongs the half-life of the inhibitor, offering a more convenient and forgiving regimen for patients - with three pills taken twice a day.
In addition to greater potency, no patients with virologic failure on the lopinavir-ritonavir combination showed evidence of resistance to the drug compared to the nelfinavir group, in which 33 per cent of failing patients developed resistance.
"Two main barriers to treatment are resistance to the drug and adherence to a therapy schedule," notes Walmsley. "With effective therapy, we anticipate that about 60 to 70 per cent of patients will have their virus level below 50 copies per ml at the end of one year. And while 60 per cent is good, we can do better, and that's where new strategies and treatments come in to make them stronger and easier for patients to take."
Walmsley cautions, however, that the lopinavir-ritonavir combination is not without side effects. General problems like nausea and diarrhea were roughly the same between the two drugs, and only three per cent of patients had to stop their treatment because of side effects. However, the researchers found that patients using lopinavir-ritonavir exhibited more abnormal lipids or fats in the blood, which are potential risk factors for heart disease.
Walmsley conducted this research with Drs. Barry Bernstein, Martin King, Anthony Japour, Scott Brun and Eugene Sun of Abbott Laboratories, who funded the research; Jose Arribas of Servico VIH-Medicina Interna II, Hopital Universitario, LaPaz, in Madrid, Spain; Gildon Beall of Harbor UCLA Medical Center in California; Peter Ruane of Tower Infectious Diseases in California; Margaret Johnson of Royal Free Hospital in London, England; David Johnson in Johannesburg, South Africa; Richard Lalonde of Royal Victoria Hospital in Montreal; and with the help of 93 investigators and their research teams in the participating centres.
The lopinavir-ritonavir combination, known commercially as Kaletra, has been approved for conditional use in Canada and the United States. The drug is now under review by the U.S. Food and Drug Administration for full approval.
Department of Medicine
U of T Public Affairs