Raltegravir

Raltegravir (MK-0518, brand name Isentress) is an antiretroviral drug produced by Merck & Co., used to treat HIV infection. It received approval by the U.S. Food and Drug Administration (FDA) in October 2007, the first of a new class of HIV drugs, the integrase inhibitors, to receive such approval.

Mechanism
Raltegravir targets integrase, an HIV enzyme that integrates the viral genetic material into human chromosomes, a critical step in the pathogenesis of HIV. The drug is metabolized away via glucuronidation.

Dosage
Raltegravir is taken orally twice daily. Doses of 200, 400, and 600 mg have been studied.

At the 2007 Conference on Retroviruses and Opportunistic Infections, researchers presented Phase III data showing that 77% of patients taking the 400 mg dose of raltegravir plus other antiretroviral drugs reached HIV viral loads below 400 copies, nearly twice as many compared with a control group.

Indications
Raltegravir was initially approved only for use in individuals whose infection has proven resistant to other HAART drugs. However, in July 2009, the FDA granted expanded approval for Raltegravir for use in all patients. As with any HAART medication, raltegravir is unlikely to show durability if used as monotherapy.

Efficacy
In a study of the drug as part of combination therapy, raltegravir exhibited potent and durable antiretroviral activity similar to that of efavirenz at 24 and 48 weeks but achieved HIV-1 RNA levels below detection at a more rapid rate. After 24 and 48 weeks of treatment, raltegravir did not result in increased serum levels of total cholesterol, low-density lipoprotein cholesterol, or triglycerides.

Research
Raltegravir significantly alters HIV viral dynamics and decay and further research in this area is ongoing. In clinical trials patients taking raltegravir achieved viral loads less than 50 copies per millitre sooner than those taking similarly potent Non-nucleoside Reverse Transcriptase Inhibitors or Protease Inhibitors. This statistically significant difference in viral load reduction has caused some HIV researchers to begin questioning long held paradigms about HIV viral dynamics and decay. Research into raltegravir's ability to affect latent viral reservoirs and possibly aid in the eradication of HIV is currently ongoing.

Research results were published in the New England Journal of Medicine on July 24, 2008. The authors concluded that "raltegravir plus optimized background therapy provided better viral suppression than optimized background therapy alone for at least 48 weeks."

Research on human cytomegalovirus (HCMV) terminase proteins demonstrated that Raltegravir may block viral replication of the herpesviruses.

Tolerability
Raltegravir was generally well tolerated when used in combination with optimized background therapy regimens in treatment-experienced patients with HIV-1 infection in trials of up to 48 weeks' duration.