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Raltegravir (RAL, Isentress, formerly MK-0518) 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) on 12 October 2007, the first of a new class of HIV drugs, the integrase inhibitors, to receive such approval.
In December 2011, it received FDA approval for pediatric use in patients ages 2–18, taken in pill form orally twice a day by prescription with two other antiretroviral medications to form the cocktail (most anti-HIV drugs regimens for adults and children use these cocktails). Raltegravir is available in chewable form, but because the two tablet formulations are not interchangeable, the chewable pills are only approved for use in children two to 11. Older adolescents will use the adult formulation.
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.
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.
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, due to the highly mutagenic nature of HIV.
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.
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." 
In January 2013, a Phase II trial was initiated to evaluate the therapeutic benefit of raltegravir in treating multiple sclerosis (MS). The drug is active against Human Endogenous Retroviruses (HERVs) and possibly Epstein-Barr Virus, which have been suggested in the pathogenesis of relapsing-remitting MS.
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.
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- HIV Antiretroviral Agents in Development
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- Drug against AIDS could be effective against herpesvirus
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- Manufacturer's website
- MK-0518 at Aidsmedscom[dead link]
- Integrase Inhibitor Raltegravir (MK-0518) Doubles HIV Suppression in Treatment-Experienced Patients (aidsmap 28 February 2007)
- RMK-0518 Abstract from CROI 2007
- Interim Results From Phase II Study Of MK-0518
- World patent covering the potassium salt
- Raltegravir Pharmacokinetics