Patients taking Selzentry, in combination with Combivir (zidovudine/lamivudine) and selected by an enhanced sensitivity tropism test to screen patients, experienced a 68 per cent rate of virologic suppression to undetectable levels, according to the Merit ES (Reanalysis of the Merit Study with the Enhanced Trofile Assay) reanalysis presented at the 48th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC)/ 46th Annual Meeting of the Infectious Diseases Society of America (IDSA) in Washington DC, USA.

Merit ES is a reanalysis of 48-week efficacy and safety data from the Merit (Maraviroc versus Efavirenz Regimens as Initial Therapy) study following retesting of screening samples using the newly launched enhanced sensitivity Trofile assay. This therefore represents a subset of the Merit 48-week primary analysis population. The enhanced sensitivity test was not available at the time of the Merit study and is the only version of Trofile currently available.

In the Merit ES reanalysis 68 per cent of patients in the Selzentry arm, and 68 per cent of patients in the efavirenz arm - a current standard of care - achieved suppression of the virus to undetectable levels (less than 50 copies/ml). When the criterion of less than 400 copies/ml was used, the results were 73 per cent with Selzentry, and 72 per cent with efavirenz.

"The results of Merit ES are exciting as they show that with an enhanced sensitivity tropism assay the efficacy rate of Selzentry shown in Merit with the original Trofile assay is improved further," said Michael Saag, Professor of Medicine and director of the Center for AIDS Research at the University of Alabama at Birmingham, who presented the results. "These findings are important for patients and physicians and offer guidance for clinical practice with the only version of Trofile currently available."

In the Merit ES population, 14.2 per cent of patients taking efavirenz discontinued due to adverse events compared to 4.2 per cent of patients taking Selzentry. This was largely driven by a greater number of cases of CNS toxicity (13 vs. 2), rash (9 vs. 0), and tuberculosis (6 vs. 1) in the efavirenz arm versus the Selzentry arm. In Merit ES, there were fewer discontinuations in the Selzentry arm due to lack of efficacy than the rate seen for the Merit full study population. In Merit ES, 9.3 per cent of patients taking Selzentry discontinued due to lack of efficacy, compared to 4 percent of patients taking efavirenz.

The enhanced sensitivity Trofile assay is able to detect dual/mixed or CXCR4-tropic variants of the HIV virus when they are present in patients in ?0.3 percent of the total viral population, a 30-fold improvement in sensitivity.

Selzentry is referred to as Celsentri in countries outside the U.S. Discovered by Pfizer scientists in 1997, Selzentry is an oral medicine that blocks viral entry to human cells. Rather than fighting HIV inside white blood cells, Selzentry prevents the virus from entering uninfected cells by blocking its predominant entry route, the CCR5 co-receptor.