Gilead Sciences is developing a fixed-dose co-formulation of two of its reverse transcriptase inhibitors, emtricitabine [Emtriva™] and tenofovir disoproxil fumarate [Viread®], for once-daily dosing in combination with other antiretrovirals for the treatment of HIV infection. Each co-formulated tablet will contain 300mg of tenofovir disoproxil fumarate and 200mg of emtricitabine.Emtricitabine [Emtriva™] is a nucleoside reverse transcriptase inhibitor (NRTI) with demonstrated potent activity against HIV and hepatitis B virus (HBV). It was first approved in the US by the FDA in July 2003 and is indicated for adults aged ≥18 years. Safety and effectiveness in paediatric patients have not been established. In antiretroviral-treatment-experienced patients, the use of emtricitabine may be considered for adults with HIV strains that are expected to be susceptible to the drug as assessed by genotypic or phenotypic testing. The recommended dose of emtricitabine is one 200mg capsule daily, with or without food.In the European Union, emtricitabine is indicated in combination with other antiretroviral agents for the treatment of HIV in adults and children, where it is also licensed as an oral 10 mg/mL solution. The oral solution is for use in infants older than 4 months, children and patients unable to swallow hard capsules, and patients with renal impairment who require dose reduction.Tenofovir disoproxil fumarate [Viread®] is a nucleotide reverse transcriptase inhibitor that is indicated in combination with other antiretroviral agents for the treatment of HIV-1 infection in treatment-experienced patients. The drug was first approved in the US in October 2001, followed by further approvals in the European Union, Australia, Iceland, Brazil, Canada and Switzerland. The drug has been launched in all these countries. In February 2003, the EMEA's advisory committee adopted a positive opinion to extend the indication of tenofovir disoproxil fumarate in all 15 member states to include the product's use in antiretroviral-naïve HIV-infected patients.In July 2003, Japan Tobacco signed an agreement with Gilead for the commercialisation of tenofovir disoproxil fumarate and emtricitabine and the future co-formulation of these two drugs within Japan. Under the terms of the agreement, Japan Tobacco will be submitting an application to the Japanese Ministry of Health, Labour and Welfare for regulatory approval of tenofovir disoproxil fumarate and emtricitabine.On 15 March 2004, Gilead announced the submission of a New Drug Application (NDA) to the US FDA and a Marketing Authorisation Application (MAA) to the EMEA for marketing approval of the fixed-dose co-formulation of emtricitabine and tenofovir disoproxil fumarate. The MAA will be reviewed under the centralised procedure, which, when finalised, will provide one marketing authorisation in all 25 member states of the enlarged European Union.[1]Gilead anticipates launching the combination pill on the US market early in 2005. Regulatory filings for marketing approval in Japan by Japan Tobacco are also expected during 2004.In August 2003, Gilead announced that enrolment had begun in a 48-week phase III study (Study 934) evaluating the efficacy of a once-daily regimen of Viread®and Emtriva™ versus Combivir®. The open-label, multicentre trial will enrol up to 500 treatment-naive, HIV-infected patients in the US and Europe. Patients in one arm will receive Viread®300mg, Emtriva™ 200mg and efavirenz 600mg once daily. Patients in the comparator arm will receive Combivir®(lamivudine 150mg/zidovudine 300mg) twice daily and efavirenz 600mg once daily.[2]