Descovy combines emtricitabine (Emtriva) and tenofovir alafenamide in 200mg/10mg and 200mg/25mg tablets. The choice of tablet strength to give is determined by the third antiretroviral given in combination with Descovy.
Emtricitabine is a nucleoside reverse transcriptase inhibitor and tenofovir alafenamide is a nucleotide reverse transcriptase inhibitor. Both are incorporated into viral DNA following absorption and metabolism, thereby disrupting HIV replication.
Tenofovir alafenamide, like tenofovir disoproxil (Viread), is converted to tenofovir in the body, but tenofovir alafenamide is metabolised and concentrated more efficiently in target cells than tenofovir disoproxil.
This means that lower doses of tenofovir alafenamide are needed to reach the same levels of tenofovir in target cells, potentially resulting in reduced risks of bone and renal toxicity.
Patients with severe renal dysfunction (creatinine clearance <30ml/min) or severe hepatic impairment (Child-Pugh Class C) should not be given Descovy. A thorough medication review is important before beginning treatment with Descovy as tenofovir alafenamide interacts with several types of drugs including anticonvulsants.
Common side-effects of emtricitabine/tenofovir alafenamide include diarrhoea, nausea and headaches, which affected 7%, 10% and 6%, respectively, of participants in clinical trials. Patients taking Descovy should be advised to seek medical advice if they experience joint aches, pain or stiffness, or movement difficulties, owing to the potential risk of osteonecrosis with combination antiretroviral therapy.
Tenofovir alafenamide was found to be non-inferior to tenofovir disoproxil when both were taken with emtricitabine in a double-blind phase III trial involving 668 patients across 78 North American and European sites. After 48 weeks, rates of virological success (defined as plasma HIV-1 RNA less than 50 copies/ml) were comparable between the two forms of tenofovir (difference 1.3% in favour of tenofovir alafenamide, 95% CI -2.5% to 5.1%).
In studies in treatment-naïve patients, emtricitabine and tenofovir alafenamide given with elvitegravir and cobicistat or with darunavir and cobicistat as a fixed-dose combination tablet (Rezolsta) was associated with smaller reductions in bone mineral density (as measured by hip and lumbar spine dual energy X-ray absorptiometry) and lower impact on renal safety parameters (eGFR, urine protein to creatinine ratio and urine albumin to creatinine ratio) than emtricitabine and tenofovir disoproxil given with elvitegravir/cobicistat or darunavir/cobicistat after 48 weeks of treatment.