The development of d4T XR has only been partially successful with regard to its objectives. Improved pharmacokinetic properties allow its once daily dosing, and although it exhibits less mitochondrial toxicity it is still hampered by its development in a significant proportion of patients. This has caused its use to be almost residual in industrialised countries. As of now, d4T XR has not been made available in developing countries, despite the extended use of the immediate-release formulation. Currently, if there is no other chance of starting combination antiretroviral therapy, d4T XR could play a role in the treatment of HIV infection.

This study was conducted to characterize the multiple-dose tolerability, pharmacokinetics, and pharmacodynamics of ACT-077825, a new direct renin inhibitor, in healthy male subjects. In this single-center, double-blind, placebo-controlled, active-controlled (20 mg of enalapril), randomized multiple-ascending dose study, ACT-077825 was administered once a day. for 7 days in the 50-1000 mg dose range to sodium- and potassium-restricted subjects. ACT-077825 pharmacokinetics on days 1 and 7 were characterized by dose-proportional increases in Cmax and AUCτ. At steady state, accumulation was modest (1.5- to 1.7-fold). Enalapril caused an increase in plasma active renin concentration and plasma renin activity (PRA). ACT-077825 dose dependently increased active renin on days 1 and 7 and inhibited PRA dose dependently only on day 1. On day 7, the maximal PRA inhibition was attained after 250 mg of ACT-077825. In contrast to enalapril, ACT-077825 did not induce any consistent lowering effect on blood pressure when compared with placebo. Of the reported adverse events, diarrhea, headache, and postural dizziness were more frequent. The incidence of diarrhea was greater in the 1000-mg group and a dose of 500 mg of ACT-077825 was identified as the maximum tolerated dose. Overall, pharmacokinetic, pharmacodynamic, and tolerability profiles warrant the further investigation of ACT-077825 in patients with hypertension.

d4T use has declined sharply since 2006 to low levels in most regions; however, a low but persistent level of d4T use remains in Eastern Europe, where new d4T initiations post 2006 are also more common. The reasons for the regional differences may be multifactorial, but it is important to ensure that all clinicians treating HIV-positive patients are aware of the potential harmful effects associated with d4T.