Virologic and Lipoprotein Changes after Halving Ritonavir Boosting in HIV-Infected Patients Stabilized on Once-Daily Fosamprenavir plus Abacavir/Lamivudine

Background: The effect of reducing ritonavir boosting doses on the efficacy and safety of fosamprenavir-based regimens has not been well studied. Methods: In a 52-week, phase 4, open-label, single-center pilot study, 26 antiretroviral-naive, HIV-infected patients with viral loads >1000 copies/mL received induction with fosamprenavir/ritonavir 1400 mg/200mg plus abacavir/lamivudine 600 mg/300mg once daily for 28 weeks. Patients achieving a viral load <50 copies/mL at week 28 were given maintenance therapy for 24 subsequent weeks with half the ritonavir dose (100 mg) plus the usual fosamprenavir, lamivudine, and abacavir doses. Results: The study population (n = 26) was diverse regarding sex (14 females/12 males) and race (16 black, 10 white). Baseline median viral load was 4.93 log10 copies/mL and CD4+ count 110/mm3. Of 12 induction/maintenance completers, 10 (83%) achieved viral loads <50 copies/mL by maintenance-week 24. Median CD4+ count increased from 110/mm3 at baseline to 292/mm3 at induction-week 28 and to 296/mm3 at maintenance-week 24. The incidence of adverse events at maintenance-week 24 did not differ from that at induction-week 28 (P > 0.05). Median fasting total-cholesterol, LDL-cholesterol, and triglycerides remained below NCEP cut-off levels. Baseline/induction-week 28/maintenance-week 24 median total-cholesterol was 130/177/183 mg/dL, LDL-cholesterol 78/107/114 mg/dL, HDL-cholesterol 33/41/43 mg/dL, total-cholesterol: HDL-cholesterol ratio 3.9/4.3/4.3, and triglycerides 93/145/119 mg/dL. During induction, total VLDL/chylomicron, LDL, and HDL particles increased; during maintenance, VLDL/chylomicron particles decreased, but LDL and HDL particle concentrations did not notably change. Conclusions: Reducing ritonavir boosting from 200 mg to 100 mg once daily in HIV-infected patients stabilized on once-daily fosamprenavir/abacavir/lamivudine resulted in maintenance of virologic suppression, enhanced CD4+ count, and improved triglycerides.