Background:  The fusion inhibitor enfuvirtide (ENF) has been a successful cornerstone of salvage therapy for patients with multidrug-resistant HIV. The integrase inhibitor raltegravir (RAL) offers another option for a novel drug class, with the advantages of easier administration and improved tolerability.

Methods:  All patients at a single clinic whose plasma viral load was <50 copies/mL and who had treatment-limiting injection site reactions on an ENF-containing regimen were offered a switch to RAL 400 mg orally twice daily, while the rest of their regimen was unchanged. RAL was obtained through the Special Access Program of Health Canada. Viral load, CD4 cell counts, and adverse events were followed according to standard clinical practice.

Results:  RAL was commenced before July 20, 2007 in 29 patients (1 female) aged 34 to 61 years (median 50). They had received ENF for 7 to 75 months (median 27.5) and had viral load of <50 copies/mL for 1 to 72 months (median 24) before starting RAL. CD4 cell counts and fractions were 90 to 770/mm³ (median 375) and 4 to 43% (median 17%), respectively, at the time of the switch. Concomitant medications included 1 to 4 (median 3) nucleosides or nucleotides, 0 to 1 NNRTI (etravirine n = 3; efavirenz n = 2; nevirapine n = 1), and 1 to 2 ritonavir-boosted protease inhibitors (PI) (1 PI n = 21; 2 PI n = 8). Viral load remained <50 copies/mL in all patients at all time-points measured:  month 1 (n = 21), month 2 (n = 13), month 3 (n = 9), and month 4 (n = 7). The new regimen was well-tolerated and resolved implementation status report (ISR) -related problems. Between months 1 and 2, 3 patients experienced adverse events:  peripheral neuropathy and diarrhea (n = 1); exacerbation of depression (n = 1); and new diagnosis of prostate cancer (n = 1). None of these was considered related to RAL. No new laboratory abnormalities were identified.

Conclusions:  Changing from ENF to RAL within a virologically suppressive regimen appears to be safe and effective over the short term among patients with multidrug-resistant HIV.