Failures of zidovudine postexposure prophylaxis

Since 1990, 11 cases of failure of zidovudine (ZDV) postexposure prophylaxis (PEP) for human immunodeficiency virus (HIV) exposure have been reported among healthcare workers (HCWs) around the world. In these cases, ZDV was begun 30 minutes to 8 days (median 1.5 hours) postexposure, at doses of 600-1,200 mg/day (median 1,000 mg/day) for 8-54 days (median 21 days). Five additional failures of ZDV PEP have been reported among non-HCWs exposed to an inoculum of HIV-infected blood larger than what would be expected from a needlestick. These non-HCW cases include one blood transfusion, one suicidal self-inoculation, one assault on a prison guard with a needle-syringe, and two instances of accidental intravenous infusion of HIV-infected blood or blood components during nuclear medicine procedures. One possible reason for these failures of ZDV PEP is that the transmitted strains of HIV may have had reduced sensitivity to ZDV. Collectively, these case reports indicate that if ZDV is protective as PEP, any protection afforded is not absolute.