Failure of zidovudine prophylaxis after exposure to HIV-1

To the Editor: In their case report of a failure of zidovudine prophylaxis after exposure to human immunodeficiency virus type 1 (HIV-1) (May 10 issue),¹ Lange and colleagues fail to mention what is perhaps the most likely explanation for the observed clinical failure: that zidovudine may lack efficacy as a prophylactic agent regardless of the dose or duration of therapy or the size or type of inoculum. Zidovudine has no virucidal activity against HIV-1, and as Lange et al. note, it may be ineffective in blocking cell-to-cell transmission or in completely inhibiting reverse transcriptase. These deficiencies may allow the establishment.