Abstract

In as much as the immunomodulatory effects of opiates and cocaine are known to modify spontaneous host defenses against infection, we investigated the effects of morphine, pentazocine and cocaine on the time course of Friend virus infection in mice. Repeated i.p. injections with increasing doses of morphine hydrochloride (10-100 mg/kg for 10 days before infection, a dose regimen which induced tolerance to the acute antinociceptive effects of the drug, followed by 30 mg/kg for 14 days postinfection) did not increase the mortality due to Friend virus infection. This regimen did not significantly affect the immune response of infected mice assessed in terms of delayed hypersensitivity (ear thickness) and the hemagglutination assay. In contrast, a single challenge with a large dose of morphine (up to 300 mg/kg), which is not lethal in noninfected mice, increased mortality markedly (up to 100%) in infected mice when administered at day 14 or 21 postinfection. Repeated i.p. injections with pentazocine (50 mg/kg b.i.d. for 5 days before infection, followed by 30 mg/kg for 14 days postinfection) had no influence on mortality or immune responses in infected mice; similar results were obtained with a single high-dose injection (up to 100 mg/kg). Lastly, repeated i.p. injections of cocaine, using the same experimental procedure as that for pentazocine, decreased immune responsiveness and slightly increased mortality, whereas a single injection was devoid of lethal effect. These findings suggest that chronic opioid treatment does not lower host resistance to viral infection but that the latter could increase the toxicity of a single high dose of morphine.(ABSTRACT TRUNCATED AT 250 WORDS)