Nonspecific enhancement of host defenses against infection: experimental evidence of a new order of efficacy and safety.

: Enhancement of nonspecific host defenses against bacterial challenge has been a long-standing goal often thwarted by variable efficacy, inconsistent bioassay, and paradoxic immunosuppression. Muramyl dipeptide provides enhanced survival after intravenous challenge with less than 8 x 10(3) Klebsiella, as well as improved local control of infection at sites of intramuscular bacterial injection, with and without a surgical foreign body. No depression of host response was seen over wide ranges of doses and intervals. Muramyl dipeptide provides a new order of efficacy and safety and warrants continued careful assessment.