Methadone: antimicrobial activity and interaction with antibiotics.

We studied the effect of methadone, alone and in combination with antimicrobial agents, on two strains each of Staphylococcus aureus, Pseudomonas aeruginosa, and Serratia marcescens isolated from blood streams of parenteral drug abusers with bacterial endocarditis. Methadone has its own antibacterial effect, although at supraphysiological concentrations, and is even synergistic with antimicrobial agents against some organisms. Thus, methadone does not interfere with the antibacterial effects of antibiotics in vitro.