Comparative review of two new wide-spectrum penicillins: mezlocillin and piperacillin.

The antimicrobial spectra, pharmacokinetics, tissue penetration, side effects, clinical trials and indications, dosage, and cost of mezlocillin (Mezlin) and piperacillin (Pipracil), two new semisynthetic beta-lactam penicillins, are reviewed. Both mezlocillin and piperacillin are active against a wider range of bacteria than previously available penicillins, but their spectra are not identical. Piperacillin is more active than mezlocillin against Pseudomonas aeruginosa; their activities against Klebsiella pneumoniae, Streptococcus faecalis, and Bacteroides fragilis are similar to one another. Neither drug is absorbed orally; both are well absorbed (60-70%) after i.m. injection. Following i.v. infusion or injection, both drugs distribute rapidly (distribution half-life = 10-20 min); neither is protein bound substantially. Both drugs are primarily excreted unchanged in the urine by glomerular filtration and tubular secretion. Elimination half-lives of both drugs are slightly prolonged in renal-failure patients. However, the half-life of mezlocillin in renal failure is longer then the half-life of piperacillin because of dose-dependent kinetics of mezlocillin at low glomecular filtration rates. Probenecid alters the disposition of both drugs. Both drugs are widely distributed throughout the body. Reported side effects are similar to those of other penicillins. Mezlocillin and piperacillin may be used to treat susceptible organisms causing the following conditions: complicated and uncomplicated urinary-tract infections, septicemia, uncomplicated gonococcal urethritis, and lower respiratory-tract, intra-abdominal, gynecologic, skin, and skin-structure infections. Piperacillin is also effective for bone and joint infections. Dosages of both antibiotics should be adjusted based on patients' clinical condition and renal status. Both agents are relatively expensive in comparison with older penicillins and cephalosporins; their daily costs are similar to third-generation cephalosporins, carbenicillin, and ticarcillin. The potential benefits of mezlocillin and piperacillin are in their extended in vitro spectra of activity and minimal toxicities. More comparative clinical trials are needed to support any claims of clinical superiority of these drugs over older, less expensive regimens.