Panipenem/betamipron (PAPM/BP), a new carbapenem, was studied in dermatology. PAPM/BP was used clinically in the treatment of skin and skin structure infections in a multicenter trial. Fifty three patients were enrolled in the trial. Clinical evaluations were made in 50 patients. Most patients received intravenous infusion of PAPM/BP in a dose of 500 mg twice daily. Other dosages were used in some patients. The overall clinical efficacy rate was 78%. When 15 cases of secondary infections were excluded, the rate was 85.7%. Adverse responses were nausea and/or vomiting in 3 patients, redness with itching in 1 patient, headache or head heaviness in 2 patients and diarrhea in 1 patient. The patient with redness and itching had also nausea and vomiting. This occurred 1 hour after the start of the first infusion of this drug. After the discontinuation of the treatment the symptoms went away on the next day. Abnormalities in laboratory test results were observed in 7 out of 53 patients. One patient with liver cirrhosis and hepatocellular carcinoma developed anemia (RBC 372 x 10(4)/mm3----275 x 10(4)/mm3, Hb 11.9 g/dl----8.8 g/dl, 35.1%----26.0%). Other abnormalities were all mild. Penetration of the drug into skin tissues after intravenous infusion of 500 mg of this drug in skin surgery patients was studied. Skin/serum concentration ratios ranged from 0.20 to 0.97. Skin concentrations were higher than the concentration of PAPM inhibiting 80% of clinical isolates over a period of 6 hours. In rats, skin concentrations were much lower than serum concentrations probably due to the difference in in vivo metabolism of PAPM. A few resistant strains of Staphylococcus aureus against PAPM and imipenem (IPM) were isolated. However, PAPM and IPM showed good antibacterial activities compared to other drugs tested. In conclusion, PAPM/BP is considered to be a useful drug in the treatment of skin and skin structure infections.