Serum concentrations and penetration into prostate of mecillinam and ampicillin

The absorption of the two antibiotic pro-drugs pivmecillinam and pivampicillin was investigated in 10 patients with normal or slightly impaired renal function. After a therapeutic dose of 200 mg pivmecillinam plus 250 mg pivampicillin, the mean peak concentration in serum was 2.3 micrograms mecillinam and 5.3 micrograms ampicillin per ml. The elimination half-life was approximately 2 hours for both antibiotics. Consequently, a ratio of 2:5 was maintained in serum during the excretion period and this ratio is within the range where optimal synergistic effect between the two antibiotics against many Gram-negative organisms is most likely to occur. Penetration of mecillinam and ampicillin into the prostate, determined in tissue homogenate obtained from 10 patients undergoing transurethral resection of the prostate showed that the antibiotics penetrated equally well with a serum tissue ratio of approximately 2:1.