Single- and multiple-dose pharmacokinetics of linezolid and co-amoxiclav in healthy human volunteers

In an open, randomized, two-period crossover study the pharmacokinetics of linezolid and co-amoxiclav were investigated after single- and multiple-dose administration in 12 healthy volunteers (six females and six males). Linezolid was given in tablets of 600 mg twice a day for 7 days and co-amoxiclav in tablets of 1000 mg (875 + 125 mg) once a day for 7 days. The wash-out period was 4 weeks between the administration of the two antibacterial agents. Blood and urine samples were collected on days 1 and 7 before and at different time points up to 24 h after medication. The concentrations of the antibiotics in serum and urine were measured by validated high-performance liquid chromatography methods. Linezolid exhibited a mean C-max of 14.5 +/- 4.6 mg/L after T-max of 47.5 +/- 20.1 min on day 1, with a significant increase to 24.0 +/- 6.9 mg/L on day 7 (P < 0.01). The AUD(tot) (total area under the data) revealed a significant increase from 140.5 +/- 28.3 mg.h/L on day 1 to 220.2 +/- 42.6 mg.h/L on day 7 (P < 0.01). There were no significant differences in terminal elimination half-life between days 1 and 7 (9.53 +/- 2.87 versus 7.97 +/- 3.08 h) or in total clearance (71.6 +/- 17.6 versus 81.5 +/- 14.7 ml/min.1.73 m(2)). Results are in agreement with the assumption of a limited accumulation of linezolid under the dosage regimen given. Serum linezolid concentrations in females were always higher than those in males. The volume of distribution V-ss/f differed significantly between females and males (41.6 +/- 4.2 versus 52.2 +/- 3.3 L/70 kg; P < 0.01). Pharmacokinetic parameters of amoxicillin and clavulanic acid found in this study were similar to previously published data. No accumulation was found with co-amoxiclav. No serious adverse event was observed with the study drugs.