Cefadroxil kinetics and dynamics in a pediatric patient with acute osteomyelitis

Cefadroxil has been used for the treatment of acute osteomyelitis. However, its pharmacokinetics and pharmacodynamics have not been studied in these patients. We evaluated the kinetics and dynamics of cefadroxil in a pediatric patient with osteomyelitis caused by Staphylococcus aureus. After initial clinical improvement on intravenous nafcillin, the patient received oral cefadroxil, 60 mg/kg every 12 h. Blood samples were collected at 0, 1, 2, 4, 6, 8 and 12 h; bactericidal titers were determined at 2 and 12 h. Cefadroxil was measured by an HPLC method. The peak and trough serum concentration of cefadroxil was 35.4 and 0.5 micrograms/ml, respectively. The oral clearance and elimination half-life were 11.5 ml/min/kg and 2.4 h, respectively. The peak bactericidal titer was 1:4 and the trough titer was less than 1:2 for the infecting organism. The child's finger appeared worse with an increase in swelling and erythema after 2 days of cefadroxil therapy. Cefadroxil was discontinued and the patient was treated successfully with intravenous nafcillin. The apparent failure of cefadroxil therapy can be explained by lower than recommended peak (greater than or equal to 1:8) and trough (greater than or equal to 1:2) titers for therapeutic success. Thus, an alternative dosage regimen of cefadroxil should be considered in the future studies.