Comparison of bone levels after intramuscular administration of cephradine ('Velosef') or flucloxacillin/ampicillin in hip replacement.

Serum and bone levels of antibiotics were measured after the intramuscular injection of either 1 g cephradine or 500 mg flucloxacillin plus 500 mg ampicillin in 48 patients undergoing total hip replacement. The results showed that both regimens produced adequate blood levels, but that the levels after cephradine were higher and more prolonged. Bone levels of cephradine were significantly higher than for flucloxacillin or ampicillin. In half of the patients studied, flucloxacillin bone levels were below the limit of detection in both cancellous and cortical bone samples. In all 24 patients, cortical levels of cephradine were satisfactory for anti-staphylococcal activity although cancellous levels were unsatisfactory in 4 patients. The penetration of the antibiotics was greater into cortical bone than into cancellous bone.