1. A rapid intravenous bolus injection of 4.0 g
Magnapen (which contains 2.0 g of
ampicillin and 2.0 g of
flucloxacillin) was to seven patients undergoing
total hip replacement immediatly before induction of
general anesthesia. Postoperatively the patients patients received 2.0 g
Magnapen by
intramuscular injection every 6 h for up to 72 h until removal of the
wound drains. 2. The plasma, bone, hip
capsule and drain fluid concentrations of
ampicillin and
flucloxacillin were measured by a differential small plate microbiological assay method using Sarcina lutea and a
penicillinase producing Staph. aureus Russell as the test organisms. 3. The mean +/- s.e. mean concentrations of
ampicillin after this regimen were 4222.2 +/- 285.0 microgram/ml (plasma), 65.6 +/- 1.3 microgram (g (hip
capsule), 19.1 +/- 3.8 microgram/g (cancellous bone), and 211.1 +/- 65.6 microgram/g (ground up bone) respectively. 4. The mean +/- s.e. mean
flucloxacillin concentrations after this regime were 137.2 +/- 28.4 microgram/ml (plasma), 61.8 +/- 15.0 microgram/g (hip
capsule), 47.1 +/- 9.5 microgram/g (cancellous bone) and 139.4 +/- 21.8 microgram/g (ground up bone) respectively. 5. An intravenous bolus injection of Magnepen (4.0 g), given immediately before induction of general anaesthesia, provides concentrations of
ampicillin and
flucloxacillin in plasma, hip
capsule, cancellous and ground up bone, and drain fluid that exceed the MICs of these
antibiotics against Staph. aureus and E. coli. 6. The plasma, hip
capsule, cancellous and ground up bone concentrations of
ampicillin after this dose of
Magnapen do not, however, exceed the MICs of the Gram negative anaerobes that sometimes cause
postoperative wound infections in these patients.