Nafcillin pharmacokinetics

For parenteral therapy, nafciUin and oxacillin offer comparable efficacy and antimicrobial spectra of activity. Although both drugs undergo hepatic metabolism, only nafcillin requires dose adjustment in patients with combined hepatic and renal insufficiency. Other pharmacokinetic data for nafcillin and oxacillin appear in Table 45.1. Indications for nafcillin or oxacillin include severe staphylococcal infections like cellulitis, empyema, endocarditis, osteomyelitis, pneumonia, septic arthritis, and toxic shock syndrome. 

B. Pharmacokinetics Penicillins vary in their resistance to gastric acid and therefote vary in their oral bioavailability. They are polar compounds and are not metabolized extensively. They are usually excreted unchanged in the urine via gloinemlar filtration and tubular secretion, the latter process being inhibited by probenecid. Ampicillin and nafcillin are excreted partly in the bile. The plasma half-lives of most penicillins vary from one-half to 1 hour. Procaine and benzathine forms of penicillin G are administered intramuscularly and have long plasma half-lives because the active drug is released very slowly into the bloodstream. Most penicillins cross the blood-brain barrier only when the meninges are inflamed. 

There appear to be no clinically significant pharmacokinetic interactions between aztreonam and amikacin, cefradine, clindamycin, gentamicin, metronidazole or nafcillin. 

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