Nafcillin — Compare Prices at US & Canada Pharmacies

Nafcillin is a penicillinase-resistant penicillin — a chemically modified penicillin, in the same family as oxacillin and dicloxacillin, engineered to resist the beta-lactamase enzyme that ordinary penicillin-producing staphylococci use to inactivate standard penicillin. It's the drug of choice for serious infections caused by methicillin-susceptible Staphylococcus aureus (MSSA) — bacteremia, endocarditis, osteomyelitis, and deep abscesses — and infectious disease specialists generally prefer it over vancomycin for confirmed MSSA infections, since it clears the bacteria faster and more reliably when the organism isn't resistant. That preference only holds for MSSA, though: the FDA label explicitly says therapy should switch to an alternative agent if susceptibility testing shows a methicillin-resistant organism (MRSA), against which nafcillin has no activity.

One practical issue specific to nafcillin is tissue damage if the IV infusion leaks outside the vein (extravasation) — nafcillin is notably irritating to tissue and can cause significant local injury, even skin necrosis, if this happens, so infusion sites are monitored closely and any signs of leakage are treated as urgent. It's also associated with a distinctive risk of acute interstitial nephritis (a kidney inflammation reaction) more than some other penicillins, and it can cause neutropenia with prolonged high-dose courses, both of which are reasons for periodic blood work during extended IV therapy.

Two drug interactions are worth flagging: high-dose nafcillin can substantially reduce warfarin's anticoagulant effect, an interaction that can persist for weeks after nafcillin is stopped, so INR needs close monitoring during and after a course; and it can lower cyclosporine levels below the therapeutic range in transplant patients, risking rejection if the interaction isn't anticipated and managed.

Contraindications

CONTRAINDICATIONS A history of a hypersensitivity (anaphylactic) reaction to any penicillin is a contraindication.

Warnings

WARNINGS SERIOUS AND OCCASIONALLY FATAL HYPERSENSITIVITY (ANAPHYLACTIC) REACTIONS HAVE BEEN REPORTED IN PATIENTS ON PENICILLIN THERAPY. THESE REACTIONS ARE MORE LIKELY TO OCCUR IN INDIVIDUALS WITH A HISTORY OF PENICILLIN HYPERSENSITIVITY AND/OR A HISTORY OF SENSITIVITY TO MULTIPLE ALLERGENS. THERE HAVE BEEN REPORTS OF INDIVIDUALS WITH A HISTORY OF PENICILLIN HYPERSENSITIVITY WHO HAVE EXPERIENCED SEVERE REACTIONS WHEN TREATED WITH CEPHALOSPORINS. BEFORE INITIATING THERAPY WITH NAFCILLIN, CAREFUL INQUIRY SHOULD BE MADE CONCERNING PREVIOUS HYPERSENSITIVITY REACTIONS TO PENICILLINS, CEPHALOSPORINS, OR OTHER ALLERGENS.

Pregnancy & breastfeeding

Pregnancy: Teratogenic Effects Pregnancy Category B Reproduction studies have been performed in the mouse with oral doses up to 20 times the human dose and orally in the rat at doses up to 40 times the human dose and have revealed no evidence of impaired fertility or harm to the rodent fetus due to nafcillin. There are, however, no adequate or well-controlled studies in pregnant women.