nafcillin
Brand: Nallpen, Unipen
Prototype: penicillin-g
Drug Class: antibiotic (penicillin)
Drug Family: antibiotic
Subclass: antistaphylococcal penicillin
Organ Systems: infectious-disease
Mechanism of Action
Antistaphylococcal penicillin resistant to staphylococcal beta-lactamase; identical spectrum and indications to oxacillin. Distinguishable by its primarily biliary excretion (vs. oxacillin renally excreted), making it preferred in patients with severe renal impairment where oxacillin dose adjustment is needed.
penicillin-binding proteins (PBPs)
Indications
- MSSA infections (bacteremia, endocarditis, osteomyelitis, skin/soft tissue)
Contraindications
- penicillin allergy
- MRSA infections
Adverse Effects
Common
- severe thrombophlebitis (requires large-bore/central line)
- hypokalemia
- nausea
Serious
- hepatotoxicity (similar to oxacillin)
- neutropenia (with prolonged high-dose therapy)
- interstitial nephritis
- anaphylaxis
Pharmacokinetics (ADME)
| Absorption | IV only for serious infections |
| Distribution | protein binding ~90%; similar to oxacillin |
| Metabolism | primarily biliary excretion; minimal renal |
| Excretion | biliary (70-90%); only ~10-20% renal |
| Half-life | 0.5-1.5 hours |
| Onset | end of infusion |
| Peak | end of infusion |
| Duration | 4-6 hours |
| Protein Binding | 90% |
| Vd | 0.35 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| warfarin | nafcillin is a CYP450 inducer; significantly reduces warfarin effect; monitor INR | major |
Nursing Considerations
- Nafcillin is a CYP inducer — may significantly reduce warfarin anticoagulation; monitor INR closely when starting or stopping nafcillin in anticoagulated patients.
- No renal dose adjustment needed (biliary elimination); preferred over oxacillin in severe renal impairment.
- Monitor CBC with prolonged high-dose therapy; neutropenia is more common with nafcillin than oxacillin.
- Severe thrombophlebitis at peripheral IV sites; central line strongly recommended for prolonged therapy.
Clinical Pearls
- Nafcillin is the only commonly used penicillin with significant CYP induction; this unexpected drug interaction with warfarin has led to subtherapeutic anticoagulation when not recognized.
- The choice between nafcillin and oxacillin for MSSA infections is largely institutional; nafcillin is preferred in renal failure, while oxacillin is preferred when CYP interactions are a concern.
Safety Profile
Pregnancy safe
Lactation use-with-caution
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.