NAFCILLIN SODIUM
Clinical safety rating: safe
Human studies have proved safety
Nafcillin exerts bactericidal activity by inhibiting bacterial cell wall synthesis via binding to penicillin-binding proteins (PBPs), thereby disrupting peptidoglycan cross-linking. It is resistant to staphylococcal beta-lactamases.
| Metabolism | Hepatic metabolism via carboxylesterases and glucuronidation; undergoes extensive biliary excretion. Only 10-30% is eliminated renally. |
| Excretion | Primarily renal (30-40% unchanged) and hepatic/biliary elimination. Approximately 10-15% excreted in bile via feces. |
| Half-life | Approximately 0.5 hour (30 minutes) in adults with normal renal function; prolonged to 1-2 hours in neonates or severe renal impairment. Clinically relevant for dosing every 4-6 hours. |
| Protein binding | Approximately 70-85% bound, primarily to albumin. |
| Volume of Distribution | 0.3-0.4 L/kg; limited distribution due to high protein binding, less penetration into CSF except with inflamed meninges. |
| Bioavailability | Oral: Very low (<10%), not clinically useful; IM: ~100% absorption. |
| Onset of Action | IV: Immediate (minutes); IM: 15-30 minutes; Oral: Not applicable (poor oral bioavailability). |
| Duration of Action | 4-6 hours for IV/IM administration; serum levels above MIC for susceptible organisms persist for about 4 hours post-dose. |
1-2 g IV every 4 hours; or 1-2 g IM every 4-6 hours.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 10-50 mL/min: same dose every 6 hours. CrCl <10 mL/min: same dose every 8 hours. |
| Liver impairment | No adjustment required for mild to moderate impairment; caution in severe impairment (Child-Pugh C) with monitoring. |
| Pediatric use | Neonates <7 days: 50 mg/kg IV/IM every 8 hours; 7-28 days: 50 mg/kg IV/IM every 6 hours. Infants/children: 50 mg/kg IV/IM every 6 hours (max 2 g/dose). |
| Geriatric use | No specific dose adjustment; monitor renal function and reduce frequency if CrCl <30 mL/min. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Warfarin metabolism is increased decreasing INR Can cause vein irritation and phlebitis with IV administration.
| Breastfeeding | Excreted into breast milk in low concentrations (M/P ratio not established). Considered compatible with breastfeeding by American Academy of Pediatrics; monitor infant for potential gastrointestinal disturbances or allergic reactions. |
| Teratogenic Risk | FDA Pregnancy Category B. Animal reproduction studies have not demonstrated fetal risk, but no adequate and well-controlled studies in pregnant women. Nafcillin crosses the placenta. No known teratogenic effects in first, second, or third trimester. |
■ FDA Black Box Warning
None
| Common Effects | Diarrhea |
| Serious Effects |
["History of immediate hypersensitivity reaction (e.g., anaphylaxis, urticaria) to penicillins or cephalosporins","Patients with HIV on anticoagulants (potential interaction with warfarin)"]
| Precautions | ["Risk of hypersensitivity reactions (including anaphylaxis) in patients with beta-lactam allergy","Caution in renal impairment (dose adjustment not typically required unless severe)","Neurotoxicity (seizures) with high doses or in renal failure","Electrolyte disturbances (sodium load from nafcillin sodium)","Hypokalemia and neutropenia associated with prolonged therapy"] |
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| Fetal Monitoring |
| Monitor maternal renal and hepatic function periodically. Assess for signs of hypersensitivity or superinfection. No specific fetal monitoring required beyond routine prenatal care. |
| Fertility Effects | No known adverse effects on fertility in animal studies or human data. Unlikely to significantly impact reproductive function. |