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. |
| Molecular Weight | 436.5 |
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 | Safe; no known teratogenic effects in animal studies; limited human data but considered low risk. |
| 2nd trimester | Safe; no fetal harm reported; indicated for infections during pregnancy. |
| 3rd trimester | Safe; no adverse fetal effects; may be used for intrapartum prophylaxis. |
Clinical note
Warfarin metabolism is increased decreasing INR Can cause vein irritation and phlebitis with IV administration.
| Placental transfer | Crosses placenta; achieves therapeutic levels in fetal serum. |
| Breastfeeding | Excreted into breast milk in small amounts; no adverse effects in nursing infants reported; generally considered compatible with breastfeeding. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Common Effects | Diarrhea |
| Serious Effects |
Hypersensitivity to nafcillin or any penicillinHypersensitivity to cephalosporins (cross-sensitivity)
| 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 |
| Food/Dietary | Alcohol may increase gastrointestinal side effects (nausea, vomiting, diarrhea) and is best avoided. No specific food restrictions; however, take oral formulations with a full glass of water on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption. |
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| L1 (Safest) |
| 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. |
| 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. |
| Clinical Pearls | Nafcillin is a penicillinase-resistant penicillin indicated for infections caused by methicillin-susceptible Staphylococcus aureus (MSSA). It has minimal renal excretion; dose adjustment is unnecessary in renal impairment. Contraindicated in penicillin allergy; cross-sensitivity with cephalosporins is rare but possible. Use with caution in patients with hepatic impairment. Monitor for hepatotoxicity, neutropenia, and phlebitis with IV administration. Extravasation can cause tissue necrosis. Incompatible in Y-site with aminoglycosides, heparin, and many other drugs. |
| Patient Advice | Take exactly as prescribed; complete the full course even if you feel better. · Notify your doctor immediately if you experience rash, hives, itching, difficulty breathing, or swelling of face/mouth (signs of allergic reaction). · Report any unusual bleeding, bruising, or signs of infection (fever, sore throat) as these may indicate low blood cell counts. · If receiving IV, report pain, redness, or swelling at the injection site. · Avoid alcohol while on this medication. · Inform your doctor of all other medications, including over-the-counter drugs and supplements. · Store at room temperature; keep solution refrigerated if not used immediately. |