UNIPEN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for UNIPEN (UNIPEN).
Unipen (nafcillin) is a penicillinase-resistant penicillin that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), blocking transpeptidation and autolysin inhibition.
| Metabolism | Hepatic metabolism, primarily via hydrolysis and conjugation; minor renal elimination. |
| Excretion | Renal: 70-90% unchanged via tubular secretion and glomerular filtration; biliary: minor (<10%); fecal: minimal. |
| Half-life | 0.5-1 hour in normal renal function; prolonged to 7-10 hours in anuria or severe renal impairment. |
| Protein binding | 20-40% bound to serum albumin and other plasma proteins. |
| Volume of Distribution | 0.2-0.3 L/kg; low Vd indicates limited tissue penetration, predominantly extracellular fluid. |
| Bioavailability | Oral: 30-50% due to acid lability and first-pass metabolism; IM: 70-90%. |
| Onset of Action | IV: immediate; IM: 15-30 minutes; oral: 30-60 minutes. |
| Duration of Action | 4-6 hours; may be extended in renal impairment. |
500 mg to 2 g orally or intravenously every 4 to 6 hours; maximum 12 g/day IV for serious infections.
| Dosage form | INJECTABLE |
| Renal impairment | For CrCl <10 mL/min: administer every 8 to 12 hours; for CrCl 10-50 mL/min: no adjustment needed; for hemodialysis: dose after dialysis. |
| Liver impairment | No specific adjustment recommended; use with caution in severe hepatic impairment due to potential increased toxicity. |
| Pediatric use | Neonates: 25-50 mg/kg/day divided every 8-12 hours (weight <2 kg) or every 6-8 hours (weight >2 kg); Infants and children: 50-100 mg/kg/day divided every 6 hours; maximum 12 g/day. |
| Geriatric use | No specific dose adjustment required; monitor renal function and adjust based on creatinine clearance to avoid accumulation. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for UNIPEN (UNIPEN).
| Breastfeeding | Nafcillin is excreted in breast milk in trace amounts. M/P ratio not established. Considered compatible with breastfeeding due to low oral bioavailability and lack of reported adverse effects in infants. |
| Teratogenic Risk | Nafcillin is FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; no adequate human studies. Avoid in first trimester unless benefits outweigh risks. Second and third trimester: Use with caution due to limited data. |
| Fetal Monitoring |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
["Known hypersensitivity to nafcillin, other penicillins, or any component of the formulation.","Prior history of severe allergic reaction (e.g., anaphylaxis) to beta-lactam antibiotics."]
| Precautions | ["Hypersensitivity reactions: Risk of anaphylaxis and severe skin reactions.","Clostridioides difficile-associated diarrhea: Consider if diarrhea occurs.","Serum potassium monitoring: Nafcillin can cause hypokalemia with high doses.","Hematologic effects: Neutropenia, thrombocytopenia, and agranulocytosis with prolonged therapy.","Drug-induced liver injury: Elevated transaminases and cholestatic hepatitis."] |
Loading safety data…
| Monitor for maternal hypersensitivity reactions, renal function, and signs of hepatotoxicity. No specific fetal monitoring required beyond routine antenatal care. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies show no impairment of fertility. |