nafcillin sodium
Nafcil, Nallpen, Unipen

Pharmacologic classification: penicillinase-resistant penicillin
Therapeutic classification: antibiotic
Pregnancy risk category B


Available forms
Available by prescription only
Capsules: 250 mg
Injection: 500 mg, 1 g, 2 g, 10 g
I.V. infusion piggyback: 1 g, 2 g

Indications and dosages
 Systemic infections caused by susceptible organisms (methicillin-sensitive Staphylococcus aureus). Adults: 250 to 500 mg P.O. q 4 to 6 hours for mild to moderate infections and 1 g q 4 to 6 hours for more severe infections. Or, 500 mg I.M. q 4 hours or 500 to 1,000 mg I.V. q 4 hours depending on severity of the infection.
Children older than age 1 month: 50 to 100 mg/kg P.O. daily, in divided doses q 6 hours. Or, 50 to 200 mg/kg daily I.V. in divided doses q 4 to 6 hours depending on the severity of the infection.
Neonates: 30 to 40 mg/kg daily P.O. divided equally into three to four doses. For mild to moderate infection, may give 50 to 100 mg/kg daily I.V. in divided doses q 6 hours. For more severe infections, 100 to 200 mg/kg daily I.V. divided q 4 to 6 hours. Or, 25 mg/kg I.V. q 12 hours (if less than 7 days old and under 2 kg [4.4 lb]) or q 8 hours (if less than 7 days old and over 2 kg or more than 7 days old and less than 2 kg) or q 6 hours (if over 7 days old and over 2 kg).
 Meningitis. Neonates older than age 7 days who weigh more than 2 kg: 50 mg/kg I.V. q 6 hours.
Neonates older than age 7 days who weigh less than 2 kg: 50 mg/kg I.V. q 8 hours.
Neonates younger than age 7 days who weigh more than 2 kg: 50 mg/kg I.V. q 8 hours.
Neonates younger than age 7 days who weigh less than 2 kg: 50 mg/kg I.V. q 12 hours.
 Acute or chronic osteomyelitis caused by susceptible organisms. Adults: 1 to 2 g I.V. q 4 hours for 4 to 8 weeks.
 Meningitis caused by susceptible organisms. Adults: 100 to 200 mg/kg daily I.V. in divided doses q 4 to 6 hours.
 Native valve endocarditis caused by susceptible organisms. Adults: 2 g I.V. q 4 hours for 4 to 6 weeks in combination with gentamicin.

Pharmacodynamics
Antibiotic action: Nafcillin is bactericidal; it adheres to bacterial penicillin-binding proteins, thus inhibiting bacterial cell wall synthesis. Nafcillin resists the effects of penicillinases-enzymes that inactivate penicillin-and is active against many strains of penicillinase-producing bacteria; this activity is most important against penicillinase-producing staphylococci; some strains may remain resistant. Nafcillin is also active against a few gram-positive aerobic and anaerobic bacilli but has no significant effect on gram-negative bacilli.

Pharmacokinetics
Absorption: Absorbed erratically and poorly from the GI tract. Food decreases absorption.
Distribution: Distributed widely; CSF penetration is poor but enhanced by meningeal inflammation. Drug crosses the placental barrier and is 70% to 90% protein-bound.
Metabolism: Metabolized primarily in the liver; it undergoes enterohepatic circulation. Dosage adjustment isn’t needed for patients in renal failure.
Excretion: Excreted primarily in bile; about 25% to 30% is excreted in urine unchanged. It may also appear in breast milk. Elimination half-life in adults is 1/2 to 1 1/2 hours.

Route Onset Peak Duration
P.O. Unknown 1/2 -2 hr Unknown
I.V. Immediate Immediate Unknown
I.M. Unknown 1/2 -1 hr Unknown


Contraindications and precautions
Contraindicated in patients hypersensitive to drug or other penicillins. Use cautiously in patients with GI distress or sensitivity to cephalosporins.

Interactions
Drug-drug. Aminoglycosides: Causes synergistic bactericidal effects against S. aureus. However, the drugs are physically and chemically incompatible and are inactivated when mixed or given together. Don’t mix in same solution.
Cyclosporines: Causes subtherapeutic cyclosporine levels. Monitor cyclosporine levels.
Hepatotoxic drugs: May increase risk of hepatotoxicity. Monitor patient carefully.
Drug-food. Carbonated beverages, fruit juice: Acidity may inactivate drug. Don’t give together.

Adverse reactions
CV: vein irritation, thrombophlebitis.
GI: nausea, vomiting, diarrhea, pseudomembranous colitis.
Hematologic: transient leukopenia, neutropenia, granulocytopenia, thrombocytopenia with high doses.
Other: hypersensitivity reactions (chills, fever, rash, pruritus, urticaria, anaphylaxis).

Effects on lab test results
• May decrease neutrophil, granulocyte, and platelet counts.

Overdose and treatment
Signs and symptoms of overdose include neuromuscular irritability or seizures.
 There are no specific recommendations. Treatment is supportive. After recent ingestion (4 hours or less), empty stomach by induced emesis or gastric lavage; follow with activated charcoal to reduce absorption. Nafcillin isn’t appreciably removed by hemodialysis.

Special considerations
• I.V. administration is the preferred route.
• Give P.O. doses on empty stomach; food decreases absorption.
• The total sodium content of 1 g of nafcillin is about 2.9 mEq (2.9 mmol).
• Drug is incompatible with aminoglycosides.
• Infuse I.V. nafcillin for short time periods (24 to 48 hours) if possible to reduce risk of thrombophlebitis.
• If used to treat infections caused by group A beta-hemolytic streptococci, continue therapy for at least 10 days to decrease risk of rheumatic fever or glomerulonephritis.
• Evaluate renal, hepatic, and hematologic systems periodically during prolonged nafcillin therapy.
Breast-feeding patients
• Nafcillin appears in breast milk. Use cautiously in breast-feeding women.
Pediatric patients
• Nafcillin that’s been reconstituted with bacteriostatic water for injection with benzyl alcohol shouldn’t be used in neonates because of toxicity.
Geriatric patients
• Half-life may be prolonged because of impaired hepatic and renal function.

Patient education
• Tell patient to take capsules on an empty stomach.
• Advise patient to take drug with water; acid in fruit juice or carbonated beverage may inactivate it.
• Tell patient to report severe diarrhea or allergic reactions promptly.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use