Nafcillin (Unipen, Nallpen)


  • Antibiotic


  • Penicillinase-Resistant Penicillin


  • Mild to moderate infections caused by penicillinase-producing staphylococci

  • Upper Respiratory Tract Infections

  • Localized soft tissue/skin infections

  • Lower Respiratory Tract Infections

  • Disseminated infections


  • None


  • Pregnancy category B

  • Use with caution in patients with penicillin or cephalosporin allergy (5-10% chance of cross-reactivity)

  • Counsel patient to finish all medication to prevent development of resistance

  • Inform patient to take at even intervals, preferably around the clock

  • Take on an empty stomach, 1 hour before or 2 hours after meals.  Food inhibits absorption

  • Parenteral dosage form is reserved for severe infections

  • Orally administered nafcillin serum levels are low and unpredictable

Adverse Reactions (Side Effects):

  • Hypersensitivity

  • Gastrointestinal: nausea, vomiting, diarrhea

  • Vaginitis  


  • Administered orally (capsules) and injectable

  • Injectable

    • Adult and children (>40kg):

      • 500mg IM q4-6h or IV q4h

    • Infants and children (<40kg):

      • 25mg/kg IM twice daily or IV in 4-6 divided doses

    • Neonates:

      • 10mg/kg IM twice daily

  • Oral

    • Adult and children (>40kg):

      • 250-500mg q4-6h (may increase to 1 gram q4-6h for severe infections)

    • Infants and children (<40kg):

      • Staphylococcal  infections:  50mg/kg/day in 4 divided doses

      • Scarlet fever and pneumonia: 25mg/kg/day in 4 divided doses

      • Streptococcal pharyngitis: 250mg tid for 10 days

    • Neonates:

      • 10mg/kg 3-4 times per day

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