Classifications: beta-lactam antibiotic; penicillin; antistaphylococcal penicillin;
Therapeutic: beta-lactam antibiotic

Prototype: Penicillin G potassium
Pregnancy Category: B


1 g, 2 g injection


Semisynthetic, acid-stable, penicillinase-resistant penicillin. Mechanism of bactericidal action is by interfering with synthesis of mucopeptides essential to formation and integrity of bacterial cell wall leading to bacterial cell lysis.

Therapeutic Effect

Effective against both penicillin-sensitive and penicillin-resistant strains of Staphylococcus aureus. Also active against pneumococci and group A beta-hemolytic streptococci.


Primarily, infections caused by penicillinase-producing staphylococci. May also be used to initiate treatment in suspected staphylococcal infections pending culture and sensitivity test results. Serum concentrations are considerably enhanced by concurrent use of probenecid.


Hypersensitivity to penicillins, cephalosporins, and other allergens; use of oral drug in severe infections, gastric dilatation, cardiospasm, or intestinal hypermotility.

Cautious Use

History of or suspected atopy or allergy (eczema, hives, hay fever, asthma); GI disease; hepatic disease; pregnancy (category B); lactation.

Route & Dosage

Staphylococcal Infections
Adult: IM/IV 500 mg–1 g q4h up to 12 g/d (max: 12 g/d)
Child: IV 100–200 mg/kg/d divided q4–6h (max: 12 g/d)
Neonate: IV 50–100 mg/kg/d divided q6–12h


  • Reconstitute each 500 mg with 1.7 mL of sterile water for injection or NaCl injection to yield 250 mg/mL. Shake vigorously to dissolve.
  • In adults: Make certain solution is clear. Select site carefully. Inject deeply into gluteal muscle. Rotate injection sites.
  • In children: The preferred IM site in children <3 y is the midlateral or anterolateral thigh. Check agency policy.
  • Label and date vials of reconstituted solution. Remains stable for 7 d under refrigeration and for 3 d at 15°–30° C (59°–86° F).
  • Note: Verify correct IV concentration and rate of infusion in neonates, infants, children with physician.

PREPARE: Direct: Reconstitute as for IM injection. Further dilute with 15–30 mL of D5W, NS, or 0.45% NaCl.  Intermittent: Dilute reconstituted solution in 100–150 mL of compatible IV solution.  Continuous: Add desired dose to a volume of IV solution that maintains concentration of drug between 2–40 mg/mL.  

ADMINISTER: Direct: Give over at least 10 min.  Intermittent: Give over 30–90 min.  Continuous: Give at ordered rate.  

INCOMPATIBILITIES Solution/additive: Aminophylline, ascorbic acid, aztreonam, bleomycin, cytarabine, gentamicin, hydrocortisone, methylprednisolone, promazine. Y-site: Diltiazem, droperidol, insulin regular, labetalol, midazolam, nalbuphine, pentazocine, vancomycin, verapamil.

  • Note: Usually, limit IV therapy to 24–48 h because of the possibility of thrombophlebitis (see Appendix F), particularly in older adults.
  • Discard unused portions 24 h after reconstitution.

Adverse Effects (≥1%)

Body as a Whole: Drug fever, anaphylaxis (particularly following parenteral therapy). GI: Nausea, vomiting, diarrhea, increase in serum transaminase activity (following IM). Hematologic: Eosinophilia, thrombophlebitis following IV; neutropenia (long-term therapy). Metabolic: Hypokalemia (with high IV doses). Skin: Urticaria, pruritus, rash, pain and tissue irritation. Urogenital: Allergic interstitial nephritis.

Diagnostic Test Interference

Nafcillin in large doses can cause false-positive urine protein tests using sulfosalicylic acid method or serum protein tests.


Drug: May antagonize hypoprothrombinemic effects of warfarin.


Peak: 30–120 min IM; 15 min IV. Duration: 4–6 h IM. Distribution: Distributes into CNS with inflamed meninges; crosses placenta; distributed into breast milk, 90% protein bound. Metabolism: Enters enterohepatic circulation. Elimination: Primarily in bile; 10–30% in urine. Half-Life: 1 h.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Perform C&S prior to initiation of therapy and periodically thereafter.
  • Obtain a careful history before therapy to determine any prior allergic reactions to penicillins, cephalosporins, and other allergens.
  • Inspect IV site for inflammatory reaction. Also check IV site for leakage; in the older adult patient especially, loss of tissue elasticity with aging may promote extravasation around the needle.
  • Note: Allergic reactions, principally rash, occur most commonly.
  • Lab tests: baseline and periodic WBC with differential; periodic LFTs, and kidney function tests with nafcillin therapy longer than 2 wk.
  • Monitor neutrophil count. Nafcillin-induced neutropenia (agranulocytosis) occurs commonly during third week of therapy. It may be associated with malaise, fever, sore mouth, or throat. Perform periodic assessments of liver and kidney functions during prolonged therapy.
  • Be alert for signs of bacterial or fungal superinfections (see Appendix F) in patients on prolonged therapy.
  • Determine IV sodium intake for patients with sodium restriction. Nafcillin sodium contains approximately 3 mEq of sodium per gram.

Patient & Family Education

  • Report promptly S&S of neutropenia (see Assessment & Drug Effects), superinfection, or hypokalemia (see Appendix F).

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2023 Last Updated On: 01/31/2023 (0)
Wait 20 seconds...!!!