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.
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.
History of or suspected atopy or allergy (eczema, hives, hay fever, asthma); GI disease; hepatic disease; pregnancy (category
Route & Dosage
Adult: IM/IV 500 mg1 g q4h up to 12 g/d (max: 12 g/d)
Child: IV 100200 mg/kg/d divided q46h (max: 12 g/d)
Neonate: IV 50100 mg/kg/d divided q612h
- Reconstitute each 500 mg with 1.7 mL of sterile water for injection or NaCl injection to yield 250 mg/mL. Shake vigorously
- 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 1530 mL of D5W, NS, or 0.45% NaCl. Intermittent: Dilute reconstituted solution in 100150 mL of compatible IV solution. Continuous: Add desired dose to a volume of IV solution that maintains concentration of drug between 240 mg/mL.
ADMINISTER: Direct: Give over at least 10 min. Intermittent: Give over 3090 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 2448 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
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.
May antagonize hypoprothrombinemic effects of warfarin.
30120 min IM; 15 min IV. Duration:
46 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; 1030% in urine. Half-Life:
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
- 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
Patient & Family Education
- Report promptly S&S of neutropenia (see Assessment & Drug Effects), superinfection, or hypokalemia (see Appendix F).