Nafcillin

NALLPEN

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Pronunciation: naf-SIL-in

Nafcillin ballicule: receptor binding, kinetics and half-life diagram — Mechanism of action: Nafcillin ballicule

What it isPenicillinase-resistant penicillin; methicillin-susceptible staphylococcal infection.

Why this oneIts unusual distinction among antibiotics is enzyme induction strong enough to undermine warfarin.

What limits itPhlebitis and extravasation injury can end IV therapy; renal adjustment is unnecessary.

Nafcillin molecular structure (skeletal formula) — Molecular structure: Nafcillin

Nafcillin prescription history

Animated chart of estimated U.S. prescriptions per year, Penicillins (oral) (1955–2026). Nafcillin enters in 1967 (estimated).

FDA-approved for

staphylococcal infections (MSSA) (1964)

Principal riskIt INDUCES CYP3A4, so warfarin fails

Classes and tags

Clinical profile

Therapeutic safety burden1 / 4

Overdose danger1 / 4

Weight-gain liability0 / 4

Sedation liability0 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism0 / 4

Embryofetal risk0 / 4

Legacy pregnancy categoryB

Defining liabilityAllergy, gastrointestinal effects and agent-specific renal, hepatic, hematologic or interaction risks.

FDA label

Read the full label on DailyMed ↗

NO BOXED WARNINGS

FDA dosing	Population	Start
Staphylococcal / susceptible infection	adult	500 mg IV q4h; 1 g q4h for severe infection
Staphylococcal / susceptible infection (IM)	adult	500 mg IM q4–6h
Susceptible infection	infants & children <40 kg	25 mg/kg IM BID
Susceptible infection	neonates	10 mg/kg IM BID

Renal No adjustment needed, including patients on hemodialysis

Hepatic Undefined

Instructions

Administer IV slowly over at least 30–60 min to minimize vein irritation and extravasation
Do not add supplementary medication to nafcillin
Continue therapy ≥14 days for severe staphylococcal infections
Inspect visually for particulate matter and discoloration before use

Available strengths

inj 1, 2 g

Contraindications

History of anaphylactic reaction to any penicillin

Cautions

Serious/fatal hypersensitivity (anaphylaxis)
Severe tissue necrosis/sloughing with extravasation; thrombophlebitis
Interstitial nephritis
Neurotoxicity with high doses (esp. hepatic + renal impairment)
Pseudomembranous colitis
Neutropenia/bone marrow depression

Adverse reactions

Allergic reactions (urticaria, pruritus, fever)
Injection-site pain/phlebitis/thrombophlebitis
GI upset (nausea, vomiting, diarrhea)
Elevated liver transaminases
Interstitial nephritis
Neutropenia

Pregnancy Undefined

Lactation Undefined

Cost

Nafcillin (NALLPEN)

Strength		#/mo	generic $/unit	CostPlus
1 g	inj	per unit		not offered
2 g	inj	per unit		not offered

NADAC is a voluntary CMS survey of what retail community pharmacies pay for the drugs they stock. Nafcillin is administered under clinical supervision and dispensed outside retail pharmacies, so it rarely appears on surveyed invoices.

Generic entryBy 2023

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Self-check

How can nafcillin undermine warfarin?
Enzyme induction.
Does nafcillin require renal adjustment?
No.