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Nafcillin Sodium

Drug Nomenclature

Synonyms: Nafcilina sódica; Nafcillinnatrium; Nafcillinum Natricum; Nafsilliininatrium; Wy-3277
BAN: Nafcillin Sodium [BANM]
USAN: Nafcillin Sodium
INN: Nafcillin Sodium [rINNM (en)]
INN: Nafcilina sódica [rINNM (es)]
INN: Nafcilline Sodique [rINNM (fr)]
INN: Natrii Nafcillinum [rINNM (la)]
INN: Натрий Нафциллин [rINNM (ru)]
Chemical name: Sodium (6R)-6-(2-ethoxy-1-naphthamido)penicillanate monohydrate
Molecular formula: C21H21N2NaO5S,H2O =454.5
CAS: 147-52-4 (nafcillin); 985-16-0 (anhydrous nafcillin sodium); 7177-50-6 (nafcillin sodium monohydrate)



The United States Pharmacopeia 31, 2008 (Nafcillin Sodium). A white to yellowish-white powder having not more than a slight characteristic odour. Freely soluble in water and in chloroform; soluble in alcohol. pH of a 3% solution in water is between 5.0 and 7.0. Store in airtight containers.


Nafcillin sodium has been reported to be incompatible with aminoglycosides and a number of other antibac-terials. It has also been reported to be incompatible with acidic and alkaline drugs.

Adverse Effects and Precautions

As for Benzylpenicillin. Thrombophlebitis may occur when nafcillin is given by intravenous injection, and tissue damage has been reported on extravasation.

Sodium content

Each g of nafcillin sodium contains about 2.2 mmol of sodium.


As for Benzylpenicillin.


For the effect of nafcillin on ciclosporin.


For the effect of nafcillin on warfarin.

Antimicrobial Action

As for Flucloxacillin.


Nafcillin is incompletely and irregularly absorbed from the gastrointestinal tract, especially when given after food.

After intramuscular injection it is absorbed more reliably, an injection of 0.5 to 1 g producing peak plasma concentrations of 5 to 8 micrograms/mL within about 0.5 to 1 hour. Up to 90% of nafcillin in the circulation is bound to plasma proteins. Nafcillin has been reported to have a plasma half-life of about 0.5 to 1.5 hours. The half-life is prolonged in neonates.

Nafcillin crosses the placenta into the fetal circulation and is distributed into breast milk.

There is little diffusion into the CSF except when the meninges are inflamed. Nafcillin is distributed into pleural and synovial fluids and into bone. Nafcillin differs from most other penicillins in that it is largely inactivated by hepatic metabolism.

It is excreted via the bile although some reabsorption takes place in the small intestine. Only about 10% of a dose given orally before food, and about 30% of a dose given intramuscularly, is excreted in the urine. Plasma concentrations are enhanced by probenecid.

Uses and Administration

Nafcillin is a penicillinase-resistant penicillin used similarly to flucloxacillin in the treatment of infections due to staphylococci resistant to benzylpenicillin. It is given by injection as the sodium salt.

Doses are expressed in terms of the equivalent amount of nafcillin; 1.1 g of nafcillin sodium is equivalent to about 1 g of nafcillin. Nafcillin sodium may be given intravenously by slow injection over 5 to 10 minutes or by slow infusion over at least 30 to 60 minutes; usual adult doses are 0.5 to 1 g of nafcillin every 4 hours, although it is usually recommended that it be used for not more than 24 to 48 hours because of the risk of thrombophlebitis.

It has also been given by intramuscular injection in a dose of 500 mg of nafcillin every 4 to 6 hours. Nafcillin sodium has also been given orally but other penicillinase-resistant penicillins are preferred.


The United States Pharmacopeia

Nafcillin for Injection; Nafcillin Injection; Nafcillin Sodium Capsules; Nafcillin Sodium for Oral Solution; Nafcillin Sodium Tablets.

Nafcillin Sodium

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