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Nafcillin (Nafcillin Sodium) - Indications and Dosage



Nafcillin is indicated in the treatment of infections caused by penicillinase-producing staphylococci which have demonstrated susceptibility to the drug. Culture and susceptibility tests should be performed initially to determine the causative organism and its susceptibility to the drug (See CLINICAL PHARMACOLOGY – Susceptibility Test Methods).

Nafcillin may be used to initiate therapy in suspected cases of resistant staphylococcal infections prior to the availability of laboratory test results. The penicillinase-resistant penicillins should not be used in infections caused by organisms susceptible to penicillin G. If the susceptibility tests indicate that the infection is due to an organism other than a resistant staphylococcus, therapy should not be continued with Nafcillin.

To reduce the development of drug-resistant bacteria and maintain the effectiveness of Nafcillin for Injection, USP and other antibacterial drugs, Nafcillin for Injection, USP should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.


Nafcillin for injection is available for intramuscular and intravenous use.

The penicillinase-resistant penicillins are available for oral administration and for intramuscular and intravenous injection. The sodium salts of methicillin, oxacillin, and nafcillin may be administered parenterally and the sodium salts of cloxacillin, dicloxacillin, oxacillin, and nafcillin are available for oral use. The usual IV dosage for adults is 500 mg every 4 hours. For severe infections, 1 g every 4 hours is recommended. Administer slowly over at least 30 to 60 minutes to minimize the risk of vein irritation and extravasation.

Drug Adults Infants and Children
<40 kg (88 lbs)
Nafcillin 500 mg IM every
4 to 6 hours
IV every 4 hours
25 mg/kg IM
twice daily
Neonates 10 mg/kg
IM twice daily
Nafcillin 1 gram IM or IV
every 4 hours
(severe infections)

Bacteriologic studies to determine the causative organisms and their susceptibility to nafcillin should always be performed. Duration of therapy varies with the type and severity of infection as well as the overall condition of the patient, therefore it should be determined by the clinical and bacteriological response of the patient. In severe staphylococcal infections, therapy with nafcillin should be continued for at least 14 days. Therapy should be continued for at least 48 hours after the patient has become afebrile, asymptomatic, and cultures are negative. The treatment of endocarditis and osteomyelitis may require a longer duration of therapy.

Concurrent administration of the penicillinase-resistant penicillins and probenecid increases and prolongs serum penicillin levels. Probenecid decreased the apparent volume of distribution and slows the rate of excretion by competitively inhibiting renal tubular secretion of penicillin. Nafcillin-probenecid therapy is generally limited to those infections where very high serum levels of nafcillin are necessary.

No dosage alterations are necessary for patients with renal dysfunction, including those on hemodialysis. Hemodialysis does not accelerate nafcillin clearance from the blood.

For patients with hepatic insufficiency and renal failure, measurement of nafcillin serum levels should be performed and dosage adjusted accordingly.

With intravenous administration, particularly in elderly patients, care should be taken because of the possibility of thrombophlebitis.

Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration whenever solution and container permit.

Do not add supplementary medication to nafcillin.

Oral preparations of the penicillinase-resistant penicillins should not be used as initial therapy in serious, life-threatening infections (see PRECAUTIONS-General). Oral therapy with the penicillinase-resistant penicillins may be used to follow-up the previous use of a parenteral agent as soon as the clinical condition warrants. For intramuscular gluteal injections, care should be taken to avoid sciatic nerve injury. With intravenous administration, particularly in elderly patients, care should be taken because of the possibility of thrombophlebitis.


For Intramuscular Use

Reconstitute with Sterile Water for Injection, USP, 0.9% Sodium Chloride Injection, USP or Bacteriostatic Water for Injection, USP (with benzyl alcohol or parabens); add 3.4 mL to the 1 g vial for 4 mL resulting solution; 6.6 mL to the 2 g vial for 8 mL resulting solution. All reconstituted vials have a concentration of 250 mg per mL.

The clear solution should be administered by deep intragluteal injection immediately after reconstitution.

Reconstituted Stability

Reconstitute with the required amount of Sterile Water for Injection, USP, 0.9% Sodium Chloride Injection, USP or Bacteriostatic Water for Injection, USP (with benzyl alcohol or parabens). The resulting solutions are stable for 3 days at room temperature or 7 days under refrigeration and 90 days frozen.

For Direct Intravenous Use

The required amount of drug should be diluted in 15 to 30 mL of Sterile Water for Injection, USP or Sodium Chloride Injection, USP and injected over a 5- to 10- minute period. This may be accomplished through the tubing of an intravenous infusion if desirable.

For Administration by Intravenous Drip

Reconstitute as directed above prior to further dilution.

Concentration mg/mL Sterile Water for Injection 0.9%
Sodium Chloride
M/6 Molar Sodium Lactate Solution 5% Dextrose
in Water
5% Dextrose in 0.45% NaCl 10% Invert Sugar Lactated Ringers Solution
10 - 200 24 Hrs 24 Hrs
30 24 Hrs
2 - 30 24 Hrs 24 Hrs
10 - 30 24 Hrs 24 Hrs
10 - 200 7 Days 7 Days
10 - 30 7 Days 7 Days 7 Days 7 Days 7 Days
FROZEN (-15°C)
250 90 Days 90 Days
10 - 250 90 Days 90 Days 90 Days 90 Days 90 Days

Only those solutions listed above should be used for the intravenous infusion of Nafcillin Sodium, USP. The concentration of the antibiotic should fall within the range specified. The drug concentration and the rate and volume of the infusion should be adjusted so that the total dose of nafcillin is administered before the drug loses its stability in the solution in use.

There is no clinical experience available on the use of this agent in neonates or infants for this route of administration.

This route of administration should be used for relatively short-term therapy (24 to 48 hours) because of the occasional occurrence of thrombophlebitis particularly in elderly patients.

If another agent is used in conjunction with nafcillin therapy, it should not be physically mixed with nafcillin but should be administered separately.


Nafcillin for Injection, USP (nafcillin sodium equivalent to 1 gram or 2 grams nafcillin per vial) is supplied as follows:

NDC Nafcillin for Injection, USP Package Factor
25021-139-10 1 gram Vial 10 vials per carton
25021-140-10 2 gram Vial 10 vials per carton

Storage Conditions

Prior to reconstitution store dry powder at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]

Sterile, Nonpyrogenic, Preservative-free.
The container closure is not made with natural rubber latex.

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