NAFCILLIN SODIUM SALT

Indications

It is effective against Gram-positive cocci and staphylococci that produce penicillinase. It is used for the same indications as methicillin. Synonyms of this drug are nafcil, nalpen, unipen, and others. Another type of semisynthetic penicillin that should undoubtedly be considered is penicillin derivatives of heteroylcarboxylic acids (as a rule an isoxazol) in the third position of which is present a substituted or nonsubstituted phenyl radical (oxacillin, cloxacillin, dicloxacillin), which plays the role of the radical in the acyl side group. These penicillins (oxacillin, cloxacillin, dicloxacillin), which are resistant to penicillinase, are active with respect to penicillin-G-resistant staphylococci. Their antimicrobial spectrum is restricted to Gram-positive microorganisms. Penicillins that are resistant to penicillinase are the drug of choice for infections resistant to penicillin G, Staph. aureus, or coagulase-negative staphylococci. They are also effective for infections caused by nonenterococcus types of streptococci, such as streptococci groups A, B, C, and G, as well as pneumococci.

Therapeutic Function

Antibacterial

Antimicrobial activity

The antibacterial spectrum is similar to that of the isoxazolylpenicillins but it is more active against streptococci and pneumococci. Activity in vitro is depressed in the presence of serum. It is more stable than the isoxazolylpenicillins to staphylococcal β-lactamase. There is complete cross-resistance with other group 3 penicillins.

Pharmacokinetics

Oral absorption: c. 35% Cmax 1 g intramuscular:8 mg/L after 1 h 500 mg intravenous:30 mg/L after 5 min Plasma half-life: 0.5 h Plasma protein binding: 90% Absorption and distribution Nafcillin is poorly absorbed after oral administration, and absorption is further depressed if the drug is given with food. Most dosing is now intravenous. Penetration into tissues is similar to that of the isoxazolylpenicillins. Penetration into normal meninges is low, but is higher in inflamed meninges. Metabolism and excretion About 60–70% is inactivated in the liver. Following intramuscular administration, about 30% appears in the urine, producing concentrations up to 1000 mg/L. Administration of probenecid reduces the urinary excretion and raises and prolongs the plasma level. About 8% of the dose is excreted in the bile.

Side effects

There is cross-allergenicity with other penicillins. Its side effects are similar to the penicillins. Pseudomembranous colitis has been reported.

Synthesis

Nafcillin, [2S-(2α,5α,6β)]-3,3-dimethyl-7-oxo-6-(2-ethoxy-1-naphthamido)-4- thia-1-azabicyclo[3.2.0]-heptan-2-carboxylic acid (32.1.1.4), is synthesized by acylating 6-APA with 2-ethoxy-1-naphthoic acid chloride in the presence of triethylamine.