Nafcillin Injection

Nafcillin Injection is an antibiotic used to treat bacterial infections caused by specific resistant staph bacteria.

• Treats infections caused by penicillinase-producing staphylococci (staph strains that break down ordinary penicillin) that have been shown — or are strongly suspected — to be susceptible to nafcillin
• May be started right away when a resistant staph infection is strongly suspected, before laboratory results confirm the bacteria type
• Should not be used for infections caused by bacteria that would respond to regular penicillin G, or for infections caused by organisms other than resistant staphylococci

Nafcillin kills bacteria by interfering with their ability to build a cell wall — the protective outer layer bacteria need to survive. Without a stable cell wall, bacteria fall apart and die. This action only works on actively multiplying bacteria, so completing the full course of treatment matters.

What makes nafcillin special is its resistance to penicillinase — an enzyme that certain staph bacteria produce to destroy ordinary penicillins. Because nafcillin can withstand this enzyme, it remains effective against those resistant strains.

NAFCILLIN Injection is given by a healthcare provider either into a vein (IV) or into a muscle (IM) — it is not taken by mouth. IV doses must be infused slowly over at least 30 to 60 minutes to protect the vein and surrounding tissue. Doses are generally given every 4 hours; the exact schedule and duration depend on the severity of the infection and the patient's overall health.

• IV route: infuse slowly over at least 30–60 minutes each dose
• IM route: injected into a muscle; peak drug levels are reached within about 30 to 60 minutes after an IM dose
• Always follow your prescriber's specific instructions — do not stop treatment early even if you feel better

Like all antibiotics, NAFCILLIN Injection can cause side effects — many are manageable, but some require prompt medical attention.

• Pain, swelling, inflammation, or skin irritation at the injection site
• Phlebitis (vein inflammation) or, rarely, serious tissue damage if the drug leaks outside the vein (extravasation)
• Nausea, vomiting, diarrhea, or mouth sores
• Skin rash, hives, itching, or fever — which can be signs of an allergic reaction
• Elevated liver enzymes or signs of cholestasis (bile flow problems), especially at higher doses
• Kidney-related effects: blood or protein in the urine, or reduced kidney function (interstitial nephritis)
• Low white blood cell counts (neutropenia or agranulocytosis) or bone marrow suppression

Seek emergency care immediately for signs of a severe allergic reaction (throat swelling, trouble breathing, low blood pressure). Call your doctor right away for severe diarrhea, signs of kidney problems, or unusual bruising or fatigue.

• Severe allergic reactions: Serious and sometimes fatal allergic reactions — including anaphylaxis (sudden, severe reaction causing breathing difficulty and blood pressure collapse) — have occurred with penicillins including nafcillin. People with a prior penicillin or cephalosporin allergy are at highest risk. Emergency treatment with epinephrine is required if this happens.
• C. difficile-associated diarrhea (CDAD): Nafcillin can disturb the gut's normal bacterial balance, allowing C. difficile bacteria to overgrow and cause severe, potentially life-threatening diarrhea or colitis. This can occur during or up to 2 months after treatment ends.
• Tissue damage from IV leakage: If nafcillin leaks out of the vein during IV infusion (extravasation), it can cause severe tissue injury and skin breakdown at that site.
• Neurotoxicity: Large IV doses can cause nervous system reactions, especially in patients who also have liver and kidney problems.
• Kidney and liver effects: Nafcillin has been linked to kidney tubule damage and liver enzyme elevations, particularly at high doses.

Nafcillin can interact with several medications — always tell your prescriber and pharmacist everything you take.

• Warfarin (blood thinner): High-dose nafcillin can reduce warfarin's anticoagulant effect, increasing clot risk; blood clotting levels (prothrombin time) must be monitored closely, and the effect can persist for up to 30 days after nafcillin is stopped
• Cyclosporine (organ transplant medication): Nafcillin can drop cyclosporine levels below the therapeutic range, risking organ rejection; levels must be monitored carefully in transplant patients
• Tetracycline antibiotics: These bacteriostatic drugs (they slow bacterial growth rather than killing bacteria) may blunt nafcillin's bacteria-killing action; combined use should be avoided
• Probenecid (gout medication): Probenecid slows nafcillin's clearance from the body, leading to higher and longer-lasting blood levels of nafcillin

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Do not use nafcillin if you have ever had a severe allergic (anaphylactic) reaction to any penicillin antibiotic — this is a firm contraindication
• Tell your doctor about any cephalosporin antibiotic allergy or history of reactions to multiple allergens, as cross-sensitivity is possible
• Tell your doctor if you have liver disease or bile duct problems — nafcillin is primarily eliminated by the liver, and serious liver dysfunction significantly slows its clearance
• Tell your doctor if you are allergic to corn or corn products — some nafcillin formulations contain dextrose that may be derived from corn
• Premature newborns and infants under 3 days old have slower drug clearance and require careful dose adjustment
• Tell your prescriber if you are pregnant, planning to become pregnant, or breastfeeding
• If you are taking cyclosporine after an organ transplant, your transplant team must be informed before nafcillin is started
• Patients with both liver and kidney disease may have significantly reduced ability to clear nafcillin and are at higher risk for toxicity

Taking too much nafcillin — particularly through large IV doses — can cause nervous system (neurotoxic) reactions similar to those seen with penicillin G, especially in patients who also have liver or kidney problems. If an overdose occurs, nafcillin should be stopped and supportive care provided. Hemodialysis (kidney dialysis) does not significantly speed up the removal of nafcillin from the blood.

Nafcillin works by blocking the construction of bacterial cell walls, which bacteria need to survive and reproduce. It is bactericidal — meaning it actively kills bacteria rather than just slowing their growth — and is most effective against bacteria that are actively multiplying. It targets methicillin-susceptible Staphylococcus aureus (MSSA) and is specifically designed to withstand the penicillinase enzymes that make many staph strains resistant to ordinary penicillins.

After an IV dose, nafcillin reaches the bloodstream quickly, with measurable levels detectable within minutes. After an intramuscular (IM) injection, peak blood levels are reached within about 30 to 60 minutes. Nafcillin binds heavily to blood proteins (about 90%), and is distributed widely throughout the body, including into the pleural fluid (around the lungs), bile, and amniotic fluid; meaningful levels also reach the brain's fluid (CSF) when the meninges are inflamed.

Unlike most penicillins, nafcillin is cleared primarily by the liver and excreted in the bile — not mainly through the kidneys. Its half-life (the time for blood levels to drop by half) is roughly 33 to 61 minutes with IV dosing. Kidney disease alone does not significantly affect nafcillin clearance, but serious liver disease slows it considerably. Premature infants and newborns under 3 days old clear nafcillin more slowly than older patients.

Prior to reconstitution store sterile powder at 20º to 25ºC (68º to 77ºF).