Nallpen (generic: nafcillin) is a prescription medication used to treat bacterial infections that cause pneumonia, urinary tract, skin, bone, joint, blood, heart valve infections, and infections within the brain. Nallpen belongs to a group of drugs called penicillin antibiotics, which work by stopping the growth of bacteria in the body.

This medication is available in an injectable form to be given directly into a vein (IV) by a healthcare professional.

Common side effects of Nallpen include an allergic reaction, pain at the site of injection, and upset stomach.