DOSING: The usual oral dose range for most infections is 250 to 500 mg 4 times daily for 7-14 days. Injectable doses range from 250 to 2000 mg 4 times daily. When used to treat gonorrhea, a single 3.5 gram dose (seven 500 mg capsules) is administered with 1 g probenecid (Benemid). The probenecid slows down the elimination of ampicillin so that ampicillin remains in the body longer. Food in the stomach reduces how much and how quickly ampicillin is absorbed. Therefore, ampicillin should be taken either 1 hour prior to or 2 hours following a meal for maximal absorption; however, for persons who experience nausea or stomach distress after taking ampicillin, it may be taken with meals.
DRUG INTERACTIONS: Probenecid (Benemid) causes an increase in the amount of ampicillin in the body. Use of ampicillin with allopurinol (Zyloprim) can increase the incidence of drug-related skin rash. Ampicillin may reduce the effect BCG live vaccine and Typhoid live vaccine .
PREGNANCY: Ampicillin is considered safe during pregnancy.
NURSING MOTHERS: Ampicillin is excreted in breast milk and may cause diarrhea or allergic responses in nursing infants. If ampicillin is used during pregnancy, the potential benefit of ampicillin for the mother should be weighed against the potential risk of side effects in the infant. Ampicillin is used for treating infants.
SIDE EFFECTS: Common side effects of ampicillin include nausea, vomiting, loss of appetite, diarrhea, abdominal pain, rash, itching, headache, confusion and dizziness. Patients with a history of allergic reactions to other penicillins should not receive ampicillin. Persons who are allergic to the cephalosporin class of antibiotics, which are related to the penicillins may or may not be allergic to penicillins [for example, cefaclor (Ceclor), cephalexin (Keflex), and cefprozil (Cefzil)]. Serious but rare reactions include seizures, severe allergic reactions (anaphylaxis), and low platelet or red blood cell count. Ampicillin can alter the normal bacteria in the colon and encourage overgrowth of some bacteria such as Clostridium difficile which causes inflammation of the colon (pseudomembranous colitis). Patients who develop signs of pseudomembranous colitis after starting ampicillin (diarrhea, fever, abdominal pain, and possibly shock) should contact their physician immediately.
Reference: FDA Prescribing Information
REFERENCE: FDA Prescribing Information
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