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Ampicillin/Ampicillin: uses, dosing, side effects & brands

Ampicillin/Ampicillin is a medicine sold in the U.S. under 5 brand and generic names. Below: what the FDA label says, every product that contains it, what the pills look like, and its recall record.

By the pharmaranks editorial teamReviewed against the FDA (openFDA label, NDC Directory & Enforcement) sourcesUpdated Jul 24, 2026How we research

Key facts

Available as
Capsule
Sold as
5 products — Ampicillin Trihydrate, Penbritin and Polycillin, and others
Prescription?
Prescription only
Generic available?
Yes

How ampicillin/ampicillin is dosed

From the FDA label for Ampicillin Trihydrate (application ANDA216554). Other ampicillin/ampicillin products — different forms, different strengths — are dosed differently. Follow the label for the one you were prescribed.

Adults and pediatric patients weighing over 20 kg: For genitourinary or gastrointestinal tract infections other than gonorrhea in men and women, the usual dose is 500 mg qid in equally spaced doses; severe or chronic infections may require larger doses. For the treatment of gonorrhea in both men and women, a single oral dose of 3.5 grams of ampicillin administered simultaneously with 1 gram of probenecid is recommended. Physicians are cautioned to use no less than the above recommended dosage for the treatment of gonorrhea. Follow-up cultures should be obtained from the original site(s) of infection 7 to 14 days after therapy. In women, it is also desirable to obtain culture test-of-cure from both the endocervical and anal canals. Prolonged intensive therapy is needed for complications such as prostatitis and epididymitis. For respiratory tract infections , the usual dose is 250 mg qid in equally spaced doses. Pediatric patients weighing 20 kg or less: For genitourinary or gastrointestinal tract infections , the usual dose is 100 mg/kg/day total, qid in equally divided and spaced doses. For respiratory tract infections, the usual dose is 50 mg/kg/day total, in equally divided and spaced doses three to four times daily. Doses for children should not exceed doses recommended for adults. All Patients, Irrespective of Age and Weight : Larger doses may be required for severe or…

Ampicillin/Ampicillin side effects

As with other penicillins, it may be expected that untoward reactions will be essentially limited to sensitivity phenomena. They are more likely to occur in individuals who have previously demonstrated hypersensitivity to penicillin and in those with a history of allergy, asthma, hay fever, or urticaria. The following adverse reactions have been reported as associated with the use of ampicillin: Infections and Infestations: Clostridioides difficile - associated diarrhea (see WARNINGS section). Gastrointestinal : glossitis, stomatitis, nausea, vomiting, enterocolitis, pseudomembranous colitis, and diarrhea. These reactions are usually associated with oral dosage forms of the drugs. Hypersensitivity Reactions : Severe cutaneous adverse reactions, including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), angioedema, and acute generalized exanthematous pustulosis (AGEP) have been reported in beta-lactam antibiotics (see WARNINGS ). An erythematous, mildly pruritic, maculopapular skin rash has been reported fairly frequently. The rash, which usually does not develop within the first week of therapy, may cover the entire body including the soles, palms, and oral mucosa. The eruption usually disappears in three to seven days. Other hypersensitivity reactions that have been reported are: skin rash,…

Who shouldn’t take ampicillin/ampicillin

The use of ampicillin is contraindicated in individuals with a history of serious hypersensitivity reactions (e.g., anaphylaxis or Stevens-Johnson syndrome) to ampicillin or to other beta-lactam antibacterial drugs. Ampicillin is also contraindicated in infections caused by penicillinase-producing organisms. Ampicillin is contraindicated in patients with a previous history of cholestatic jaundice/hepatic dysfunction associated with treatment with ampicillin.

Ampicillin/Ampicillin drug interactions

When administered concurrently, the following drugs may interact with ampicillin. Allopurinol : Substantially increased incidence of skin rashes in patients receiving both drugs as compared to patients receiving ampicillin alone. It is not known whether this potentiation of ampicillin rashes is due to allopurinol or the hyperuricemia present in these patients. Bacteriostatic Antibiotics : Chloramphenicol, erythromycins, sulfonamides, or tetracyclines may interfere with the bactericidal effect of penicillins. This has been demonstrated in vitro; however, the clinical significance of this interaction is not well-documented. Oral Contraceptives : May be less effective and increased breakthrough bleeding may occur. Probenecid : May decrease renal tubular secretion of ampicillin resulting in increased blood levels and/or ampicillin toxicity.

Every ampicillin/ampicillin product we track (5)

Same active ingredient — different manufacturer, form, price and FDA recall record. That last one is what our independent score measures.

Ampicillin/Ampicillin products
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Frequently asked questions

What is ampicillin/ampicillin?

To reduce the development of drug-resistant bacteria and maintain the effectiveness of ampicillin and other antibacterial drugs, ampicillin should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria. DESCRIPTION Ampicillin trihydrate is a semisynthetic penicillin derived from the basic penicillin nucleus, 6-aminopenicillanic acid.

Can you take ampicillin/ampicillin with other medicines?

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run ampicillin/ampicillin against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

What brand names is ampicillin/ampicillin sold under?

We track 5 ampicillin/ampicillin-containing products in the U.S.: Ampicillin Trihydrate, Penbritin, Polycillin, Principen '250' and Principen '500'. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.

What forms does ampicillin/ampicillin come in?

Across the brands we track, ampicillin/ampicillin is currently marketed as capsule, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

Is there a generic ampicillin/ampicillin?

Yes. Our catalog lists 1 generic ampicillin/ampicillin product alongside the brand versions. A generic has the same active ingredient and must meet the FDA's bioequivalence standard; it usually costs less. Ask your pharmacist which one your plan covers.

Cite this page
APA
pharmaranks. (2026, July 24). Ampicillin/Ampicillin: uses, dosing, side effects & brands. https://pharmaranks.com/drugs/ampicillin-ampicillin
MLA
“Ampicillin/Ampicillin: uses, dosing, side effects & brands.” pharmaranks, 24 July 2026, https://pharmaranks.com/drugs/ampicillin-ampicillin.

We summarise public FDA and NIH sources — for a clinical claim, cite the primary source we link to as well.

Sources: FDA openFDA drug label, National Drug Code Directory, and Enforcement (recall) database. This page reproduces public FDA data and is not medical advice. Dosing is set by your prescriber.

Read the full FDA label for ampicillin/ampicillin on DailyMed (NIH) ↗.