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Omnipen Side Effects

Generic name: ampicillin

Medically reviewed by Last updated on Jan 23, 2024.

Note: This document contains side effect information about ampicillin. Some dosage forms listed on this page may not apply to the brand name Omnipen.

Applies to ampicillin: oral capsules, oral for suspension, parenteral powder for injection or infusion.

Side effects include:

GI effects (diarrhea, nausea), rash.

For Healthcare Professionals

Applies to ampicillin: compounding powder, injectable powder for injection, oral capsule, oral powder for reconstitution.


Very common (10% or more): Rash, pruritus, exanthema, itching

Common (1% to 10%): Morbilliform rash

Uncommon (0.1% to 1%): Angioneurotic edema, allergic vasculitis, exfoliative dermatitis, exudative erythema multiforme, urticaria, Stevens-Johnson syndrome, toxic epidermal necrolysis

Frequency not reported: Erythematous maculopapular rash (including mildly pruritic), macular rash, purpura, maculopapular rash, skin reactions (e.g., erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis), other skin rashes, erythematous eruptions, acute generalized exanthematous pustulosis[Ref]


Very common (10% or more): Diarrhea, nausea, vomiting, flatulence/meteorism, soft stools, abdominal pain

Uncommon (0.1% to 1%): Glossitis, stomatitis, enterocolitis, pseudomembranous colitis

Frequency not reported: Oral candidiasis/moniliasis, black hairy tongue, Clostridium difficile-associated diarrhea, hemorrhagic colitis, sore mouth/tongue, pancreatitis, gastritis, generalized abdominal cramps[Ref]

Glossitis, stomatitis, black hairy tongue, nausea, vomiting, enterocolitis, pseudomembranous colitis, and diarrhea were typically associated with oral formulations.

Acute pancreatitis has been reported and confirmed by rechallenge with this drug in a patient in whom there was no other obvious cause of pancreatitis.[Ref]


Common (1% to 10%): Localized phlebitis

Frequency not reported: Phlebitis at IV administration site, pain at IM administration site[Ref]


Common (1% to 10%): Swelling and pain, exanthema and enanthem in the oral region

Uncommon (0.1% to 1%): Infection with fungi/resistant bacteria (especially during prolonged and/or repeated use), drug fever

Frequency not reported: Fever (including high fever)[Ref]


Uncommon (0.1% to 1%): Serious allergic reactions (e.g., serum sickness, allergic nephritis)

Rare (0.01% to 0.1%): Life-threatening anaphylactic shock

Frequency not reported: Anaphylaxis, serum sickness-like reactions, hypersensitivity reactions (including urticarial rash, erythema multiforme, exfoliative dermatitis, edema, hypotension, fever, eosinophilia, dyspnea, interstitial nephritis, Henoch-Schonlein purpura, focal glomerulonephritis, Stevens-Johnson syndrome, bullous pemphigoid, hypersensitivity myocarditis, toxic epidermal necrolysis, fixed drug eruptions)[Ref]


Anemia, thrombocytopenia, hemolytic anemia, thrombocytopenic purpura, eosinophilia, leukopenia, and agranulocytosis have been reported during treatment with penicillins. In general, these reactions were reversible after stopping therapy and were believed to be sensitivity reactions.

Neutropenia was described in a case report of 3 pediatric patients who received high doses (150 to 400 mg/kg) of this drug IV. In all 3 cases, white blood cell and neutrophil counts returned to normal after discontinuation of therapy.[Ref]

Uncommon (0.1% to 1%): Thrombocytopenia, thrombocytopenic purpura, leukopenia, anemia, eosinophilia, agranulocytosis, hemolytic anemia

Very rare (less than 0.01%): Granulocytopenia, pancytopenia, prolonged bleeding time, prolonged prothrombin time

Frequency not reported: Prolonged activated partial thromboplastin time, platelet aggregation abnormalities, neutropenia, Henoch Schonlein purpura, red cell aplasia[Ref]

Nervous system

Seizures have been reported with renal dysfunction or at very high IV doses.

Seizures have been reported in patients with high serum drug levels, although these patients were otherwise very ill. High cerebral spinal fluid (CSF) levels of some penicillins were known to be potentially neurotoxic, and the CSF level of this drug increased significantly in meningitis.

Generalized seizures have been described in 2 patients during use of this drug, although in both cases, there were underlying disease factors that may have predisposed the patients to seizure activity.

Encephalopathy has occurred when blood drug level reached 800 mg/L.

Toxic symptoms (e.g., drowsiness, hyperreflexia, myoclonic twitches, convulsions, coma) have occurred at lower drug levels in patients with meningitis; the blood-brain barrier became more permeable in meningitis.[Ref]

Rare (0.01% to 0.1%): Headache, dizziness, myoclonus, seizures

Frequency not reported: Encephalopathy, drowsiness, hyperreflexia, myoclonic twitches, convulsions, coma[Ref]


Uncommon (0.1% to 1%): Acute interstitial nephritis

Very rare (less than 0.01%): Acute renal failure with excretion of urine crystals

Frequency not reported: Interstitial nephritis, nephropathy, glomerulonephritis[Ref]


Uncommon (0.1% to 1%): Transaminase elevation

Frequency not reported: Hepatitis, cholestatic jaundice, elevated AST, moderately increased transaminases (transient), elevated ALT, cholestasis[Ref]

Mild, temporary elevation in AST reported in patients who received larger (2 to 4 times) and more frequent IM injections than usual. Evidence indicated AST was released at IM injection sites for this drug and increased AST did not necessarily indicate liver involvement.[Ref]


Uncommon (0.1% to 1%): Crystalluria

Frequency not reported: Vaginal candidiasis/moniliasis[Ref]

Crystalluria has been reported with high-dose IV administration.[Ref]


Uncommon (0.1% to 1%): Laryngeal edema

Frequency not reported: Laryngeal stridor[Ref]


Frequency not reported: Arthralgia


Frequency not reported: Anorexia


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3. Dolovich J, Ruhno J, Sauder DN, Ahlstedt S, Hargreave FE (1988) "Isolated late cutaneous skin test response to ampicillin: a distinct entity." J Allergy Clin Immunol, 82, p. 676-9

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13. Koklu S, Yuksel O, Filik L, Uskudar O, Altundag K, Altiparmak E (2003) "Recurrent cholestasis due to ampicillin." Ann Pharmacother, 37, p. 395-7

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.