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Penicillin v potassium Side Effects

Medically reviewed by Last updated on Aug 31, 2023.

Applies to penicillin v potassium: oral for solution, oral tablets.

Side effects include:

Adverse GI effects (e.g., nausea, vomiting, epigastric distress, diarrhea, black hairy tongue), hypersensitivity reactions (e.g., fever, eosinophilia, rash, urticaria, serum sickness-like reactions).

For Healthcare Professionals

Applies to penicillin v potassium: oral powder for reconstitution, oral tablet.


The most common side effects are gastrointestinal effects and hypersensitivity reactions. In general, hypersensitivity reactions have been reported much less frequently after oral than after parenteral therapy; however, all degrees of hypersensitivity (including fatal anaphylaxis) have been reported with oral penicillin.[Ref]


Onset of Clostridium difficile-associated diarrhea has been reported during or after antibacterial therapy.[Ref]

Common (1% to 10%): Nausea, vomiting, abdominal pain, diarrhea

Rare (0.01% to 0.1%): Sore mouth, black hairy tongue (discoloration of tongue), pseudomembranous colitis

Frequency not reported: Epigastric distress, stomatitis, glossitis, soft stools, pancreatitis, intestinal necrosis, blood in the stool[Ref]


Hypersensitivity reactions with penicillin were more common and more serious with IV therapy, but have also been reported with oral therapy. An initial sensitizing exposure is required to stimulate the production of antigen-specific IgE before clinical manifestations of hypersensitivity were seen on the second exposure. There were numerous "hidden" environmental or occupational exposures to penicillin including in utero exposure, breast milk exposure, and occupational exposure.[Ref]

Common (1% to 10%): Allergic reactions (usually manifested as skin reactions)

Rare (0.01% to 0.1%): Severe allergic reactions (causing angioedema, laryngeal edema, anaphylaxis [severe or fatal])

Frequency not reported: Serum sickness-like reactions (chills, fever, edema, arthralgia, prostration), hypersensitivity/allergic reactions (including skin eruptions [maculopapular to exfoliative dermatitis], pruritus, urticaria, angioneurotic edema, erythema multiforme, joint pain, fever, eosinophilia, hypersensitivity myocarditis, hemolytic anemia, interstitial nephritis, anaphylactic shock [sometimes fatal] with collapse, anaphylactoid reactions [asthma, purpura, gastrointestinal symptoms])[Ref]


Common (1% to 10%): Rash (urticarial, erythematous, morbilliform), pruritus

Rare (0.01% to 0.1%): Exfoliative dermatitis

Frequency not reported: Peeling, mucosal ulceration, urticaria[Ref]


Very rare (less than 0.01%): Changes in blood counts, hemolytic anemia, leukopenia, thrombocytopenia, neutropenia, eosinophilia, agranulocytosis

Frequency not reported: Coagulation disorders (including prolonged bleeding time, platelet dysfunction), anemia, lymphadenopathy[Ref]


Very rare (less than 0.01%): Hepatitis, cholestatic jaundice

Frequency not reported: Increased AST, reversible hepatotoxicity, jaundice, prolonged cholestasis[Ref]


Very rare (less than 0.01%): Interstitial nephritis

Frequency not reported: Nephropathy[Ref]

Nephropathy has typically been associated with high doses of parenteral penicillin.[Ref]

Nervous system

CNS toxicity has been reported, especially with high doses or in severe renal dysfunction. Paresthesia has been reported with prolonged use. Neuropathy has typically been associated with high doses of parenteral penicillin.

Severe neurologic reactions were most often seen with penicillin doses of 18 to 80 million units daily. These reactions frequently abated after discontinuation of penicillin. In several cases, penicillin was restarted at a lower dose with no further sequelae. In 1 review, the authors found that cerebral spinal fluid (CSF) penicillin levels were higher in patients with seizures than in those without. CSF penicillin levels ranged from 12 to 61 units/mL in the seizure group with the highest CSF levels, compared to 7.8 units/mL in the group without seizures.[Ref]

Frequency not reported: Central nervous system (CNS) toxicity (including convulsions), paresthesia, neuropathy, myoclonus, seizures, decreased mentation, abnormal taste perception, tinnitus, neurologic reactions, aseptic meningitis[Ref]


Frequency not reported: Overgrowth of nonsusceptible organisms (e.g., Candida), fatigue, asthenia, pain, aggravation of existing disorders[Ref]


Frequency not reported: Vulvovaginitis[Ref]


Frequency not reported: Auditory hallucinations, visual hallucinations


Frequency not reported: Hypoxia, apnea, dyspnea


1. Product Information. Veetids (penicillin). Apothecon Inc. 2001.

2. Cerner Multum, Inc. UK Summary of Product Characteristics.

3. Cerner Multum, Inc. Australian Product Information.

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.