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Pen-V Side Effects

Generic Name: penicillin v potassium

Note: This page contains side effects data for the generic drug penicillin v potassium. It is possible that some of the dosage forms included below may not apply to the brand name Pen-V.

For the Consumer

Applies to penicillin v potassium: capsule, powder for solution, powder for suspension, solution, suspension, syrup, tablet, tablet for suspension, tablet chewable, tablet extended release

As well as its needed effects, penicillin v potassium (the active ingredient contained in Pen-V) may cause unwanted side effects that require medical attention.

Stop taking penicillin v potassium and get emergency help immediately if any of the following effects occur:

Less common:
  • Fast or irregular breathing
  • fever
  • joint pain
  • lightheadedness or fainting (sudden)
  • puffiness or swelling around the face
  • red, scaly skin
  • shortness of breath
  • skin rash, hives, itching

Major Side Effects

If any of the following side effects occur while taking penicillin v potassium, check with your doctor immediately:

  • Abdominal or stomach cramps and pain (severe)
  • abdominal tenderness
  • convulsions (seizures)
  • decreased amount of urine
  • diarrhea (watery and severe), which may also be bloody
  • mental depression
  • nausea and vomiting
  • pain at place of injection
  • sore throat and fever
  • unusual bleeding or bruising
  • yellow eyes or skin
Rare - For penicillin G procaine only
  • Agitation or combativeness
  • anxiety
  • confusion
  • fear of impending death
  • feeling, hearing, or seeing things that are not real

Minor Side Effects

Some penicillin v potassium side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

More common:
  • Diarrhea (mild)
  • headache
  • sore mouth or tongue
  • vaginal itching and discharge
  • white patches in the mouth and/or on the tongue

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]


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

Very rare (less than 0.01%): Interstitial nephritis
Frequency not reported: Nephropathy[Ref]

Nervous system

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]

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: 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, Plainsboro, NJ.

2. Cerner Multum, Inc. "Australian Product Information." O 0

3. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

It is possible that some side effects of Pen-V may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.