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A-Cillin Side Effects

Generic Name: penicillin v potassium

Note: This page contains information about the side effects of penicillin v potassium. Some of the dosage forms included on this document may not apply to the brand name A-Cillin.

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

In addition to its needed effects, some unwanted effects may be caused by penicillin v potassium (the active ingredient contained in A-Cillin). In the event that any of these side effects do occur, they may 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

You should check with your doctor immediately if any of these side effects occur when taking penicillin v potassium:

  • 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 of the side effects that can occur with penicillin v potassium may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

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


In general, side effects associated with oral penicillin therapy have been reported much less frequently than with parenteral penicillin therapy. However, all degrees of hypersensitivity, including fatal anaphylaxis, have been reported with oral penicillin.[Ref]


Gastrointestinal side effects have included nausea, vomiting, epigastric distress, diarrhea, and black hairy tongue. Clostridium difficile associated diarrhea has been reported and may occur during or after therapy. Pancreatitis, intestinal necrosis, and blood in the stool have also been reported.[Ref]


Hypersensitivity reactions with penicillin are more common and more serious with intravenous 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 are seen on the second exposure. There are numerous "hidden" environmental or occupational exposures to penicillin including in utero exposure, breast milk exposure, and occupational exposure.[Ref]

Hypersensitivity side effects have included skin eruptions (maculopapular to exfoliative dermatitis), pruritus, urticaria, laryngeal edema, fever, eosinophilia, hypersensitivity myocarditis, serum sickness-like reactions (chills, fever, edema, arthralgia, and prostration), severe or fatal anaphylaxis, shock, and death.[Ref]


Dermatologic side effects have included rash, peeling, mucosal ulceration, and urticaria.


Hematologic side effects have included hemolytic anemia, anemia, leukopenia, thrombocytopenia, and lymphadenopathy.


Hepatic side effects have included increased SGOT, reversible hepatotoxicity, jaundice, and prolonged cholestasis.

Nervous system

Nervous system side effects have included severe reactions with high dose penicillin therapy or in patients with renal dysfunction. These reactions have included myoclonus, seizures, auditory and visual hallucinations, and decreased mentation. Neurologic reactions occurred frequently in patients with renal dysfunction. Aseptic meningitis has been reported.

Severe neurologic reactions were most often seen with penicillin doses of 18 million 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 one 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 concentrations, compared to 7.8 units/mL in the group without seizures.


Other side effects have included fatigue, asthenia, pain, abnormal taste perception, tinnitus, and aggravation of existing disorders.


Respiratory side effects have included hypoxia, apnea, and dyspnea.


1. "Product Information. Veetids (penicillin)." Apothecon Inc, Plainsboro, NJ.

Not all side effects for A-Cillin may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

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