by Nicole Evans M.D.

Created on: April 04, 2010   Last Updated: December 15, 2010

Amoxicillin is a commonly used prescription antibiotic in the penicillin family.  Amoxicillin is available as syrups (liquid elixirs), tablets and capsules, and is often confused with the antibiotic Ampicillin which is only available as an intravenous medication.

Amoxicillin is FDA approved for the treatment of acute otitis media (ear infection), bacterial sinusitis (sinus infection), upper and lower respiratory tract bacterial infections,  pharyngitis (sore throat), skin and urinary tract caused by bacteria susceptible to Amoxicillin, and more.

Amoxicillin is associated with numerous side effects and contraindications.  This antibiotic is particularly contraindicated in individuals with severe allergic reactions, or anaphylactic reactions, to penicillin and related antibiotics known as beta-lactam.  Serious and occasionally fatal anaphylactic reactions have been reported in patients on penicillin therapy.

The adverse effects of Amoxicillin can affect almost every system of the body.  According to the drug database LexiComp, the frequency with which each specific side effect occurs has not been documented.  Known side effects of Amoxicillin include:

Effects on the central nervous system such as agitation, anxiety, behavioral changes, confusion, dizziness, headache, transient hyperactivity, insomnia and seizures.

Mild to serious adverse skin reactions including acute exanthematous pustulosis, erythematous maculopapular rash, erythema multiforme, exfoliative dermatitis, hypersensitivity vasculitis, mucocutaneous candidiasis, Stevens-Johnson syndrome, toxic epidermal necrolysis and urticaria.

Gastrointestinal side effects such as a black “hairy” tongue, diarrhea, hemorrhagic colitis, nausea, pseudomembranous colitis, C. difficile associated diarrhea (CDAD), vomiting and rarely tooth discoloration that may be brown, yellow, or gray.

Hematologic changes that can become quite severe including agranulocytosis, anemia, eosinophilia, hemolytic anemia, leukopenia, thrombocytopenia, thrombocytopenic purpura and a serum sickness-like reaction.

Adverse effects on the liver ranging from transient enzyme elevation (increased AST and ALT) to actual liver disease acute cytolytic hepatitis, cholestatic jaundice, and hepatic cholestasis.

Renal side effects that include the formation of crystals in the urine (crystalluria) predisposing some individuals to kidney stones.

A particularly interesting side effect of Amoxicillin occurs in individuals with infectious mononucleosis or “mono”.  People with mono tend to have a sore throat that may be mistaken for Strep throat and thus treated with Amoxicillin.  However, a high percentage of patients with infectious mononucleosis develop an unpleasant characteristic rash when given Amoxicillin.

Amoxicillin is an antibiotic used with great frequency to treat infections in both children and adults.  This medication is associated with numerous side effects.  Individuals concerned about the adverse effects of Amoxicillin should speak with their physician.

Source: LexiComp Online. Accessed Apr 3, 2010.

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