Pyrimethamine Side Effects

Medically reviewed by Drugs.com. Last updated on May 8, 2022.

For the Consumer

Applies to pyrimethamine: oral tablet

Side effects requiring immediate medical attention

Along with its needed effects, pyrimethamine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking pyrimethamine:

Rare

• Chest pain
• dry cough
• fever
• rapid or trouble breathing
• skin rash
• unusual tiredness or weakness

Incidence not known

• Black, tarry stools
• bleeding gums
• blistering, peeling, or loosening of the skin
• blood in the urine or stools
• chills
• cough
• diarrhea
• difficulty swallowing
• dizziness
• fainting spells
• fast or irregular heartbeat
• hives, itching
• irritation or soreness of the tongue
• joint or muscle pain
• lower back or side pain
• puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
• painful or difficult urination
• pale skin
• pinpoint red spots on the skin
• red, irritated eyes
• red skin lesions, often with a purple center
• sore throat
• sores, ulcers, or white spots on the lips or in the mouth
• swollen glands
• tightness in the chest
• unusual bleeding or bruising

Side effects not requiring immediate medical attention

Some side effects of pyrimethamine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

• Loss of appetite
• vomiting
• weight loss

For Healthcare Professionals

Applies to pyrimethamine: compounding powder, oral tablet

General

Since this drug is coadministered with a sulfonamide, the manufacturer product information for the relevant sulfonamide should be consulted for sulfonamide-related side effects.^[Ref]

Gastrointestinal

Very common (10% or more): Nausea, vomiting, diarrhea, colic

Uncommon (0.1% to 1%): Dry mouth, dry throat

Very rare (less than 0.01%): Buccal ulceration

Frequency not reported: Glossitis, atrophic glossitis^[Ref]

Nervous system

Precipitation of a grand mal attack in a patient predisposed to epilepsy was reported; clinical significance was not established.^[Ref]

Very common (10% or more): Headache

Common (1% to 10%): Dizziness

Very rare (less than 0.01%): Convulsions/seizures

Frequency not reported: Ataxia, tremors, precipitation of grand mal attack^[Ref]

Hematologic

Very common (10% or more): Anemia

Common (1% to 10%): Thrombocytopenia, leukopenia

Very rare (less than 0.01%): Pancytopenia

Frequency not reported: Megaloblastic anemia, neutropenia, agranulocytosis^[Ref]

Dermatologic

Very common (10% or more): Rash

Uncommon (0.1% to 1%): Abnormal skin pigmentation, dermatitis

Other

Uncommon (0.1% to 1%): Fever, malaise

Psychiatric

Insomnia was reported when this drug was given weekly at higher than recommended doses.

Uncommon (0.1% to 1%): Depression

Very rare (less than 0.01%): Insomnia

Respiratory

Rare (0.01% to 0.1%): Pulmonary eosinophilia

Very rare (less than 0.01%): Pneumonia with cellular and eosinophilic pulmonary infiltration^[Ref]

Pneumonia with cellular and eosinophilic pulmonary infiltration was observed when this drug was administered once a week with sulfadoxine.^[Ref]

Hypersensitivity

Frequency not reported: Hypersensitivity reactions (included erythema multiforme, Stevens-Johnson Syndrome, toxic epidermal necrolysis, Lyell's syndrome, hepatitis, anaphylaxis, pulmonary reactions, maculopapular rashes)^[Ref]

Cardiovascular

Circulatory collapse was reported in patients treated with higher than recommended doses.^[Ref]

Very rare (less than 0.01%): Circulatory collapse

Frequency not reported: Disorders of cardiac rhythm, arrhythmias^[Ref]

Metabolic

Hyperphenylalaninemia was reported in neonates treated for congenital toxoplasmosis.^[Ref]

Very rare (less than 0.01%): Hyperphenylalaninemia

Frequency not reported: Anorexia^[Ref]

Genitourinary

Very rare (less than 0.01%): Hematuria

Oncologic

A 51-year-old female developed chronic granulocytic leukemia after taking this drug for 2 years for toxoplasmosis and a 56-year-old patient developed reticulum cell sarcoma after taking this drug for 14 months for toxoplasmosis.^[Ref]

Frequency not reported: Chronic granulocytic leukemia, reticulum cell sarcoma^[Ref]

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.

Medical Disclaimer