Pyrimethamine Dosage

Medically reviewed by Drugs.com. Last updated on Jul 31, 2023.

Usual Adult Dose for Toxoplasmosis

Starting dose: 50 to 75 mg orally once a day (with 1 to 4 g/day of a sulfapyrimidine-type sulfonamide [e.g., sulfadoxine])

Comments:

• This starting dose is generally continued for 1 to 3 weeks, depending on patient response and tolerance to therapy.
• After using the starting dose for 1 to 3 weeks, the dosage for each drug may be reduced to about one-half and continued for an additional 4 to 5 weeks.
• The dose must be carefully adjusted to provide maximum therapeutic effect and minimum of side effects; young patients may tolerate higher doses than older patients.

Use: With a sulfonamide, for the treatment of toxoplasmosis

US CDC Recommendations:

• Loading dose: 100 mg orally on the first day
• Maintenance dose: 25 to 50 mg orally per day

Duration of therapy: 4 to 6 weeks

US CDC, National Institutes of Health (NIH), and HIV Medicine Association of the Infectious Diseases Society of America (HIVMA/IDSA) Recommendations for HIV-Infected Adults:

• Loading dose: 200 mg orally once
• Maintenance dose:
• Weight less than 60 kg: 50 mg orally once a day
• Weight at least 60 kg: 75 mg orally once a day

Duration of Therapy: At least 6 weeks

Comments:

• US CDC: With leucovorin and sulfadiazine, recommended for ocular toxoplasmosis (the classic therapy)
• US CDC: Treatment for ocular diseases should be based on a complete ophthalmologic evaluation; therapy should be followed by reevaluation of the patient's condition.
• HIV-Infected Adults: With leucovorin and sulfadiazine, recommended as part of the preferred regimen for treating Toxoplasma gondii encephalitis; if this drug is unavailable or obtaining it is delayed, sulfamethoxazole-trimethoprim should be used instead of this drug and sulfadiazine.
• HIV-Infected Adults: With leucovorin and (clindamycin or atovaquone), recommended as part of alternative regimens for treating T gondii encephalitis
• HIV-Infected Adults: Duration of therapy may be longer if clinical/radiologic disease is extensive or incomplete response at 6 weeks.
• HIV-Infected Adults: After completion of acute therapy, all patients should be continued on chronic maintenance therapy.
• Current guidelines should be consulted for additional information.

Usual Adult Dose for Toxoplasmosis - Prophylaxis

US CDC, NIH, and HIVMA/IDSA Recommendations for HIV-Infected Adults:
Primary Prophylaxis: 50 or 75 mg orally once a week OR 25 mg orally once a day

Chronic Maintenance Therapy:

• Preferred regimen and alternative regimen with clindamycin: 25 to 50 mg orally once a day
• Alternative regimen with atovaquone: 25 mg orally once a day

Comments:

• With (dapsone or atovaquone) and leucovorin, recommended as part of an alternative regimen for preventing the first episode of T gondii encephalitis (primary prophylaxis)
• With leucovorin and sulfadiazine, recommended as part of the preferred regimen (and with leucovorin and [clindamycin or atovaquone], recommended as part of alternative regimens) for chronic maintenance therapy (secondary prophylaxis) for T gondii encephalitis
• Current guidelines should be consulted for additional information.

Usual Adult Dose for Pneumocystis Pneumonia Prophylaxis

US CDC, NIH, and HIVMA/IDSA Recommendations for HIV-Infected Adults:
Primary and Secondary Prophylaxis: 50 or 75 mg orally once a week OR 25 mg orally once a day with food

Comments:

• With (dapsone or atovaquone) and leucovorin, recommended as part of an alternative regimen for preventing the first episode of Pneumocystis pneumonia (PCP) (primary prophylaxis) and preventing subsequent episodes of PCP (secondary prophylaxis)
• Current guidelines should be consulted for additional information.

Usual Adult Dose for Protozoan Infection

US CDC, NIH, and HIVMA/IDSA Recommendations for HIV-Infected Adults:

• Acute Infection: 50 to 75 mg orally once a day
• Chronic Maintenance Therapy: 25 mg orally once a day

Comments:

• With leucovorin, recommended as alternative therapy for treating cystoisosporiasis (formerly isosporiasis) due to Cystoisospora belli (formerly Isospora belli); recommended for acute infection and for chronic maintenance therapy (secondary prophylaxis) in patients with CD4 count less than 200 cells/mm3
• Current guidelines should be consulted for additional information.

Usual Pediatric Dose for Toxoplasmosis

1 mg/kg/day orally divided into 2 equal daily doses; after 2 to 4 days, may reduce to one-half and continue for about 1 month

Comments:

• The dose must be carefully adjusted to provide maximum therapeutic effect and minimum of side effects; young patients may tolerate higher doses than older patients.
• The usual pediatric sulfonamide dosage should be used with this drug.

Use: With a sulfonamide, for the treatment of toxoplasmosis

US CDC Recommendations for Pediatrics:
Congenitally-infected neonates and infants:

• Loading dose: 2 mg/kg/day orally in 2 divided doses for the first 2 days
• Maintenance dose (starting day 3): 1 mg/kg orally per day for 2 months (or 6 months if symptomatic), then 1 mg/kg orally 3 times a week

Duration of therapy: 12 months

Ocular toxoplasmosis:

• Loading dose: 2 mg/kg orally on the first day
• Maintenance dose: 1 mg/kg orally per day

Duration of therapy: 4 to 6 weeks

US CDC, NIH, HIVMA/IDSA, and Pediatric Infectious Disease Society (PIDS) Recommendations for HIV-Exposed and HIV-Infected Children:
Congenital Toxoplasmosis:

• Loading dose: 2 mg/kg orally once a day for 2 days
• Maintenance dose: 1 mg/kg orally once a day for 2 to 6 months, then 1 mg/kg orally 3 times a week

Duration of therapy: 12 months

Acquired Toxoplasmosis (Acute Induction Therapy):

• Loading dose: 2 mg/kg orally once a day for 3 days
• Maximum dose: 50 mg/dose
• Maintenance dose: 1 mg/kg orally once a day
• Maximum dose: 25 mg/dose

Duration of therapy: At least 6 weeks

US CDC, NIH, and HIVMA/IDSA Recommendations for HIV-Infected Adolescents:

• Loading dose: 200 mg orally once
• Maintenance dose:
• Weight less than 60 kg: 50 mg orally once a day
• Weight at least 60 kg: 75 mg orally once a day

Duration of Therapy: At least 6 weeks

Comments:

• US CDC: With leucovorin and sulfadiazine, recommended for ocular toxoplasmosis (the classic therapy) and congenital toxoplasmosis
• US CDC: Treatment for ocular diseases should be based on a complete ophthalmologic evaluation; therapy should be followed by reevaluation of the patient's condition.
• HIV-Infected Children: With leucovorin and sulfadiazine, recommended as part of the first-choice regimen for congenital toxoplasmosis and acquired toxoplasmosis
• HIV-Infected Adolescents: With leucovorin and sulfadiazine, recommended as part of the preferred regimen for treating T gondii encephalitis; if this drug is unavailable or obtaining it is delayed, sulfamethoxazole-trimethoprim should be used instead of this drug and sulfadiazine.
• HIV-Infected Adolescents: With leucovorin and (clindamycin or atovaquone), recommended as part of alternative regimens for treating T gondii encephalitis
• HIV-Infected Children (acquired toxoplasmosis) and Adolescents: Duration of therapy may be longer if clinical/radiologic disease is extensive or incomplete response at 6 weeks.
• HIV-Infected Children (acquired toxoplasmosis) and Adolescents: After completion of acute induction therapy/acute therapy, all patients should be continued on chronic suppressive/maintenance therapy.
• Current guidelines should be consulted for additional information.

Usual Pediatric Dose for Toxoplasmosis - Prophylaxis

US CDC, NIH, HIVMA/IDSA, and PIDS Recommendations for HIV-Exposed and HIV-Infected Children:
Primary and Secondary Prophylaxis: 1 mg/kg or 15 mg/m2 orally once a day
Maximum dose: 25 mg/dose

US CDC, NIH, and HIVMA/IDSA Recommendations for HIV-Infected Adolescents:
Primary Prophylaxis: 50 or 75 mg orally once a week OR 25 mg orally once a day

Chronic Maintenance Therapy:

• Preferred regimen and alternative regimen with clindamycin: 25 to 50 mg orally once a day
• Alternative regimen with atovaquone: 25 mg orally once a day

Comments:

• Children: With leucovorin and (dapsone [aged 1 month or older] or atovaquone [aged 4 to 24 months]), recommended as part of an alternative regimen for primary prophylaxis of toxoplasmosis
• Children: With leucovorin and sulfadiazine, recommended as part of the first-choice regimen for secondary prophylaxis (suppressive therapy) of toxoplasmosis; with leucovorin and (atovaquone [aged 4 to 24 months] or clindamycin), recommended as part of alternative regimens for secondary prophylaxis of toxoplasmosis
• Children: Atovaquone plus leucovorin may be used with or without this drug for primary and secondary prophylaxis.
• Adolescents: With (dapsone or atovaquone) and leucovorin, recommended as part of an alternative regimen for preventing the first episode of T gondii encephalitis (primary prophylaxis)
• Adolescents: With leucovorin and sulfadiazine, recommended as part of the preferred regimen (and with leucovorin and [clindamycin or atovaquone], recommended as part of alternative regimens) for chronic maintenance therapy (secondary prophylaxis) for T gondii encephalitis
• Current guidelines should be consulted for additional information.

Usual Pediatric Dose for Pneumocystis Pneumonia Prophylaxis

US CDC, NIH, and HIVMA/IDSA Recommendations for HIV-Infected Adolescents:
Primary and Secondary Prophylaxis: 50 or 75 mg orally once a week OR 25 mg orally once a day with food

Comments:

• With (dapsone or atovaquone) and leucovorin, recommended as part of an alternative regimen for preventing the first episode of PCP (primary prophylaxis) and preventing subsequent episodes of PCP (secondary prophylaxis)
• Current guidelines should be consulted for additional information.

Usual Pediatric Dose for Protozoan Infection

US CDC, NIH, HIVMA/IDSA, and PIDS Recommendations for HIV-Exposed and HIV-Infected Children:

• Treatment: 1 mg/kg orally once a day for 14 days
• Secondary Prophylaxis: 1 mg/kg orally once a day

Maximum dose: 25 mg/dose

US CDC, NIH, and HIVMA/IDSA Recommendations for HIV-Infected Adolescents:

• Acute Infection: 50 to 75 mg orally once a day
• Chronic Maintenance Therapy: 25 mg orally once a day

Comments:

• Children: With leucovorin (folinic acid), recommended as an alternative regimen for the treatment of cystoisosporiasis and for secondary prophylaxis
• Children (treatment): The optimum duration of therapy has not been established.
• Adolescents: With leucovorin, recommended as alternative therapy for treating cystoisosporiasis due to C belli; recommended for acute infection in patients with sulfa intolerance and for chronic maintenance therapy (secondary prophylaxis) in patients with CD4 count less than 200 cells/mm3
• Current guidelines should be consulted for additional information.

Renal Dose Adjustments

Renal dysfunction: Caution recommended.

Liver Dose Adjustments

Liver dysfunction: Caution recommended.

Precautions

CONTRAINDICATIONS:
Known hypersensitivity to the active component or any of the ingredients; documented megaloblastic anemia due to folate deficiency

Consult WARNINGS section for additional precautions.

Dialysis

Data not available

Other Comments

Administration advice:

• All patients being treated for toxoplasmosis: Coadminister leucovorin (strongly recommended).
• May administer with meals

General:

• This drug should be used with a sulfonamide since synergism exists with this combination.
• The manufacturer product information for the relevant sulfonamide (synergistic agent) should be consulted.

Monitoring:

• Hematologic: Blood counts, including platelet counts, in patients receiving high dosage (semiweekly)

Patient advice:

• Stop this drug and seek medical attention immediately at first sign of skin rash.
• Stop this drug and seek medical treatment if sore throat, pallor, purpura, or glossitis develops; may be early indications of serious disorders
• Females of childbearing potential: Avoid becoming pregnant during therapy.
• Do not exceed recommended doses.
• May minimize anorexia and vomiting by taking the drug with meals

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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