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a folic acid antagonist used as an antimalarial agent, especially for suppressive prophylaxis, and also used concomitantly with a sulfonamide in treatment of toxoplasmosis.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.



Pharmacologic class: Folic acid antagonist

Therapeutic class: Antiprotozoal, antimalarial

Pregnancy risk category C


Inhibits reduction of dihydrofolic acid to tetrahydrofolic acid (folinic acid) by binding to and reversibly inhibiting dihydrofolate reductase


Tablets: 25 mg

Indications and dosages

To control plasmodia transmission and suppress susceptible strains Adults and children ages 10 and older: 25 mg P.O. daily for 2 days, given with a sulfonamide


Adults: Initially, 50 to 75 mg P.O. daily for 1 to 3 weeks, given with a sulfonamide. Depending on response and tolerance, reduce dosages of both drugs by 50% and continue therapy for 4 to 5 more weeks.

Children: 1 mg/kg P.O. daily in two equally divided doses for 2 to 4 days, then reduced to 0.5 mg/kg/day for approximately 1 month. Alternatively, 2 mg/kg (up to 100 mg) P.O. daily in two equally divided doses for 3 days, then 1 mg/kg (up to 25 mg) in two equally divided doses for 4 weeks, given with sulfadiazine for 4 weeks.

Prophylaxis of malaria caused by susceptible plasmodia strains

Adults and children older than age 10: 25 mg P.O. weekly

Children ages 4 to 10: 12.5 mg P.O. weekly

Infants and children younger than age 4: 6.25 mg P.O. weekly

Off-label uses

• Isosporiasis

• Prophylaxis of Pneumocystis jiroveci pneumonia


• Hypersensitivity to drug

• Megaloblastic anemia caused by folate deficiency

• Concurrent folate antagonist therapy


Use cautiously in:

• anemia, bone marrow depression, hepatic or renal impairment, G6PD deficiency

• history of seizures

• patients more than 16 weeks pregnant

• breastfeeding patients.


• Administer with meals.

• When giving tablets to young children, crush them and administer as oral suspension in water, cherry syrup, or sweetened solution.

• Know that because of worldwide resistance to pyrimethamine, its use alone to prevent or treat acute malaria is no longer recommended.

• Be aware that fixed combination of pyrimethamine and sulfadoxine is available and has been used for uncomplicated mild to moderate malaria caused by chloroquineresistant Plasmodium falciparum and for presumptive self-treatment by travelers.

Adverse reactions

CNS: headache, light-headedness, insomnia, malaise, depression, seizures

CV: arrhythmias

EENT: dry throat

GI: nausea, vomiting, diarrhea, anorexia, atrophic glossitis

GU: hematuria

Hematologic: megaloblastic anemia, leukopenia, pancytopenia, thrombocytopenia

Metabolic: hyperphenylalaninemia

Respiratory: pulmonary eosinophilia

Skin: pigmentation changes, dermatitis, erythema multiforme, toxic epidermal necrolysis, Stevens-Johnson syndrome

Other: fever, anaphylaxis


Drug-drug. Lorazepam: hepatotoxicity Myelosuppressants (including antineoplastics): increased risk of bone marrow depression

Drug-diagnostic tests. Platelets, white blood cells: decreased counts

Patient monitoring

• Monitor CBC. Watch for evidence of blood dyscrasias.

• Assess for signs and symptoms of folic acid deficiency.

• Closely monitor neurologic and cardiovascular status. Stay alert for seizures and arrhythmias.

Watch for evidence of erythema multiforme, including sore throat, cough, mouth sores, rash, iritic lesions, and fever. Report early signs before condition can progress to Stevens-Johnson syndrome.

Patient teaching

• Advise patient to take with meals.

Tell patient to discontinue drug and contact prescriber at first sign of rash.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.


McGraw-Hill Nurse's Drug Handbook, 7th Ed. Copyright © 2013 by The McGraw-Hill Companies, Inc. All rights reserved


(pī′rə-mĕth′ə-mēn′, -mĭn)
A folic acid antagonist, C12H13ClN4, often administered in combination with a sulfonamide, used as an antimalarial and to treat toxoplasmosis.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Parasitology An anti-protozoal combined with sulfadiazine for managing toxoplasmosis Adverse effects BM damage, rashes; folic acid deficiency can cause a painful burning tongue, loss of taste, anemia. See Toxoplasmosis.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


A drug used in the treatment of MALARIA and TOXOPLASMOSIS. The drug is on the WHO official list. Brand names are Daraprim and, with other antimalarial drugs, Fansidar and Maloprim.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
References in periodicals archive ?
Trimethoprim/sulfamethoxazole (10 mg/kg/d trimethoprim) was first initiated because of limited availability of pyrimethamine plus sulfadiazine at the time, but acute liver toxicity developed on treatment day 6 (increases in levels of aminotransferase/alanine aminotransferase from 24/20 IU/L to 127/145 IU/L[(reference 10-42 IU/L]).
Treatment with pyrimethamine, sulfadiazine and folic acid is used for patients who are immunocompromised and those immunocompetent patients with severe or persistent symptoms.4 Short course of corticosteroids can be used in toxoplasmosis encephalitis patients with significant cerebral edema and elevated intracranial pressure.
The pyrimethamine component in the sample [4.sub.3][Y.sub.12] (ATS/SM/PYR: 100/250/12.5 mg) was borderline compliant by SQ-TLC (115%) but was noncompliant by HPLC (113%), while the same API in the sample [3.sub.2][P.sub.10] (SDX/PYR: 500/25 mg), found to be borderline compliant by SQ-TLC (89.5%), was compliant by HPLC (94%).
The most common side effects were associated with pyrimethamine medication and included hematologic complications, such as thrombocytopenia and leucopenia, despite folinic acid supplementation [9].
He covers malaria and anti-malarials; the painkiller aspirin; ether, chloroform, cocaine, morphine, heroine, and anesthesia; the pill; diabetes and insulin; smallpox and vaccination; vaccines to combat infectious diseases; the pox syphilis and Salvarsan; Prontosil, Pyrimethamine, and penicillin; AIDS, HIV, and anti-retrovirals; organ transplantation and Cyclosporine; and malaria, madness, and Chlorpromazine.
Mefloquine in combination with sulfadoxine and pyrimethamine (MSP) at a single dose of 15/30/1.5 mg/kg, respectively, also became ineffective.
The combination of sulfadiazine at 2g/day and pyrimethamine at 25mg/day has also been used to some success for maintenance therapy.
They wrote: "Under the current pricing structure, it is estimated the annual cost of treatment for toxoplasmosis, for the pyrimethamine component alone, will be [euro]302,000 for patients who weigh less than 60kg and [euro]571,500 for patients who weigh more than 60kg."
Daraprim (pyrimethamine) is an antiparasitic indicated for the treatment of toxoplasmosis when used conjointly with a sulfonamide.
Pyrimethamine with sulphadoxine complex is the most recommended and efficient antifolate prescribed against PfDHFR.