Pirimetamina

Uses

Treatment of Toxoplasmosis: Pirimetamina is used for the treatment of toxoplasmosis when used conjointly with a sulfonamide, since synergism exists with this combination.

Treatment of Acute Malaria: Pirimetamina is also used for the treatment of acute malaria. It should not be used alone to treat acute malaria. Fast-acting schizonticides such as chloroquine or quinine are used and preferable for the treatment of acute malaria. However, conjoint use of Pirimetamina with a sulfonamide (e.g., sulfadoxine) will initiate transmission control and suppression of susceptible strains of plasmodia.

Chemoprophylaxis of Malaria: Pirimetamina is used for the chemoprophylaxis of malaria due to susceptible strains of plasmodia. However, resistance to pyrimethamine is prevalent worldwide. It is not suitable as a prophylactic agent for travelers to most areas.

Pirimetamina is also used to associated treatment for these conditions: Plasmodium Infections, Toxoplasmosis, Acute Malaria

How Pirimetamina works

Pirimetamina inhibits the dihydrofolate reductase of plasmodia and thereby blocks the biosynthesis of purines and pyrimidines, which are essential for DNA synthesis and cell multiplication. This leads to failure of nuclear division at the time of schizont formation in erythrocytes and liver.

Dosage

Pirimetamina dosage

For Treatment of Toxoplasmosis: The dosage of Pirimetamina for the treatment of toxoplasmosis must be carefully adjusted so as to provide maximum therapeutic effect and a minimum of side effects. At the dosage required, there is a marked variation in the tolerance to the drug. Young patients may tolerate higher doses than older individuals. Concurrent administration offolinic acidis strongly recommended in all patients.

The adultstartingdose is 50 to 75 mg of the drug daily, together with 1 to 4 g daily of a sulfonamide of the sulfapyrimidine type, e.g. sulfadoxine. This dosage is ordinarily continued for 1 to 3 weeks, depending on the response of the patient and tolerance to therapy. The dosage may then be reduced to about one half that previously given for each drug and continued for an additional 4 to 5 weeks.

The pediatric dosage of Pirimetamina is 1 mg/kg/day divided into 2 equal daily doses; after 2 to 4 days this dose may be reduced to one half and continued for approximately 1 month. The usual pediatric sulfonamide dosage is used in conjunction with Pirimetamina.

For Treatment of Acute Malaria: Pirimetamina is NOT recommended alone in the treatment of acute malaria. Fast-acting schizonticides, such as chloroquine or quinine, are indicated for treatment of acute malaria. However, Pirimetamina at a dosage of 25 mg daily for 2 days with a sulfonamide will initiate transmission control and suppression of non-falciparum malaria.Pirimetamina is only recommended for patients infected in areas where susceptible plasmodia exist. Should circumstances arise wherein Pirimetamina must be used alone in semi- immune persons, the adult dosage for acute malaria is 50 mg for 2 days; children 4 through 10 years old may be given 25 mg daily for 2 days. In any event, clinical cure should be followed by the once-weekly regimen described below for chemoprophylaxis. Regimens which include suppression should be extended through any characteristic periods of earlyrecrudescenceand late relapse, i.e., for at least 10 weeks in each case.

For Chemoprophylaxis of Malaria:

• Adults and pediatric patients over 10 years: 25 mg (1 tablet) once weekly
• Children 4 through 10 years:12.5 mg (½ tablet) once weekly
• Infants and children under 4 years: 6.25 mg (¼ tablet) once weekly.

Side Effects

Hypersensitivity reactions, occasionally severe (such as Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme, and anaphylaxis), and hyperphenylalaninemia, can occur particularly when pyrimethamine is administered concomitantly with a sulfonamide. Consult the complete prescribing information for the relevant sulfonamide for sulfonamideassociated adverse events. With doses of pyrimethamine used for the treatment of toxoplasmosis, anorexia and vomiting may occur. Vomiting may be minimized by giving the medication with meals; it usually disappears promptly upon reduction of dosage. Doses used in toxoplasmosis may produce megaloblastic anemia, leukopenia, thrombocytopenia, pancytopenia, neutropenia, atrophic glossitis, hematuria, and disorders of cardiac rhythm.

Precaution

The recommended dosage for chemoprophylaxis of malaria should not be exceeded. Pirimetamina should be used with caution in patients with impaired renal or hepatic function or in patients with possible folate deficiency, such as individuals with malabsorption syndrome, alcoholism, or pregnancy, and those receiving therapy, such as phenytoin, affecting folate levels

Interaction

Pirimetamina may be used with sulfonamides, quinine and other antimalarials, and with other antibiotics. However, the concomitant use of other antifolic drugs or agents associated with myelosuppression including sulfonamides or trimethoprim-sulfamethoxazole combinations, proguanil, zidovudine, or cytostatic agents (e.g., methotrexate), while the patient is receiving pyrimethamine, may increase the risk of bone marrow suppression. If signs of folate deficiency develop, pyrimethamine should be discontinued. Folinic acid (leucovorin) should be administered until normal hematopoiesis is restored

Food Interaction

• Administer folic acid supplement. Folic acid need is increased.
• Take with food. Food reduces irritation.

Pirimetamina Drug Interaction

Moderate: calcium / vitamin dUnknown: aspirin, charcoal, epinephrine, albendazole, albumin human, allopurinol, amoxicillin, RHO Immunoglobulin , azithromycin, multivitamin, multivitamin with minerals, multivitamin, ipratropium, acetaminophen, penicillin v potassium, phenytoin, valproic acid, ascorbic acid, cholecalciferol

Pirimetamina Disease Interaction

Major: folate deficiencyModerate: liver disease, renal dysfunction, seizure disorders

Elimination Route

Well absorbed with peak levels occurring between 2 to 6 hours following administration

Half Life

96 hours

Pregnancy & Breastfeeding use

Pregnancy Category C. Pirimetamina has been shown to be teratogenic in rats when given in oral doses 7 times the human dose for chemoprophylaxis of malaria or 2.5 times the human dose for treatment of toxoplasmosis. At these doses in rats, there was a significant increase in abnormalities such as cleft palate, brachygnathia, oligodactyly, and microphthalmia. Pirimetamina has also been shown to produce terata such as meningocele in hamsters and cleft palate in miniature pigs when given in oral doses 170 and 5 times the human dose, respectively, for chemoprophylaxis of malaria or for treatment of toxoplasmosis.

There are no adequate and well-controlled studies in pregnant women. Pirimetamina should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Concurrent administration of folinic acid is strongly recommended when used for the treatment of toxoplasmosis during pregnancy.

Nursing Mothers: Pirimetamina is excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from pyrimethamine and from concurrent use of a sulfonamide with Pirimetamina for treatment of some patients with toxoplasmosis, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother

Contraindication

Use of Pirimetamina is contraindicated in patients with known hypersensitivity to pyrimethamine or to any component of the formulation. Use of the drug is also contraindicated in patients with documented megaloblastic anemia due to folate deficiency.

Special Warning

Geriatric Use: Clinical studies of Pirimetamina did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

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