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What is Pyrimethamine 25 mg used for?

In the pharmaceutical industry, Pyrimethamine 25 mg is a potent folic acid antagonist and an essential antiparasitic agent. As a pharmacist and manufacturer, I classify this as a “specialty anti-infective,” primarily used for serious protozoal infections rather than standard bacterial ones.

Primary Clinical Uses

  • Toxoplasmosis: This is the primary indication. It is used in combination with a sulfonamide (like Sulfadiazine) to treat Toxoplasma gondii infections, which can be life-threatening in immunocompromised patients (e.g., those with HIV/AIDS) or during pregnancy (congenital toxoplasmosis).

  • Malaria Treatment: It is often used as a component of SP (Sulfadoxine-Pyrimethamine) for the treatment of uncomplicated malaria.

  • Malaria Prophylaxis: In specific high-risk regions, it is used for the prevention of malaria, particularly in pregnant women as part of Intermittent Preventive Treatment (IPTp).

  • Cystoisosporiasis: Occasionally used off-label to treat infections caused by the parasite Cystoisospora belli.

Mechanism of Action: Inhibition of Dihydrofolate Reductase

Pyrimethamine works by disrupting the parasite’s ability to synthesize DNA.

Enzyme Blockade: It selectively inhibits the enzyme dihydrofolate reductase (DHFR) in the parasite.

Folic Acid Depletion: By blocking this enzyme, the parasite cannot convert dihydrofolate into tetrahydrofolate (the active form of folic acid).

DNA Synthesis Failure: Without active folate, the parasite cannot produce the purines and pyrimidines required for DNA replication, leading to its death.

Selectivity: The drug has a much higher affinity for the protozoal DHFR enzyme than the human version, though it can still affect human folate levels over time.

The Manufacturer’s Perspective: Technical & Safety

From a production and B2B standpoint at your WHO-GMP facility in Mumbai, Pyrimethamine 25 mg involves critical technical considerations:

  • The “Leucovorin” Requirement: As a pharmacist, you know that long-term Pyrimethamine therapy can cause bone marrow suppression. For your B2B clients, a major “professional touch” is recommending the co-administration of Leucovorin (Folinic Acid) to protect the patient’s blood cells without interfering with the drug’s effect on the parasite.

  • Fixed-Dose Combinations (FDCs): While the 25 mg standalone tablet is essential, the most popular export format for malaria is the FDC with Sulfadoxine (Sulfadoxine 500 mg + Pyrimethamine 25 mg). Listing both on your marketplace is a smart move.

  • Stability & API Sourcing: The API is relatively stable but must be protected from light. At our facility, we utilize opaque PVC/PVDC or Alu-Alu blister packaging to ensure a 36-month shelf life for export to Zone IVb regions.

  • Dossier Support: Because this is an “Essential Medicine” for HIV/AIDS and Malaria programs, we provide full CTD/eCTD Dossiers to support international NGO tenders and ministry of health registrations.

Pyrimethamine Sulphadoxine Tablets