What is pyrimethamine?
Pyrimethamine (brand name: Daraprim®) is a systemic antiprotozoal medication used to treat parasitic infections including those caused by Hepatozoon americanum (a tick-borne parasite that causes canine hepatozoonosis) and Toxoplasma gondii (a parasite that causes the infection toxoplasmosis).
Its use in cats, dogs and other species to treat certain parasitic infections is “off label” or “extra label”. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.
How do I give my pet pyrimethamine?
- Pyrimethamine is given by mouth as a tablet, or it can be given as a compounded liquid medication.
- It can be given with or without food.
- It has an unpleasant taste, so mixing the medication into food is not recommended.
- Pregnant women or those that may become pregnant should handle this medication carefully.
It will take a few days before noting any effects, and the medication’s full effects may not be obvious for several weeks.
What if I miss giving my pet the medication?
If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.
Are there any potential side effects?
Pyrimethamine may cause the following side effects:
- anorexia
- tiredness/lack of energy
- vomiting
- depression
- decreased blood cell counts
- inaccurate test results for vitamin B12 and folic acid
In cats, side effects may be more severe.
This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.
Are there any risk factors for this medication?
Pyrimethamine should NOT BE USED in:
- pets that are allergic to it
- lactating animals, unless the offspring can be weaned onto a milk replacement solution to avoid drug exposure, and even then, should be used with caution
It should be USED WITH CAUTION in:
- pets with a folate deficiency
- pets with a preexisting blood disorder
- pets with liver or kidney disease
- cats (potentially severe side effects)
- pregnant or breeding animals (the risk versus the benefit must be weighed)
Are there any drug interactions I should be aware of?
Certain medications should be used cautiously with pyrimethamine, including:
- folic acid
- sulfonamides
- trimethoprim
It is important to tell your veterinarian about any medications (including vitamins, supplements or herbal therapies) that your pet is taking before starting any treatment.
Is any monitoring needed with this medication?
- Your veterinarian will monitor your pet to be sure the medication is working.
- Your veterinarian will take blood samples to monitor for low blood cell counts.
- Monitor your pet for bleeding, extreme lethargy, or fever, and contact your veterinarian immediately if these signs are noted.
How do I store pyrimethamine?
- Store the pill form of this medication at 15°C-25°C (59°F-77°F).
- Store away from light and in a tight container.
- If compounded into a liquid suspension, it can be stored at room temperature for 7 days, and then should be discarded.
What should I do in case of emergency?
If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.
