Toltrazuril/Pyrimethamine Paste

Paste medications are thick and sticky, usually given by mouth using a syringe or tube. They’re often used for dewormers or other oral meds in horses, dogs, and cats. The key is to aim for the back of the mouth so your pet swallows the paste instead of spitting it out.

For Horses:

1. Set the dose on the syringe if it has markings (usually based on weight).
2. Stand beside your horse, not in front, and have someone hold them if possible.
3. Gently insert your thumb into the side of the horse’s mouth (between the teeth) to open it.
4. Insert the syringe into that gap and squirt the paste toward the back of the tongue.
5. Lift the horse’s head slightly and encourage swallowing by stroking the throat or gently blowing on the nostrils.
6. Watch for licking or chewing—that means they swallowed. If paste spills out, check how much was lost and contact your vet if unsure.
7. You can offer a little water afterward and reward them with a treat like a carrot if allowed.

For Dogs & Cats:

1. Gently open your pet’s mouth or slip the syringe into the side of it.
2. Aim toward the back of the tongue and squirt the paste in.
3. Hold the mouth closed briefly, and rub the throat or blow gently on the nose to encourage swallowing.
4. Give praise or a treat afterward to make it a positive experience.

Aftercare:

1. Wipe your pet’s mouth if needed.
2. Clean or recap the syringe as instructed.
3. Store the tube according to label directions.

Tip: Paste can feel weird to pets at first. For horses, try giving applesauce by syringe ahead of time so they get used to the sensation.

This compounded formulation combines toltrazuril, an antiprotozoal, with pyrimethamine, an antiprotozoal (folate-pathway inhibitor) — two different drug classes. In compounding practice, clinicians may consider a combination like this for a multi-targeted approach. Your veterinarian determines whether it is appropriate based on your animal's diagnostic findings.

At a pharmacological level, toltrazuril acts as a triazinone derivative that disrupts the intracellular stages of parasite development by acting on the apicoplast and mitochondria. This interference inhibits the replication and survival of the protozoal organism within the host's tissues. Pyrimethamine acts as a folic acid antagonist by inhibiting the enzyme dihydrofolate reductase. This action is understood to inhibit the parasite from synthesizing the folic acid necessary for DNA and RNA production. This combination is intended to manage the parasitic landscape more thoroughly than single-agent protocols. Your veterinarian will determine if this combination is appropriate based on your horse's weight, neurological status and individual diagnostic findings.

This description reflects the general pharmacology of the active ingredient's drug class; your veterinarian determines whether this approach is appropriate for your animal.

Prescription only. Use only under the direction of a licensed veterinarian. This information is not a substitute for veterinary diagnosis, prescribing or monitoring. Compounded drugs are not approved by the FDA for safety or effectiveness.

Commonly observed effects of toltrazuril/pyrimethamine administration include mild gastrointestinal changes such as loose stools, flatulence or a temporary decrease in appetite. Because pyrimethamine influences folate metabolism, your veterinarian will monitor for signs of hematological changes such as anemia or decreased white blood cell counts during the course of the prescription. Owners should monitor for any changes in coordination, alertness or gait, as neurological conditions can be sensitive to physiological shifts during therapy.

This medication is typically used with caution in pregnant or lactating mares, as the safety profile for developing foals has not been extensively characterized for this specific combination. It is essential to provide your veterinarian with a complete history of all other supplements and prescriptions your horse is receiving, as concurrent use of certain medications can influence the overall metabolic and folate profile. Your veterinarian is the best resource for designing a comprehensive approach to patient monitoring and support during the administration period. Contact your veterinarian promptly if you observe significant stumbling, persistent diarrhea or signs of physical distress.