Pseudoephedrine HCI USP and Pyrilamine Maleate USP

Drugs and medications image
Drugs and medications image EquiMed


soo-doe-eh-FED-reen, pye-RIL-uh-meen MA-le-ate - Pronunciation guide

Brand Names

  • HistaGranules
  • Tri-Hist Granules


Rx symbolPseudoephedrine HCI USP and Pyrilamine Maleate USP are combined in equal measures, usually 600 mg each, in a palatable corn meal base for use in horses when an antihistamine decongestant is needed.

The pseudoephedrine HCI USP acts as a decongestant and Pyrilamine Maleate USP acts as an anti-histamine.

Histamines are substances released from some types of cells when the cells become damaged. Histamines cause inflammation, swelling and itching. Antihistamines compete with histamine for uptake at the histamine receptors on sensitive cells in the respiratory tract, intestines, blood vessels and skin.


Tri-Hist Granules is the brand name of a pseudoephedrine and pyrilamine maleate combination that acts as a bronchodilator and is used as a histamine antagonizing preparation in treating allergic problems in horses such as hives, swelling due to bee stings, insect bites or contact with an irritating substance.

Dosage and Administration

Prescription medicationPseudoephedrine and Pyralimine Maleate
Method Dosage
(click row for calculator)
Concentration Period Duration
Oral (granules) 0.5 ounce/1000lbs   Every 12 hours as needed NA


  • Federal law restricts this drug to use by or on the order of a licensed veterinarian.
  • Extra-label use of drugs in treating animals is allowable only by licensed veterinarians within the context of a valid veterinarian-client-patient relationship, and does not include drug use in treating animals by the layman (except under the supervision of a licensed veterinarian).
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your equine appears to feel better, the entire treatment plan should be completed to prevent relapse.
  • This medication may be available in forms and concentrations not noted in the above table. Always check the label and literature provided with the medication about the form and concentration and DO NOT USE the calculator if the information differs.

Side Effects

Sedation is the most common side effect, although excitement, fine tremors, colic and loss of appetite are possible.


Do not use at least 72 hours before sporting events.

Not for use in horses intended for human consumption.

Tri-Hist Granules are FDA approved for use in horses. Federal law restricts this drug to use by or on the order of a licensed veterinarian.

Check with the appropriate individual regulatory group regarding use in competition horses.


Antihistamines have an additive effect when combined with other central nervous system depressant drugs such as tranquilizers.

Antihistamines may affect the activity of anticoagulants such as warfarin.


Quinidine Sulfate TabletsQuinidine Sulfate Tablets

Tri-Hist GranulesTri-Hist Granules


About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.