PYRILAMINE MALEATE

Chemistry - An ethylenediamine antihistamine, pyrilamine maleate occurs as a white, crystallinepowder with a melting range of 99-103°. One gram is soluble in approximately 0.5 ml of water or 3ml alcohol.

Storage, Stability, Compatibility

Avoid freezing the injectable product.

Pharmacology - PYRILAMINE MALEATE

Antihistamines (H1-receptor antagonists) competitively inhibit histamine at H1receptor sites. They do not inactivate, nor prevent the release of histamine, but can prevent histamine's action on the cell. Besides their antihistaminic activity, these agents also have varyingdegrees of anticholinergic and CNS activity (sedation). Pyrilamine is considered to be less sedatingand have much less anticholinergic effects when compared to most other antihistamines.

Uses, Indications

Antihistamines are used in veterinary medicine to reduce or help preventhistamine mediated adverse effects.

Pharmacokinetics - PYRILAMINE MALEATE

The pharmacokinetics of this agent have apparently not been extensivelystudied.
Contraindications/Precautions - The manufacturer indicates that the use of this product "shouldnot supercede the use of other emergency drugs and procedures."

Adverse Effects, Warnings

Adverse effects in horses can include CNS stimulation (nervousness, insomnia, convulsions, tremors, ataxia), palpitation, GI disturbances, CNS depression (sedation), muscular weakness, anorexia, lassitude and incoordination.
Overdosage - Treatment of overdosage is basically supportive and symptomatic. The manufacturer(Schering - Histavet-P®) suggests using "careful titration" of barbiturates to treat convulsions, andanaleptics (caffeine, ephedrine, or amphetamines) to treat CNS depression. Most toxicologistshowever, recommend avoiding the use of CNS stimulants in the treatment of CNS depressantoverdoses. Phenytoin (IV) is recommended in the treatment of seizures caused by antihistamineoverdose in humans; barbiturates and diazepam are to be avoided.

Drug Interactions

Increased sedation can occur if diphenhydramine is combined with other
CNS depressant drugs.
Antihistamines may partially counteract the anticoagulation effects of heparin or warfarin.
Pyrilamine may enhance the effects of epinephrine.
Laboratory Interactions - Antihistamines can decrease the wheal and flare response to antigenskin testing. In humans, it is suggested that antihistamines be discontinued at least 4 days beforetesting.