Veterinary Drug Handbook (VDH) is the reference veterinarians turn to when they want an independent source of information on the drugs that are used in veterinary medicine today.


Chemistry - An ethanolamine-derivative antihistamine, doxylamine succinate occurs as a white tocreamy-white powder with a characteristic odor. It has a melting range of 103-108°C and pKavalues of 5.8 and 9.3. Doxylamine succinate has solubilities of 0.5 g/ml in alcohol and 1 g/ml inwater. The commercially available injection has an approximate pH of 4.8 - 5.2.

Storage, Stability, Compatibility

Tablets should be stored in well-closed, light-resistant packaging at room temperature. No information on the storage, stability, or compatibility was found regarding the injectable product.


Like other antihistamines, doxylamine competitively inhibits histamine at H1receptors. It also has substantial sedative and anticholinergic effects.

Uses, Indications

This drug is recommended (by the manufacturer) "for use in conditions inwhich antihistaminic therapy may be expected to alleviate some signs of disease in dogs, cats, andhorses."


Pharmacokinetic parameters are apparently unavailable for domestic animals.
Doxylamine has a serum half-life of approximately 10 hours in human adults.
Contraindications/Precautions - The manufacturer recommends that the injectable productshould not be administered by the IV route in dogs or cats, and that IM and SQ injection sites bedivided. Inject slowly IV in horses. Do not use in horses intended for food purposes.
Doxylamine is also contraindicated in patients who are hypersensitive to it or other antihistaminesin its class. Because of their anticholinergic activity, antihistamines should be used with caution inpatients with angle closure glaucoma, prostatic hypertrophy, pyloroduodenal or bladder neckobstruction, and COPD if mucosal secretions are a problem. Additionally, they should be used withcaution in patients with hyperthyroidism, cardiovascular disease or hypertension.

Adverse Effects, Warnings

The manufacturer lists CNS depression, incoordination and GI disturbances as adverse effects at therapeutic dosages.
Overdosage - The manufacturer includes CNS stimulation (excitement, seizures) and ataxia assymptoms associated with overdosage. Treatment should be supportive, as outlined in the previousantihistamine monographs.

Drug Interactions

Potential drug interactions for doxylamine include, increased sedation ifdoxylamine is combined with other CNS depressant drugs.
Antihistamines may partially counteract the anticoagulation effects of heparin or warfarin.
Doxylamine 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.

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