Diphenhydramine
Also known as: Benadryl, Banophen, Genahist, AllerMax, Diphenhist, Dytan, Siladryl, Tusstat, Nytol
> **Important**: Do not use human combination cold or allergy products (which may contain toxic ingredients like xylitol, decongestants, or pain relievers) without consulting your veterinarian. * **What to expect**: The most common side effect is sleepiness or lethargy. However, some pets (especially cats) may experience paradoxical excitement and become hyperactive or agitated. * **Administration**: The liquid form tastes very bitter to cats; they may drool excessively if given the liquid. Tablets or capsules hidden in a treat are usually preferred. * **Side Effects**: May cause dry mouth (you might notice your pet smacking their lips or drinking more water) and occasionally vomiting or diarrhea. * **Testing**: If your pet is scheduled for allergy skin testing, this medication usually needs to be stopped several days in advance. Ask your veterinarian for specific instructions.
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
What it is used for
- As an antihistamine
- As an antihistamine
- As an antihistamine
- For severe urticaria and angioedema
- For adjunctive treatment of pancreatitis
- Prevaccination
- Pretreatment before doxorubicin
- For adjunctive therapy of anaphylaxis
- For adjunctive therapy of aseptic laminitis
- For adjunctive therapy of anaphylaxis
- For allergic skin diseases (atopy)
- For allergic skin diseases (atopy)
- For adjunctive tx of pruritus
How it is given
Possible side effects
- CNS depression (lethargy, somnolence)
- Anticholinergic effects (dry mouth, urinary retention)
- GI effects (diarrhea, vomiting, anorexia)
- Paradoxical excitement (especially in cats)
- Sedation/lethargy
- Dry mouth (xerostomia)
- Urinary retention
- Tachycardia
- Gastrointestinal disturbances (diarrhea, vomiting, anorexia)
Cautions & contraindications
- Hypersensitivity to diphenhydramine or other antihistamines in its class
- Angle closure glaucoma
- Prostatic hypertrophy
- Pyloroduodenal or bladder neck obstruction
- COPD (if mucosal secretions are a problem)
- Hyperthyroidism (use with caution)
- Cardiovascular disease or hypertension (use with caution)
- Seizure disorders (use with caution)
- Known hypersensitivity to diphenhydramine
- Glaucoma (due to anticholinergic effects)
- Prostatic hypertrophy or urinary retention
- Gastrointestinal obstruction
- Use with caution in working dogs due to sedation
Drug interactions
- Anticholinergic drugs (including tricyclic antidepressants): May potentiate anticholinergic effects
- CNS depressant drugs: Increased sedation can occur
- CNS Depressants (e.g., opioids, benzodiazepines, barbiturates): Additive sedation and central nervous system depression
- Anticholinergic drugs: Additive anticholinergic effects (dry mouth, tachycardia, urinary retention)
- Monoamine Oxidase Inhibitors (MAOIs): May prolong and intensify the anticholinergic effects of antihistamines
- CNS Depressants (e.g., Diazepam, Phenobarbital, Gabapentin): Additive CNS depression and sedation
- Anticholinergic drugs (e.g., Atropine, Glycopyrrolate): Additive anticholinergic effects (tachycardia, dry mouth, ileus)
- Tricyclic Antidepressants (e.g., Amitriptyline): Increased risk of anticholinergic toxicity and sedation
Frequently asked questions
What is Diphenhydramine used for in pets?
> **Important**: Do not use human combination cold or allergy products (which may contain toxic ingredients like xylitol, decongestants, or pain relievers) without consulting your veterinarian. * **What to expect**: The most common side effect is sleepiness or lethargy. However, some pets (especially cats) may experience paradoxical excitement and become hyperactive or agitated. * **Administration**: The liquid form tastes very bitter to cats; they may drool excessively if given the liquid. Tablets or capsules hidden in a treat are usually preferred. * **Side Effects**: May cause dry mouth (you might notice your pet smacking their lips or drinking more water) and occasionally vomiting or diarrhea. * **Testing**: If your pet is scheduled for allergy skin testing, this medication usually needs to be stopped several days in advance. Ask your veterinarian for specific instructions.
Is Diphenhydramine safe for my pet?
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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