Cyproheptadine

Overview

Cyproheptadine (Periactin®) is a first-generation antihistamine with additional serotonin-antagonist properties. In veterinary medicine it is most commonly used in cats as an appetite stimulant and may also be used in dogs and cats to help manage serotonin syndrome.

Although classified as an antihistamine, cyproheptadine has shown limited or inconsistent effectiveness for treating allergic pruritus in dogs and cats and has not demonstrated reliable benefit for feline asthma. Its clinical effects are primarily related to its antihistamine, antiserotonin, and anticholinergic actions.

Mechanism of Action (MOA): Cyproheptadine acts mainly as a competitive antagonist at histamine H1 receptors, reducing the effects of histamine on target tissues. It also has strong antiserotonin activity, along with anticholinergic and mild calcium channel–blocking effects, which contribute to its clinical actions.

Indications

Cyproheptadine is used in dogs and cats primarily for its antihistamine and antiserotonin properties. Its effectiveness as a traditional antihistamine is variable, but it may still be useful in selected clinical situations.

• Appetite stimulation (cats): Cyproheptadine is commonly used to help stimulate appetite in cats with reduced food intake or chronic illness.
• Serotonin syndrome (dogs and cats): Because of its strong antiserotonin activity, the drug may be used in the management of serotonin syndrome in small animals.
• Allergic disease: May be used as an antihistamine for management of allergic conditions, although its antipruritic effectiveness in dogs and cats is often limited.
• Aortic thromboembolism (cats): Cyproheptadine has been used as an adjunct therapy in cats with aortic thromboembolism because serotonin contributes to collateral vasoconstriction.

Dosage (Reference)

Dog

In dogs, cyproheptadine is administered orally. The dose may vary depending on the clinical purpose such as management of allergic conditions or serotonin-related toxicity.

Cat

In cats, cyproheptadine is commonly administered orally and is often used as an appetite stimulant. The dosing range is similar to that used in dogs.

Warnings & Precautions

Cyproheptadine should be used cautiously in veterinary patients because of its anticholinergic and central nervous system effects. Careful patient evaluation is recommended before starting therapy, particularly in animals with pre-existing systemic disease.

• Hypersensitivity: Cyproheptadine is contraindicated in animals with a known hypersensitivity to the drug.
• Urinary or gastrointestinal obstruction: Because of its anticholinergic activity, the drug should be used cautiously in patients with urinary retention or pyloroduodenal obstruction.
• Angle-closure glaucoma: Use with caution in animals with glaucoma or increased intraocular pressure.
• Cardiovascular disease: Use cautiously in animals with severe cardiac disease or congestive heart failure.
• Neurologic disorders: Cyproheptadine may lower the seizure threshold and has been reported to increase seizure severity in experimental models.
• Handling in systemic illness: Caution is advised in patients with conditions such as hyperthyroidism, hypertension, or prostatic enlargement because anticholinergic effects may worsen these conditions.

Drug Interactions

Cyproheptadine may interact with several medications due to its antihistamine, anticholinergic, and antiserotonin effects. When used with the following drugs, additional monitoring or dose adjustments may be necessary.

• Anticholinergic drugs (e.g., atropine, glycopyrrolate, oxybutynin, amantadine): Concurrent use may increase anticholinergic effects such as dry mucous membranes, tachycardia, decreased gastrointestinal motility, and urinary retention.
• Cholinergic agonists (e.g., pilocarpine): Cyproheptadine may reduce the effectiveness of cholinergic medications.
• CNS depressants (e.g., acepromazine, anesthetic agents, diazepam, gabapentin, methocarbamol, phenobarbital): Concurrent use may increase sedation and central nervous system depression.
• Monoamine oxidase inhibitors (MAOIs) (e.g., amitraz, selegiline): May cause prolonged or intensified anticholinergic effects; the combination is considered contraindicated in humans.
• Mirtazapine: Concurrent use should generally be avoided because the drugs have opposing pharmacologic effects.
• Opioids (e.g., morphine, buprenorphine): May increase anticholinergic and central nervous system depressant effects.
• Selective serotonin reuptake inhibitors (SSRIs) (e.g., fluoxetine, paroxetine, sertraline): Cyproheptadine may reduce the therapeutic effects of these drugs.
• Tricyclic antidepressants (TCAs) (e.g., amitriptyline, clomipramine): Cyproheptadine may decrease the clinical effectiveness of these medications.
• Tramadol: Cyproheptadine may reduce the analgesic effectiveness of tramadol.

Side Effects & Overdose

Side Effects

The most common adverse effects of cyproheptadine in dogs and cats are related to its central nervous system depressant and anticholinergic properties. These effects are usually mild but may become more pronounced at higher doses.

• CNS depression: Sedation or drowsiness is the most frequently observed effect in veterinary patients.
• Paradoxical excitement (cats): Some cats may develop agitation or hyperexcitability instead of sedation; this typically resolves after reducing the dose or discontinuing the drug.
• Anticholinergic effects: Dry mucous membranes, decreased gastrointestinal motility, tachycardia, urinary retention, and hyperthermia may occur.
• Polyphagia: Increased appetite may occur and can be undesirable when the drug is used for indications other than appetite stimulation.

Overdose

There is no specific antidote for cyproheptadine overdose. Toxic effects are generally an extension of the drug’s pharmacologic actions, particularly CNS and anticholinergic effects.

• CNS effects: Marked sedation may occur, although CNS stimulation can also be seen in some cases.
• Anticholinergic toxicity: Signs may include dry mucous membranes, tachycardia, urinary retention, hyperthermia, and reduced gastrointestinal motility.
• Hypotension: Low blood pressure may develop in severe cases.
• Management: Treatment is mainly supportive. Gastrointestinal decontamination may be considered when appropriate.
• Severe anticholinergic signs: Physostigmine may be considered in serious cases.
• Seizure control: Benzodiazepines may be used if seizures occur.

Key Notes

Practical clinical points that may help optimize the use of cyproheptadine in dogs and cats in everyday veterinary practice:

• Serotonin antagonist activity: Cyproheptadine is one of the commonly used medications for managing serotonin syndrome because it blocks serotonin receptors.
• Variable antihistamine response: Like many antihistamines, clinical response can vary significantly between individual animals.
• Onset of appetite stimulation: When used as an appetite stimulant in cats, improvement in food intake may take several doses before becoming noticeable.
• Individual variability: Response and tolerance may differ between patients, so dosing and frequency may need adjustment based on clinical response.
• Regular administration for allergies: Antihistamines are generally more effective when given consistently rather than only after clinical signs develop.
• Administration with food: The drug may be given with or without food; giving it with food may help reduce gastrointestinal upset in some animals.