Cyproheptadine

Cyproheptadine, marketed under the brand name Periactin, was one of the first antihistamines developed to treat allergies in humans. Since its creation, this medication has been used successfully in other mammals, including canines, to treat acute and chronic allergic reactions. This medication has additional applications as a sedative and appetite stimulant in felines. Researchers have also studied cyproheptadine's effectiveness in alleviating the symptoms of Cushing's disease.

Cyproheptadine's mechanism of action is similar to other first-generation antihistamines like Benedryl, in that it inhibits the body's histamine response. Histamine is a biochemical that's stored within the granules of mast cells. Though mast cells can be found in nearly all bodily tissues, they're especially prevalent in the epithelium, gastrointestinal tract, and airways. 

Histamine molecules are one of the body's primary defense mechanisms against potentially harmful substances that the body may come in contact with. Unfortunately for canine allergy sufferers, sometimes the body triggers a "false alarm," causing a histamine response to completely harmless substances.

When the histamine is activated, it causes the mast cells within body tissues to create immunoglobulin antibodies. These antibodies trigger common allergy symptoms such as coughing, sneezing, watery eyes, and a runny nose in an attempt to clear the airways. 

Antihistamines like cyproheptadine prevent histamine from binding to the H1 receptors throughout the body, which stops the reaction and its symptoms.

Dosage

Therapeutic dosages of cyproheptadine can vary significantly and depend on the condition for which the drug is prescribed. The typical dosage of cyproheptadine for dogs with allergies is between 0.15 and 1 mg per lb. Much stronger dosages are usually needed for appetite stimulation, with dosages averaging between 1 mg and 4 mg per lb.

Dosage instructions

Cyproheptadine for dogs comes in a 4 mg pill form and a liquid suspension. If you have a smaller dog, your vet may advise you to split the tablet to the appropriate size for your pet. If your dog doesn't take medication voluntarily, you can tuck the pill inside a soft treat or as a slice of meat and feed it to them. 

Efficacy

A 1975 clinical study of 3 human patients with Cushing's disease found that cyproheptadine successfully induced remission and decreased the characteristic features of the disease in the study group. Suddenly stopping treatment caused a symptomatic flare-up in one participant. 

A study of children and adults with cystic fibrosis deemed cyproheptadine a helpful and safe appetite stimulant, noting few side effects except for drowsiness. A similar study on rats found that moderate doses of this medication increased appetite in anorexic animals, but stated its positive results were limited to a specific dosage range.

Unfortunately, research of cyproheptadine's efficacy as a histamine antagonist and sedative is limited. However, there is much anecdotal data on its successful clinical applications for these purposes in both humans and canines. 

Side effects

The side effects of cyproheptadine for dogs are usually mild, with drowsiness being the most prevalent. Here are some other common symptoms your pet may experience when taking this medication:

• Sleeping a lot

• Straining to urinate

• Unusual thirst

• Excitability

• Diarrhea

• Nausea

• Vomiting 

• Change in appetite

• Change in behavior 

• Fever

• Elevated heart rate

Considerations

Avoid combining this medication with any other antihistamines or sedatives, as this can significantly amplify drowsiness. 

Due to its decongestant effects, cyproheptadine can dry up the milk within the milk ducts and sinuses in lactating dogs. Do not use this medication in postpartum dogs who are still nursing.

This medication can worsen some conditions, particularly in dogs with glaucoma, epilepsy, and those with heart problems. Since this medication can cause urinary retention, it's not recommended for dogs with a history of urinary blockages. 

Drug interactions

• MAOIs

• Xanax

• Ativan

• Benzodiazepines

• Valium

• Opioids 

• Pramlintide

• Selegiline

• Prozac (Fluoxetine) 

• Zoloft

• Zyrtec

• Topiramate (Topamax)

• Benedryl

• Lyrica (Pregabalin) 

• Potassium chloride

• Potassium citrate

• Potassium acid phosphate 

• Potassium phosphate

• Phenergan

Allergic reactions and sensitivity

Do not give this medication to canines with a known allergy to first-generation antihistamines. 

Examples of first-generation antihistamines include:

• Benedryl

• Chlorpheniramine

• Clemastine

• Carbinoxamine

• Diphenhydramine

• Brompheniramine

• Histex

• Dramamine

• Hydroxyzine

• Promethazine (Phenergan)

• Triprolidine

• Vistaril

Seek immediate veterinary treatment if your dog experiences swelling of the tongue, throat, or face, or has trouble breathing after taking this medication. 

Frequently asked questions

Should I give cyproheptadine on an empty stomach?

You can give cyproheptadine with or without a meal, though some dogs tolerate it better with food. 

Is cyproheptadine available over the counter?

No, you'll need to obtain a prescription from your vet. 

Should I continue giving my dog Benedryl while they're on cyproheptadine?

No, you shouldn't combine this medication with any other antihistamines or medications with tranquilizing effects. Consult with your vet if cyproheptadine isn't helping your dog's symptoms. The vet may need to prescribe a stronger drug.