Cyproheptadine

Cyproheptadine is a potent competitive antagonist of both serotonin and histamine receptors. It is used primarily to treat allergic symptoms, though it is perhaps more notable for its use in appetite stimulation and its off-label use in the treatment of serotonin syndrome.

Cyproheptadine is a combined serotonin and histamine antagonist used in the treatment of allergic symptoms, for appetite stimulation, and off-label in the treatment of serotonin syndrome.

In the US, prescription cyproheptadine is indicated for the treatment of various allergic symptomatologies - including dermatographia, rhinitis, conjunctivitis, and urticaria - as well as adjunctive therapy in the management of anaphylaxis following treatment with epinephrine. In Canada, cyproheptadine is available over-the-counter and is indicated for the treatment of pruritus and for appetite stimulation. In Australia, cyproheptadine is additionally indicated for the treatment vascular headaches.

Cyproheptadine is also used off-label for the treatment of serotonin syndrome.

• Allergic Reactions caused by Transfusions
• Anaphylaxis
• Angioedema and urticaria
• Cold urticaria
• Conjunctivitis allergic caused by Food Allergy
• Conjunctivitis allergic caused by inhalant allergens
• Perennial Allergic Rhinitis (PAR)
• Pruritus
• Seasonal Allergic Rhinitis
• Serotonin Syndrome
• Vasomotor Rhinitis
• Dermatographism
• Appetite stimulation

Cyproheptadine has been observed to antagonize several pharmacodynamic effects of serotonin in laboratory animals, including bronchoconstriction and vasodepression, and has demonstrated similar efficacy in antagonizing histamine-mediated effects. The reason for its efficacy in preventing anaphylactic shock has not been elucidated, but appears to be related to its anti-serotonergic effects.

Cyproheptadine appears to exert its antihistamine and antiserotonin effects by competing with free histamine and serotonin for binding at their respective receptors. Antagonism of serotonin on the appetite center of the hypothalamus may account for cyproheptadine's ability to stimulate the appetite.

A single study examining the difference in absorption of orally administered versus sublingually administered cyproheptadine in five healthy males demonstrated a mean C_max of 30.0 mcg/L and 4.0 mcg/L, respectively, and a mean AUC of 209 mcg.h/L and 25 mcg.h/L, respectively. The T_max of orally and sublingually administered cyproheptadine was 4 hours and 9.6 hours, respectively.

Approximately 2-20% of the radioactivity from an orally administered radio-labeled dose of cyproheptadine is excreted in the feces, of which approximately 34% is unchanged parent drug (less than 5.7% of the total dose). At least 40% of radioactivity is recovered in the urine.

Overdosage with cyproheptadine is likely to result in significant sedation - although paradoxical stimulation has been noted in pediatric patients - and anticholinergic adverse effects such as dry mouth and flushing. Most patients appear to recover without incident, as a review of cyproheptadine overdose cases in Hong Kong found the majority of patients had no or mild symptoms following intentional overdose.

In the event of overdosage with cyproheptadine, prescribing information recommends the induction of vomiting (if it has not occurred spontaneously) using syrup of ipecac. Gastric lavage and activated charcoal may also be considered. Vasopressors may be used to treat hypotension and intravenous physostigmine salicylate may be considered for the treatment of significant CNS symptoms depending on the clinical picture.

• Avoid alcohol. Co-administration with alcohol may potentiate the sedative effects of cyproheptadine.