Allergic Conditions 
Cyproheptadine hydrochloride shares the actions and uses of the other antihistamines. In addition, cyproheptadine is used for the treatment of cold urticaria, and some clinicians consider it the drug of choice for the treatment of this condition.
Cushing's Syndrome
Cyproheptadine has been effective in some patients for the treatment of Cushing's syndrome† secondary to pituitary disorders. Clinical remissions and normalization of cortisol indexes (i.e., cortisol secretion rate, plasma cortisol concentration, urinary free cortisol excretion) reportedly occur in up to 60% of patients, generally within 1-3 months after beginning treatment. Although almost all of these patients relapse after discontinuance of cyproheptadine, prolonged remission (e.g., for at least 2.5-3 years) has occurred in a few patients following discontinuance of the drug. If relapse occurs, additional courses of therapy usually produce further responses. The role of cyproheptadine in the treatment of Cushing's syndrome secondary to pituitary disorders remains to be clearly established; in most patients, other therapy (e.g., surgery, radiation therapy) is preferred.
Sexual Dysfunction
Cyproheptadine has been effective for the management of inhibited male or female orgasm† (anorgasmy) induced by tricyclic antidepressants, monoamine oxidase inhibitors, fluoxetine, or antipsychotic agents. Ability to achieve orgasm was restored when cyproheptadine was administered 1-2 hours before anticipated sexual activity (e.g., 4-12 mg) or daily (e.g., 1-16 mg daily). Although not clearly established, the efficacy of cyproheptadine in these patients may be related to its serotonin antagonist or anticholinergic activity. However, the potential for drug interaction (possibly resulting in anticholinergic toxicity or additive CNS depression) in patients receiving any of these drugs concomitantly with cyproheptadine should be kept in mind. In a limited number of patients receiving cyproheptadine for fluoxetine-induced ejaculatory dysfunction, cyproheptadine reversed the antidepressant effects of fluoxetine. The mechanism of this drug interaction is not known, but it has been postulated that cyproheptadine, a serotonin antagonist, may inhibit the serotonergic effects of fluoxetine.
Anorexia Nervosa
Although there are few indications for clinical use, cyproheptadine has been shown to stimulate appetite and weight gain in children and adults. There is evidence that cyproheptadine may be of some value in the management of anorexia nervosa†, but the drug may be more effective in patients with anorexia nervosa who do not undertake periodic episodes of binge eating (nonbulimic) than those who do (bulimic).
Headache
Cyproheptadine reportedly has been effective in some patients for the management of vascular headaches† (e.g., migraine). While clinical efficacy of cyproheptadine in the prophylaxis of migraine headache has not been established in randomized controlled studies, some experts consider the drug to be effective based on consensus and clinical experience. For further information on management and classification of migraine headache, see Vascular Headaches: General Principles in Migraine Therapy, under Uses in Sumatriptan 28:32.28.
Other Uses
Cyproheptadine reportedly has been effective in some patients for the management of Nelson's syndrome†, virilizing congenital adrenal hyperplasia† in adult females, galactorrhea-amenorrhea syndrome†, and carcinoid syndrome†.
Cyproheptadine has been used as an adjunct to somatropin (human growth hormone) therapy in a limited number of children with somatotropin (endogenous growth hormone) deficiency†. Combined therapy with the drugs was more effective in promoting weight gain and linear growth in these children than somatropin alone, but additional study is necessary.
Cyproheptadine hydrochloride shares the toxic potentials of other antihistamines, and the usual precautions of antihistamine therapy should be observed. (See Cautions in the Antihistamines General Statement 4:00.)
Pediatric Precautions
Safety and efficacy of cyproheptadine in children younger than 2 years of age have not been established and, like other antihistamines, the drug should not be used in premature or full-term neonates. (See Cautions: CNS Effects and see Pediatric Precautions, in the Antihistamines General Statement 4:00.
Geriatric Precautions
Clinical studies of cyproheptadine did not include sufficient numbers of patients 65 years of age and older to determine whether geriatric patients respond differently than younger patients. While clinical experience generally has not revealed age-related differences in response to the drug, care should be taken in dosage selection of cyproheptadine. Because of the greater frequency of decreased hepatic, renal, and/or cardiac function and of concomitant disease and drug therapy in geriatric patients, the manufacturer suggests that patients in this age group receive initial dosages of the drug in the lower end of the usual range.
Mutagenicity and Carcinogenicity
Long-term studies to determine the carcinogenic potential of cyproheptadine have not been performed to date. No evidence of cyproheptadine-induced mutagenic activity was seen in vitro in the Ames microbial mutagen test, although concentrations of the drug greater than 0.5 mg/plate inhibited bacterial growth. Chromosomal abnormalities also were not evident in in vitro mammalian (human lymphocytes or fibroblasts) test systems, but high concentrations were cytotoxic.
Pregnancy, Fertility, and Lactation
Pregnancy
Reproduction studies in rabbits, mice, and rats using oral or subcutaneous cyproheptadine hydrochloride dosages up to 32 times the maximum recommended human oral dosage have not revealed evidence of harm to the fetus. Although the drug has been fetotoxic in rats when administered intraperitoneally at dosages 4 times the maximum recommended human oral dosage, experience in a limited number of women who received cyproheptadine orally during the first, second, and/or third trimesters of pregnancy did not reveal evidence of an increased risk of fetal abnormalities, nor were teratogenic effects observed in neonates born to these women. No evidence of adverse fetal effect was evident in an infant born to a woman who had received 12 mg of cyproheptadine hydrochloride daily throughout pregnancy for the treatment of Cushing's syndrome; the infant developed normally until 4 months of age when he developed gastroenteritis and died. Nevertheless, because the reported experience to date in humans cannot exclude the possibility of adverse fetal effects of the drug, cyproheptadine should be used during pregnancy only when clearly needed.
Fertility
Reproduction studies in animals using cyproheptadine hydrochloride dosages up to 32 times the maximum recommended human oral dosage have not revealed evidence of impaired fertility. Successful pregnancy has occurred in several women who received cyproheptadine for the treatment of Cushing's syndrome†; the women were amenorrheic prior to therapy with the drug.
Lactation
It is not known whether cyproheptadine hydrochloride is distributed into milk. Because of the potential for serious adverse reactions to cyproheptadine in nursing infants, a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman.
Pharmacology
Cyproheptadine has potent antihistaminic and serotonin antagonist properties; the drug also has anticholinergic and sedative effects and reportedly has calcium-channel blocking activity. While the exact mechanisms of action are complex and have not been fully elucidated, the beneficial effects of cyproheptadine in the treatment of Cushing's syndrome† are generally believed to result from the drug's serotonin antagonist activity.
Pharmacokinetics
Absorption
Cyproheptadine hydrochloride appears to be well absorbed following oral administration. Following a single oral dose of radiolabeled drug in fasting healthy adults in one study, peak plasma concentrations of radioactivity occurred 6-9 hours after administration; the radioactivity appeared to represent cyproheptadine metabolites.
Distribution
Distribution of cyproheptadine into human body tissues and fluids has not been characterized. It is not known if the drug is distributed into milk.
Elimination
The metabolic and excretory fate of cyproheptadine has not been fully elucidated. The drug appears to be almost completely metabolized, principally to the quaternary ammonium glucuronide conjugate. The drug also undergoes aromatic ring hydroxylation, N -demethylation, and heterocyclic ring oxidation. Most cyproheptadine metabolites appear to be conjugated with glucuronic acid or sulfate.
Cyproheptadine metabolites are excreted principally in urine, almost completely as conjugates. The drug does not appear to be excreted unchanged in urine. Cyproheptadine and some metabolites are excreted in feces following oral administration; whether such excretion occurs via biliary elimination remains to be established. Following a single oral dose of cyproheptadine hydrochloride in healthy adults, about 30% of the dose is excreted as metabolites in urine within 24 hours, about 50% within 48 hours, and about 65-75% within 6 days; the remainder of the dose is excreted in feces. The principal urinary metabolite is the quaternary ammonium glucuronide conjugate; during chronic administration of 12-20 mg of cyproheptadine daily in patients with anorexia nervosa who had normal renal and hepatic function, an average of 24% of the daily dose was excreted in urine as this metabolite. Elimination of cyproheptadine is reduced in renal insufficiency.
Chemistry and Stability
Chemistry
Cyproheptadine is an antihistamine and a serotonin antagonist. The drug is structurally and pharmacologically related to azatadine. Cyproheptadine hydrochloride occurs as a white to slightly yellow, odorless or practically odorless, crystalline powder. The drug has solubilities of approximately 3.64 mg/mL in water and 28.6 mg/mL in alcohol. Cyproheptadine has a pKa of 9.3. Commercially available cyproheptadine hydrochloride oral solution occurs as a clear, yellow, syrupy liquid and has a pH of 3.5-4.5.
Stability
Cyproheptadine hydrochloride oral solution and tablets should be stored in tight or well-closed containers, respectively, at 15-30°C; freezing (i.e., storage at temperatures colder than -20°C) of the oral solution should be avoided.
Additional Information
For further information on chemistry, pharmacology, pharmacokinetics, uses, cautions, acute toxicity, drug interactions, laboratory test interferences, and dosage and administration of cyproheptadine hydrochloride, see the Antihistamines General Statement 4:00. The American Society of Health-System Pharmacists, Inc. represents that the information provided in the accompanying monograph was formulated with a reasonable standard of care, and in conformity with professional standards in the field. Readers are advised that decisions regarding use of drugs are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and that the information contained in the monograph is provided for informational purposes only. The manufacturer's labeling should be consulted for more detailed information. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information contained in the monograph is not a substitute for medical care.
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