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Clemastine

Generic name: clemastine systemic

Brand names: Allerhist-1, Tavist-1, Tavist, Dailyhist-1, Contac 12 Hour Allergy, Tavist Allergy, Dayhist-1, Leader Allerhist, Dayhist Allergy, 12 Hour Allergy Relief

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product

Tablet, Oral, as fumarate:

Dayhist Allergy 12 Hour Relief: 1.34 mg [scored; sodium free]

Tavist Allergy: 1.34 mg [DSC] [scored; sodium free]

Generic: 1.34 mg [DSC], 2.68 mg

Pharmacology

Mechanism of Action

Competes with histamine for H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract; anticholinergic and sedative effects are also seen.

Pharmacokinetics/Pharmacodynamics

Absorption

Rapidly and nearly completely absorbed

Distribution

Vd: ~800 L (range: 500 to 1000 L) (Sharma 2003)

Metabolism

Hepatic; metabolized via unidentified enzymes by O-dealkylation followed by alcohol dehydration, aliphatic oxidation, aromatic oxidation, and direct oxidation; significant first-pass effect (Sharma 2003)

Excretion

Urine (~42% as metabolites) (Sharma 2003)

Onset of Action

2 hours after administration; Peak effect: Therapeutic: 5 to 7 hours

Time to Peak

2 to 4 hours

Duration of Action

10 to 12 hours; may persist for up to 24 hours

Half-Life Elimination

~21 hours (range: 10 to 33 hours) (Sharma 2003)

Use: Labeled Indications

Allergic rhinitis: Relief of symptoms associated with allergic rhinitis or other upper respiratory allergies (eg, sneezing, rhinorrhea, pruritus, and lacrimation) in children ≥12 years of age and adults (tablets and syrup) and in children 6 to 12 years (syrup only)

Urticaria/angioedema: Relief of mild, uncomplicated allergic skin manifestations of urticaria and angioedema in children ≥12 years of age and adults (tablets and syrup) and in children 6 to 12 years (syrup only)

OTC Labeling: Common cold/hay fever/upper respiratory allergies: Relief of symptoms associated with the common cold (eg, rhinorrhea, sneezing, throat/nose pruritus, lacrimation) in children ≥12 years of age and adults

Contraindications

Hypersensitivity clemastine, any component of the formulation, or to other antihistamines of similar chemical structure; use with monoamine oxidase inhibitors; newborn or premature infants; breast-feeding women; lower respiratory tract symptoms (eg, asthma)

Dosage and Administration

Dosing: Adult

Allergic rhinitis: Oral: Clemastine fumarate 1.34 mg (1 mg base) twice daily; may be increased as needed or a single 2.68 mg dose, repeat as needed up to a maximum of 2.68 mg 3 times a day. Maximum daily dose: Clemastine fumarate 8.04 mg/day (6 mg/day base)

Common cold/hay fever/upper respiratory allergies (OTC labeling): Oral: Clemastine fumarate 1.34 mg (1 mg base) twice daily. Maximum daily dose: Clemastine fumarate 2.68 mg/day (2 mg/day base)

Urticaria/angioedema: Oral: Clemastine fumarate 2.68 mg (2 mg base) twice daily or a single 2.68 mg dose, repeat as needed up to a maximum of 2.68 mg 3 times a day. Maximum daily dose: Clemastine fumarate 8.04 mg/day (6 mg/day base)

Dosing: Geriatric

Avoid use (Beers Criteria [AGS 2019]).

Dosing: Pediatric

Allergic rhinitis: Oral:

Children 6 to <12 years: Syrup: 0.67 mg clemastine fumarate (0.5 mg base) twice daily; dosage may be increased as required; single doses up to 3 mg clemastine fumarate (2.25 mg base) have been tolerated; maximum daily dose: 4.02 mg/day clemastine fumarate (3 mg/day base)

Children ≥12 years and Adolescents: Syrup/Tablet: 1.34 mg clemastine fumarate (1 mg base) twice daily; dosage may be increased as required up to 2.68 mg clemastine fumarate (2 mg base) 3 times daily; maximum daily dose: 8.04 mg/day clemastine fumarate (6 mg/day base)

Common cold, hayfever, upper respiratory allergies: OTC labeling: Oral: Tablets: Children ≥12 years and Adolescents: 1.34 mg clemastine fumarate (1 mg base) twice daily; maximum daily dose: 2.68 mg/day clemastine fumarate (2 mg base/day)

Urticaria; angioedema: Oral:

Children 6 to <12 years: Syrup: 1.34 mg clemastine fumarate (1 mg base) twice daily; maximum daily dose 4.02 mg/day clemastine fumarate (3 mg/day base)

Children ≥12 years and Adolescents: Syrup, Tablet: 2.68 mg clemastine fumarate (2 mg base) twice daily or a single 2.68 mg clemastine fumarate dose (2 mg base), repeat as needed up to a maximum of 2.68 mg clemastine fumarate (2 mg base) 3 times daily; maximum daily dose: 8.04 mg/day clemastine fumarate (6 mg/day base)

Storage

Store at controlled room temperature, between 20°C and 25°C (68°F and 77°F).

Clemastine Images

Drug Interactions

Acetylcholinesterase Inhibitors: May diminish the therapeutic effect of Anticholinergic Agents. Anticholinergic Agents may diminish the therapeutic effect of Acetylcholinesterase Inhibitors. Monitor therapy

Aclidinium: May enhance the anticholinergic effect of Anticholinergic Agents. Avoid combination

Alcohol (Ethyl): CNS Depressants may enhance the CNS depressant effect of Alcohol (Ethyl). Monitor therapy

Alizapride: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Amantadine: May enhance the anticholinergic effect of Anticholinergic Agents. Monitor therapy

Amezinium: Antihistamines may enhance the stimulatory effect of Amezinium. Monitor therapy

Amphetamines: May diminish the sedative effect of Antihistamines. Monitor therapy

Anticholinergic Agents: May enhance the adverse/toxic effect of other Anticholinergic Agents. Monitor therapy

Azelastine (Nasal): CNS Depressants may enhance the CNS depressant effect of Azelastine (Nasal). Avoid combination

Benzylpenicilloyl Polylysine: Antihistamines may diminish the diagnostic effect of Benzylpenicilloyl Polylysine. Management: Suspend systemic H1 antagonists for benzylpenicilloyl-polylysine skin testing and delay testing until systemic antihistaminic effects have dissipated. A histamine skin test may be used to assess persistent antihistaminic effects. Consider therapy modification

Betahistine: Antihistamines may diminish the therapeutic effect of Betahistine. Monitor therapy

Blonanserin: CNS Depressants may enhance the CNS depressant effect of Blonanserin. Consider therapy modification

Botulinum Toxin-Containing Products: May enhance the anticholinergic effect of Anticholinergic Agents. Monitor therapy

Brexanolone: CNS Depressants may enhance the CNS depressant effect of Brexanolone. Monitor therapy

Brimonidine (Topical): May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Bromopride: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Bromperidol: May enhance the CNS depressant effect of CNS Depressants. Avoid combination

Buprenorphine: CNS Depressants may enhance the CNS depressant effect of Buprenorphine. Management: Consider reduced doses of other CNS depressants, and avoiding such drugs in patients at high risk of buprenorphine overuse/self-injection. Initiate buprenorphine at lower doses in patients already receiving CNS depressants. Consider therapy modification

Cannabidiol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Cannabis: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Chloral Betaine: May enhance the adverse/toxic effect of Anticholinergic Agents. Monitor therapy

Chlormethiazole: May enhance the CNS depressant effect of CNS Depressants. Management: Monitor closely for evidence of excessive CNS depression. The chlormethiazole labeling states that an appropriately reduced dose should be used if such a combination must be used. Consider therapy modification

Chlorphenesin Carbamate: May enhance the adverse/toxic effect of CNS Depressants. Monitor therapy

Cimetropium: Anticholinergic Agents may enhance the anticholinergic effect of Cimetropium. Avoid combination

CNS Depressants: May enhance the adverse/toxic effect of other CNS Depressants. Monitor therapy

Dimethindene (Topical): May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Doxylamine: May enhance the CNS depressant effect of CNS Depressants. Management: The manufacturer of Diclegis (doxylamine/pyridoxine), intended for use in pregnancy, specifically states that use with other CNS depressants is not recommended. Monitor therapy

Dronabinol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Droperidol: May enhance the CNS depressant effect of CNS Depressants. Management: Consider dose reductions of droperidol or of other CNS agents (eg, opioids, barbiturates) with concomitant use. Exceptions to this monograph are discussed in further detail in separate drug interaction monographs. Consider therapy modification

Eluxadoline: Anticholinergic Agents may enhance the constipating effect of Eluxadoline. Avoid combination

Esketamine: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Flunitrazepam: CNS Depressants may enhance the CNS depressant effect of Flunitrazepam. Consider therapy modification

Gastrointestinal Agents (Prokinetic): Anticholinergic Agents may diminish the therapeutic effect of Gastrointestinal Agents (Prokinetic). Monitor therapy

Glucagon: Anticholinergic Agents may enhance the adverse/toxic effect of Glucagon. Specifically, the risk of gastrointestinal adverse effects may be increased. Monitor therapy

Glycopyrrolate (Oral Inhalation): Anticholinergic Agents may enhance the anticholinergic effect of Glycopyrrolate (Oral Inhalation). Avoid combination

Glycopyrronium (Topical): May enhance the anticholinergic effect of Anticholinergic Agents. Avoid combination

Hyaluronidase: Antihistamines may diminish the therapeutic effect of Hyaluronidase. Management: Patients receiving antihistamines (particularly at larger doses) may not experience the desired clinical response to standard doses of hyaluronidase. Larger doses of hyaluronidase may be required. Consider therapy modification

HYDROcodone: CNS Depressants may enhance the CNS depressant effect of HYDROcodone. Management: Avoid concomitant use of hydrocodone and benzodiazepines or other CNS depressants when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Consider therapy modification

HydrOXYzine: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Ipratropium (Oral Inhalation): May enhance the anticholinergic effect of Anticholinergic Agents. Avoid combination

Itopride: Anticholinergic Agents may diminish the therapeutic effect of Itopride. Monitor therapy

Kava Kava: May enhance the adverse/toxic effect of CNS Depressants. Monitor therapy

Lemborexant: May enhance the CNS depressant effect of CNS Depressants. Management: Dosage adjustments of lemborexant and of concomitant CNS depressants may be necessary when administered together because of potentially additive CNS depressant effects. Close monitoring for CNS depressant effects is necessary. Consider therapy modification

Levosulpiride: Anticholinergic Agents may diminish the therapeutic effect of Levosulpiride. Avoid combination

Lofexidine: May enhance the CNS depressant effect of CNS Depressants. Management: Drugs listed as exceptions to this monograph are discussed in further detail in separate drug interaction monographs. Monitor therapy

Magnesium Sulfate: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Methotrimeprazine: CNS Depressants may enhance the CNS depressant effect of Methotrimeprazine. Methotrimeprazine may enhance the CNS depressant effect of CNS Depressants. Management: Reduce adult dose of CNS depressant agents by 50% with initiation of concomitant methotrimeprazine therapy. Further CNS depressant dosage adjustments should be initiated only after clinically effective methotrimeprazine dose is established. Consider therapy modification

MetyroSINE: CNS Depressants may enhance the sedative effect of MetyroSINE. Monitor therapy

Mianserin: May enhance the anticholinergic effect of Anticholinergic Agents. Monitor therapy

Minocycline (Systemic): May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Mirabegron: Anticholinergic Agents may enhance the adverse/toxic effect of Mirabegron. Monitor therapy

Monoamine Oxidase Inhibitors: May enhance the anticholinergic effect of Clemastine. Exceptions: Linezolid; Rasagiline; Safinamide; Selegiline. Monitor therapy

Nabilone: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Nitroglycerin: Anticholinergic Agents may decrease the absorption of Nitroglycerin. Specifically, anticholinergic agents may decrease the dissolution of sublingual nitroglycerin tablets, possibly impairing or slowing nitroglycerin absorption. Monitor therapy

Opioid Agonists: CNS Depressants may enhance the CNS depressant effect of Opioid Agonists. Management: Avoid concomitant use of opioid agonists and benzodiazepines or other CNS depressants when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Consider therapy modification

Orphenadrine: CNS Depressants may enhance the CNS depressant effect of Orphenadrine. Avoid combination

Oxatomide: May enhance the anticholinergic effect of Anticholinergic Agents. Avoid combination

Oxomemazine: May enhance the CNS depressant effect of CNS Depressants. Avoid combination

OxyCODONE: CNS Depressants may enhance the CNS depressant effect of OxyCODONE. Management: Avoid concomitant use of oxycodone and benzodiazepines or other CNS depressants when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Consider therapy modification

Paraldehyde: CNS Depressants may enhance the CNS depressant effect of Paraldehyde. Avoid combination

Perampanel: May enhance the CNS depressant effect of CNS Depressants. Management: Patients taking perampanel with any other drug that has CNS depressant activities should avoid complex and high-risk activities, particularly those such as driving that require alertness and coordination, until they have experience using the combination. Consider therapy modification

Piribedil: CNS Depressants may enhance the CNS depressant effect of Piribedil. Monitor therapy

Pitolisant: Antihistamines may diminish the therapeutic effect of Pitolisant. Avoid combination

Potassium Chloride: Anticholinergic Agents may enhance the ulcerogenic effect of Potassium Chloride. Management: Patients on drugs with substantial anticholinergic effects should avoid using any solid oral dosage form of potassium chloride. Avoid combination

Potassium Citrate: Anticholinergic Agents may enhance the ulcerogenic effect of Potassium Citrate. Avoid combination

Pramipexole: CNS Depressants may enhance the sedative effect of Pramipexole. Monitor therapy

Pramlintide: May enhance the anticholinergic effect of Anticholinergic Agents. These effects are specific to the GI tract. Consider therapy modification

Ramosetron: Anticholinergic Agents may enhance the constipating effect of Ramosetron. Monitor therapy

Revefenacin: Anticholinergic Agents may enhance the anticholinergic effect of Revefenacin. Avoid combination

ROPINIRole: CNS Depressants may enhance the sedative effect of ROPINIRole. Monitor therapy

Rotigotine: CNS Depressants may enhance the sedative effect of Rotigotine. Monitor therapy

Rufinamide: May enhance the adverse/toxic effect of CNS Depressants. Specifically, sleepiness and dizziness may be enhanced. Monitor therapy

Secretin: Anticholinergic Agents may diminish the therapeutic effect of Secretin. Management: Avoid concomitant use of anticholinergic agents and secretin. Discontinue anticholinergic agents at least 5 half-lives prior to administration of secretin. Consider therapy modification

Selective Serotonin Reuptake Inhibitors: CNS Depressants may enhance the adverse/toxic effect of Selective Serotonin Reuptake Inhibitors. Specifically, the risk of psychomotor impairment may be enhanced. Monitor therapy

Sodium Oxybate: May enhance the CNS depressant effect of CNS Depressants. Management: Consider alternatives to combined use. When combined use is needed, consider minimizing doses of one or more drugs. Use of sodium oxybate with alcohol or sedative hypnotics is contraindicated. Consider therapy modification

Suvorexant: CNS Depressants may enhance the CNS depressant effect of Suvorexant. Management: Dose reduction of suvorexant and/or any other CNS depressant may be necessary. Use of suvorexant with alcohol is not recommended, and the use of suvorexant with any other drug to treat insomnia is not recommended. Consider therapy modification

Tapentadol: May enhance the CNS depressant effect of CNS Depressants. Management: Avoid concomitant use of tapentadol and benzodiazepines or other CNS depressants when possible. These agents should only be combined if alternative treatment options are inadequate. If combined, limit the dosages and duration of each drug. Consider therapy modification

Tetrahydrocannabinol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Tetrahydrocannabinol and Cannabidiol: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Thalidomide: CNS Depressants may enhance the CNS depressant effect of Thalidomide. Avoid combination

Thiazide and Thiazide-Like Diuretics: Anticholinergic Agents may increase the serum concentration of Thiazide and Thiazide-Like Diuretics. Monitor therapy

Tiotropium: Anticholinergic Agents may enhance the anticholinergic effect of Tiotropium. Avoid combination

Topiramate: Anticholinergic Agents may enhance the adverse/toxic effect of Topiramate. Monitor therapy

Trimeprazine: May enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Umeclidinium: May enhance the anticholinergic effect of Anticholinergic Agents. Avoid combination

Zolpidem: CNS Depressants may enhance the CNS depressant effect of Zolpidem. Management: Reduce the Intermezzo brand sublingual zolpidem adult dose to 1.75 mg for men who are also receiving other CNS depressants. No such dose change is recommended for women. Avoid use with other CNS depressants at bedtime; avoid use with alcohol. Consider therapy modification

Adverse Reactions

Frequency not defined.

Cardiovascular: Hypotension, palpitations, tachycardia

Central nervous system: Ataxia, confusion, dizziness, drowsiness (slight to moderate), fatigue, headache, insomnia, irritability, nervousness, restlessness, sedation

Dermatologic: Skin photosensitivity, skin rash

Gastrointestinal: Constipation, diarrhea, epigastric distress, nausea, vomiting, xerostomia

Genitourinary: Difficulty in micturition, urinary frequency, urinary retention

Hematologic & oncologic: Agranulocytosis, hemolytic anemia, thrombocytopenia

Hypersensitivity: Anaphylaxis

Ophthalmic: Blurred vision

Otic: Tinnitus

Respiratory: Thickening of bronchial secretions

Warnings/Precautions

Concerns related to adverse effects:

  • CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving).

Disease-related concerns:

  • Asthma: Use with caution in patients with a history of asthma. Antihistamines should not be used to treat lower respiratory symptoms (including asthma).
  • Cardiovascular disease: Use with caution in patients with cardiovascular disease (including hypertension and ischemic heart disease).
  • Increased intraocular pressure: Use with caution in patients with increased intraocular pressure or angle-closure (narrow angle) glaucoma.
  • Prostatic hyperplasia/urinary obstruction: Use with caution in patients with prostatic hyperplasia, bladder neck obstruction, and/or GU obstruction.
  • Pyloroduodenal obstruction: Use with caution in patients with pyloroduodenal obstruction (including stenotic peptic ulcer).
  • Thyroid dysfunction: Use with caution in patients with thyroid dysfunction.

Concurrent drug therapy issues:

  • Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

Monitoring Parameters

Monitor therapeutic response (eg, reduction of rhinitis, urticaria, eczema, pruritus, or other allergic symptoms)

Pregnancy

Pregnancy Risk Factor

B

Pregnancy Considerations

Maternal clemastine use has generally not resulted in an increased risk of birth defects. Antihistamines are recommended for the treatment of rhinitis, urticaria, and pruritus with rash in pregnant women (although second generation antihistamines may be preferred). Antihistamines are not recommended for treatment of pruritus associated with intrahepatic cholestasis in pregnancy.

Patient Education

  • Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)
  • Patient may experience fatigue, dizziness, or abdominal pain. Have patient report immediately to prescriber change in balance (HCAHPS).
  • Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for healthcare professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience and judgment in diagnosing, treating and advising patients.

Source: Wolters Kluwer Health. Last updated January 15, 2020.