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.
