Clemastine, also known as meclastin, is a first-generation
H1 histamine antagonist (
antihistamine) with
anticholinergic properties (drying) and sedative side effects.[1] Like all first-generation antihistamines, it is sedating.[2][3]
Patented in 1960, it came into medical use in 1967.[4]
Medical uses
Clemastine is used to relieve
hay fever and
allergy symptoms, including sneezing; runny nose; and red, itchy, tearing eyes. Prescription strength clemastine is also used to relieve the itching and swelling of
hives.[5]
Side effects
Overdosage symptoms are paradoxical, ranging from
CNS depression to stimulation. Stimulation is most common in children, and is usually followed by excitement,
hallucinations,
ataxia, loss of coordination,
muscle twitching,
athetosis,
hyperthermia,
cyanosis, convulsions,
tremors, and
hyperreflexia. This may be followed by
postictal depression and
cardiovascular/respiratory arrest. Other common overdose symptoms include dry mouth, fixed dilated pupils, flushing of the face, and
pyrexia. In adults, overdose usually leads to CNS depression, ranging from drowsiness to
coma.[6]
Continuous and/or cumulative use of
anticholinergic medications, including first-generation antihistamines, is associated with higher risk of cognitive decline and dementia in older people.[7][8]
Clemastine is an antihistamine with
anticholinergic and
sedative effects. Antihistamines competitively bind to
histamine receptor sites, thus reducing the neurotransmitter's effects. Effects of histamine (which are countered by antihistamines) include:
Clemastine inhibits both the
vasoconstrictor and
vasodilator effects of histamine. Depending on the dose, the drug can produce paradoxical effects, including CNS stimulation or depression.
Most antihistamines exhibit some type of
anticholinergic activity. Antihistamines act by competitively binding to H1-receptor sites, thus blocking the binding of endogenous histamine. Antihistamines do not chemically inactivate or prevent the normal release of histamine.
Clemastine is rapidly absorbed from the
gastrointestinal tract and peak plasma concentrations are attained in 2–4 hours. Antihistamines are thought to be metabolized in the liver, mostly by mono-/didemethylation and glucuronide conjugation. It is an inhibitor of cytochrome P450
CYP2D6 and may interfere with other drugs metabolized by this isozyme.
Mechanism of action
Clemastine is a selective histamine H1 antagonist. It binds to the histamine H1 receptor, thus blocking the action of
endogenous histamine, which leads to temporary relief of the negative symptoms caused by histamine.[medical citation needed]
Society and culture
Clemastine is an
OTC drug, and is available under many names and dosage forms worldwide. Most common brand name is Tavegyl.[10]
Research
Clemastine has been studied for its potential to treat several psychiatric and neurological disorders, including possibly promoting
remyelination and myelin repair in conditions like
multiple sclerosis (MS).[11][12] Early phase II clinical trials showed promise for promoting remyelination in patients with MS, with clemastine improving nerve conduction velocity in the optic nerve.[13][14] However, a clinical trial (TRAP-MS) was halted in early 2024 after researchers found the disability progression was occurring at a significantly faster rate than anticipated in three participants with MS receiving clemastine.[15][16][17]
^Moghaddasi M, Nabovvati M, Koushki A, Soltansanjari M, Sardarinia M, Mohebi N, Rabani S (June 2020). "Randomized control trial of evaluation of Clemastine effects on visual evoked potential, nerve fiber layer and ganglion cell layer complex in patients with optic neuritis". Clinical Neurology and Neurosurgery. 193: 105741.
doi:
10.1016/j.clineuro.2020.105741.
PMID32145678.