Drug information of Methdilazine


Methdilazine is a phenothiazine compound with antihistaminic activity. It is used in the treatment of various dermatoses to relieve pruritus

Mechanism of effect

Methdilazine binds to the histamine H1 receptor. This blocks the action of endogenous histamine, which subsequently leads to temporary relief of the negative symptoms brought on by histamine.


Histamine, acting on H1-receptors, produces pruritis, vasodilatation, hypotension, flushing, headache, tachycardia, and bronchoconstriction. Histamine also increases vascular permeability and potentiates pain. Methdilazine is a histamine H1 antagonist. It competes with histamine for the normal H1-receptor sites on effector cells of the gastrointestinal tract, blood vessels and respiratory tract. It provides effective, temporary relief of sneezing, watery and itchy eyes, and runny nose due to hay fever and other upper respiratory allergies.


Absorption: Well absorbed in the digestive tract.




Usual adult and adolescent dose
Antihistaminic (H 1-receptor)
Oral, 8 mg every six to twelve hours as needed.
Usual pediatric dose
Antihistaminic (H 1-receptor)
Children up to 3 years of age: Use is not recommended.
Children 3 to 12 years of age: Oral, 4 mg every six to twelve hours as needed.


Patients sensitive to other phenothiazines may be sensitive to methdilazine, promethazine, and trimeprazine also.

» Bladder neck obstruction or
» Prostatic hypertrophy, symptomatic or
» Urinary retention, predisposition to    (anticholinergic effects may precipitate or aggravate urinary retention)
Bone marrow depression    (increased risk of leukopenia and agranulocytosis)
Cardiovascular disease    (increased risk of transient hypotension)
» Coma    (may be exacerbated)
» Glaucoma, angle-closure or predisposition to    (mydriatic effect resulting in increased intraocular pressure may precipitate an attack of angle-closure glaucoma)
Glaucoma, open-angle    (mydriatic effect may cause a slight increase in intraocular pressure; glaucoma therapy may need to be adjusted)
Hepatic function impairment    (metabolism may be decreased; higher serum concentrations may increase sensitivity to CNS effects)
Sensitivity to the antihistamine used
Caution is recommended when phenothiazine-derivative antihistamines are used, since their antiemetic action may impede diagnosis of such conditions as appendicitis and obscure signs of toxicity from overdosage of other drugs

Points of recommendation

Importance of not taking more medication than the amount recommended
Missed dose: If on scheduled dosing regimen—Using as soon as possible; not using if almost time for next dose; not doubling doses
Taking with food, water, or milk to minimize gastric irritation
Swallowing extended-release dosage forms whole
Possible interference with skin tests using allergens; need to inform physician of using medication
May mask ototoxic effects of large doses of salicylates
Avoiding use of alcohol or other CNS depressants
Caution if drowsiness occurs
Possible dryness of mouth; using sugarless gum or candy, ice, or saliva substitute for relief; checking with physician or dentist if dry mouth continues for more than 2 weeks
Need to inform physician of use: Possible interference with diagnosis of appendicitis; may mask signs of toxicity from overdosage of other drugs

Pregnancy level

Group c - Not adequate studies in pregnant women

Related drugs

Promethazine , Trimeprazine

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