One of the histamine H1 antagonists with little sedative action. It is used in treatment of hay fever, rhinitis, allergic dermatoses, and pruritus.
H1-Receptor Antagonist; Sedating Antihistamine
Pheniramine competes with histamine for the histamine H1 receptor, acting as an inverse agonist once bound. The reduction in H1 receptor activity is responsible for reduced itching as well as reduced vasodilation and capillary leakage leading to less redness and edema. This can be seen in the suppression of the histamine-induced wheal (swelling) and flare (vasodilation) response. Inverse agonism of the H1 receptor in the CNS is also responsible for the sedation produced by first-generation antihistamines like pheniramine. The binding of pheniramine to H4 receptors, and subsequent inverse agonism, may also contribute to reduced itching by antagonizing inflammation.
ORAL Allergic conditions: Adult: As maleate: Syrup: 15-30 mg bid or tid. Tablet: Up to 45 mg tid. Max: 3 mg/kg/day. ChiId:As maleate: 5-10 yr: Half a 45-mg tab up to tid; >10 yr: Syrup: 15-30mg bid or tid. Tablet: Up to 45 mg tid. Max: 3 mg/kg/day. Elderly:As maleate: Syrup: 15-30 mg bid or tid. Tablet: Up to 45 mg tid. Max: 3 mg/ kg/day. Prophylaxis of motion sickness: Adult: As maleate: Syrup: 15-30 mg bid or tid. Tablet: Up to 45 mg tid. Max: 3 mg/kg/ day. Take 1st dose at least 30 mm before travelling.ChiId:As maleate: 5-10 yr: Half a 45-mg tab up to tid; >10 yr: Syrup: 15-30 mg bid or tid. Tablet: Up to 45 mg tid. Max: 3 mg/kg/day. Take 1st dose at least 30 min before travelling.
MAO-inhibitors may prolong and intensify the anticholinergic effect of pheniramine (see Contraindications).
Adverse CNS effects of pheniramine may be enhanced when it is taken with alcohol or other CNS depressants (eg. hypnotics, sedatives, tranquilizers).
Atropine and related drugs may enhance the anticholinergic activity of pheniramine.
Symptomatic prostatic hypertrophy; neonates & premature infants. May impair ability to drive or operate machinery. Has potential for abuse. Narrow angle glaucoma, asthma or severe CV disease. Antiemetic effect may mask signs of other conditions. Pregnancy & lactation. Elderly.
Oral: Sedation. Hypersensitivity reactions. Lassitude, dizziness, tinnitus, inability to concentrate, incoordination, irritability, insomnia & tremors. Nausea, vomiting, diarrhoea, colic, epigastric pain, anorexia, dryness of mouth & constipation. Urinary retention. Palpitations, headache. Blurred vision, increased intraocular pressure. Muscular weakness. Rarely, blood dyscrasias e.g. agranulocytosis, haemolytic anaemia. Ophthalmic: Temporarily enlarged pupils, eye redness (overuse).
There are no controlled data in human pregnancy. Acetaminophen/pheniramine/phenylephrine is only recommended for use during pregnancy when there are no alternatives and benefit outweighs risk. There are no data on the excretion of pheniramine into human milk. Small amounts of phenylephrine are secreted in breast milk.
Symptoms: Antihistamine drugs in toxic doses produce a complex of CNS excitatory and depressant effects. Accidental ingestion in small children has resulted in convulsions and sometimes death.
Management: As there is no specific antidote, treatment should be symptomatic and supportive. Induction of vomiting should only be used immediately after ingestion as the sedative action of any absorbed antihistamine can lead to life-threatening pulmonary aspiration during emesis. Gastric lavage with a cuffed endotracheal tube in situ may be useful for some time after ingestion of antihistamines as their anticholinergic action slows down gastric emptying. Stimulants should not be used as they may precipitate convulsions. Diazepam or short-acting barbiturates may be used to control convulsions. Vasopressors may be used to treat hypotension. Mechanical support of respiration may be required if respiration is seriously depressed. Continuous ECG monitoring is recommended if cardiac toxicity develops, which can be treated with centrally-acting anticholinesterases such as physostigmine.
Store in a cool and dry place, protected from light. Do not use later than the date of expiry. Keep all medicines out of the reach of children. To be dispensed only on the prescription of a registered physician.
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