Fenimex

Doses must be individually determined in all cases and should be taken with or soon after food. Treatment should be commenced at the lowest possible dose because experience has shown that antihistamines are often effective at low doses. The maximum dose of 3 mg/kg per day should not be exceeded. Elderly patients should use the adult dose with caution.

To prevent travel sickness, it is recommended that the first dose be taken at least 30 minutes before traveling. Due to the risk of drowsiness, the patient should not drive a motor vehicle or operate machinery after taking a dose.

Pheniramine Maleate tablets:

• In adults and children over 10 years of age: Treatment is commenced with half a tablet taken up to three times daily. This dose may be increased to one tablet taken up to three times daily if required.
• Children 5-10 years of age: Half a tablet up to three times daily. Pheniramine Maleate tablets are not recommended in children under 5 years of age.

The most common adverse reaction is sedation, which often disappears after a few days if tolerance is acquired. Hypersensitivity reactions have been reported.

• Central Nervous System: Lassitude, dizziness, tinnitus, inability to concentrate, incoordination, irritability, insomnia and tremors. Agitation and convulsions, especially in children and restlessness, disorientation and hallucinations in adults, are common symptoms following overdose.
• Gastrointestinal: Nausea, vomiting, diarrhoea, colic, epigastric pain, anorexia, dryness of mouth and constipation.
• Genitourinary: Urinary retention.
• Cardiovascular: Palpitations, headache.
• Ocular: Blurred vision, increased intraocular pressure.
• Musculoskeletal: Muscular weakness.
• Haematological: Rare cases of blood dyscrasias including agranulocytosis and haemolytic anaemia have been reported.

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.

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.

Sedating Anti-histamine