Adult: As conventional tab: 4 mg 4-6 hourly. Max: 24 mg daily. As extended-release tab: 12 mg 12 hourly. Max: 24 mg daily. Elderly: Dose reduction may be needed. Max: 12 mg daily. Child: 1-<2 years 1 mg bid; 2-5 years 1 mg 4-6 hourly. Max: 6 mg daily; 6-<12 years 2 mg 4-6 hourly. Max: 12 mg daily; ≥12 years Same as adult dose. Dosage recommendations may vary among countries or individual products. Refer to specific product guidelines.
Parenteral Allergic conditions
Adult: 10-20 mg via IM, SC or slow IV inj over 1 minute. Max: 40 mg daily. Child: 1 month to <1 year 0.25 mg/kg; 1-5 years 0.2 mg/kg or 2.5-5 mg; 6-12 years 0.2 mg/kg or 5-10 mg; >12 years 0.2 mg/kg or 10-20 mg.
Administration
May be taken with or without food.
Incompatibility
Incompatible with Ca chloride, kanamycin sulfate, norepinephrine acid tartrate, pentobarbital Na and meglumine adipiodone.
Contraindications
Narrow-angle glaucoma, symptomatic prostate hypertrophy, acute asthma attacks, stenosing peptic ulcer, bladder neck or pyloroduodenal obstruction. Concomitant or within 14 days of MAOI use.
Special Precautions
Patient with CV disease (e.g. ischaemic heart disease, hypertension), increased intraocular pressure, thyroid dysfunction, asthma or other chronic breathing disorders (e.g. bronchitis), epilepsy, prostatic hyperplasia, genitourinary obstruction. Hepatic or renal impairment. Children and elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Sedation; excitation (in young children). Eye disorders: Blurred vision. Gastrointestinal disorders: Dry mouth, nausea, vomiting, diarrhoea, epigastric pain. General disorders and administration site conditions: Fatigue, lassitude. Metabolism and nutrition disorders: Anorexia, increased appetite. Nervous system disorders: Somnolence, disturbance in attention, abnormal coordination, dizziness, headache.
Patient Counseling Information
This drug may cause drowsiness, dizziness, blurred vision and psychomotor impairment, if affected, do not drive or operate machinery.
Overdosage
Symptoms: Sedation, paradoxical excitation of the CNS, toxic psychosis, apnoea, convulsions, anticholinergic effects, dystonic reactions, CV collapse (e.g. arrhythmias). Management: Symptomatic and supportive treatment. Gastric lavage or induced emesis using syrup of ipecacuanha may be considered. Activated charcoal can be given if overdosage is by the oral route, provided there are no contraindications for use and the overdose is recent (within 1 hour of ingestion). CNS convulsions may be treated with IV diazepam. Hypotension and arrhythmias should be treated vigorously. For severe cases, haemoperfusion may be used.
Drug Interactions
Enhanced sedative effect with other CNS depressants (e.g. barbiturates, hypnotics, opioid analgesics, sedatives, antipsychotics. Inhibits phenytoin metabolism which may lead to phenytoin toxicity. Potentially Fatal: Increased anticholinergic effects with MAOIs.
Food Interaction
Enhanced CNS depression with alcohol.
Lab Interference
May suppress the wheal and flare reactions to skin test antigens.
Action
Description: Mechanism of Action: Chlorphenamine, an alkylamine derivative, is a sedating antihistamine that competitively and reversibly inhibits histamine H1- receptor in the gastrointestinal and respiratory tract and blood vessels. This prevents the release of histamine, prostaglandins and leukotrienes, and also prevents the migration of inflammatory mediators. Synonym: Chlorpheniramine. Onset: Within 30 minutes. Duration: 4-6 hours. Pharmacokinetics: Absorption: Readily absorbed from the gastrointestinal tract. Bioavailability: 25-50%. Time to peak plasma concentration: 2.5-6 hours. Distribution: Widely distributed in the body, including the CNS. Enters breast milk. Volume of distribution: 6-12 L/kg. Plasma protein binding: Approx 70%. Metabolism: Extensively metabolised in the liver by CYP enzymes, including CYP2D6 to active and inactive metabolites, including desmethyl- and didesmethylchlorphenamine; undergoes extensive first-pass metabolism. Excretion: Mainly via urine (approx 22%, as unchanged drug); faeces (trace amounts). Elimination half-life: 2-43 hours.
Chemical Structure
Chlorphenamine Source: National Center for Biotechnology Information. PubChem Database. Chlorpheniramine, CID=2725, https://pubchem.ncbi.nlm.nih.gov/compound/Chlorpheniramine (accessed on Jan. 21, 2020)
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