Chlorphenamine 4mg Tablets

Chlorphenamine 4mg Tablets

Each tablet contains chlorphenamine maleate 4mg

Tablet; Yellow uncoated convex tablet with a breakline on one side


Therapeutic indications
The symptomatic control of allergic conditions which respond to antihistamines including ha fever, urticaria, vasomotor rhinitis, food allergy, drug and serum reactions, pruritus vulvae, pruritus ani, and insect bites.

Posology and method of administration
The route of administration for chlorphenamine tablets is oral
  1. Adults and the elderly: 4mg every 4 – 6 hours (maximum of 24mg daily)
  2. Children 6 – 12 years: 2mg every 4 – 6 hours (maximum of 12mg daily)
  3. Not recommended for use in children under 6 years of age

Use in patients hypersensitive to chlorphenamine or any other constituent of the tablet
Coma or pre-coma states
Known brain damage or epilepsy

The anticholinergic properties of chlorphenamine are intensified by monoamine oxidase inhibitors (MAOIs). Chlorphenamine is, therefore contraindicated in patients who have been treated with MAOIs within the last fourteen days.

Special warnings and precautions for use
In common with other drugs having anticholinergic effects, chlorphenamine should be used with caution in conditions such as raised intra-ocular pressure including glaucoma, prostatic hypertrophy, urinary retention, severe hypertension or cardiovascular disease, hepatic disease,
bronchitis, bronchiectasis, asthma, pyloroduodenal obstruction and thyrotoxicosis.

Children and the elderly are more susceptible to the neurological anticholinergic effects of chlorphenamine.

The effects of alcohol may be increased and therefore concurrent use should be avoided.

Should not be used with other antihistamine-containing products, including antihistamine-containing cough and cold medicines.

Contains lactose. For patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.
Contains the colouring agent Sunset Yellow (E110), which can cause hypersensitivity reactions including asthma. Allergy is more common in those people who are allergic to aspirin.

Interaction with other medicinal products and other forms of interaction
  1. Chlorphenamine may potentiate the sedative effects of alcohol and other CNS depressants.
  2. Increased anticholinergic and sedative effects may occur with concurrent use of monoamine oxidase inhibitors. The effects of other anticholinergic drugs may also be potentiated.
  3. Concurrent use of chlorphenamine may result in increased serum levels of phenytoin.
  4. There is a theoretical interaction (antagonistic effect) between betahistine and other antihistamines.

Pregnancy and lactation
There are no adequate controlled studies of chlorphenamine in pregnant women.
Chlorphenamine should only be used during pregnancy when clearly needed, and when the potential benefits outweigh the unknown risks to the foetus. Use during the third trimester may result in undesirable effects in neonates.

Anticholinergic agents such as chlorphenamine may inhibit lactation and may be secreted in breast milk. The use of chlorphenamine in mothers breast-feeding their babies requires that the therapeutic benefits of the drug should be weighed against the potential hazards to the mother and baby.
Infants may be very sensitive to the effects of anticholinergic medications.

Effects on the ability to drive and use machines
The anticholinergic properties of chlorphenamine may cause drowsiness, dizziness, blurred vision and psychomotor impairment in some patients which may seriously affect the ability to drive and use machinery.

Undesirable effects
Modern clinical data required to determine the frequency of undesirable effects are lacking for chlorphenamine. Sedation is the most common side effect, varying from slight drowsiness to deep sleep.
The following adverse events may also occasionally occur:
  1. Blood and lymphatic system disorders: Blood dyscrasias including haemolytic anaemia
  2. Immune system disorders: Hypersensitivity, angioedema, anaphylactic reactions
  3. Metabolism and nutrition disorders: Anorexia
  4. Psychiatric disorders: Depression, confusion
  5. Paradoxical stimulation may occur, especially in high dosage or in children, with symptoms such as irritability, nervousness, insomnia and nightmares.
  6. Nervous system disorders: Drowsiness, sedation, disturbance in attention, fatigue, headache, dizziness, abnormal co-ordination, tremor, convulsions
  7. Children and the elderly are more likely to experience neurological anticholinergic effects.
  8. Eye disorders: Blurred vision
  9. Ear and labyrinth disorders: Tinnitus
  10. Cardiac disorders: Tachycardia, palpitation, cardiac arrhythmias
  11. Vascular disorders: Hypotension
  12. Respiratory, thoracic or mediastinal disorders: Increased viscosity of bronchial secretions
  13. Gastrointestinal disorders: Dry mouth, dyspepsia, nausea, vomiting, diarrhoea, abdominal pain
  14. Hepatobiliary disorders: Hepatitis, jaundice
  15. Skin and subcutaneous tissue disorders: Skin rash, urticaria, exfoliative dermatitis, photosensitivity
  16. Musculoskeletal and connective tissue disorders: Muscle twitching, muscular weakness
  17. Renal and urinary disorders: Urinary retention
  18. General disorders: Chest tightness, hyperpyrexia

The estimated lethal dose of chlorphenamine is 25 to 50 mg/kg body weight.
Overdose with chlorphenamine is associated with antimuscarinic, extrapyramidal, gastrointestinal and central nervous system effects. In infants and children, CNS stimulation predominates over CNS depression, causing hallucinations, excitement, psychosis, ataxia, in-coordination, athetosis and convulsions. 

The convulsion sometimes heralded by muscular tremor and athetoid movements are of the intermittent tonic-clonic type and difficult to control. Hyperpyrexia, fixed dilated pupils, dry mouth, facial flushing, urinary retention and sinus tachycardia may occur. Deepening coma and cardiorespiratory collapse and death may follow. 

In adults, CNS depression is more common with drowsiness, coma and convulsions, progressing to respiratory failure or possibly arrhythmias and cardiovascular collapse.

Consider the use of activated charcoal if the patient presents within 1 hour of ingestion of a significant overdose.
Protracted or recurrent convulsions may be controlled by lorazepam or diazepam given by slow intravenous injection into a large vein although the risk of further CNS depression should be considered. Vasopressors may be required to control hypotension. Other treatment is supportive and symptomatic and may include artificial respiration, external cooling for hyperpyrexia and intravenous fluids. Forced diuresis, peritoneal dialysis or hemodialysis appear to be of limited benefit.


Pharmacodynamic properties

Mechanism of action
Chlorphenamine is a potent antihistamine (H1-antagonist). Antihistamines diminish or abolish the actions of histamine in the body by competitive reversible blockade of histamine-H1- receptor sites on tissues. Chlorphenamine also has anticholinergic activity.

Pharmacodynamic effects
Antihistamines act to prevent the release of histamine, prostaglandins and leukotrienes and have been shown to prevent the migration of inflammatory mediators. The actions of chlorphenamine include inhibition of histamine on smooth muscle, capillary permeability and hence reduction of oedema and wheal in hypersensitivity reactions such as allergy and anaphylaxis.

Pharmacokinetic properties

Chlorphenamine is well absorbed from the gastrointestinal tract and following oral administration the effects develop within 30 minutes, and are maximal within 1 to 2 hours and last about 4 to 6 hours. The plasma half life has been estimated to be 12 to 15 hours.

The drug is widely distributed throughout the body including the CNS.

The main site of metabolic transformation is in the liver. Chlorphenamine is metabolised to the monodesmethyl and didesmethyl derivatives. About 22% of an oral dose is excreted unchanged in the urine.

Little if any is excreted unchanged in the urine; most appears there as degradation products that are almost completely excreted within 24 hours. The drug is eliminated more rapidly by children than by adults.

Shelf life
3 years
Do not use after the expiry date given on the pack.

Special precautions for storage
Store below 25°C, protect from light.

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