Generic Name : Chlorpheniramine.

Trade Name     : Anallerge.

Drug Class      : Anti-histamines  (1st Generation).

Forms of The Drug

  1. Tablet: 4mg, 8mg, 12mg.
  2. Syrup: 2mg/5mL.

Mechanism of Action

Chlorpheniramine is a first-generation antihistamine with a mechanism of action similar to other drugs in its class. It is widely used for the treatment of allergic conditions such as hay fever, allergic rhinitis, and allergic conjunctivitis. The mechanism of action of chlorpheniramine involves its interaction with histamine receptors and other neurotransmitter systems. Here’s how it works:

  1. Histamine Receptor Antagonism: Chlorpheniramine acts primarily by competitively antagonizing histamine receptors, particularly the H1 receptors. Histamine is a chemical released by mast cells and basophils during allergic reactions, leading to symptoms such as itching, sneezing, runny nose, and watery eyes. By blocking the H1 receptors, chlorpheniramine prevents histamine from binding and exerting its effects, thereby alleviating allergic symptoms.
  2. Inhibition of Histamine Release: Chlorpheniramine has been shown to inhibit the release of histamine from mast cells and basophils. This further reduces the concentration of histamine available to bind to its receptors, amplifying its antiallergic effects.
  3. Anticholinergic Effects: Chlorpheniramine possesses anticholinergic properties, meaning it blocks the action of acetylcholine, a neurotransmitter in the nervous system. This action contributes to its ability to dry mucous membranes and reduce secretions, such as nasal discharge and tearing, often associated with allergic reactions.
  4. Sedative Effects: Chlorpheniramine, like many first-generation antihistamines, can penetrate the blood-brain barrier and exert sedative effects by antagonizing histamine receptors in the central nervous system. This sedation can be beneficial for individuals experiencing allergic symptoms, particularly those associated with insomnia or nighttime allergies. However, it can also lead to drowsiness and impair psychomotor function, which may limit its use in certain situations.
  5. Other Neurotransmitter Effects: Chlorpheniramine may interact with other neurotransmitter systems in the brain, such as serotonin and dopamine receptors, although the significance of these interactions in its therapeutic effects is not fully understood.


  1. Allergic Rhinitis.
  2. Allergic Conjunctivitis.
  3. Urticaria (Hives).
  4. Pruritus (Itching).
  5. Allergic Dermatological Conditions: such as atopic dermatitis or contact dermatitis, including itching, redness, and inflammation.
  6. Insect Bites and Stings.
  7. Angioedema.
  8. Motion Sickness.


  1. Hypersensitivity.
  2. Narrow-Angle Glaucoma.
  3. Severe Lower Respiratory Tract Symptoms: such as asthma exacerbations, acute bronchitis, or chronic obstructive pulmonary disease (COPD).
  4. Acute Asthma Attack.
  5. Newborns and Premature Infants.
  6. Breastfeeding.
  7. Use with MAOIs.
  8. Bladder Neck Obstruction.

Side Effects

  1. CNS depression.
  2. Drowsiness.
  3. Sedation ranging from mild drowsiness to deep sleep (most frequent).
  4. Dizziness.
  5. Lassitude.
  6. Disturbed coordination.
  7. Muscular weakness.
  8. Restlessness, insomnia, tremors, euphoria, nervousness, delirium, palpitation, seizures is less common.
  9. Epigastric distress.
  10. Anorexia.
  11. Nausea.
  12. Vomiting.
  13. Diarrhea.
  14. Constipation.
  15. Cholestasis, hepatitis, hepatic failure, hepatic function abnormality, jaundice is rare.
  16. Tachycardia, palpitation ECG changes (eg, widened QRS).
  17. Arrhythmias (eg, extrasystole, heart block).
  18. Hypotension.
  19. Hypertension.
  20. Dizziness, sedation, and hypotension may occur in geriatric patients.

Drug Interaction

  1. Central Nervous System Depressants such as benzodiazepines, opioids, barbiturates, and alcohol.
  2. Anticholinergic effects, such as tricyclic antidepressants, antipsychotics, certain antispasmodics, and certain medications for overactive bladder.
  3. Monoamine Oxidase Inhibitors (MAOIs).
  4. Selective Serotonin Reuptake Inhibitors (SSRIs) and Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs).
  5. CNS stimulants, such as amphetamines or methylphenidate.
  6. Antihypertensive Medications: such as beta-blockers or alpha-blockers.
  7. Anticholinesterase Inhibitors.
  8. Urinary Alkalizers, such as sodium bicarbonate or potassium citrate.


  1. Pregnancy: Category B.
  2. Lactation: Chlorpheniramine is excreted into breast milk, and its use during lactation is generally considered compatible with breastfeeding.

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