Histafren (Cetirizine Dihydrochloride)

Histafren is indicated for the temporary relief of symptoms associated with several allergic conditions.

• Allergic rhinitis (hay fever) symptoms such as sneezing, nasal congestion, and runny nose.
• Seasonal allergic conjunctivitis causing itchy, watery eyes.
• Chronic idiopathic urticaria (hives) with itching and rash.
• Relief of itching and swelling associated with insect bites or mild skin allergies.
• Management of symptoms from allergic asthma as an adjunct to prescribed inhaled therapy (note: not a primary treatment).

• Cetirizine dihydrochloride acts as a selective peripheral H1‑receptor antagonist. By binding competitively to H1 receptors on mast cells, basophils and other target cells, it blocks the action of endogenous histamine released during allergic responses. This inhibition reduces vasodilation, increased vascular permeability, and sensory nerve stimulation, thereby diminishing typical allergy symptoms without significant penetration of the central nervous system in the brain.

Like other antihistamines, Histafren may cause unwanted effects, most of which are mild and transient.

Common

• Drowsiness or mild sedation.
• Dry mouth, throat, or nasal passages.
• Headache.
• Fatigue or feeling of weakness.
• Nausea or mild gastrointestinal discomfort.
• Dizziness or light‑headedness.
• Insomnia or difficulty sleeping.
• Transient blurred vision or difficulty focusing.
• Increased sensitivity to sunlight (photosensitivity).

Serious

• Severe skin reactions such as Stevens‑Johnson syndrome or toxic epidermal necrolysis.
• Anaphylaxis or severe allergic reaction to the medication.
• Cardiac arrhythmias (rare).
• Significant liver enzyme elevation.
• Persistent or worsening edema.
• Vision changes or blurred vision.
• Unexplained bleeding or bruising.
• Severe abdominal pain or pancreatitis.

Precautions for Histafren focus on patient characteristics, existing conditions, and appropriate use to minimize risk.

• Use with caution in patients with renal or hepatic impairment; dose adjustment may be required.
• Avoid in individuals with known hypersensitivity to cetirizine or other piperazine antihistamines.
• Not recommended for children under six years of age unless directed by a healthcare professional.
• Pregnant or breastfeeding women should consult a physician, although the drug is classified as pregnancy category B.
• Caution when operating machinery or driving, especially if drowsiness occurs.
• Concomitant use with alcohol or central nervous system depressants may increase sedation.
• Patients with a history of cardiac arrhythmias should discuss use with their doctor.

Histafren can interact with other medicines, affecting its efficacy or safety profile.

Avoid

• Concurrent use with potent CYP3A4 inhibitors (e.g., ketoconazole, erythromycin) that may increase cetirizine plasma levels.
• Combining with other sedating antihistamines or CNS depressants when significant drowsiness must be avoided.

Use with caution

• Alcohol consumption, which can enhance sedation.
• Other H1‑antagonists, as additive antihistaminic effects may increase side‑effects.
• Theophylline, which may slightly raise cetirizine concentrations.
• Certain antidepressants (e.g., fluoxetine) that share metabolic pathways.
• Herbal supplements such as St. John’s wort that induce CYP enzymes.