Histisynt (Levocetirizine Dihydrochloride)

Histisynt is indicated for the symptomatic relief of allergic conditions that involve histamine release.

• Allergic rhinitis (seasonal or perennial)
• Chronic idiopathic urticaria (hives)
• Other histamine‑mediated skin reactions such as pruritus
• Relief of nasal congestion, sneezing, itching and watery eyes associated with allergies

• Levocetirizine dihydrochloride acts as a selective peripheral H1‑receptor antagonist. By binding competitively to H1 receptors on mast cells, basophils and other target cells, it prevents histamine from triggering the intracellular cascade that leads to vasodilation, increased vascular permeability, and sensory nerve stimulation. This blockade reduces the early‑phase allergic response without crossing the blood‑brain barrier in significant amounts, thereby limiting central sedation.

Like other antihistamines, levocetirine may cause adverse reactions, most of which are mild and transient.

Common

• Drowsiness or mild sedation
• Headache
• Dry mouth
• Fatigue

Serious

• Severe skin reactions such as Stevens‑Johnson syndrome
• Anaphylactic‑type hypersensitivity

Before starting Histisynt, certain precautions should be considered to ensure safe use.

• Assess renal function; dose may need adjustment in severe impairment
• Use caution in patients with a history of hypersensitivity to levocetirizine or related piperazine antihistamines
• Avoid driving or operating machinery if drowsiness occurs
• Consider pregnancy and breastfeeding status; consult a healthcare professional
• Review concomitant medications that may increase sedation
• Monitor for early signs of skin reactions during initial treatment

Levocetirizine can interact with other substances, influencing its efficacy or safety profile.

Avoid

• Strong CYP3A4 inhibitors (e.g., ketoconazole, erythromycin) that may raise plasma levels

Use with caution

• Alcohol or other central nervous system depressants that may enhance sedation
• Additional antihistamines or sedating drugs, increasing drowsiness risk
• Theophylline, because both are metabolized by similar pathways
• Antacids containing aluminum or magnesium if taken simultaneously, as they may affect absorption