HAYZINE

Indications

• Chronic idiopathic urticaria
• Perennial allergic rhinitis
• Seasonal allergic rhinitis
• Allergic asthma
• Physical urticaria
• Atopic dermatitis

Dosage

Children: For children aged 6 to 12 years, the dosage is typically 5 mg to 10 mg once daily depending on the severity of symptoms. For children aged 2 to 6 years, the usual dose is 2.5 mg to 5 mg once daily. Specific dosing should refer to the BNF for Children.

Adults: The typical adult dose is 10 mg once daily, which can be adjusted based on the severity of symptoms and patient response.

Mechanism of action

Cetirizine selectively inhibits peripheral H1 receptors, effectively blocking the action of histamine, which is responsible for allergic symptoms. It has demonstrated negligible anticholinergic and antiserotonergic effects, and studies indicate minimal penetration into the central nervous system, reducing the likelihood of sedation.

Pharmacodynamics

Cetirizine exhibits antihistaminic activity that effectively minimizes or eliminates symptoms of various allergic conditions such as chronic idiopathic urticaria and allergic rhinitis. It has anti-inflammatory properties that may assist in asthma management and can significantly reduce the duration and dosage of topical anti-inflammatory treatments for conditions like atopic dermatitis. Its effects can be observed within 20 minutes of administration, lasting up to 24 hours.

Pharmacokinetics

Cetirizine is well absorbed orally with peak plasma concentrations occurring approximately 1 hour after dosing. It has a half-life of about 8 hours, allowing for once-daily dosing in most cases. The drug is primarily excreted in the urine, with minimal hepatic metabolism, making it suitable for patients with liver impairment.

Adverse effects

• dry mouth
• drowsiness
• fatigue
• headache
• nausea

Precautions

• Use with caution in patients with renal impairment
• Caution advised in individuals with a history of seizures

Pregnancy

Cetirizine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Cetirizine is excreted in breast milk; caution is advised when administered to breastfeeding mothers.

Storage

Store at room temperature, away from moisture and heat.

Formulations

• tablets
• oral solution
• syrup

Dosage

Children: Refer to specific drug guidelines, as dosing varies widely based on the hydrochloride formulation.

Adults: Refer to specific drug guidelines, as dosing varies widely based on the hydrochloride formulation.

Mechanism of action

The mechanism of action depends on the specific drug in question, as many different medications can be available as hydrochloride salts. Generally, hydrochloride salts dissociate in solution, allowing the active drug to exert its pharmacological effects by interacting with specific receptors or enzymes in the body.

Pharmacodynamics

Pharmacodynamics varies based on the specific drug. Typically, hydrochloride forms allow for increased solubility and absorption, leading to a more predictable pharmacological response. This can include actions such as receptor agonism or antagonism, enzyme inhibition, or modulation of physiological processes.

Pharmacokinetics

Pharmacokinetics of hydrochloride salts is characterized by improved absorption due to enhanced solubility. The drug's distribution, metabolism, and excretion will depend on its specific properties, including half-life, bioavailability, and route of administration. Specific pharmacokinetic profiles should be referenced for each individual hydrochloride compound.

Contra-indications

• Hypersensitivity to hydrochloride or any component of the formulation
• Severe renal impairment
• Severe liver disease

Adverse effects

• Nausea
• Vomiting
• Diarrhea
• Dizziness
• Headache
• Dry mouth
• Fatigue
• Hypotension

Interactions

• May interact with antihypertensive medications leading to additive effects
• Caution when used with other medications that can cause renal impairment

Precautions

• Use with caution in patients with pre-existing renal or hepatic conditions
• Monitor electrolytes, especially in long-term use
• Assess hydration status before initiation

Pregnancy

Use only if the potential benefit justifies the potential risk to the fetus. Consult relevant guidelines.

Breast-feeding

Use with caution, as it is not known whether it is excreted in human milk. Consult relevant guidelines.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Tablets
• Capsules
• Oral solution
• Injectable solution

Mechanism of action

Cetirizine, a metabolite of _hydroxyzine_, is an antihistamine drug. Its main effects are achieved through selective inhibition of peripheral H1 receptors. The antihistamine activity of cetirizine has been shown in a variety of animal and human models. _In vivo_ and _ex vivo_ animal models have shown insignificant anticholinergic and antiserotonergic effects. In clinical studies, however, dry mouth was found to be more frequent with cetirizine than with a placebo. In vitro receptor binding studies have demonstrated no detectable affinity of cetirizine for histamine receptors other than the H1 receptors. Studies with radiolabeled cetirizine administration in the rat have demonstrated insignificant penetration into the brain. _Ex vivo_ studies in the mouse have shown that systemically administered cetirizine does not occupy cerebral H1 receptors significantly. Cetirizine, a human metabolite of hydroxyzine, is an antihistamine; its principal effects are mediated via selective inhibition of peripheral H1 receptors. The antihistaminic activity of cetirizine has been clearly documented in a variety of animal and human models. In vivo and ex vivo animal models have shown negligible anticholinergic and antiserotonergic activity. In clinical studies, however, dry mouth was more common with cetirizine than with placebo. In vitro receptor binding studies have shown no measurable affinity for other than H1 receptors. Autoradiographic studies with radiolabeled cetirizine in the rat have shown negligible penetration into the brain. Ex vivo experiments in the mouse have shown that systemically administered cetirizine does not significantly occupy cerebral H1 receptors.

Pharmacodynamics

**General effects and respiratory effects** Cetirizine, the active metabolite of the piperazine H₁-receptor antagonist hydroxyzine, minimizes or eliminates the symptoms of chronic idiopathic urticaria, perennial allergic rhinitis, seasonal allergic rhinitis, allergic asthma, physical urticaria, and atopic dermatitis. The clinical efficacy of cetirizine for allergic respiratory diseases has been well established in numerous trials. **Effects on urticaria/anti-inflammatory effects** It has anti-inflammatory properties that may play a role in asthma management. There is evidence that cetirizine improves symptoms of urticaria. Marked clinical inhibition of a wheal and flare response occurs in infants, children as well as adults within 20 minutes of one oral dose and lasts for 24 h. Concomitant use of cetirizine reduces the duration and dose of topical anti-inflammatory formulas used for the treatment of atopic dermatitis.