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Healthcare Communications

Cetirizine

 

 

Histamine H1 receptor

- allergic reactions H2 receptor
- gastric acid secretion

 

 

 

Antihistamines

- Compete with histamine and block histamine H1 receptor
- Conventional antihistamines may also block other receptors, i.e., muscarinic, serotinergic, dopaminergic & adrenergic, causing adverse effects such as dryness of mouth, etc.
- Crossing of blood brain barrier leads to CNS effects, e.g., sedation

 

 

Cetirizine

- Selective antihistamine, with action chiefly on histamine H1 receptor
- Negligible effect on muscarinic, serotinergic, dopaminergic & adrenergic receptors
- Poor ability to cross blood brain barrier
- Hence better tolerability than older antihistamines

 

Phases of Allergy

Early Phase
Type I (anaphylactic) reaction results in release of histamine and other substances, resulting in inflammatory manifestations of allergy
Late Phase
Other factors including eosinophil activity, result in release of chemical mediators which produce cytotoxic and other effects and further aggravate the inflammatory response

 

Actions of Cetirizine

On Early Phase
Blocks histamine receptors, hence inhibits early phase reaction
Late Phase
Inhibits eosinophil activity, hence suppresses late phase reaction

 

Advantages of Cetirizine

Thus cetirizine is superior to older antihistamines :
1. Efficacy :
Inhibition of early and late phase allergic responses, whereas older anhistamines inhibit early reaction only
2. Tolerability :
Selectivity of action avoids atropine like adverse effects and sedation, which are commonly encountered with older agents

 

Pharmacokinetics

- Rapidly absorbed from G.I. Tract
- Peak plasma concentrations in 1 hour
- Good distribution in tissues, including respiratory tract and skin
- Poor penetration into CSF
- Half life - 11 hours approx.
- Excreted primarily via urine, and mainly as unchanged drug

Indications

- Seasonal and Perennial Allergic Rhinitis
- Chronic Idiopathic Urticaria
- Allergic Conjunctivitis
- Atopic Dermatitis
- Pruritus
- Adjunct to Antiasthmatic Therapy

 

Dosage

Adults
Usual dosage 10 mg once daily In severe cases, 10 mg b.d.
In renal impairment,
5 mg o.d.
Children (> 6 years)
5-10 mg once daily
Children (2-5 years)
2.5-5 mg once daily

 

Adverse Effects
- Well tolerated
- Drowsiness, headache, dry mouth, G.I.effects may occur
- No important drug interactions

Contraindications
- Hypersensitivity Precautions
- Renal impairment (reduce dosage),
- Pregnancy (inadequate data)

 

Salient Features

- Selective antihistamine
- Blocks both early and late phase allergic reactions
- Avoids adverse effects of older antihistamines
- Non sedating
- Convenient once daily dosage
- Effective in allergic rhinitis and conjunctivitis, urticaria, atopic dermatitis and pruritus and as adjunct in bronchial asthma

 

Cetirizine + Pseudoephedrine

 

Pseudoephedrine

- Widely used nasal decongestant
- Alpha adrenergic receptor agonist
- Produces vasoconstriction leading to reduction in mucosal oedema and swelling
- Less adverse effects (e.g., CNS effects, elevated BP and palpitation) than ephedrine
- Less rebound congestion

 

Pharmacokinetics of pseudoephedrine

- Rapidly absorbed from G.I. Tract
- Well distributed in the body
- Some metabolism in liver (1%)
- Excreted unchanged in urine
- Half life 5-8 hours

 

Rationale of combination

- Cetirizine is a highly effective antihistamine, but is more suited for preventing attacks of allergic rhinitis
- Pseudoephedrine relieves nasal congestion thus producing symptomatic relief
- This combination will do both
- relieve symptoms and prevent attacks
- thus is an ideal agent
- In perennial rhinitis, nasal congestion is often a consistent feature. A combination such as this will be particularly useful here

 

Indication

Allergic Rhinitis

 

Dosage

Fixed dose combinations are available as Cetirizine 5 mg + Pseudoephedrine 120 mg
Dosage
1 tablet 12 hourly

 

 

Adverse Effects & Precautions

- Pseudoephedrine can cause palpitations, headache, dizziness, restlessness, anxiety, tremor, insomnia, hypertension
- Concomitant administration of pseudoephedrine with sympathomimetic decongestants, appetite suppressants and MAO inhibitors can cause increased BP and hypertensive crisis
- Antihypertensive activity of some antihypertensives e.g., methylodopa, reserpine and beta blockers may be countered by pseudoephedrine