Zyrtec Tab 30 s 

Potential Overview:

Brand Name: Zyrtec

Generic Name: Cetirizine

Pack Size:30 tablets

Strength:10 mg per tablet

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Zyrtec (Cetirizine) is an antihistamine commonly used to relieve symptoms of allergy such as sneezing, runny nose, and itchy or watery eyes. It is also effective in treating hay fever, hives, and other allergic skin reactions. Zyrtec provides relief with minimal drowsiness, making it suitable for daily use.

Mechanism of Action (MOA):

Zyrtec (Cetirizine) is a second-generation antihistamine that works by selectively inhibiting the H1 histamine receptor. Histamine is a chemical involved in allergic responses, and its release leads to symptoms such as itching, swelling, and inflammation. By blocking the H1 receptor, Cetirizine reduces these allergic symptoms without crossing the blood-brain barrier as much, leading to less sedation compared to first-generation antihistamines.

Indications:

1. Allergic Rhinitis (Hay Fever):
   Zyrtec is used to treat seasonal and perennial allergic rhinitis, relieving symptoms like sneezing, runny nose, itchy nose, and watery eyes caused by pollen, dust, and pet dander.
2. Chronic Urticaria (Chronic Hives):
   Zyrtec helps reduce itching and hives (urticaria) in people with chronic idiopathic urticaria, a condition that causes red, raised welts on the skin.
3. Other Allergic Conditions:
   It may be used off-label for conditions such as insect stings or bites, food allergies, or other symptoms involving histamine release.

Dosage:

1. Adults and Children 6 years and older:
   • Oral tablet: 10 mg once daily.
   • Oral syrup: 10 mg once daily (equivalent to one 10 mg tablet).
2. Children 2–5 years old:
   • Oral syrup: 5 mg (half a 10 mg tablet) once daily.
3. Children under 2 years old:
   • The dosage should be determined by a healthcare provider, usually based on weight.

Note: If a dose is missed, take it as soon as you remember, but do not take two doses at the same time to make up for a missed dose.

Side Effects:

1. Common Side Effects:
   • Drowsiness (though less than first-generation antihistamines)
   • Dry mouth
   • Headache
   • Fatigue
   • Nausea
2. Serious Side Effects (Rare):
   • Rapid heartbeat
   • Severe dizziness or fainting
   • Swelling of the face, lips, tongue, or throat (signs of a serious allergic reaction)
   • Difficulty breathing or swallowing

Precautions:

1. Kidney or Liver Impairment:
   Use with caution in patients with kidney or liver problems, as Cetirizine is excreted through the kidneys. Dose adjustments may be necessary in such patients.
2. Pregnancy and Breastfeeding:
   Zyrtec should only be used during pregnancy if clearly needed, as there is limited safety data. Cetirizine passes into breast milk, so it should be used cautiously in breastfeeding mothers.
3. Elderly Patients:
   Older adults may be more sensitive to the sedative effects, although Cetirizine is less sedating than first-generation antihistamines.
4. Operating Heavy Machinery:
   Although it is less sedating, Zyrtec can still cause drowsiness in some individuals, so caution is advised when performing tasks requiring mental alertness, such as driving or operating machinery.

Contraindications:

1. Hypersensitivity to Cetirizine or Hydroxyzine:
   Zyrtec should not be used by individuals who are allergic to Cetirizine or related drugs (e.g., Hydroxyzine), as it could cause a serious allergic reaction.
2. Severe Kidney Disease:
   In patients with severe renal impairment, Zyrtec should be avoided unless advised by a healthcare professional, as the drug is primarily excreted by the kidneys.

Pharmacist Related Data

Chemical Formula:

• Cetirizine: C21H25ClN2O2

Half-life:

• Elimination Half-Life: 7 to 10 hours in healthy adults. It may be prolonged in patients with renal or hepatic impairment.

Metabolism:

• Cetirizine is primarily metabolized in the liver by the CYP3A4 enzyme (to a small extent) and CYP2D6. However, the drug undergoes minimal metabolism, with most of the active compound excreted unchanged via the kidneys.
• The major metabolite is an inactive metabolite, which has no significant pharmacological activity.

Drug Interactions:

With Food:

• Food can slow the absorption of Cetirizine, but it does not significantly affect its overall efficacy. Therefore, Zyrtec can be taken with or without food.

With Medicines:

1. CNS Depressants:
   • Combining Zyrtec with other CNS depressants (such as alcohol, benzodiazepines, or opioids) can increase the sedative effects, leading to excessive drowsiness or impaired mental function.
2. Anticholinergic Drugs:
   • Drugs with anticholinergic properties (e.g., certain antidepressants, antihistamines, or antipsychotics) may increase the risk of dry mouth, urinary retention, and other anticholinergic effects.
3. Ritonavir and other CYP3A4 Inhibitors:
   • Strong inhibitors of CYP3A4 (like Ritonavir) may increase Cetirizine levels, raising the risk of side effects, although Cetirizine’s metabolism via this pathway is limited.
4. Theophylline:
   • Concurrent use of theophylline (a bronchodilator) and Cetirizine may slightly increase the blood levels of Cetirizine, although the clinical significance is usually minimal.
5. Other Antihistamines:
   • Combining Cetirizine with other antihistamines is not recommended due to the increased risk of adverse effects such as drowsiness or dry mouth.

Pharmacodynamics:

• Mechanism of Action:
  Zyrtec (Cetirizine) is a selective H1 receptor antagonist that prevents histamine from binding to histamine receptors on cells. Histamine is responsible for causing symptoms like itching, swelling, and inflammation during allergic reactions.
• Effect:
  • Reduces the effects of histamine, leading to the relief of allergy symptoms, such as sneezing, itching, watery eyes, and runny nose.
  • Cetirizine also reduces symptoms of chronic urticaria (hives), such as itching and rash, by blocking histamine-induced effects on the skin.
• Onset of Action:
  • Cetirizine typically starts working within 1 hour of administration.
• Duration of Action:
  • The effects last for about 24 hours, making it suitable for once-daily dosing.

Pharmacokinetics:

1. Absorption:
   • Cetirizine is well-absorbed from the gastrointestinal tract.
   • Peak plasma concentrations occur within 1 hour of oral administration.
   • The bioavailability is about 70-75%, and food may delay absorption but does not significantly affect the overall bioavailability.
2. Distribution:
   • Cetirizine is widely distributed in the body, with a volume of distribution of about 0.5 L/kg.
   • It has a moderate plasma protein binding of about 93%.
3. Metabolism:
   • Cetirizine undergoes minimal metabolism in the liver (via CYP3A4 and CYP2D6), with most of the drug excreted unchanged in the urine.
   • The small amount of metabolism results in an inactive metabolite, which has no pharmacological activity.
4. Excretion:
   • Approximately 60% of the drug is excreted unchanged in the urine.
   • The remainder is excreted as a metabolite.
   • The drug has a half-life of about 7 to 10 hours in healthy adults, but this may be prolonged in patients with renal or hepatic dysfunction.