Usage
Mizolastine is prescribed for the symptomatic relief of allergic rhinitis (hay fever) and urticaria (hives). It belongs to the pharmacological classification of second-generation antihistamines. Mizolastine works by selectively blocking peripheral histamine H1 receptors. This action prevents histamine from binding to these receptors, reducing the allergic symptoms associated with histamine release.
Alternate Names
Mizolastine is also known by the brand names Mizollen and Mistamine.
How It Works
Pharmacodynamics: Mizolastine exerts its therapeutic effect by selectively antagonizing peripheral H1 receptors. This prevents histamine from binding to these receptors and triggering the cascade of events that lead to allergic symptoms. It also exhibits mast cell stabilizing properties, inhibiting the release of histamine and other inflammatory mediators. Unlike first-generation antihistamines, it has minimal sedative effects due to its low affinity for central H1 receptors.
Pharmacokinetics: Mizolastine is rapidly absorbed after oral administration, reaching peak plasma concentrations in approximately 1.5 hours. It has a half-life of around 13 hours in healthy adults, which may be prolonged in elderly patients and those with renal insufficiency. Mizolastine is primarily metabolized in the liver, and its metabolites are excreted mainly through the bile and, to a lesser extent, in the urine. The drug’s metabolism is primarily mediated by CYP3A4, and some interactions with inhibitors or inducers of this enzyme are possible.
Mode of Action: Mizolastine competitively binds to peripheral H1 receptors, preventing histamine from binding and initiating the allergic response.
Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Mizolastine primarily binds to peripheral H1 receptors. It has shown minimal binding to central H1 receptors, which explains its low sedative profile. Mizolastine’s metabolism is mediated by CYP3A4, with potential for drug interactions with inhibitors or inducers of this enzyme. It does not significantly affect other neurotransmitter systems.
Elimination Pathways: Mizolastine is primarily metabolized in the liver and excreted mainly through bile, with a smaller portion excreted in urine.
Dosage
Standard Dosage
Adults:
The standard adult dosage is 10 mg once daily, taken orally with water.
Children:
The standard dose for children over 12 years of age is the same as the adult dose (10 mg once daily). Mizolastine is not recommended for children under 12.
Special Cases:
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Elderly Patients: While the half-life may be slightly prolonged in the elderly, dosage adjustments are not usually required. Monitoring for potential side effects is advised.
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Patients with Renal Impairment: Caution is advised in patients with severe renal impairment. Dose adjustments may be necessary.
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Patients with Hepatic Dysfunction: Mizolastine is contraindicated in patients with severe hepatic impairment due to reduced metabolic capacity.
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Patients with Comorbid Conditions: Use with caution in patients with cardiac disease or a history of cardiac arrhythmias, especially QT prolongation.
Clinical Use Cases
Mizolastine is not typically used in the context of intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations. Its primary indication is for the management of allergic rhinitis and urticaria.
Dosage Adjustments
Dose adjustments may be required for patients with renal or hepatic impairment. The exact dose modification should be determined based on the patient’s individual clinical condition and the degree of impairment. Genetic polymorphisms affecting CYP3A4 activity could influence mizolastine metabolism, although specific dose adjustments based on genotype are not routinely recommended. Close monitoring of patient response and potential side effects is advisable in such cases.
Side Effects
Common Side Effects
Headache, dry mouth, dizziness, nausea, abdominal pain, increased appetite, and weight gain. These side effects are typically mild and transient.
Rare but Serious Side Effects
Hypersensitivity reactions (including angioedema, bronchospasm, and anaphylaxis), liver function abnormalities, and cardiovascular effects like palpitations and tachycardia.
Long-Term Effects
No specific long-term adverse effects have been consistently reported.
Adverse Drug Reactions (ADR)
Clinically significant ADRs requiring immediate intervention include hypersensitivity reactions (angioedema, bronchospasm, and anaphylaxis), severe liver dysfunction, and significant cardiac arrhythmias.
Contraindications
Hypersensitivity to mizolastine, severe hepatic impairment, concomitant use of macrolide antibiotics or systemic imidazole antifungals, clinically significant heart disease, history of symptomatic arrhythmias, QT interval prolongation, clinically significant bradycardia, and electrolyte imbalance (especially hypokalemia).
Drug Interactions
Mizolastine’s metabolism is primarily mediated by CYP3A4. Consequently, drugs that inhibit CYP3A4 (e.g., ketoconazole, erythromycin, itraconazole) can increase plasma concentrations of mizolastine, potentially increasing the risk of adverse effects. Conversely, CYP3A4 inducers (e.g., rifampicin, St. John’s Wort) may decrease mizolastine levels and its efficacy. Co-administration with other CNS depressants (alcohol, sedatives, tranquilizers) may enhance sedative effects, though mizolastine itself has minimal sedative properties. Combining mizolastine with other antihistamines or anticholinergic drugs can increase anticholinergic side effects. Concomitant use with drugs that prolong the QT interval (e.g., some antiarrhythmics, antibiotics) should be avoided. Grapefruit juice can interact with mizolastine and should be avoided. Caution should be exercised when using mizolastine with ciclosporin, nifedipine, adenosine, and cimetidine.
Pregnancy and Breastfeeding
The safety of mizolastine in human pregnancy has not been definitively established. Animal studies have not shown evidence of teratogenicity, but mizolastine should be avoided, especially during the first trimester, unless the potential benefit clearly outweighs the risk. Mizolastine is excreted in breast milk and is not recommended during breastfeeding.
Drug Profile Summary
- Mechanism of Action: Selectively antagonizes peripheral H1 receptors; mast cell stabilizing properties.
- Side Effects: Headache, dry mouth, dizziness, nausea, abdominal pain (common); hypersensitivity reactions, liver dysfunction, cardiac arrhythmias (rare but serious).
- Contraindications: Hypersensitivity, severe hepatic impairment, concomitant use of macrolides or imidazole antifungals, cardiac disease, QT prolongation, bradycardia, electrolyte imbalance.
- Drug Interactions: CYP3A4 inhibitors/inducers, CNS depressants, anticholinergics, QT prolonging drugs.
- Pregnancy & Breastfeeding: Avoid in pregnancy, especially first trimester; not recommended during breastfeeding.
- Dosage: 10 mg once daily for adults and children over 12 years.
- Monitoring Parameters: Liver function tests, ECG (in patients with cardiac risk factors).
Popular Combinations
No popular fixed-dose combinations containing mizolastine are commonly used.
Precautions
Assess for pre-existing conditions like liver/kidney disease, heart problems, and electrolyte imbalances. Advise patients about potential drowsiness and caution against driving or operating machinery if affected. Evaluate concomitant medications for potential interactions.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Mizolastine?
A: 10 mg once daily for adults and children 12 years and older.
Q2: What are the common side effects?
A: Headache, dry mouth, dizziness, nausea, and abdominal pain.
Q3: Is Mizolastine safe during pregnancy?
A: Mizolastine should be avoided during pregnancy, especially in the first trimester, unless the potential benefit outweighs the risk.
Q4: Can I take Mizolastine if I am breastfeeding?
A: Mizolastine is excreted in breast milk and is not recommended during breastfeeding.
Q5: Does Mizolastine cause drowsiness?
A: While considered a non-sedating antihistamine, mizolastine can cause mild drowsiness in some individuals.
Q6: What medications should be avoided while taking Mizolastine?
A: Macrolide antibiotics, systemic imidazole antifungals, and drugs that prolong the QT interval should be avoided. Caution is advised with CYP3A4 inhibitors/inducers.
Q7: What are the serious side effects to watch for?
A: Hypersensitivity reactions (angioedema, bronchospasm), liver dysfunction, and cardiac arrhythmias.
Q8: How does Mizolastine differ from first-generation antihistamines?
A: It is less sedating due to its reduced ability to cross the blood-brain barrier.
Q9: What should I do if I miss a dose?
A: Take the missed dose as soon as you remember, unless it is almost time for your next dose. Do not double the dose.
Q10: Can I drink alcohol while taking Mizolastine?
A: While mizolastine itself is not highly sedating, combining it with alcohol may enhance sedative effects. It is best to avoid or limit alcohol consumption while on this medication.
