Usage
- Epinastine is prescribed for the prevention of itching associated with allergic conjunctivitis.
- Pharmacological Classification: Antihistamine, mast cell stabilizer.
- Mechanism of Action: Epinastine exerts its therapeutic effect through a dual mechanism:
- H1 Receptor Antagonism: It blocks the action of histamine at the H1 receptor site, mitigating the allergic response. It also antagonizes H2 receptors to a lesser extent.
- Mast Cell Stabilization: Prevents the release of inflammatory mediators (histamine, leukotrienes, prostaglandins, etc.) from mast cells, further reducing the allergic cascade.
Alternate Names
- Epinastine hydrochloride
- Brand Names: Elestat, Relestat, Epinast, and various generic formulations.
How It Works
- Pharmacodynamics: Epinastine primarily acts by blocking H1 and H2 histamine receptors in the conjunctiva, thereby reducing itching, redness, and tearing. Its mast cell stabilizing properties further attenuate the inflammatory response.
- Pharmacokinetics:
- Absorption: After topical ocular administration, epinastine achieves therapeutic concentrations in the tears. Systemic absorption is minimal, resulting in low plasma levels, reducing the likelihood of systemic side effects.
- Metabolism: Epinastine undergoes minimal metabolism.
- Elimination: Primarily eliminated through renal excretion, with a half-life of approximately 12 hours.
- Mode of Action: Epinastine competitively binds to H1 and, to a lesser degree, H2 histamine receptors on conjunctival mast cells and blood vessels. This inhibits histamine-mediated vasodilation, vascular permeability, and itching. Additionally, epinastine stabilizes mast cell membranes, preventing the degranulation and release of other inflammatory mediators.
- Receptor Binding/Enzyme Inhibition: Selective H1 and H2 receptor antagonist. No significant enzyme inhibition is associated with epinastine.
- Elimination Pathways: Predominantly renal excretion.
Dosage
Standard Dosage
Adults: Instill one drop of 0.05% epinastine ophthalmic solution into each affected eye twice daily.
Children:
- Children aged 2 years and older: Same as adult dosage (one drop in each affected eye twice daily).
- Children under 2 years: Safety and efficacy not established.
Special Cases:
- Elderly Patients: No dose adjustment typically required, but monitor for any signs of adverse effects.
- Patients with Renal Impairment: No dose adjustment recommended.
- Patients with Hepatic Dysfunction: No dose adjustment recommended.
- Patients with Comorbid Conditions: Exercise caution in patients with cardiovascular disease or other systemic conditions. Closely monitor for any unusual reactions.
Clinical Use Cases
Epinastine is specifically indicated for allergic conjunctivitis. It is not generally used in settings such as intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations.
Side Effects
Common Side Effects:
- Burning or stinging sensation in the eyes
- Eye redness
- Headache
- Rhinitis, sinusitis, increased cough, pharyngitis (some of these might be related to the underlying allergic condition)
Rare but Serious Side Effects:
- Severe allergic reactions (rash, itching/swelling, dizziness, trouble breathing)
- Eye pain, swelling, vision changes
Long-Term Effects:
No significant long-term adverse effects have been reported with topical ophthalmic use.
Contraindications
- Known hypersensitivity to epinastine or any component of the formulation.
Drug Interactions
No clinically significant drug interactions have been established with topical epinastine. However, inform patients to disclose all medications they are using, including over-the-counter drugs and supplements.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: C (Animal studies have shown adverse effects, but adequate human studies are lacking. Use only if potential benefit outweighs risk.)
- Breastfeeding: Epinastine is excreted in rat milk. It is unknown whether it is excreted in human milk. Exercise caution when administering to nursing mothers.
Drug Profile Summary
- Mechanism of Action: Dual-acting H1 and H2 receptor antagonist and mast cell stabilizer.
- Side Effects: Burning/stinging, eye redness, headache. Rarely, severe allergic reactions.
- Contraindications: Hypersensitivity to epinastine.
- Drug Interactions: No clinically significant interactions known.
- Pregnancy & Breastfeeding: Category C; use with caution in breastfeeding.
- Dosage: 1 drop in each eye twice daily.
- Monitoring Parameters: Monitor for allergic reactions and eye irritation.
Popular Combinations
Epinastine is typically used as monotherapy for allergic conjunctivitis. In some cases, it might be combined with other ocular medications (e.g., artificial tears) for symptomatic relief, but administer with at least a 10-minute interval between instillations.
Precautions
- General Precautions: Avoid contact of the dropper tip with any surface to prevent contamination. Advise patients not to wear contact lenses if their eyes are red.
- Specific Populations: As detailed above in the Pregnancy and Breastfeeding and Special Cases sections.
- Lifestyle Considerations: May cause temporary blurred vision, so caution patients about driving or operating machinery immediately after instillation.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Epinastine?
A: One drop in each affected eye twice daily for adults and children 2 years and older.
Q2: Can Epinastine be used in children?
A: Yes, for children 2 years and older, the dosage is the same as for adults. Safety and efficacy have not been established in children under 2 years of age.
Q3: What are the common side effects of Epinastine?
A: Burning/stinging, eye redness, and headache are the most common side effects.
A: Contact lenses should be removed before instilling Epinastine and can be reinserted after 10 minutes. Advise patients not to wear contact lenses if their eyes are red.
Q5: Is Epinastine safe during pregnancy?
A: Epinastine is Pregnancy Category C. Use only if the potential benefit justifies the potential risk to the fetus.
Q6: Can I use Epinastine while breastfeeding?
A: Epinastine is excreted in rat milk. It is unknown if it is excreted in human milk. Exercise caution if administering to a nursing woman. Discuss the risks and benefits with the patient.
Q7: What should I do if I miss a dose of Epinastine?
A: Instill the missed dose as soon as remembered. If it is almost time for the next dose, skip the missed dose and continue with the regular schedule. Do not double the dose.
Q8: How long should I continue using Epinastine?
A: Continue treatment throughout the period of allergen exposure, even if symptoms are absent. Your doctor will determine the duration of therapy.
Q9: Can Epinastine interact with other medications?
A: No clinically significant drug interactions have been established. However advise patients to inform you of all concomitant medications, including over-the-counter products and supplements.
Q10: What are the signs of an allergic reaction to Epinastine?
A: Watch for rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, and trouble breathing. Seek immediate medical attention if these occur.
