EPINASTINE HYDROCHLORIDE
Clinical safety rating: safe
Animal studies have demonstrated safety
Selective histamine H1-receptor antagonist. Inhibits histamine release from mast cells and basophils, and reduces chemotaxis and activation of eosinophils. Also suppresses cytokine production from T lymphocytes.
| Metabolism | Hepatic metabolism primarily via CYP3A4 (minor role of CYP2D6). Also undergoes non-CYP-mediated metabolism (O-glucuronidation and N-oxidation). |
| Excretion | Renal excretion accounts for approximately 39% of the administered dose, with about 28% as unchanged drug and 11% as metabolites. Fecal excretion is minimal at approximately 10%. Biliary excretion is not a significant route. Overall, renal clearance is the primary elimination pathway. |
| Half-life | The terminal elimination half-life is approximately 5.7 to 9.2 hours in healthy adults. In elderly patients, the half-life may be prolonged due to reduced renal function. The half-life supports twice-daily dosing for most indications. |
| Protein binding | Plasma protein binding is approximately 96 to 98%, primarily to albumin. This high binding limits distribution and affects the free drug concentration. |
| Volume of Distribution | The volume of distribution is approximately 1.2 to 1.5 L/kg, indicating extensive tissue distribution beyond the vascular space. This is consistent with its lipophilic properties and ability to penetrate tissues such as the eye and respiratory tract. |
| Bioavailability | Oral bioavailability is approximately 40% due to first-pass metabolism. For ophthalmic use, systemic bioavailability is minimal (less than 1%) after topical administration, as most of the dose is absorbed locally. |
| Onset of Action | For ophthalmic solution: Onset of action is within 3 to 5 minutes for reduction of ocular itching. For oral formulation (not available in all countries): Onset is approximately 1 to 2 hours for systemic allergic symptoms. |
| Duration of Action | Ophthalmic solution: Duration of action is up to 8 hours for relief of ocular itching associated with allergic conjunctivitis. Twice-daily dosing is recommended to maintain effect. Oral formulation: Duration is approximately 12 hours, supporting twice-daily administration. |
| Molecular Weight | 285.77 |
For allergic rhinitis and urticaria: 10 mg twice daily orally (20 mg/day). For ophthalmic use: 1 drop in affected eye(s) twice daily of 0.05% solution.
| Dosage form | SOLUTION |
| Renal impairment | No specific dose adjustment recommended for mild to moderate renal impairment. For severe renal impairment (CrCl <30 mL/min): use with caution, consider reducing dose to 10 mg once daily. |
| Liver impairment | No specific dose adjustment provided for hepatic impairment; use with caution in severe hepatic impairment. |
| Pediatric use | For allergic rhinitis: children 6-11 years: 10 mg once daily; children 12 years and older: same as adult dose. For urticaria: children 6-11 years: 10 mg once daily; children 12 years and older: same as adult dose. Ophthalmic: children 2 years and older: 1 drop twice daily. |
| Geriatric use | No specific dose adjustment required; monitor for adverse effects such as sedation and dizziness. |
| 1st trimester | Limited data; no well-controlled studies in pregnant women. Animal studies show no evidence of harm at clinically relevant doses. Use only if potential benefit justifies risk. |
| 2nd trimester | Same as T1; no known increased risk of major malformations. |
| 3rd trimester | Use near term may cause transient neonatal CNS depression or irritability. Consider risk-benefit. |
Clinical note
No significant drug interactions For ophthalmic use only may cause mild transient burning or stinging.
| Placental transfer | Epinastine crosses the placenta in animals; human data limited. Molecular weight (285.77 Da) suggests likely passive diffusion. |
| Breastfeeding | Epinastine is excreted into breast milk in small amounts. Relevance to nursing infants is likely minimal due to low oral bioavailability. Caution is advised, especially in premature or jaundiced infants. |
■ FDA Black Box Warning
No FDA black box warning.
| Common Effects | Headache |
| Serious Effects |
Hypersensitivity to epinastine or any excipientsSevere hepatic impairment
| Precautions | May cause drowsiness; caution when driving. Use with caution in patients with hepatic impairment or epilepsy. Caution in elderly patients due to increased risk of sedation and falls. |
| Food/Dietary | No significant food interactions; epinastine is administered topically to the eye and systemic absorption is minimal. Avoid alcohol if drowsiness occurs (though systemic effects are rare). |
Loading safety data…
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | FDA Pregnancy Category C. No adequate studies in pregnant women. Animal studies showed embryofetal toxicity (increased resorptions, decreased fetal weight) at doses 3-4 times human topical ocular dose. First trimester: theoretical risk, avoid if possible. Second/third trimesters: use only if potential benefit justifies risk. No known human teratogenicity reported. |
| Fetal Monitoring | Monitor maternal ocular symptoms and signs of hypersensitivity. For systemic use, monitor liver function tests (LFTs) and renal function. No specific fetal monitoring required, but pregnancy status should be assessed before prescribing. |
| Fertility Effects | No known adverse effects on fertility in animal studies. No human data available. Potential for minor hormonal effects with systemic use, but highly unlikely with topical ocular route. |
| Clinical Pearls | Epinastine hydrochloride is a topical ophthalmic antihistamine and mast cell stabilizer. Onset of action is within minutes, but maximal effect may require several days of use. It can cause transient stinging upon instillation. Rebound conjunctivitis is not reported with topical epinastine. Its dual mechanism provides both acute and prophylactic relief for allergic conjunctivitis. |
| Patient Advice | Remove contact lenses before instilling the eye drops and wait at least 10 minutes before reinserting them. · Do not touch the dropper tip to any surface, including the eye, to avoid contamination. · Use exactly as prescribed; do not use more frequently than recommended. · Report any persistent eye pain, vision changes, or severe itching to your healthcare provider. · The solution may cause temporary stinging or burning upon instillation; this usually resolves quickly. |