Effects
Antihistamine eye drops have antihistamine and antiallergic properties. They are more or less selective antagonists of histamine at the H1 receptor, abolish histamine effects and thus relieve symptoms such as itching, redness, swelling, and tearing. Compared with oral antihistamines, the effect occurs after only a few minutes and lasts up to 12 hours. Many agents are also mast cell stabilizing or anti-inflammatory, which is considered a therapeutic advantage.
Indications
Antihistamine eye drops are used for symptomatic treatment of allergic conjunctivitis, for example, hay fever, mite allergy, and cat allergy. Without a doctor’s prescription, they may only be used for the treatment of seasonal allergic conjunctivitis, i.e. in the case of pollen allergy, according to the specialist information. They have not yet been approved for prevention.
Dosage
According to the SmPC. As a rule, 1 drop is placed in each eye twice daily. In severe cases, the dose may be increased to 1 drop 4 times daily. The maximum duration of treatment is limited to two weeks in self-medication. If prescribed by a doctor, they can be used for several weeks and, depending on the active ingredient, during months. See also under Administering eye drops.
Active ingredients
In self-medication:
- Antazoline (spersallerg)
- Azelastine (Allergodil seasonal)
- Emedastine (Emadine)
- Levocabastine eye drops (Livostin)
Only if prescribed by a doctor:
- Azelastine (Allergodil)
- Epinastine (Relestat)
- Ketotifen eye drops (Zaditen)
- Olopatadine (Opatanol)
Contraindications
The use is contraindicated in case of hypersensitivity. For children, due to insufficient data, the age limit is different, ranging from 2 to 12 years, depending on the active ingredient. Studies are also lacking for the elderly for some drugs. The eye drops in the vial are usually preserved with benzalkonium chloride, which can become embedded in soft contact lenses. Wearing contact lenses is generally not recommended during treatment. It is also known that benzalkonium chloride can cause allergies and rarely ocular diseases (keratopathies). For this reason, medicines without preservatives in single doses should be preferred. The use of the drops may affect vision for a short time. During this time, do not drive vehicles or operate machinery. Additional precautions must be observed with medicines that also contain sympathomimetics, such as tetryzoline or naphazoline. Vasoconstrictors may increase efficacy somewhat, but may also lead to adverse effects and reactive hyperemia after discontinuation. In our view, combined drops should therefore be used only in the short term, with restraint, and as a 2nd-line agent.
Interactions
Drug-drug interactions are not known to date and are not expected because of the low concentrations in plasma. As a precaution, other eye drops should be used approximately 10 minutes apart.
Adverse effects
Possible adverse effects include local reactions to the eye such as red eye, burning eye, irritation, allergic reactions, dry eye, blurred vision, sensitivity to light, fatigue, eye tearing, foreign body sensation, corneal discoloration, and punctate erosion of the corneal epithelium (benzalkonium chloride). Some drops have a bitter taste of their own. As the liquid drains down the nose into the throat, it may come into contact with the tongue, causing taste disturbances. Systemic adverse effects are rare and include headache, weakness, dream disturbances, and skin rashes.