Alpha-2 agonists

What are Alpha- 2- agonists?

Alpha-2 agonists activate alpha-2 receptors by binding to them. They cause the sympathetic nervous system to be inhibited by a negative feedback mechanism. In the body, the natural agonists are adrenaline and noradrenaline. In medicine, synthetic alpha-2 agonists such as clonidine are used in the treatment of high blood pressure and glaucoma. Find out which symptoms can occur with glaucoma: Symptoms of glaucoma


Binding to alpha-receptors leads to a reduced production of aqueous humor.

Fields of application

Alpha-2 agonists are also used in glaucoma therapy. The substances are also used in tablet form for cardiovascular diseases. The following substances are used in ophthalmology: Apraclonidine (Iopidine), Brimonidine (Alphagan), Clonidine (Glaucopres). The substances should be taken 2-3 times a day in the form of eye drops. The washout time is 1-3 days.


Alpha-2 agonists are used in the therapy of high blood pressure (hypertension) as so-called anithypertensives. Furthermore, the derivative of clonidine, apraclonidine, is used in glaucoma therapy (glaucoma). It lowers the production of aqueous humor and thus the intraocular pressure.


The dosage of alpha-2 agonists as a medication must be prescribed by a doctor. In high blood pressure therapy this depends on the severity of the hypertension, in glaucoma therapy on the level of intraocular pressure. The dosage is therefore patient-dependent.

In addition, each drug has a usual dosage, which can be found in the package insert. Iopidine®, which is used in the treatment of glaucoma, is administered 3 times daily with one drop each into the diseased eye. Catapresan® is taken in tablet form for high blood pressure.

There are Catapresan 75, 150 and 300. 300 is prescribed for severe high blood pressure. The number of tablets starts at one tablet twice a day. However, the dosage must also be adjusted individually.

Alternatives to alpha-2 agonists

In the therapy of glaucoma, other active ingredients are important in addition to alpha-2-agonists. They relieve the intraocular pressure by either reducing the production of aqueous humor or by promoting the drainage of aqueous humor. Beta-2-blockers: Timolol, Betaxolol Carboanhydrase inhibitors: Dorzolamide, Brinzolamide Promote the outflow of aqueous humor: Prostaglandins: Latanoprost, Bimatoprost Cholinergics: Pilocarpine, Carbachol The following active ingredients are approved for the therapy of high blood pressure: ACE inhibitors: ramipril, enalapril etc.

Thiazides: hydrochlorothiazide etc. Calcium antagonists: Amlodipine, etc. Beta blockers: Metoprolol etc.

  • Beta-2 blockers: timolol, betaxolol
  • Carboanhydrase inhibitors: dorzolamide, brinzolamide
  • Prostaglandins: Latanoprost, Bimatoprost
  • Cholinergics: pilocarpine, carbachol
  • ACE inhibitors: Ramipril, Enalapril etc. – Thiazides: hydrochlorothiazide etc. – Calcium antagonists: Amlodipine etc. – Beta blockers: Metoprolol etc.

Side effects

In addition to relatively frequent allergies, there is also a temporary red coloration of the eye (conjunctival hyperemia) as well as fatigue and dry mouth, drop in blood pressure, slowing of the pulse and constipation.