Alpha-2 agonists

What are alpha 2 agonists?

Alpha-2 agonists activate alpha-2 receptors by attaching to them.
Through a negative feedback mechanism, they cause the sympathetic nervous system to be inhibited.
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 (glaucoma).

Learn what glaucoma symptoms can occur:
Glaucoma symptoms


A binding to alpha receptors leads to a reduced production of aqueous humor.

application areas

Alpha-2 agonists are also used in glaucoma therapy. In addition, 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 in the form of eye drops 2-3 times a day. The washout time is 1-3 days.


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


The dosage of alpha-2 agonists as a drug must be prescribed by the doctor.
In high blood pressure therapy this depends on the severity of the high blood pressure, in glaucoma therapy on the level of the 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 instilled into the diseased eye 3 times a day with one drop each time.

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

Alternatives to Alpha-2 Agonists

In addition to alpha-2 agonists, other active ingredients are important in glaucoma therapy.
They relieve intraocular pressure by either reducing the production of aqueous humor or by promoting the outflow of aqueous humor.

Lower the aqueous humor production:

  • Beta-2 blockers: timolol, betaxolol

  • Carbonic anhydrase inhibitors: dorzolamide, brinzolamide

Promote the outflow of aqueous humor:

  • Prostaglandins: latanoprost, bimatoprost

  • Cholinergics: pilocarpine, carbachol

The following active ingredients are approved for the treatment of high blood pressure:

  • ACE inhibitors: Ramipril, Enalapril etc.

  • Thiazides: hydrochlorothiazide etc.

  • Calcium antagonists: amlodipine etc.

  • Beta blockers: metoprolol etc.

Side effects

In addition to relatively frequent Allergies the eye also turns red at times (conjunctival hyperemia) as well as tiredness and dry mouth, drop in blood pressure, slow pulse and constipation.


Patient with a AV block, sick sinus syndrome, or aortic stenosis, or those with low blood pressure or heart rate should not be given this medication.