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Old 03-12-2010
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Question Why clonidine causes miosis?

As given in Toxicology section, Kaplan notes-
Why does clonidine [being an alpha2 agonist] causes miosis????
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Old 03-13-2010
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Clonidin is an alpha 2 agonist.

Stimulation of alpha 2 receptors will decrease the prejunctional availability of norepinephrine.

When you have less epinephrine you have less alpha 1 receptor stimulation. (that's why clonidin was used in hypertension

So the sympathetic effect on the pupil radial muscle which dilates the pupil has stopped.

So what's left is only the parasympathetic affecting M3 receptors on the sphincter muscle and so you get miosis.
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Old 03-13-2010
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It seems that you did not take Step 1 and that's why you are asking this in a CK forum.
It recommended that you take step 1 first. See this thread
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