Clonidine, dexmedetomidine and guanfacine.
Mechanism: in therapeutic dose
- It stimulates presynaptic α2 receptors on the nerve endings → inhibition of NA release.
- Inhibition of central sympathetic outflow (stimulates presynaptic α2 receptors in NTS).
- So, it inhibits central &peripheral NE release
- It inhibits dopamine hydroxylase enzyme → inhibition of NA synthesis.
- It inhibits renin release and plasma renin activity.
Therapeutic uses:
- Moderate to severe hypertension.
- Prophylaxis of migraine.
- In opiate withdrawal to decrease symptoms of sympathetic over activity.
- As a sedative to reduce anxiety in preanesthetic medication.
Diarrhea of autonomic neuropathy
Side effects: SSSS
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Sedation and dry mouth (xerostomia).
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Severe hypertension Can occur with overdoses due to stimulation of α1 receptors as a result of loss of selectivity. ((Note to patient before taking higher dose, they must measure their blood pressure prior to taking their medication, they may confuse headache with high blood pressure which is mostly not the case))
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Sudden withdrawal can lead to hypertensive crisis (treated by combined α & β blockers), so it must be stopped gradually.
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Salt and water retention.
