Drugs of this class are used to treat hypertension, as they reduce peripheral resistance by stimulating presynaptic α2 adrenoreceptors in the central nervous system.
These drugs may be used in patients with renal disease as they do not cause a decrease in blood flow to the kidney.
The primary mechanism of action of alpha-2 agonists is stimulation of presynaptic alpha-2 receptors in the central nervous system. Drugs of this class are centrally acting and decrease sympathetic outflow, as they activate medullary presynaptic α2 adrenoceptors. Remember that α2 activation decreases sympathetic outflow.
Clonidine activates α receptors, which causes inhibition of norepinephrine release from synaptic vesicles. Clonidine is frequently administered with a diuretic, and may produce side effects of lethargy, dry mouth and constipation.
An adverse side effect of clonidine includes severe rebound hypertension in the case of abrupt withdrawal.
Methyldopa decreases total peripheral resistance by reducing sympathetic outflow from the CNS. It is used to treat moderate or mild hypertension and can be used together with a diuretic for increased effect.
This drug may be used to treat hypertension during pregnancy.
Methyldopa usage may lead to drug-induced immune-mediated hemolysis, leading to a positive direct Coombs test.
Patients taking methyldopa may develop an SLE-like syndrome, with symptoms like fever, pericarditis, arthralgias and malaise, with positive anti-nuclear antibodies.
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