Midodrine Hydrochloride

Midodrine hydrochloride is a selective α1-adrenoceptor agonist. It does not cross the blood-brain barrier, thus lacking central nervous system side effects. In postural orthostatic tachycardia syndrome (POTS), the drug significantly decreases venous capacitance, which helps reduce venous pooling in the lower extremities upon standing. By increasing peripheral vascular resistance and improving venous return, midodrine attenuates the excessive heart rate response to orthostatic stress. Treatment with midodrine significantly reduced the heart rate difference during standing test from 38±2.4 to 21±1.4 beats/min. The improvement in orthostatic tolerance is attributed to its vasoconstrictive effects on both arteries and veins without affecting blood pressure at therapeutic doses. This mechanism directly counteracts the sympathetic dysfunction and impaired vasoconstriction underlying POTS pathophysiology.

Fig. 1 Kaplan-Meier curve shows lower symptom recurrence in children with POTS on midodrine. (Chen L.; et al. 2011)