Levodopa is a dopamine precursor used in various forms to treat Parkinson's disease and dopa-responsive dystonia. It is typically co-administered with an inhibitor of peripheral decarboxylation (DDC, dopa decarboxylase), such as carbidopa or benserazide. Inhibitors of alternative metabolic route for dopamine by catechol-O-methyl transferase are also used. These include entacapone and tolcapone.
Peripheral effects
Dopamine also has effects when administered through an IV line outside the central nervous system. The brand name of this preparation is known as Intropin. The effects in this form are dose dependent.
- Dosages from 2 to 5 μg/kg/min are considered the "renal dose." At this low dosage, dopamine binds D1 receptors, dilating blood vessels, increasing blood flow to renal, mesenteric, and coronary arteries; and increasing overall renal perfusion. Dopamine therefore has a diuretic effect, potentially increasing urine output from 5 ml/kg/hr to 10 ml/kg/hr.
- Intermediate dosages from 5 to 10 μg/kg/min additionally have a positive inotropic and chronotropic effect through increased β1 receptor activation. It is used in patients with shock or heart failure to increase cardiac output and blood pressure.
- High doses from 10 to 20 μg/kg/min is the "pressor" dose. This dose causes vasoconstriction, increases systemic vascular resistance, and increases blood pressure through α1 receptor activation;
Further Reading
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