It is absorbed orally and is actively secreted into the tubule in addition to filtration and is then passively reabsorbed. Lower doses have primarily a diuretic effect, higher doses will cause metabolic acidosis. It is useful as an acute diuretic but compensatory mechanisms of the body quickly diminish its efficacy. It is primarily indicated for treatment of glaucoma and to alkalinize the urine and may be of benefit in treating motion sickness. It is safe due to extremely low toxicity.
Renal vasodilators act indirectly as diuretics.
Dopamine and dopaminergic agonists relax renal arteries via direct actions in vascular D1 dopamine receptors. Fenoldopam is a D1 selective agonist. They increase renal blood flow and glomerular filtration rate. They are used primarily for other purposes, diuretic actions are more a side-effect than an indication. There is the potential for inadvertent poisoning.