The development of this orally and rapidly acting highly efficacious diuretic was a breakthrough. Its maximal natriuretic effect is much greater than that of other classes. The diuretic response goes on increasing with increasing dose: up to 10 L of urine may be produced in a day. It is active even in patients with relatively severe renal failure. The onset of action is prompt (i.v. 2-5 min., i.m. 10-20 min., oral 20-40 min.) and duration short (3-6 hours) The major site of action is the thick Asc LH (site II) where furosemide inhibits Na+- K+-2Cl cotransport. A minor component of action on PT has also been indicated. It is secreted in PT by organic anion transport and reaches Asc LH where it acts from luminal side of the membrane. It abolishes the corticomedullary osmotic gradient and blocks positive as well as negative free water clearance. K+ excretion is increased mainly due to high Na+ load reaching DT. However, at equinatriuretic doses, K+ loss is less than that with thiazides. Identification test was done by estimation of drug, infra-red spectroscopy, FTIR, UV-Spectroscopy, Melting point determination etc.
