The objective of the Biopharmaceutics Classification System is to allow prediction of in vivo pharmacokinetic performance of drııg products from in vitro measurements; therefore, it is important to determine the solubility and permeabihty of drııg substances. Furosemide (FŞM) is a loop diuretic commonly used in the treatment of edematous States associated chronic renal failure, hvpertension, congestive heart failure and cirrhosis of the liver. The aim of this studv was to develop and validate an HPLC method for quantifıcation of FŞM in the samples obtained from the in vitro solubility studies performed atfive differentpH values (pF[ 1.0, 2.9, 3.9, 4.9 and 7.5). ChromatographicseparationofFSM was achieved on a reverse phase column (JVaters Spherisorb ODS2 Çl8 250x4.6 mm 5 pm) with a mobile phase consisted of 0.01M KH2P04 (pH 5.5) and methanol (70:30 v/v),. Analvses were run at a flow rate 1 nıL/min and IJV detection was performed at 235 nm. Under these conditions, the retention time of FSM w as about 7.0 min. The method was linear in the concentration range of 0.5 to 50 pg/mL, and limit of cpıantifıcation was 320 ng/mL. Developed and validated HPLC method was proved to be simple, reliable and also sııitable as a single method for studying the solubility of FSM as a function ofpH. Finallv, based on our results, solubility of FŞM was dependent on pH. İts solubility was lo\v between pH 1.0 and 4.9, and was high at pH 7.5.

Keywords: Furosemide, HPLC method, BCS, Solubility class, Dose niimher