Eighteen volunteers have been treated with different oral formulations of butamirate citrate according to 2 randomized 2-way crossover designs. In the first study (study I) the test preparation was a syrup (Demotussol Hustensirup, Demopharm), and the reference preparation was a syrup already marketed (Sinecod Sirup, Zyma SA). A test preparation (Demotussol Tabletten) was compared to a solution (Demotussol Hustentropfen) in the second study (study II). Within the 2 study periods the volunteers received single 45 mg doses of the test and the reference formulation, respectively. Blood samples have been drawn immediately prior to each administration and at 17 sampling points within 96 h after dosing. A wash-out period of 1 week was maintained between successive drug doses. The plasma concentration of one of the main metabolites, 2-phenylbutyric acid, was determined by a validated reversed-phase HPLC method with UV detection, with a lower limit of quantification of 50 ng/ml. The following mean values have been obtained in study I (syrup preparations) for the test: AUC0-infinity 46.9 micrograms x h/ml, Cmax of 1.77 micrograms/ml at 1.1 h, t1/2 28 h and after administration of the reference: AUC0-infinity 50.4 micrograms x h/ml, Cmax 1.86 micrograms/ml, tmax 1.5 h, t1/2 26 h. In study II the following mean values have been obtained for the test preparation (tablet): AUC0-infinity 54.7 micrograms x h/ml, Cmax of 1.88 micrograms/ml at 1.1 h, t1/2 27 h and for the reference (solution): AUC0-infinity 54.5 micrograms x h/ml, Cmax 1.94 micrograms/ml, tmax 1.1 h, t1/2 26 h. Both preparations have been proven to be bioequivalent to their corresponding references regarding extent and rate of absorption.