The interactions of L-serine and L-threonine with drug metformin hydrochloride (Metformin-HCl) as a function of temperature have been investigated by combination of volumetric and acoustic methods. Densities and speeds of sound of L-serine and L-threonine in (0.00, 0.03, 0.045, 0.06 and 0.09) mol.kg(-1) aqueous solutions of Metformin-HCl have been measured at T = (305.15, 310.15 and 315.15) K and experimental pressure p = 0.1 MPa. The apparent molar volume V-phi, the partial molar volume V-phi degrees and standard partial molar volumes of transfer Delta V-phi degrees /for L-serine and L-threonine from water to aqueous Metformin-HCl solutions have been calculated from density data. Partial molar isentropic compression K-phi,K-s; s and partial molar isentropic compression of transfer Delta K-phi,K-s degrees have been calculated from speed of sound data. The pair and triplet interaction coefficient have also been calculated. The results have been explained based on competing patterns of interactions of co-solvents and the solute. (C) 2015 Elsevier Ltd. All rights reserved.