It is described the use of 0.5 g/100 ml to 10 g/100 ml L-carnitine and/or its alkanoyl devivatives where alkanoyl is direct or branched alifatic group with 2 to 8 carbon atoms, optionally in the form of a pharmaceutically acceptable salt as osmotic agent in the solutions for medical use.It is described the use of 0.5 g/100 ml to 10 g/100 ml L-carnitine and/or its alkanoyl devivatives where alkanoyl is direct or branched alifatic group with 2 to 8 carbon atoms, optionally in the form of a pharmaceutically acceptable salt as osmotic agent in the solutions for medical use.