The Laboratories "Mauricio Díaz Müller", is currently renewing the sanitary registries of its products, exclusively in the line of oral liquids, among them the Theophylline 80mg / 15ml Elixir. This product was registered in November 2004, complying with the regulatory requirements of that time. Currently the regulatory requirements in force to renew this product have undergone changes, one of them is that, the medicines indicated for children should not contain alcohol and the other thing is that the product specification the pH changed, according to current bibliographic references. In the present study it was considered to use the cosolvency technique to modify the solubility of anhydrous theophylline, to then formulate the theophylline 80mg / 15ml oral solution, made without alcohol. In principle, the dielectric requirement of the active ingredient was identified. In a ternary system of water-soluble solvents at different concentrations, 4 trials of Theophylline 80 mg / 15 ml oral solution were prepared, to which the following qualitative-quantitative variables were determined: active: aqueous solubility, to the product: the organoleptic characteristics, identification, quantification and pH. With this study it was possible to increase the solubility of P.A. in 142% of the ternary system, during the investigation the compliance of the variables under study was monitored.