Raphael Paus

Influence of excipients on solubility and dissolution of pharmaceuticals.

In this work, solubilities and dissolution profiles of the active pharmaceutical ingredients (APIs) indomethacin and naproxen were measured in water in the presence of one excipient out of polyethylene glycol (PEG) 2000, 6000 and 12000, polyvinylpyrrolidone (PVP) K 25 and mannitol. It was found that the solubility of indomethacin and naproxen was increased with an addition of the selected excipients, which was also predicted by the perturbed-chain statistical associating fluid theory (PC-SAFT). The two-step chemical-potential-gradient model was applied to investigate the dissolution mechanism of indomethacin and naproxen in water in the presence of the excipient. It was found that the dissolution mechanisms of indomethacin and naproxen were changed by the presence of excipients. Although the solubility of the API was increased by the addition of excipients, the dissolution rate of the API was decreased in some cases. This was mainly due to the combination of the molecular interactions between the API and the polymer with the influence of the excipients on the kinetic part (rate constant of the surface reaction or diffusion of the API or both) of API dissolution as function of PEG molar mass as well as of the API type. Based upon the determined rate constants, the dissolution profiles were modeled with a high accuracy compared with the experimental data.

A Novel Approach for Analyzing the Dissolution Mechanism of Solid Dispersions

ABSTRACTPurposeTo analyze the dissolution mechanism of solid dispersions of poorly water-soluble active pharmaceutical ingredients (APIs), to predict the dissolution profiles of the APIs and to find appropriate ways to improve their dissolution rate.MethodsThe dissolution profiles of indomethacin and naproxen from solid dispersions in PVP K25 were measured in vitro using a rotating-disk system (USP II). A chemical-potential-gradient model combined with the thermodynamic model PC-SAFT was developed to investigate the dissolution mechanism of indomethacin and naproxen from their solid dispersions at different conditions and to predict the dissolution profiles of these APIs.ResultsThe results show that the dissolution of the investigated solid dispersions is controlled by dissolution of both, API and PVP K25 as they codissolve according to the initial API loading. Moreover, the dissolution of indomethacin and naproxen was improved by decreasing the API loading in polymer (leading to amorphous solid dispersions) and increasing stirring speed, temperature and pH of the dissolution medium. The dissolution of indomethacin and naproxen from their amorphous solid dispersions is mainly controlled by the surface reaction, which implies that indomethacin and naproxen dissolution can be effectively improved by formulation design and by improving their solvation performance.ConclusionsThe chemical-potential-gradient model combined with PC-SAFT can be used to analyze the dissolution mechanism of solid dispersions and to describe and predict the dissolution profiles of API as function of stirring speed, temperature and pH value of the medium. This work helps to find appropriate ways to improve the dissolution rate of poorly-soluble APIs.

A novel approach for predicting the dissolution profiles of pharmaceutical tablets

In this paper, the intrinsic dissolution profiles of naproxen (NAP) at pH values of 1.5 and 3.0 and of trimethoprim (TMP) at pH values of 1.5, 3.0, 5.0, 6.5 and 7.2 were measured. Meanwhile, the dissolution profiles of NAP and TMP from cylindrical tablets were measured at different temperatures (298.15K, 305.15K, 301.15K and 310.15K) and stirring speeds (50rpm, 100rpm and 150rpm) as well as at different pH values (1.5, 3.0, 5.0, 6.5 and 7.2). Additionally the pH-dependent solubilities of both APIs were measured and modeled. The chemical-potential-gradient model combined with the perturbed-chain statistical associating fluid theory (PC-SAFT) was applied to predict the dissolution profiles of the cylindrical tablets of NAP and TMP under different conditions based on the analysis of their intrinsic dissolution profiles as well as on the determination of the surface-area reduction of the API tablets during dissolution. It was shown that the predicted dissolution profiles of the tablets under different conditions were in a good accordance with the experimental findings.