Browsing by Subject "heikko emäs"

In vivo dissolution of drug molecules depends on the conditions in the gastrointestinal tract, like pH, composition of the fluids and hydrodynamics. Weakly basic compounds dissolve rapidly in low pH in stomach but in intestinal conditions forming of supersaturated solution may occur. This unstable state is the driving force either for rapid absorption from small intestine or for possible precipitation of drug. Difference in precipitation and thus in bioavailability between fasted and fed states can be significant. In this study behaviour of three weakly basic drugs, dipyridamole, ketoconazole and compound A, were studied with aid of two-phase microdissolution method. Three clinically relevant doses were used in the studies. In the study both fasted and fed states were tested as well as the effect of different pH in stomach phase and significance of biorelevant solutions over general buffer solutions. Dissolution of the drugs were examined in the media that simulate gastric fluids (SGF pH 1,2, SGF pH 4,0, FaSSGF pH 1,6 and acetate buffer pH 5,0). When biorelevant simulated intestinal fluid (FaSSIF or FeSSIF) was added to the solution to simulate the drug transfer out of stomach into small intestine, precipitation of different doses were analysed. Also the level of supersaturation compared to solubility results was examined. In addition the effects of various mixing speeds (300 rpm and 150 rpm) and scales (USP I and minidissolution) on precipitation were studied. Concentrations were measured directly from dissolution vessels with fibre optic probes. Re-dissolution of the drugs in small intestine and influence of physical properties on dissolution rate were evaluated with flow through dissolution method. In the fed state simulated microdissolution tests even the high doses of the drugs did not precipitate. Instead, in the tests simulating fasted state the effect of dose was clear and the relative part of dissolved drug were the smaller the higher was the dose. The high doses precipitated fast while the small doses remained much supersaturated. When FaSSGF was used the solutions staid longer in supersaturated state. Higher pH in stomach phase had remarkable impairing effect on the dissolved part of the drug in the small intestine phase and no supersaturated solutions were formed. In the microdissolution smaller mixing speed seemed to cause more precipitation and ranges of the results were larger. Different hydrodynamics in different scale dissolution methods as well caused divergent results. The effect of physical properties of precipitate to re-dissolution could be observed with the flow through dissolution tests. According to this study, two-phased dissolution method fit for few milligrams of API and it can be used to evaluate the precipitation potential of basic drugs in fasted and fed states. Also the effect of higher pH in the stomach on dissolved portion of API can be analysed. The method can be used as a risk assessment method for example when you want to know when the dose raises the risk to precipitation or as a tool to be used in early formulation development. As such dissolution tests can be used to get qualitative data of precipitation phenomenon when comparing basic drug compounds. The dissolution, precipitation and re-dissolution parameters will in future be utilised in pharmacokinetic model to evaluate the effect and significance of these phases on the drug absorption in vivo.