[The effect of different variables on the in vitro dissolution of a theophylline sustained-release preparation]. / Einfluss verschiedener Variablen auf die In-vitro-Freisetzung eines Theophyllin-Retardpräparates.

In vitro dissolution studies are valuable tools to judge quality and stability of sustained release dosage forms and are often utilised to predict the in vivo performance. For this reason, in vitro dissolution experiments with varying pH, osmolarity, rotation speed, and with addition of surfactants were performed with a sustained release theophylline (CAS 58-55-9) dosage form (Bronchoretard). In order to mimic the physiological situation of the gastrointestinal tract more closely, the pH of the dissolution media was changed and human bile was added at different time points. The results obtained show that the in vitro dissolution of the dosage form differs only slightly for the parameters pH, osmolarity and stirring speed and always lies within in vivo verified dissolution limits. However, the addition of sodium dodecyl sulphate to the dissolution medium markedly altered the dissolution rate whereas addition of the physiologically surface active human bile did not change the dissolution rate. A comparison with in vivo results indicated, that only the physiologically adapted model guarantees reliable results whereas the addition of synthetic surfactants cannot allow for the prediction of bile or food effects. The meaning of in vitro dissolution tests thus is limited to development studies of dosage forms and to routine quality and stability control testing. For judging the in vivo characteristics in vitro studies have only limited value and have to be verified by pharmacokinetic studies.

[Manufacture and in vitro characterization of a new fluid theophylline sustained-release form. Sachets with microcapsules for administration in a drinkable sustained-release suspension]. / Herstellung und In-vitro-Charakterisierung einer neuen flüssigen Theophyllin-Retardarzneiform. Sachets mit Mikrokapseln zur Bereitung einer trinkfertigen Retardsuspension.

The administration of currently available theophylline (CAS 58-55-9) sustained release preparations with high drug doses (hard capsules, tablets) presents difficulties for certain patient groups as children and elderly, due to the large geometry of these dosage forms. Therefore, a suspension for easy administration based on the novel Liquitard technology was developed using theophylline microcapsules. This paper describes the manufacturing procedure of the new dosage form and its in vitro release characteristics as a function of various parameters. During manufacturing, the suspension-forming excipients are first granulated and then filled into sachets together with the microcapsules. The sustained release suspension is prepared by the patient himself immediately before administration. The in vitro release of theophylline from the dosage form is neither affected by the suspension-forming excipients nor by the drug amount. This allows for the manufacture of sachets with different drug strength maintaining the same qualitative composition. Furthermore, the in vitro release is independent of pH, osmolality, agitation and of the addition of surfactants and native bile to the dissolution medium. The new dosage form thus meets the current EC-guidelines for oral sustained release dosage forms. The in vitro limits of the dissolution testing were verified on the basis of the bioequivalence of the batches at the upper and lower specification limits.

Stability behaviour of molsidomine-containing pellet formulations.

Molsidomine in mixtures with different inactive ingredients has been subjected to a stability test. The fingerprint chromatogram obtained by HPLC with diode-array detection of mixtures of molsidomine with povidone 25 revealed decomposition products; the detection wavelength of 210 nm resulted in easy detection of the degradation products. Molsidomine-containing pellets were manufactured according to a compact procedure and by applying the active ingredient to placebo pellets. Compared with the nonpareil pellet formulations, compact pellets have a considerably higher water content and undergo decomposition of the active ingredient after storage for 50 months under different conditions. It is assumed that the decomposition of molsidomine is accelerated by the peroxide found in povidone.