The influence of type and quantity of model drug on the extrusion/spheronization of mixtures with microcrystalline cellulose I. Extrusion parameters

Five model drugs, (methyl, propyl and butyl paraben, 4-hydroxybenzoic acid and propyl gallate), similar in their chemical structure were mixed with mi crocrystalline cellulose and water in different proportions and forced thro ugh a ram extruder. The overall water movement was measured by the differen ce between the initial water in the formulation and the water content in th e plug remaining after extrusion was completed. The differences in theoreti cal and practical volume occupancy of the materials inside the barrel were calculated to look for trapped air inside the barrel. The steady-state extr usion force for each formulation was recorded. All five materials demonstra ted differences in behaviour during extrusion. The relationship between eac h of the three properties measured and both the drug-load and initial water content was examined, to establish the potential relationship that existed between the differences due to the drug models. The five drug models were divided into two sub-groups, when examining the way that they underwent ext rusion. Methyl, propyl and butyl paraben formed one group while 4-hydroxybe nzoic acid and propyl gallate formed the other group. Within the former gro up the relationship between steady-state extrusion force and the percentage of drug and water present tended to be lower than those in the latter grou p. For the former group these relationships were non-linear. (C) 2001 Elsev ier Science B.V. All rights reserved.