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The assessment of crystal growth of an organic pharmaceutical material by specific surface measurement

It is frequently necessary to ensure that pharmaceutically active materials of low aqueous solubility meet minimum requirements for specific surface in order to achieve their desired therapeutic activity. The paper describes work on a compound with a very slight aqueous solubility where the need for control over specific surface is indicated. It is customary and often convenient to establish the relationship between surface area and particle size, and to determine the latter, as modern instrumentation allows the rapid measurement of size distribution. For this compound this approach was not feasible as particle size determination proved difficult. The determinations were therefore made directly as surface area measurements using the dynamic flow technique based on the BET nitrogen adsorption technique. Laboratory scale preparations of the compound achieved a sufficiently high specific surface consistent with small particle size, and crystal shape. As these materials were used in early bioavailability studies, it was necessary to achieve a comparable specific surface on scale-up. This initially proved difficult to achieve. A programme of work has been conducted to establish the causes of the lower specific surface observed in these preparations, and to examine the conditions of the precipitation isolation process. The conclusions from the study allowed successful further scale-up of the precipitation to pilot plant scale, achieving acceptable specific surface values.