Design of a fixed-dose paediatric combination of artesunate and amodiaquine hydrochloride

Fixed-dose combinations of artesunate and amodiaquine hydrochloride provide challenges in product development due to the incompatibility of the two agents. This is particularly critical for paediatric preparations which can often be presented in liquid form. The studies reported in this article aimed to develop an understanding of the factors responsible for this incompatibility, whilst assessing the feasibility of developing a stable paediatric formulation. The stability characteristics of fast-disintegrating granular formulations containing intimate mixtures of both agents and single agent granules blended prior to production of unit doses were therefore studied under a range of storage conditions. The granular products remained stable over the 3-month period under stressed accelerated conditions, in contrast to control samples containing both drugs in combined granular form, which demonstrated reductions in artesunate content at elevated humidity. It was hypothesized that loss of active agent content for artesunate was accelerated by access to the water of crystallization of amodiaquine as demonstrated by the more facile dehydration of amodiaquine when a mixture of the two agents was analysed by differential scanning calorimetry (DSC). It was therefore concluded that a stable, versatile paediatric preparation of the two drugs could be prepared by blending pre-formulated granules containing the individual constituents rather than producing a combined granule comprising intimate mixtures of the two agents.