Effects of Interactions between Cellulose Ethers and Polysorbate 80 on the Stability of Pyrantel Pamoate Suspensions

Viscometric and cloud-point data for aqueous dispersions of polysorbate 80 and a cellulose ether (one of two varieties of hydroxypropylmethylcellulose (HPMC) or sodium carboxymethylcellulose (NaCMC) which differ regarding molecular mass) indicated the existence of physico-chemical interactions between aggregated surfactant molecules and polymer macromolecules. The implications of these interactions for interfacial adsorption onto pyrantel pamoate particles suspended in various formulations of these polymer-surfactant dispersions were evaluated. Both HPMCs and also the NaCMC of a higher molecular mass were adsorbed, though in smaller amounts than in the absence of the surfactant owing to the weak adsorption activity of the polymer-surfactant associations. No adsorption of polysorbate 80 was detected in these suspensions. By contrast, in suspensions containing the lower molecular mass NaCMC, polysorbate 80 was adsorbed while the polymer apparently was not. The zeta potential and several indicators of physical stability varied among the various suspensions incorporating ionic polymers, and also among those incorporating non-ionic polymers, in a markedly different way from the corresponding formulations which incorporated a polymer or additive alone. Both polymers and alos the polysorbate 80 strongly promoted rapid dissolution of the pyrantel pamoate.