Dose uniformity and redispersibility of pharmaceutical suspensions 2: assessment of three commercial erythromycin ethyl succinate oral liquids.

The content of active ingredient of single doses of a suspension depends to a large extent upon the redispersibility of the product. Mathematical and technical aspects of a procedure to test this property have been discussed in a preceding article. Here, the method is applied to three commercial erythromycin ethylsuccinate suspensions obtained from community pharmacies in Germany. Three specimens of each product were tested in parallel. For approximately two weeks, samples were taken t.i.d. at 9 am, 1 pm and 5 pm after shaking the bottles on a prototype testing apparatus with an intensity of 134m(2)/s(3) per cycle corresponding to the 25th percentile of a group of 79 subjects, whose shaking habits had been assessed previously. In order to minimize volumetric errors, 2.5ml samples were drawn using a syringe. They were assayed by HPLC with electrochemical detection using oleandomycin as an internal standard. While one of the products performed satisfactorily and one showed moderate shortcomings, the dose uniformity of two specimens of the third product was clearly deficient. The problem seems to be associated with poor wetting behaviour of the solids.