During dissolution testing of solid dosage forms in the United States Pharmacopoeia (USP) Apparatus 2, samples are manually withdrawn from the medium in the vessel prior to the analysis. Probes permanently inserted in the medium can automate the sampling process but can also alter the system's hydrodynamics, possibly resulting in different dissolution-testing results. In this work, dissolution tests were conducted in a USP Apparatus 2 with and without an arch-shaped fiber optic probe using prednisone tablets fixed at nine different locations on the vessel bottom. The resulting dissolution profiles were compared using statistical tools. Dissolution rates obtained with the probe were typically higher than those obtained without the probe. The magnitude of the difference between dissolution profiles depended on the tablet location: Larger differences were observed with tablets located immediately downstream of the probe. The differences in dissolution profiles were generally small enough to satisfy the US Food and Drug Administration criteria (f1 and f2 values), although a paired t-test [P(t-test)] indicated that most of the profiles were statistically different [P(t-test) <0.05]. The hydrodynamic effects generated by the arch-shaped fiber optic probe resulted in detectable differences in the dissolution profiles, which, although limited, were clearly measurable and could introduce variations in test results.
Keywords: USP Dissolution Testing Apparatus; dissolution curve; dissolution rate; sampling probe.
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