Effect of a Fiber-Optic Probe on the Dissolution of Salicylic Acid Tablets in USP Apparatus 2

Fiber-optic probes permanently inserted in the dissolution medium in dissolution vessels can automate the sampling process but can also potentially affect the hydrodynamics in the vessel, possibly resulting in increased drug dissolution rates. In this work, dissolution experiments with non-disintegrating salicylic acid calibrator tablets were conducted in dissolution testing Apparatus 2 in both the presence and absence of a commercially available fiber-optic probe (Opt-Diss). Tests were conducted using tablets dropped in the medium according to USP guidelines, as well as with tablets fixed at nine positions on the vessel bottom (i.e., either centered in the vessel or placed at different off-center locations with respect to the vessel vertical centerline). The results were compared using statistical tools. In many cases, the presence of the probe resulted in slightly faster dissolution rates. The difference between the results obtained in experimental systems with the probe and those obtained with the control system without the probe depended on tablet position. Larger differences were observed when the tablets were on inner circle positions (10° off-center circle), especially when the tablets were located immediately downstream of the probe. A paired t-test as well as the difference factor (f1) and similarity factor (f2) were used to statistically analyze the results. In most cases, the results obtained with the inserted probe were statistically different, according to the paired t-test, from those obtained without it. It can be concluded that fiber-optic sampling probes can often result in small but measurable enhancements in the dissolution rates, which can produce appreciable variations in test results.