Cause of high variability in drug dissolution testing and its impact on setting tolerances

Characterization of the Drug Release Process by Investigation of Its Temperature Dependence

Temperature-dependent drug release from disintegrating tablets made of NaCl-containing agglomerated micronized cellulose (AMC) granules has been studied to characterize the release process. Release measurements on tablets compacted at three different compaction pressures; 50, 100, and 200 MPa, were performed at seven different temperatures; 6, 23, 33, 43, 50, 55, and 63 degrees C using the recently developed alternating ionic current method. Tablets compacted at different compaction pressures showed similar release rates. The release process was found to be diffusion-controlled, and the activation energy of the diffusion coefficient was comparable to that obtained for diffusion in pure water. The results show that the AMC granules in contact with water swell to a size and shape that is only slightly affected by their compaction history and the ion diffusion operates mainly within liquid-filled pores within the AMC granules. By using the temperature dependence of the release process, it was possible to reach this conclusion without any assumptions concerning the number and radii of the granules into which the tablets disintegrated. Further, the magnitude of the effective diffusion coefficient was found to be approximately 7.5 x 10(-10) cm(2)/s, which is approximately four orders of magnitude lower than for unhindered diffusion of Na(+) and Cl(-) in water but similar to the diffusion coefficient for protons and OH(-) ions in microcrystalline cellulose.

Abnormal dissolutions of chlorpromazine hydrochloride tablets in water by paddle method under a high agitation condition

All sugar-coated tablets of chlorpromazine hydrochloride except for those produced by one manufacture showed concave dissolution profiles in water by paddle method at 100 rpm but not at 50 rpm. The study was undertaken to clarify the agitation-dependent abnormal dissolutions. The strange dissolutions were also observed in water at different ionic strengths but not in buffer solutions of pH 1.2, 4.0 and 6.8. When monitored, the pH's of water in dissolution vessels for the abnormal tablets increased with time at 100 rpm and some of them exceeded pH 8 but did not at 50 rpm. The solubility of chlorpromazine hydrochloride decreased with the increase of pH which was too low to dissolve the whole amount of drug contained in a tablet at pH 8. The elevation of pH seemed to be mainly brought about by dissolution of calcium carbonate popularly used for sugar-coated tablets, because larger amount of calcium ion was dissolved out from the abnormal tablets at 100 rpm than from a normal tablet and from them at 50 rpm. These findings indicate that the concave dissolution profiles should be caused by the decrease of drug solubility with increase in pH of water, probably because of dissolution of calcium carbonate. We should pay attention to the change in pH of water which may differ depending on the agitation speed of dissolution tests.

Applications of a new device (spindle) for improved characterization of drug release (dissolution) of pharmaceutical products

A crescent spindle (patent pending) is described which may be used in place of the USP paddle component in USP dissolution apparatus 2. The new spindle is curve shaped, corresponding to the bottom of a dissolution vessel, with attached bristles to fill in the gap between the spindle and the surface of the vessel. The geometry of the new spindle provides more efficient mixing than the USP paddle and prevents accumulation of disintegrated material (no cone formation). Using the new spindle, in comparison with the USP paddle, dissolution characteristics of three drug products: 250 mg amoxicillin capsules, 15.6 g acetylsalicylic acid (ASA) boluses and 200 mg carbamzepine tablets were evaluated. The experimental conditions for dissolution testing with the two stirring devices included; 900 ml of 0.05 M phosphate buffer, pH 6.8 with 50 rpm, 900 ml of 0.05 M acetate buffer, pH 4.5-ethanol (7:3) with 50 rpm, and water containing 1% sodium lauryl sulphate with 75 rpm for amoxicillin capsules, ASA boluses and carbamazepine tablets, respectively. Uncharacteristic of the test products, which are fast release, the USP paddle provides significantly slower drug release. For example, 90 min for <80% drug release vs. 10 min for >90% for amoxicillin capsules and 6 h for 80% vs. 30 min for >90% for ASA boluses with USP paddle vs. the new spindle. In case of the carbamazepine tablets, three products which are bioequivalent and prescribed interchangeably, the USP paddle method shows significantly different dissolution characteristics. However, with the new device, all these products show similar drug release characteristics, a better reflection of product release characteristics and in vivo drug release behaviour. Compared with the USP paddle, the suggested device (spindle) provides improved stirring and mixing which appears to provide more appropriate (biorelevant) characterization of pharmaceutical products.

Comparison of dissolution profiles of Ibuprofen pellets

In this work we use both model dependent and independent techniques to assess the difference between dissolution profiles in which ibuprofen, in the form of uncoated pellets, is used as a model drug. The choice of a proper regression function, the relevance of the estimated parameters and the influence of the choice of dissolution points in the assessment of differences is discussed. The results obtained via mean dissolution times (MDT) and fit-factors (f(1) and f(2)) are also discussed and a non-quantitative method based on profiles correlation with graphical representation (concentration vs. concentration and rate vs. rate) presented. The tested methods discriminate similarly between curves, although not in all cases, but those based on modeling, MDT and fit-factors have shown to be less informative than the correlation approach.

Simulating the hydrodynamic conditions in the United States Pharmacopeia paddle dissolution apparatus

The objective of this work was to examine the feasibility of developing a high-performance computing software system to simulate the United States Pharmacopeia (USP) dissolution apparatus 2 (paddle apparatus) and thus aid in characterizing the fluid hydrodynamics in the method. The USP apparatus was modeled using the hydrodynamic package Fluent. The Gambit program was used to create a "wireframe" of the apparatus and generate the 3-dimensional grids for the computational fluid dynamics solver. The Fluent solver was run on an IBM RS/6000 SP distributed memory parallel processor system, using 8 processors. Configurations with and without a tablet present were developed and examined. Simulations for a liquid-filled vessel at a paddle speed of 50 rpm were generated. Large variations in fluid velocity magnitudes with position in the vessel were evident. Fluid velocity predictions were in good agreement with those previously published, using laser Doppler velocity measurements. A low-velocity domain was evident directly below the center of the rotating paddle. The model was extended to simulate the impact of the presence of a cylindrical tablet in the base of the dissolution vessel. The presence of the tablet complicated the local fluid flow, and large fluid shear rates were evident at the base of the compact. Fluid shear rates varied depending on the tablet surface and the location on the surface and were consistent with the reported asymmetrical dissolution of model tablets. The approach has the potential to explain the variable dissolution results reported and to aid in the design/prediction of optimal dissolution conditions for in vitro--in vivo correlations.