A precise colour determination method for tablets--an application of instrumental colour measurement in the pharmaceutical development.

ICH guideline Q6A requires a quantitative procedure to investigate changes in colour. For such purpose, it is necessary to conduct the instrumental colour measurement according to USP 28 <1061>. An adequate, precise, reproducible, and reliable equipment is introduced and the equipment qualification data presented. The colour of tablets coated with inorganic pigments like red and yellow ferric oxide, and white titanium dioxide shows the within-batch and batch-to-batch variabilities the extent of which is tested by CIELAB. Visual colour matching data reveal a considerable variability during the stability program while the mean CIELAB values do not vary. The visual matching should rather be replaced by the instrumental colour matching because the latter is free from the variabilities caused by human perception. The instrumental colour matching method is presented and proven to be reproducible, reliable and precise.

A new method to determine discoloration kinetics of uncoated white tablets occurring during stability testing-an application of instrumental color measurement in the development pharmaceutics.

The tristimulus color coordinates CIELAB and associated parameter Color Intensity (CI) have been shown to be a quantifiable variable for whiteness of uncoated tablets. Whereas any of L*, a* or b* indicates the discoloration of white tablets to a certain degree, it alone cannot reflect the full extent of discoloration. The CI has been defined which is able to describe the discoloration kinetics with acceptable regression coefficients. The evaluation of the CIELAB values from the stability data has shown that the discoloration of the white tablets means an intensification of yellowish or brownish color which is manifested by more or less constant hue angle (hab) values and increasing chroma (Cab*) values. In the view of these data the discoloration kinetics can physically be expressed by the CI. With the CI values the discoloration kinetics can be calculated by linear or polynomial regression with acceptable confidence intervals. The discoloration rates determined under several storage temperatures follow the Arrhenius equation and the activation energy can be estimated for the products. The CI values are unambiguously connected to the visual perception of the corresponding tablets. By means of the discoloration kinetics based on the CI values, it has become possible to statistically determine, the period of time uncoated tablets remain white.

Pharmacokinetics of the controlled-release nisoldipine coat-core tablet formulation.

UNLABELLED: The pharmacokinetics, safety, and tolerability of the novel once-daily "coat-core" formulation of the calcium antagonist nisoldipine were investigated in 4 randomized nonblind studies A-D in 52 healthy volunteers. Immediate-release or intravenous formulations were administered as reference in 3 studies. The objective of the present studies was to select the optimum controlled-release formulation (A), compare it to the immediate-release tablet at steady-state (B), determine the absolute bioavailability (C), and investigate bioequivalence after a small change in composition (D). Comparative pharmacokinetic properties: Mean residence time and apparent terminal half-life of nisoldipine in the coat-core formulation were significantly increased in comparison to administration via the intravenous route or the oral immediate-release formulation. Concentration profiles could be described with a 3-segment input model. Steady-state conditions were established with the second dose of nisoldipine coat-core and accumulation from first dose to steady-state accounted for 46% as expected due to the contribution of AUC beyond 24 h. At steady-state the coat-core formulation produced a plateau-shaped profile of nisoldipine plasma concentrations throughout the 24 h dosing interval and the peak-trough fluctuation was reduced by approximately 4-fold, compared to the immediate-release tablet in a b.i.d. regimen. While the absolute bioavailability of the drug in the coat-core tablet was 5.5%, its relative bioavailability was greater by 1.5-fold compared to the immediate-release tablet. This can be attributed to release of drug in the colon where the contribution of the gut wall to presystemic metabolism is reduced resulting in an increase in bioavailability as compared to stomach and small intestine. The intersubject variability of nisoldipine coat-core pharmacokinetics was comparable to that of the immediate-release tablet. The within-subject (intraindividual) variability was considerably smaller. Based on its pharmacokinetic profile the side chain-hydroxylated metabolite M 9 is not expected to contribute significantly to the antihypertensive effect of nisoldipine coat-core. In vitro/in vivo correlation: There was a rank order correlation between in vitro release rate of 3 different nisoldipine coat-core formulations and their noncompartmental pharmacokinetic parameters, a decrease in dissolution rate leading to increased bioavailability in vivo. Likewise, the mean dissolution times in vitro and in vivo were correlated in rank order. A linear (level A) correlation could be established within approximately 0-6 hours (in vitro) corresponding to 0-12 hours in vivo. The change in slope of the correlation curve after approximately 12 hours (in vivo) most likely reflects changes in both rate and extent of nisoldipine absorption in different sections of the gastrointestinal tract. SAFETY: In the present studies the drug was safe and well tolerated, adverse events related to peripheral vasodilatation being less frequent with the coat-core tablet compared to intravenous or immediate-release formulations.