Determination of time course of tablet disintegration I: numerical method

Progressive tools and critical strategies for development of best fit PBPK model aiming better in vitro-in vivo correlation

Nowadays, conducting discriminative dissolution experiments employing physiologically based pharmacokinetic modeling (PBPK) or physiologically based biopharmaceutical modeling (PBBM) is gaining significant importance in quantitatively predicting oral absorption of drugs. Mechanistic understanding of each process involved in drug absorption and its impact on the performance greatly facilitates designing a formulation with high confidence. Unfortunately, the biggest challenge scientists are facing in current days is the lack of standardized protocol for integrating dissolution experiment data during PBPK modeling. However, in vitro-in vivo drug release interrelation can be improved with the consideration and development of appropriate biorelevant dissolution media that closely mimic physiological conditions. Multiple reported dissolution models have described nature and functionality of different regions of the gastrointestinal tract (GI) to more accurately design discriminative dissolution media. Dissolution experiment data can be integrated either mechanistically or without a mechanism depending primarily on the formulation type, biopharmaceutics classification system (BCS) class and particle size of the drug substance. All such parameters are required to be considered for selecting the appropriate functions during PBPK modeling to produce a best fit model. The primary focus of this review is to critically discuss various progressive dissolution models and tools, existing challenges and approaches for establishing best fit PBPK model aiming better in vitro-in vivo correlation (IVIVC). Strategies for proper selection of dissolution models as an input function in PBPK/PBBM modeling have also been critically discussed. Logical and scientific pathway for selection of different type of functions and integration events in the commercially available in silico software has been described through case studies.

Quantitative assessment of disintegration rate is important for predicting the oral absorption of solid dosage forms containing poorly soluble weak base drugs

This study aimed to develop a novel in silico modeling and simulation that considers the disintegration rate in the stomach to predict the in vivo performance of oral solid dosage forms with slow disintegration rates containing poorly soluble weak base drugs. Oxatomide and manidipine hydrochloride were used as model drugs. First, the in vitro disintegration rate and dissolution rate were determined in biorelevant media that simulate the gastrointestinal fluids in fasted humans using a USP apparatus II paddle dissolution tester. Next, the oral absorption of the dosage forms was predicted using the novel simulation model coupled with not only the dissolution rate but also the estimated disintegration rate. As the in vitro disintegration time was 45 min or longer for both drugs in Fasted State Simulated Gastric Fluid, the disintegration rate of these dosage forms was considered slow as immediate release (IR) tablets. While the predicted and observed pharmacokinetic profiles of both drugs were comparable using the new model, the conventional model, which did not consider the disintegration step, underestimated the oral absorption of both drugs. Thus, our novel simulation model coupled with the disintegration rate estimated from in vitro tests is promising for predicting the in vivo performance of oral solid dosage forms with slow disintegration rates containing poorly soluble weak base drugs.

Dissolution of a soluble drug substance from vinyl polymer matrices

It was shown that vinyl polymers form good bases for in vitro sustained-release matrices, and that the character of the release curves is basically in line with their pH-solubility profiles. For a flow cell, the release curves may be approximated by the equation: In (m/m0) = - K(t -ti), where m is the amount not dissolved, m0 is the initial drug content, K is a dissolution constant, t is time, and ti is a lag time. Furthermore, it was shown that K is a function of tablet hardness (H) and polymer content (Q, percent). This functionality is well represented by the equation: In K = alpha H + gamma ln Q + epsilon, where alpha, gamma, and epsilon are polymer-dependent parameters. Matrix erosion is represented by an exponential decay: (p/p0) = exp(-Dt + a), where p is the amount not eroded, p0 is the initial weight, D is an erosion constant, and a is a soluble polymer-dependent parameter. In the case of these soluble polymers, K is not solely a function of D.

Simple methods for estimating percent disintegrated--time data

Two techniques are described for the treatment of dissolution rates to estimate the percent disintegrated--time data for tablets and capsules. The first is an extension of an equation derived previously with the assumption of first-order disintegration and dissolution processes; whereas, the second involves the determination of the rate constant from the terminal segment of the curve and the use of numerical derivatives according to a disintegration kinetics-independent approach. The dissolution data of six commercial tablet and capsule formulations were treated according to the described techniques. Good agreement was found between the percent disintegrated--time data estimated by the second approach for an acetaminophen tablet and those obtained by a well-established model where a Weibull function was employed.

Disintegration-dissolution analysis of percent dissolved-time data

A simple, graphical method is described for the disintegration--dissolution analysis of cumulative percent dissolved--time data. The technique is based on a biexponential equation with the assumption of first-order disintegration and dissolution according to a simple dissolution model. The dissolution data obtained for six commercial tablets and capsules adequately fit the developed equation. The described method is simple and can handle initial data points that are usually ignored by other techniques.

Concentration profile for the dissolution of drug tablets undergoing simultaneous degradation

An empirical approach to the concentration-time history of a dissolving drug has resulted in a cube-root equation in which the characteristic constant of the equation embodies the important physical variables of the system. This expression has been used to study the dissolution of a drug that degrades simultaneously in the test solution. An alternative representation of the dissolution process is first-order kinetics. These two approaches are compared by fitting the experimental data of the dissolution of digoxin and melphalan tablets in various media, and a new method for the proper analysis of data for the dissolution of tablets that simultaneously degrade in the test solution is presented.

Time and temperature dependence of disintegration and correlation between dissolution and disintegration rate constants

Commercial prednisone tablets were subjected to dissolution tests by USP basket and paddle methods. It was found experimentally that disintegration adheres to an exponential decay law: ln(W/Wo) = -d(t-ti), where W is the nondisintegrated weight, d is a disintegration constant, t is time, and ti is a lag time. Dissolution has been reported to adhere to a similar law, where the dissolution constant K, follows a pseudo-Arrhenius relationship with changing temperature. Within a certain temperature range, this relationship also exists for the disintegration rate constant, d. A correlation exists in these tablets between K and d. The shaft length in the dissolution apparatus plays a part in the disintegration (and hence dissolution) rate and, therefore, is an important apparatus parameter affecting reproducibility.

Determination of time course of tablet disintegration II: Method using continuous functions

An analysis of the disintegration-dissolution sequence of drug release from a tablet leads to a mathematical expression relating disintegration to the dissolution profile of the tablet and the dissolution rate of the primary drug particles in the tablet. The equation describing the disintegration of an acetaminophen tablet is determined to demonstrate the application of the theory.