Legislation
Resolution

Resolution - RE nº 482, of March 19, 2002
(Official Journal of 20/03/2002)

The Director of the Collegiate Board of Directors of the National Sanitary Surveillance Agency, in the use of the attributions vested in him under Administrative Rule 724, issued by the Director-Chairman, on October 10, 2000,

WHEREAS

paragraph 3 of article 111, of the Bylaws approved by Administrative Rule 593, of August 25, 2000, re-published in the Official Journal of the Union of December 22, 2000;
that the matter was submitted to the examination of the Collegiate Board of Directors, which approved the matter in a meeting held on March 13, 2002, decides:

Article 1 - To determine the publication of the "Guide for Studies of In Vitro-In Vivo Correlation (CIVIV)", attached.

Article 2 - This Resolution enters into force on the date of its publication.

GONZALO VECINA NETO

GUIDE FOR IN VITRO-IN VIVO CORRELATION (IVIVC) STUDIES - 1/2002

1. INTRODUCTION

The in vitro-in vivo correlation refers to the establishment of a rational relation among biological properties, or parameters derived from those properties, produced by a dosage form and its physical-chemical properties or characteristics.

The most commonly used biological properties are one or more pharmacokinetics parameters such as the area under the curve of plasmatic concentrations time curve (AUC) or maximum plasmatic concentration (Cmax), obtained after the administration of the dosage form.

The physical-chemical characteristic most employed is the in vitro dissolution behavior (e.g., the percentage of drug dissolved under specific experimental conditions). The relationship between the two properties, biological and physical-chemical is thus expressed quantitatively.

2. LEVELS OF IN VITRO-IN VIVO CORRELATION

Three levels of correlation may be defined and classified in a descending order of usefulness. The concept of correlation is based on its ability to reflect the entire plasmatic concentration time curve, obtained after the administration of the dosage form. It is the relationship between the entire in vitro dissolution curve to the entire curve of plasmatic levels of drug which defines the correlation.

2.1. Level A Correlation

It is the highest obtainable level of correlation. It represents a relation point to point between the in vitro dissolution, and in vivo input rate (sometimes referred to as in vivo dissolution) of the drug from the dosage form. At this level of correlation, the in vitro and in vivo dissolution curves are directly superimposable, or may be superimposed using a constant (scale factor). The mathematical description of both is the same. This relation is more easily obtained for modified release dosage forms, which display in vitro release essentially independent from the dissolution media commonly used in tests. Nevertheless, this is not a requirement for a level A correlation.

This correlation is generally obtained through a procedure involving two steps: deconvolution of the plasmatic concentration data for obtaining the fraction of drug absorbed versus time (absorption curve), followed by the comparison between the fraction of the drug absorbed and that dissolved in vitro for the same periods of time. The fraction absorbed versus time curve may be obtained through the use of mass balance model-dependent techniques, such as the Wagner-Nelson procedure, in case the absorption curve adjusts to a model of one compartment, or the Loo-Riegelman method, in case the adjustment is significant for a model of two compartments, or by model-independent, mathematical deconvolution.

The advantages of level A correlation are:

a) unlike other levels, a point to point correlation is developed using every plasma level and every dissolution percentage obtained in vitro, thus reflecting the complete plasma level curve. As a result, the in vitro dissolution profile can serve as a substitute of in vivo performance. Thus, modifications of manufacturing site or method, change of raw materials supplier, small changes in the formulation or in the product strength, using the same formulation, may be assessed without the need for additional studies on human beings;

b) definition of a quality control procedure which can predict the in vivo performance;

c) the extreme limits of in vitro quality control standards can be justified by a convolution or deconvolution procedure.

2.2. Level B Correlation

Level B correlation uses the same principles of statistical moment analysis. The in vitro average dissolution time is compared to the mean residence time (MRT) or to the in vivo average dissolution time (ADT). In the same way as level A, level B uses all the in vitro and in vivo data, but it is not considered a point to point correlation, because it does not reflect the actual plasma level curve, since a series of different in vivo curves may produce similar values of the mean residence time (MRT). For this reason, unlike level A correlation, it is not possible to consider only level B correlation to assess formulation changes, manufacturing site changes, excipients supplier changes, among others. Moreover, the in vitro data of such correlation can not be used to obtain the extreme limits of the quality control standard.

2.3. Level C Correlation

This category relates a dissolution time point (t50%, t90%, etc) to a pharmacokinetic parameter such as AUC, Cmax or Tmax. It represents a single point correlation. It does not reflect the complete shape of the plasma concentration time curve, a critical factor to define the performance of the modified release products. Since this type of correlation does not allow prediction of the actual performance of the in vivo product, it is useful only as a guide to the development of formulations or as a production quality control routine. Due to its limitations, its usefulness for predicting in vivo drug performance is restricted and is subject to the same restrictions as level B correlation, regarding its capacity to evaluate changes in the product and its manufacturing site, as well as its capacity to provide the extremes of the quality control standard.

3. DEVELOPMENT OF AN IN VITRO-IN VIVO CORRELATION

The procedure described below may be used as a guide to the development of a level A correlation.

The data of urinary excretion or plasmatic levels obtained in a definitive bioavailability study of a modified release dosage form are treated by a deconvolution method. The resulting data may represent the drug input rate of the dosage form, as well as the in vivo dissolution when the rate controlling step of the dosage form is its dissolution (that is, the drug absorption is considered to be instantaneous after the drug is dissolved). Any deconvolution procedure (mass balance or mathematical deconvolution) will produce acceptable results.

The batch used in the bioavailability study (biobatch) is subject to in vitro dissolution evaluation and the effect of varying the dissolution conditions investigated. Some of the variable which can be studied are: the dissolution apparatus, the agitation intensity and the dissolution medium (pH, enzymes, surfactants, osmotic pressure and ionic strength). It is not always necessary to study the dosage form dissolution behavior under all the conditions indicated. The number of conditions under investigation will depend on the correlation that can be found with the results obtained in vitro, under the most commonly studied conditions, such as: the dissolution apparatus, the agitation intensity or dissolution medium and pH value. Each formulation and each drug represents an individual situation. The in vitro evaluation of the dosage form should be done independently from the correlation level being developed.

The in vitro dissolution curve is then compared to the drug input rate curve, which may be obtained through various methods. The simple superimposition of the two mentioned curves may indicate the existence of a correlation. This can then be quantified by defining an equation for each curve and comparing the correspondent constants, by means of an appropriate statistical significance test. The simplest way of demonstrating a correlation is to plot the fraction absorbed in vivo versus the fraction released in vitro. With the level A correlation, this relation is often linear with a slope greater than 0,95. The intercept may or may not be 0, depending on: a) the existence of a lag time, before the system starts releasing the drug in vivo, or b) the non-instantaneous absorption rate, resulting in the presence of a finite quantity of dissolved drug, but not absorbed. In both cases it is a point to point or level A correlation, when the relation is linear, with slope greater than 0,95. This indicates that the curves are essentially superimposable.

In the studies previously mentioned, if the modified release dosage form exhibits an in vitro dissolution behavior independent of the variables studied and a level A correlation is demonstrated, it is probable that the correlation is general and may be extrapolated within reasonable range for that formulation. Nevertheless, if the dosage form exhibits a dissolution behavior which varies with the in vitro conditions, the dissolution conditions which best correlate with the in vivo performance must be determined. It may then be established whether the correlation is real or false. This is obtained by preparing at least two formulations with significant differences in their in vitro behavior. One of them should show faster release and the other slower in relation to that shown by the biobatch. A pilot bioavailability and bioequivalence study should be undertaken with those formulations and the previously established correlation demonstrated for both. The changes in the formulations of these batches must be based on the formulation factors which may influence the modified release mechanisms of the product. Changes in those formulations factors may influence the dosage form's release rate. Once a level A correlation is established, it is possible to use an in vitro test to establish the effects of changes in the manufacturing process such as minor alterations of formulation, manufacturing site, equipment, excipients supplier and the drug strength. It is questionable whether such extrapolation would be possible as far as levels B and C correlations are concerned.

4. ESTABLISHMENT OF THE DISSOLUTION SPECIFICATION LIMITS

The biobatch dissolution behavior may be used to define the quantity of drug to be released at each time point. In the case of a level A correlation this may be done in two ways, both using an in vitro-in vivo correlation, convolution and deconvolution.

4.1 Convolution
Upper and lower dissolution values are selected for each established time point, based on the drug dissolution profile in the biobatch.

The dissolution specification may be established using the average dissolution of the batches produced during development, with a standard deviation range of ±2,5 a 3,0. It is expected that average dissolution values are approximately the same as those of the biobatch. The dissolution curves defined by the upper and lower extreme points are submitted to the convolution technique to project and anticipate the plasma level curves which would result from the administration of these formulations to the same group to which the biobatch was administered. In case the resulting data of plasmatic levels are within the 95% CI, obtained in the definitive bioavailability and bioequivalence study, those ranges may be considered acceptable. An alternative acceptance approach for drugs with a defined therapeutic range is to establish an upper and lower limit, in the case the results of convolution remain within the therapeutic range, even if they are outside the confidence interval. In this case, a more limited range must be established.

4.2. Deconvolution

Acceptable plasma level data are established for both the faster release batch and the slower release batch in relation to the biobatch. These data may be selected using the extreme points of the 95% confidence interval or ± 1 standard deviation from the average plasma level curve. These curves are submitted to deconvolution and the resulting input rate curve is used to establish the upper and lower dissolution specifications at each time point.

In the cases of level B and C correlations, batches of the product must be prepared within the proposed upper and lower dissolution limits and it must be demonstrated that these batches are acceptable by performing a bioavailability-bioequivalence study.

5. GENERAL CONSIDERATIONS ABOUT IMMEDIATE RELEASE DRUG PRODUCTS

As the mechanisms for drug release of the modified release drug products are more complex and varied in relation to those associated to immediate release drug products, it is believed that it would be easier to develop an in vitro-in vivo correlation for the latter. Unfortunately most correlation studies undertaken with immediate release drug products is based on level C correlation in spite of the existence of studies which employ the theory of statistical moment (level B). Although conceivably the same level A correlation may be used with immediate release drug products, level B and C correlations are the best that can be recommended for those drug products.