Biopharmaceutical classification of drugs using intrinsic dissolution rate Essay

The solubility and disintegration rate of active ingredients are of major importance in preformulation surveies of pharmaceutical dose signifiers. In the present survey passively absorbed drugs are classified based on their intrinsic disintegration rate ( IDR ) and their enteric permeablenesss. Intrinsic disintegration rate was determined by mensurating the disintegration of a non-disintegrating disc of drug and effectual enteric permeableness of tried drugs in rat jejunum was determined utilizing individual perfusion technique. The obtained intrinsic disintegration rate values were in the scope of 0.035-56.8 mg cm-2 min-1 for tried drugs. The minimal and maximal enteric permeablenesss in rat bowel were determined to be 1.6A-10-5 and 2A-10-4 cm/sec severally. Four categories of drugs were defined, i.e. Class I: Peff, rat & gt ; 5A- 10-5 ( cm/sec ) or Peff, human & gt ; 4.7A- 10-5 ( cm/sec ) , IDR & gt ; 1 ( mg/min/cm2 ) , Category II: Peff, rat & gt ; 5A- 10-5 ( cm/sec ) or Peff, human & gt ; 4.7A- 10-5 ( cm/sec ) , IDR & lt ; 1 ( mg/min/cm2 ) , Category III: Peff, rat & lt ; 5A- 10-5 ( cm/sec ) or Peff, human & lt ; 4.7A- 10-5 ( cm/sec ) , IDR & gt ; 1 ( mg/min/cm2 ) and Category IV: Peff, rat & lt ; 5A- 10-5 ( cm/sec ) or Peff, human & lt ; 4.7A- 10-5 ( cm/sec ) , IDR & lt ; 1 ( mg/min/cm2 ) . Harmonizing the obtained consequences and proposed categorization for drugs, it is concluded that drugs could be categorized right based on their intrinsic disintegration rate and enteric permeableness values.

Keywords: Intrinsic disintegration rate, enteric Permeability, Biopharmaceutics.


The solubility and disintegration rate of active ingredients are of major importance in preformulation surveies of pharmaceutical dose signifiers ( 1-6 ) . The preparation features including shelf life, procedure behaviour, and even the bioavailability are affected by physicochemical belongingss of drug molecules ( 7 ) . The intrinsic disintegration rate ( IDR ) has been used to qualify solid drugs for many old ages ( 8, 9 ) . For illustration it could be used to understand the relationship between the disintegration rate and crystalline signifier and besides to analyze the effects of wetting agents and pH on the solubilization of ill soluble drugs ( 10, 11 ) . IDR is by and large defined as the disintegration rate of a pure drug substance under the status of changeless surface country, agitation or stirring velocity, pH and ionic strength of the disintegration medium. The true intrinsic disintegration rate may be better described as the rate of mass transportation from the solid surface to the liquid stage. The setup for intrinsic disintegration testing was originally developed by John Wood which enables the computation of the disintegration rate per centimetre squared of the intrinsic ingredients of pharmaceutical merchandises ( 12-14 ) . It has been suggested that it might be executable to utilize IDR to sort drugs alternatively of solubility ( 9 ) . The ground is that, merely like permeableness, IDR is a rate phenomenon alternatively of an equilibrium phenomenon. Therefore it might correlate better with in vivo drug disintegration rate than solubility, although for drugs holding either highly high or low dosage, disagreements may be between the solubility and IDR methods ( 9 ) since dosage is considered in the categorization of solubility while intrinsic disintegration does non see the consequence of dosage. On the other manus there are a figure of in vitro and in situ experimental theoretical accounts have been developed which determine the enteric absorbent potency of a drug and the mechanism of soaking up ( 15, 16 ) . Among these methods single-pass enteric perfusion ( SPIP ) attack is the most often used technique which provides conditions closer to what is faced following unwritten disposal. SPIP technique possesses a preserved microclimate above the enteric membrane which makes it less sensitive to pH fluctuations. This technique provides the alone advantages of experimental control ( compound concentration and enteric perfusion rate ) and the ability to analyze regional differences ; factors that may act upon the enteric soaking up of a compound. In the present survey the intrinsic disintegration rate and rat enteric permeableness ( utilizing SPIP technique ) were measured for drugs with different physicochemical belongingss. The suitableness of IDR-permeability for biopharmaceutical categorization of drugs was evaluated.

Materials and methods


Naproxen, Tenormin, Lopressor, propranolol, verapamil hydrochloride and isobutylphenyl propionic acid were provided from Shasun ( Shasun Chemical & A ; Drugs LTD, India ) . Ketoprofen and antipyrine were from Sigma ( Sigma, Canada ) and Hoechst ( Hoechst, Germany ) severally. Furosemide and Microzide was provided from Fls ( Fls, Italy ) . Ranitidine and Tagamet were obtained from Uquifa ( Uquifa, Spain ) and Feldene was from Ciba-Geigy ( Barcelona, Spain ) . Monobasic K phosphate ( KH2PO4 ) and sodium hydrated oxide ( NaOH ) were purchased from Merck ( Darmstadt, Germany ) .


Procedure of IDR measuring

A measure of 100 milligrams of each drug was compressed at an mean compaction force of 7.84 MPa for 1 minute to do non-disintegrating compacts utilizing dice and clout with diameter of 6 millimeter. In order to forestall capping, in the instance of Feldene and carbamazepine the compaction force were 1.96 and 19.6 MPa severally. The surface country of the compacts was 0.2826 cm2. The improved method of wood et Al was used for disc disintegration surveies ( 14 ) . Compacts were placed in a liquefied beeswax-mold in such a manner that merely one face could be in contact with disintegration medium. Dissolution survey was conducted utilizing USP II disintegration setup utilizing 900mL of phosphate buffer ( pH=6.8 ) at temperature of 37A°C A± 1A°C as the disintegration media with paddle revolving at 100 revolutions per minute. Samples were collected through 0.45-Aµm syringe filters over a period of 8 hours for low-soluble and 20 proceedingss for extremely soluble drugs. Sampling clip intervals were 30 min and 2 min severally. All surveies were carried out in triplicate. Optical densities were determined in triplicate utilizing a UV-Vis spectrophotometer ( UV160, Shimadzu, Kyoto, Japan ) at the maximal optical density wavelength for each active tested ( Table 1 ) . The cumulative sum dissolved per surface unit of the compact was plotted against clip for each vas. The incline of the additive part ( R2a‰? 0.95 ) was taken as intrinsic disintegration rate. IDR is easy calculated by

G = ( dw/dt ) ( 1/S ) = DCs/h Eq.1

where G is intrinsic disintegration rate ( mg/min/cm2 ) ; dw is the alteration in drug dissolved ( milligram ) ; dt is the alteration in clip ( proceedingss ) ; S is the surface country of the compact ( cm2 ) ; D is diffusion coefficient ( cm2/sec ) ; Cs is solubility ( mg/cm3 ) and H is dead bed thickness ( centimeter ) .

Solubility surveies

Solubilities were determined in at least triplicates by equilibrating extra sum of drugs in phosphate buffer solutions ( pH=6.8 ) . The samples were kept in thermostated H2O bath at 37A°C and shaked at a rate of 150 revolutions per minute for 24 hours. The optical densities of filtered and appropriately diluted samples were measured with an UV-VIS spectrophotometer ( ( UV160, Shimadzu, Kyoto, Japan ) at the maximal optical density wavelength for each active tested. The solubilities were calculated utilizing standardization curves determined for each drug.

Measurement of rat enteric permeableness coefficients:

The anaesthesia and surgery were performed in conformity with a antecedently validated in situ enteric perfusion method in rats ( 17 ) . Detailss of the process, analytical methods and besides permeableness coefficient computation were explained in writers published plants ( 16, 18, 19 ) . Briefly, male Wistar rats ( weight, 250-300 g ; age, 7-9 hebdomads ) were maintained on 12 h light- dark rhythm and fasted 12-18 H before experiment. On the twenty-four hours of experiment a individual base on balls changeless flow ( 2 ml/min ) of drug incorporating perfusate ( PBS pH=7.2, 37oC ) was established through the ligated rat jejunal section and the mercantile establishment samples were collected every 10 min in microtubes up to 90 min and stored at -20oC until analysis. Finally the animate being was euthanitized with a cardiac injection of concentrated solution of KCl. In all carnal surveies “ Guide to the attention and usage of experimental animate beings ” by Canadian Council on Animal Care, was followed ( 20 ) . Permeability values were calculated utilizing following equation harmonizing to the parallel tubing theoretical account:

Peff = -Q ln ( Cout ( corrected ) /Cin ) /2Iˆrl Eq.2

In which Cin and Cout are the recess and mercantile establishment concentrations of compound severally. Cout is corrected for volume alteration in section utilizing phenol ruddy concentration in recess and mercantile establishment tube. Q is the flow rate ( 0.2 ml/min ) , R is the rat enteric radius ( 0.18 centimeter ) and cubic decimeter is the length of the enteric section ( 16, 21 ) .


Current BCS counsel defines an API as “ extremely soluble ” when the highest dosage recommended is soluble in 250 milliliter or less of aqueous media over the pH scope of 1.2 to 7.5 ( 22 ) . However the pH 6.8 is scientifically justified over pH 7.4 ( 22, 23 ) . In order to put a status for BCS categorization of compounds and since little bowel is the major site for drug soaking up, where the pH is about 6.8, IDR measurings were conducted in pH 6.8. Table 1 shows the solubility of theoretical account drugs at 37A°C in pH=6.8. The high solubility of Zantac in experimental status and making viscose solution in high concentrations made it hard to assay its exact solubility ( 24 ) . The determined intrinsic rates of disintegration are besides given in Table 1. The presence of sink status in disintegration medium during the experiment is upholded by comparing of the concluding concentration of drugs and their solubility in disintegration medium. As seen in the Table 1, the superior order of aqueous solubility and IDR are about but non precisely the same. In general, compounds with high solubility exhibited IDR of greater than 3 mg/cm2/min but compounds with low solubility had IDR of less than 1 mg/cm2/min. However antipyrin which showed greatest IDR amongst the tried compounds, was determined to be less soluble than Zantac and Lopressor. Furosemide exhibited higher IDR but somewhat lower solubility in comparing to naproxen. In the same manner Feldene exhibited higher IDR but somewhat lower solubility in comparing to carbamazepine. This could be explained by the fact that unlike solubility, IDR is a rate phenomenon and besides solubility is dependent on wetability and diffusivity of the compound ( 25 ) .

The ascertained enteric permeableness values in rats for tested drugs ( 16 ) are besides presented in Table 1. For comparing the several enteric permeableness and fraction of dose absorbed in homo are besides cited. Categorization of tested drugs based on their enteric permeableness and IDR for human and rat is shown in Fig. 1 and Fig. 2 severally.


Drugs are scientifically identified based on their solubility and human enteric permeableness ( 26 ) . The biopharmaceutics categorization system ( BCS ) , consists of four drug classs: category I ( extremely soluble and extremely permeable ) , category II ( low soluble and extremely permeable ) , category III ( extremely soluble and low permeable ) and category IV ( low soluble and low permeable ) . Since human enteric permeableness could be predicted with precise utilizing the rat effectual permeableness values ( 16 ) , the same categorization can be constructed using the solubility and rat enteric permeableness values ( 27 ) . IDR is a parametric quantity which could be used easy to qualify the pure drug substance. The finding of this parametric quantity allows labs to screen experimental drug preparations and to understand their behaviour under different bio-physical conditions. Table 1 shows the obtained solubility and IDR values in the present work for tried drugs. The obtained IDR values on the tested drugs in the present work are somewhat greater than those reported by Yu et Al. ( 9 ) . It might be ascribed to the different method of IDR measuring by the two probes. However the superior order of the obtained IDR values is the same. The obtained solubility informations was in understanding with those in literature as good ( 28 ) .

Comparing rat Peff values with those of human showed a high arrested development correlativity ( R2=0.93, P & lt ; 0.0001 ) for passively captive compounds corroborating a close relationship between rat and human permeablenesss ( 16 ) . The fraction of dose absorbed ( Fa ) in homo is the footing of the permeableness categorization. In the FDA Guidance, an active pharmaceutical ingredient is extremely permeable when the fraction of dose absorbed is 90 % or more. The late revised WHO Guidelines sets a lower bound of 85 % . ( 29-31 ) . Yu et Al. proposed to cut down the high permeableness demand for biowaiver from 90 to 85 % ( 22, 32 ) . On the footing of the relationship between permeableness and fraction of dose absorbed ( 16 ) , Peff values greater than 5.09A-10-5 and 4.7 A-10-5 cm/sec in rat and human severally corresponds to Fa & gt ; 85, which were set as cut-off points for extremely permeable drugs.

On the other manus, IDR correlates with the BCS solubility categorization with 1-2 mg/min/cm2 as a category boundary. It is seen that antipyrin, Zantac and Lopressor with IDRs of 56.79, 42.18 and 34.64 mg/cm2/min severally have the higher values in comparing to others whereas carbamazepine and Feldene have the lowest intrinsic disintegration rate in the series ( IDR=0.035 and 0.07 mg/cm2/min severally ) . As was mentioned before, this order is about the same for solubility of mentioned drugs. However in the instance of permeableness this agreement is non expected. The ground is that the investigated drugs belong to all four biopharmaceutical categories. That means a drug with high IDR value may belong to high or low permeableness categories.

In the present survey passively absorbed drugs are classified based on their intrinsic disintegration rates and human enteric permeableness values. IDR was expected to correlate more closely with in vivo disintegration kineticss of drug than solubility ( 9 ) . Therefore it might be used to rectify assignment of a drug to a specific BCS category. The proposed categorization is presented in Fig. 1 and Fig. 2 utilizing human and rat jejunal permeableness severally. Based on this categorization, drugs are placed in four explicitly defined classs ( I-IV ) which are made by intersections of dotted lines drawn at the cutoff points for permeableness and IDR. These categories are characterized as below:

Class I: Peff, rat & gt ; 5A- 10-5 ( cm/sec ) or Peff, human & gt ; 4.7A- 10-5 ( cm/sec ) , IDR & gt ; 2 ( mg/min/cm2 )

Examples of the compounds of this class include propranolol, Lopressor, Calan and antipyrin which exhibit a high disintegration and soaking up. However harmonizing to enteric permeableness estimations in rat, Lopressor is assigned in category III.

Category II: Peff, rat & gt ; 5A- 10-5 ( cm/sec ) or Peff, human & gt ; 4.7A- 10-5 ( cm/sec ) , IDR & lt ; 1 ( mg/min/cm2 )

Drugs like Orudis, naproxen, Feldene, isobutylphenyl propionic acid and carbamazepine are included in this class. Class II drugs have a high soaking up but a low disintegration therefore soaking up is limited chiefly by drug disintegration in the GI piece of land ( 26 ) .

Category III: Peff, rat & lt ; 5A- 10-5 ( cm/sec ) or Peff, human & lt ; 4.7A- 10-5 ( cm/sec ) , IDR & gt ; 2 ( mg/min/cm2 )

Class III drugs, have high disintegration and low soaking up. In vivo permeableness is rate restricting measure for drug soaking up ( 26 ) . Examples are atenolol, Zantac and Tagamet.

Category IV: Peff, rat & lt ; 5A- 10-5 ( cm/sec ) or Peff, human & lt ; 4.7A- 10-5 ( cm/sec ) , IDR & lt ; 1 ( mg/min/cm2 )

Furosemide is an illustration of drugs of this class which exhibit a batch of jobs for effectual unwritten disposal.

From the obtained consequences it is provided that the presented categorization based on IDR and human enteric permeableness of drugs is in high understanding with antecedently introduced categorization and most of the compounds are placed in right classs they belong to ( 26 ) . Although utilizing the rat enteric permeableness values alternatively of human enteric permeableness, Lopressor was about misclassified, sing non-feasibility of utilizing human in enteric perfusion surveies, which is the major trouble in delegating drugs to BCS categories, it may be suggested that determined enteric permeableness of drugs in rats could be used as a standard for biopharmaceutical categorization of compounds.

On the other manus, it was proposed that a biopharmaceutics drug temperament categorization system ( BDDCS ) based on extent of drug metamorphosis could supply an alternate simple method to delegate drugs in category I for a release of in vivo bioequivalence surveies ( 33-35 ) . Harmonizing to this categorization extremely metabolized drugs exhibit high permeableness. Therefore a drug is considered to be category I if it is extremely soluble and extremely metabolized. However this definition excludes drugs that have high soaking up but are excreted unchanged in to bile and urine ( 33 ) . Comparison of our consequences with BDDCS categorization ( a‰?50 % being defined as extended metamorphosis ) of drugs ( 35 ) shows high understanding ( 92 % and 85 % utilizing human and rat enteric permeableness severally ) in categorization of tried compounds ( Table 1 ) .

Another categorization system viz. dissolution-based categorization was developed by Papadopoulou et Al ( 36 ) utilizing average enteric theodolite clip ( MITT ) , average disintegration clip ( MDT ) and average soaking up clip ( MAT ) . The comparing of this categorization with our consequences is besides shown in Table 1. However in dissolution-based categorization propranolol and carbamazepine are classifies as category II and category IV drugs severally which are expected to be assigned in category I and II severally as was shown in other categorizations in Table 1.

It seems that the presented categorization could be used to relinquish in vivo bioavailability and bioequivalence surveies for immediate release solid unwritten dose signifiers which allows pharmaceutical companies to predate clinical bioequivalence surveies, if their drug merchandise meets the needed specification. Furthermore it may besides be applied to new drug application ( NDA ) and brief new drug application ( ANDA ) blessings every bit good as to scale-up and station blessing alterations in drug fabrication. BCS categorization can therefore save pharmaceutical companies a important sum in development clip and cut down costs.A


In this survey a biopharmaceutical categorization system was developed based on two rule belongingss, intrinsic disintegration rate at pH 6.8 and rat/human enteric permeableness of passively absorbed drugs. This categorization is about in understanding with antecedently introduced categorization system on the footing of drug ‘s solubility and human enteric permeableness.