protocol to conduct equilibrium …...working document qas/17.699/rev.2 page 2 schedule for the...

Working document QAS/17.699/Rev.2

July 2018

Draft document for comments

PROTOCOL TO CONDUCT EQUILIBRIUM SOLUBILITY 1

EXPERIMENTS FOR THE PURPOSE OF 2

BIOPHARMACEUTICS CLASSIFICATION SYSTEM-BASED 3

CLASSIFICATION OF ACTIVE PHARMACEUTICAL 4

INGREDIENTS FOR BIOWAIVER 5

(July 2018) 6

TAKEN FROM DRAFT NOTES ON THE CONDUCT OF SOLUBILITY STUDIES (AUGUST 2017) 7

REVISED DRAFT FOR DISCUSSION 8

9

© World Health Organization 2018 10 All rights reserved. 11 This draft is intended for a restricted audience only, i.e. the individuals and organizations having received this draft. The 12 draft may not be reviewed, abstracted, quoted, reproduced, transmitted, distributed, translated or adapted, in part or in whole, 13 in any form or by any means outside these individuals and organizations (including the organizations' concerned staff and 14 member organizations) without the permission of the World Health Organization. The draft should not be displayed on any 15 website. 16 Please send any request for permission to: 17 Dr Sabine Kopp, Group Lead, Medicines Quality Assurance, Technologies Standards and Norms, Department of Essential 18 Medicines and Health Products, World Health Organization, CH-1211 Geneva 27, Switzerland, fax: (41-22) 791 4856, 19 e-mail: [email protected]. 20 The designations employed and the presentation of the material in this draft do not imply the expression of any opinion 21 whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or 22 of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted lines on maps represent approximate 23 border lines for which there may not yet be full agreement. 24 The mention of specific companies or of certain manufacturers’ products does not imply that they are endorsed or 25 recommended by the World Health Organization in preference to others of a similar nature that are not mentioned. Errors 26 and omissions excepted, the names of proprietary products are distinguished by initial capital letters. 27 All reasonable precautions have been taken by the World Health Organization to verify the information contained in this 28 draft. However, the printed material is being distributed without warranty of any kind, either expressed or implied. The 29 responsibility for the interpretation and use of the material lies with the reader. In no event shall the World Health 30 Organization be liable for damages arising from its use. 31 This draft does not necessarily represent the decisions or the stated policy of the World Health Organization. 32

Should you have any comments on the attached text, please send these to Dr Valeria Gigante, Technical

Officer, Medicines Quality Assurance, Technologies Standards and Norms ([email protected]) with a

copy to Mrs Xenia Finnerty ([email protected] ) by 30 September 2018.

Working documents are sent out electronically and they will also be placed on the Medicines website

(http://www.who.int/medicines/areas/quality_safety/quality_assurance/guidelines/en/) for comments

under the “Current projects” link If you have not already received our draft guidelines, please send

your e-mail address to [email protected] and we will add you to our electronic mailing list.

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mailto:[email protected]



http://www.who.int/medicines/areas/quality_safety/quality_assurance/guidelines/en/



page 2

SCHEDULE FOR THE PROPOSED USE OF DOCUMENT QAS/17.699/Rev.2: 33

PROTOCOL TO CONDUCT EQUILIBRIUM SOLUBILITY EXPERIMENTS FOR THE 34

PURPOSE OF BIOPHARMACEUTICS CLASSIFICATION SYSTEM-BASED 35

CLASSIFICATION OF ACTIVE PHARMACEUTICAL INGREDIENTS FOR 36

BIOWAIVER 37

Presentation to the forty-seventh meeting of the WHO Expert

Committee on Specifications for Pharmaceutical Preparations (ECSPP).

ECSPP recommended to update the WHO Biowaiver List.

October 2012

Presentation to the forty-eighth meeting of the WHO ECSPP. ECSPP

recommended to continue revisions and to align the WHO Biowaiver

List with the 18th Model List of Essential Medicines (EML).

October 2013

Discussion during an informal consultation held together with

regulatory experts from national regulatory authorities, the WHO

Prequalification Team: medicines (PQTm) and the WHO Collaborating

Centre for Research on Bioequivalence Testing of Medicines,

Frankfurt/Main, Germany.

5–6 July 2014

Presentation to the forty-ninth meeting of the ECSPP. ECSPP

recommended to continue revisions of the WHO Biowaiver List in a

format that facilitates updating in line with the EML.

October 2014

Presentation to the fiftieth meeting of the ECSPP and discussion of the

remaining revisions before public consultation. Adoption of the revised

Multisource (Generic) Pharmaceutical Products: Guidelines on

Registration Requirements to Establish Interchangeability (WHO

Technical Report Series, No. 992, 2015) which includes a chapter on in

vitro equivalence testing in the context of the Biopharmaceutics

Classification System (BCS) and qualification for a biowaiver based on

the BCS.

October 2015

Visit of the WHO Collaborating Centre for Research on Bioequivalence February 2016


page 3

Testing of Medicines, from Frankfurt/Main, Germany, to review and

discuss the progress made.

Presentation of the WHO Biowaiver List and revisions at the Biowaiver

Working Group of the International Generic Drug Regulators

Programme (IGDRP).

May 2016

Discussion during an informal consultation held together with

regulatory experts from national regulatory authorities, PQTm and the

WHO Regulatory Systems Strengthening team (RSS).

8–9 July 2016

Presentation to the 51st meeting of the ECSPP. October 2016

Development of the proposal for conduct of solubility studies by Dr

John Gordon in connection with the Proposal to Waive In Vivo

Bioequivalence Requirements for WHO Model List of Essential

Medicines, Immediate-Release, Solid Oral Dosage Forms (WHO

Technical Report Series, No. 937, 2006, Annex 8).

March 2017

Proposal discussed with experts from national quality control

laboratories and specialists in assessing bioequivalence data. April–June 2017

Proposal discussed during the Joint Meeting on Regulatory Guidance

for Multisource Products with Regulators with the WHO Medicines

Quality Assurance group, the Prequalification of Medicines team

(PQTm), and the Regulatory Systems Strengthening team held in

Copenhagen, Denmark.

7–8 July 2017

Revision of text including feedback received. August 2017

Mailing and posting of the working document on the WHO website for

public consultation. September 2017

Compilation of comments received. October 2017

Presentation to the 52nd ECSPP .* 16–20 October 2017

Preparation of draft Protocol to conduct equilibrium solubility

experiments for the purpose of BCS-based classification of APIs for November 2017

http://www.who.int/entity/medicines/areas/quality_safety/quality_assurance/ProposalWaiveVivoBioequivalenceRequirementsModelListEssentialMedicinesImmediateReleaseSolidOralDosageFormsTRS937Annex8.pdf?ua=1




page 4

biowaiver and the Model Certificate of equilibrium solubility

experiments for BCS-based classification of APIs for biowaiver (Annex

1) by Dr Valeria Gigante, WHO Medicine Quality Assurance group

(MQA), Dr John Gordon from PQTm, Professor Giovanni Pauletti,

Professor Marival Bermejo, Professor Virginia Merino Sanjuán,

Professor Carla M. Caramella, Mr Xu Mingzhe and Professor Jin

Shaohong.

Circulation for comments to experts and compilation of comments

received for the Protocol and the Model Certificate of equilibrium

solubility experiments for BCS-based classification of APIs for

biowaiver.

December 2017

Start of APIs equilibrium solubility studies for BCS-based classification

by Professor Giovanni Pauletti, Professor Marival Bermejo, Professor

Virginia Merino Sanjuán, Mr Xu Mingzhe and Professor Jin Shaohong.

Collation of regulatory information from the European Medicines

Agency (EMA), Agência Nacional de Vigilância Sanitária (ANVISA)

and PQTm.

February 2018

Protocol and Model Certificate (Annex 1) optimization during the WHO

pilot project for BCS-based classification of API for biowaiver. March–April 2018

Presentation of regulatory documents and tests results during the Joint

Meeting on Regulatory Guidance for Multisource Products

with MQA and PQTm in Copenhagen, Denmark.

18–19 May 2018

Updated Protocol and Model Certificate of equilibrium solubility

studies for BCS-based classification of APIs mailed and posted for

public consultation.

June–September 2018

Consolidation of comments received. September 2018

Presentation of updated Protocol and Model Certificate of equilibrium

solubility experiments for BCS-based classification of APIs for

biowaiver to the 53rd meeting of the ECSPP.

22–26 October 2018

Any other follow-up action as required.


page 5

*Background Information 38

Extract from the 52nd ECSPP. WHO Technical Report Series, No. 1010, 2018: 39

8.2.1. Revision of the biowaiver list 40

As part of its 2006 guidance on waiving of bioequivalence requirements for immediate-release oral solid dosage 41

forms on the WHO EML, WHO had provided a list of APIs that are eligible for biowaivers. The intention is for this 42

list to be updated and maintained as a living document on the WHO website. In 2016 it was agreed that the list 43

should be based on verified laboratory data instead of a literature-based approach. The WHO Secretariat intends 44

to coordinate a new multicentre project to determine the solubility profiles of APIs contained in medicines on the 45

WHO EML to enable an informed decision on whether a biowaiver could safely be granted. The WHO Secretariat 46

proposed that the Expert Committee contribute to updating the biowaiver list by proposing appropriate 47

laboratories to perform the tests, review experimental protocol templates, review laboratory results, determine the 48

APIs’Biopharmaceutics Classification System (BCS) class, and/or participate in the publication of results. A 49

number of members responded positively to the WHO Secretariat’s call for support for the envisaged studies. 50

The Committee noted the report on the update of the WHO biowaiver list. WHO gratefully acknowledged the 51

support offered by the members of the Expert Committee. 52

8.2.2 Conduct of solubility studies 53

During the design of studies to support the revision of the WHO biowaiver list, it became apparent that more 54

guidance was needed on how to design and conduct solubility studies for the purpose of classifying APIs within 55

the BCS. A guidance text was drafted in March 2017, building on recently adopted WHO guidance on 56

equilibrium solubility experiments and on the general chapter on solubility measurements included in the 57

Brazilian Pharmacopoeia in 2016. The proposed guidance was discussed with relevant specialists and at a 58

joint meeting on regulatory guidance held in July 2017. The proposal was further revised and circulated for 59

public consultation in September 2017. It was presented to the Committee at its fifty-second meeting together 60

with comments received. 61

The Committee noted the update on this draft guidance and endorsed the proposed approach to conducting the 62

solubility studies, using this guidance as part of the protocol. Equilibrium solubility experiments for the 63

purpose of classification of active pharmaceutical ingredients according to the biopharmaceutics classification 64

system, Appendix 2 to Multisource (generic) pharmaceutical products: Guidelines on registration requirements 65

to establish interchangeability. In: WHO Expert Committee on Pharmaceutical Preparations. Fifty-first report. 66

Geneva: World Health Organization; 2017: Annex 6 (WHO Technical Report Series, No. 1003). 67

The Committee endorsed the proposed approach to conducting solubility studies for the purpose of revising the 68

WHO biowaiver list.” 69


July 2018


PROTOCOL TO CONDUCT EQUILIBRIUM SOLUBILITY EXPERIMENTS FOR 70

THE PURPOSE OF BIOPHARMACEUTICS CLASSICIATION SYSTEM-BASED 71

CLASSIFICATION OF ACTIVE PHARMACEUTICAL INGREDIENTS FOR 72

BIOWAIVER 73

74

1. OBJECTIVE OF THE DOCUMENT 75

The objective of this document is to provide guidance on the design and conduct of equilibrium 76

solubility studies undertaken for the purpose of active pharmaceutical ingredient (API) 77

classification within the Biopharmaceutics Classification System (BCS) (1,2). Notably, the 78

definition and guidance given in this document to perform solubility studies apply to APIs and 79

there might be differences in requirement from the conditions for dissolution studies applicable 80

to finished solid pharmaceutical products (FPP). 81

A study protocol has been developed to provide a harmonized approach when performing 82

solubility studies. 83

2. EXPERIMENTAL CONSIDERATIONS 84

Overall, the API sample should be dissolved/suspended in the buffer, then separated by 85

appropriate methods and, in the end, its concentration should be determined in the liquid 86

phase/supernatant. 87

According to the World Health Organization (WHO) definition given in the guidance document 88

Multisource (Generic) Pharmaceutical Products: Guidelines on Registration Requirements to 89

Establish Interchangeability (3), an API is considered highly soluble when the highest single 90

therapeutic dose as determined by the relevant regulatory authority, typically defined by the 91

labelling for the innovator product, is soluble in 250 mL or less of aqueous media over the pH 92

range of 1.2–6.8. The pH solubility profile of the API should be determined at 37 ± 1 °C in 93

aqueous media. A minimum of three replicate determinations of solubility at each pH condition 94

is recommended (3). 95


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In general, equilibrium solubility experiments should be employed. However, in exceptional 96

cases, where the API is not available in sufficient quantities, and is prohibitively expensive, or 97

when it is not possible to maintain the pH of the medium with pharmacopoeial buffers, 98

experiments where the highest therapeutic single dose as recommended by the approved 99

label/summary of product characteristics (SmPC) is examined in a 250 mL volume, or a 100

proportionally smaller amount examined in a proportionally smaller volume of buffer, can be 101

considered. As these are equilibrium solubility experiments, small volumes of solubility media 102

(e.g. 50 mL) may be employed without issue if the available experimental apparatus will permit 103

it. 104

The source and purity of the API should be reported according to the Model Certificate of 105

equilibrium solubility experiments for BCS-based classification of APIs for biowaiver (Annex 106

1). Additional characterization of the solid API used in the solubility experiments may be 107

necessary. The depth of the characterization will depend on the existing knowledge of the solid-108

state properties of the API in question. For example, if it has been established that the API 109

exists as a single polymorphic form, then less solid-state characterization is necessary. 110

111

The “shake flask” method for solubility determination is recommended; a mechanical agitation 112

device should be used (e.g. orbital shaker) and an appropriate validation method should also be 113

employed. The device used should be capable of maintaining a temperature of 37 ± 1 °C and an 114

appropriate agitation speed that ensures particle contact with the diluent. The agitation speed 115

should be optimized based on the shape of the flask or tube and volume of the liquid in order to 116

prevent particle agglomeration and ensure particle contact with the diluent. Vortex formation 117

should be avoided. With an optimized agitation rate, it is expected that samples will generally 118

reach equilibrium within 24 hours (4). Samples should be taken at several time points to verify 119

that equilibrium has been reached. 120

121

To address issues such as poor wettability and the tendency of the API to float on the surface of 122

the solubility medium, it may be necessary to include tools such as glass microspheres to aid in 123

the de-aggregation of the particles with agitation or sonication (4). Once wetting is successfully 124

achieved, the solubility experiment should proceed toward equilibrium. 125

126

127


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3. BUFFERS FOR EQUILIBRIUM SOLUBILITY DETERMINATION 128

The pH-solubility profile of the API should be determined over the pH range of 1.2–6.8, with 129

the API’s solubility classification being based on the lowest solubility measured over this pH 130

range. Measurements should be made in triplicate or more, according to the study variability, 131

under at least three pH conditions, pH 1.2, 4.5 and 6.8 using, for example, 0.1 M HCl solution or 132

simulated gastric fluid without enzymes pH 1.2, acetate buffer pH 4.5, and phosphate buffer pH 133

6.8 solution. If there are any known solubility minima for the API in aqueous media within that 134

pH range (for example the pKa of the API when within this range), data should also be collected 135

at that pH. Pharmacopoeial buffer solutions are recommended for use in solubility experiments 136

as reported below. Adjust the pH of the buffers at the same temperature as the equilibrium 137

solubility experiments are performed, i.e. at 37 °C +1 °C. The pH should be verified after 138

addition of the API and at the end of the experiment with a calibrated pH meter. If the pH of the 139

buffer changes upon combination with the solute, adjustment of the pH with an appropriate acid 140

or base solution may be sufficient to address the issue, or a buffer with a stronger buffering 141

capacity may be employed. After adjustment of the pH, the solution should be allowed to re-142

equilibrate for at least an hour before a sample is taken. 143

3.1 Buffers composition 144

Buffer pH 1.2, TS (test solution) 145

Dissolve 2.52 g of sodium chloride R (Reagent) in 900 mL of water R, adjust 146

the pH to 1.2 with hydrochloric acid (~70 g/L) TS and dilute to 1000 mL with 147

water R. 148

Buffer pH 4.5, TS 149

Dissolve 2.99 g of sodium acetate R in 900 mL of water R, adjust the pH to 150

4.5 by adding about 14 mL of acetic acid (~120 g/L) TS and dilute to 1000 mL 151

with water R. 152

Buffer pH 6.8, TS 153

Dissolve 6.9 g of sodium dihydrogen phosphate R and 0.9 g of sodium 154

hydroxide R in 800 mL of water R, adjust the pH to 6.8 with sodium 155

hydroxide (~80g/L) TS and dilute to 1000 mL with water R. 156


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Information on the reagents to be used can be found by consulting the International 157

Pharmacopoeia, Reagents, Test Solutions and Volumetric Solutions Section, 158

http://apps.who.int/phint (5). 159

160

4. EXPERIMENTAL DESIGN 161

162

The details of the solubility experiment’s design should be based on the characteristics of the 163

API under investigation. It is recommended that preliminary testing be conducted to assess the 164

amount of API required and the length of time required for the pivotal solubility experiment. 165

166

5. PRELIMINARY ASSESSMENT OF TIME TO EQUILIBRIUM AND 167

EXPECTED SOLUBILITY 168

169

Preliminary estimation of solubility from chemical structure is suggested as a starting point, 170

using an open source tool (e.g. ChemSpider www.chemspider.com; Virtual Computational 171

Chemistry Laboratory http://www.vcclab.org; Swiss ADME http://www.swissadme.ch ) or 172

by estimating this data. 173

174

From this calculation, determine the amount of solid needed to have approximately 30–40% 175

excess of undissolved solid in 5 mL (or the selected working volume) of buffer solutions at 176

pH 1.2, 4.5, and 6.8. Weigh this amount of solid and put in, for instance a 10 mL tube, if 5 177

mL of the buffer will be used (corresponding to the expected minimum solubility condition). 178

If the solubility is greater than expected, reduce volume to 3 mL while if the expected 179

solubility is low and the API is available in sufficient quantity, use higher volumes. 180

181

Alternatively, the volume can be kept at 5 mL and the mass can be increased or reduced as 182

appropriate. 183

184

Check for the presence of undissolved solid; if the entire solid dissolves when adding the 185

buffer, additional solid should be added until such time that some solid remains undissolved 186

in the tube. To solve any potential issues related to solid wettability or agglomeration, put the 187

tubes in the agitation system such as shaker or magnetic stirrer adding glass beads. 188

http://apps.who.int/phint

http://www.chemspider.com/

http://www.vcclab.org/

http://www.swissadme.ch/


page 10

When the amount of solute and volume of buffer has been determined to obtain a saturated 189

solution, minimum three replicates samples for each pH should be prepared to allow 190

measurements at 2, 4, 8, 24, 48, and 72 hours to identify the equilibration time. 191

192

Filtration is normally recommended to remove undissolved API from collected samples, 193

although centrifugation is a valid alternative method, particularly if the medium volume is small. 194

Filter the samples (using, for example, a filter pore size of 0.45 μ) immediately after withdrawal 195

or separate dissolved from undissolved API by centrifugation as appropriate. 196

197

Solubility experiments are performed at 37 +1 ºC; therefore, if samples are to be left at room 198

temperature until analysis, samples should be diluted immediately after centrifugation or 199

filtration in order to avoid precipitation of the solute. This should be taken into account for 200

back calculations. 201

202

To determine equilibrium solubility, the concentration of the solution should be measured at 203

different time points (approximately six; i.e. 2, 4, 8, 24, 48, and 72 hours) until it does not 204

deviate significantly between each measurement. The shortest time needed for reaching the 205

plateau of drug concentration against time could be considered a suitable equilibration time. 206

Collect samples over time to establish a plateau for the amount of solute dissolved and also to 207

monitor stability of the API at each pH (see below). 208

209

Measure the pH value of the buffer solutions after establishing the time to obtain equilibrium. 210

211

6. STABILITY 212

213

The API’s stability across the pH range should be monitored in order to measure true solubility 214

(6,7). 215

216

To distinguish the drug substance from its degradation products, a validated, stability-indicating 217

analytical method should be employed for solubility determination of APIs such as those 218

indicated in the Ph. Int. or other Pharmacopoeias adapted as appropriate, if available, e.g. high-219

performance liquid chromatographic (HPLC) analysis (see chapter 1.14.4 High-performance 220

liquid chromatography in The International Pharmacopoeia (5)) or an alternative, validated 221

stability-indicating assay. An advantage of an HPLC method over a spectrophotometric method 222


page 11

is that the HPLC method can also be employed to detect impurities and instability (6,7). If 223

degradation of the drug substance is observed as a function of buffer composition and/or pH, it 224

should be reported. If a stability-indicating analytical method is not available, separate stability 225

experiments will be necessary to demonstrate that the API is stable in the buffer media 226

employed. 227

228

7. RECOMMENDATIONS FOR THE ANALYTICAL METHOD 229

230

Construct calibration curves, ideally with 5–6 standards for regression and estimation of 231

intercept, slope, and correlation coefficient and three additional control standards 232

independently prepared for precision and accuracy estimation. 233

234

If necessary, dilute samples to be on the range of the calibration curve, recording the dilution 235

factor for back calculations. 236

237

Run each sample in duplicate and establish a calibration curve. It is anticipated that at least 3 238

to 4 analytical runs are expected (e.g., the first for the samples of 2, 4, 8 hours and then 239

possibly another three for 24, 48 and 72 hours samples), depending on the stability of the 240

samples. In the end, data for intra, inter-day accuracy and precision estimation should be 241

available. In general, the control standards are intercalated with the samples. 242

243

To check filter influence, control standards could be injected without and after filtration. 244

Recovery should be between 98–102% (if less than this value there is some adsorption 245

happening; if more some filter component is affecting the analysis). If necessary, change the 246

filter type. 247

248

Estimate specificity, linearity, range, accuracy, repeatability, and intermediate precision (7), 249

which should meet the minimum acceptance limits. 250

251

8. PIVOTAL EXPERIMENT 252

Pivotal experiments should be designed considering the results of preliminary experiments. The 253

following steps are presented as a general example of a pivotal solubility experiment: 254


page 12

1. in triplicate, for each pH condition to be evaluated, weigh approximately a 10% 255

excess amount of API (as determined during the preliminary test) and combine 256

with an appropriate volume of the necessary buffer solutions (at least pH 1.2, 4.5 257

and 6.8 buffers) in a flask; 258

2. mix and measure the pH value; 259

3. stop and secure the flask to the orbital shaker with controlled temperature and 260

shaker speed: 261

4. collect an aliquot of the supernatant solution at the time equilibrium was 262

established in the preliminary experiment; 263

5. immediately separate dissolved from undissolved API by filtration or 264

centrifugation; 265

6. record the PH value of the solution at the end of the experiment; 266

7. dilute the sample to avoid precipitation before quantifying; and 267

8. determine the concentration of the API. 268

269

9. REPORTING OF RESULTS 270

271

Test results should be reported in the Model Certificate of Equilibrium Solubility Experiments 272

for Biopharmceutics Classification System-based classification of Active Pharmaceutical 273

Ingredients for Biowaiver appended to this Protocol as Annex 1. The report should include 274

information on the API (chemical structure, molecular weight, known dissociation constants, 275

etc.), the actual experimental conditions, including information on buffer composition and the 276

analytical method, results (raw data plus mean values with standard deviations), and any 277

observations such as, for example, the degradation of an API due to pH or buffer composition. 278

The section describing the experimental conditions should include initial and equilibrium pH of 279

solutions and de facto buffer concentrations. If samples are filtered, the type and pore size of 280

the filter should be recorded, along with data from filter adsorption studies. If samples are 281

centrifuged the conditions of centrifugation should be recorded. A graphic representation of 282

mean pH-solubility profile should be provided. 283

284

Any deviations from the protocol should be noted and duly justified. 285

286


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The solubility should be reported in mg/mL. The relative standard deviation (RSD) between the 287

obtained solubility results should not be more than 10% between the replicates of each test 288

condition. 289

The dose: solubility volume (DSV) represents the volume of liquid necessary to completely 290

dissolve the highest single therapeutic dose of the API (as recommended by the approved label/ 291

SmPC) at the pH where lowest solubility was observed. Based on the lowest solubility 292

calculated in mg/mL, the DSV can be calculated by dividing the highest therapeutic dose (in 293

milligrams) by the solubility (in milligrams per milliliter) obtained in the study. An API is 294

considered highly soluble when the DSV is < than 250 mL over the entire pH range 1.2-6.8. 295

296

REFERENCES 297

1. Amidon GL, Lennemas H, Shah VP, Crison JR. A Theoretical Basis for a 298

Biopharmaceutic Drug Classification: The Correlation of In Vitro Drug Product 299

Dissolution and In Vivo Bioavailability. Pharmaceutics Research, 1995, 12:413–300

420. 301

302

2. Proposal to Waive In Vivo Bioequivalence Requirements for WHO model list of 303

essential medicines, Immediate-Release, Solid Oral Dosage Forms. WHO 304

Technical Report Series, No. 937, 2006, Annex 8. 305

306

3. Multisource (Generic) Pharmaceutical Products: Guidelines on Registration 307

Requirements to Establish Interchangeability. WHO Technical Report Series, No. 308

1003, 2017, Annex 6. 309

310

4. Apley M. et al., 2015. Determination of Thermodynamic Solubility of Active 311

Pharmaceutical Ingredients for Veterinary Species: A New USP General Chapter. 312

313

5. The International Pharmacopoeia, http://www.who.int/medicines/ 314

publications/pharmacopoeia/en/. 315

316

6. Stability Testing of Active Pharmaceutical Ingredients and Finished 317

Pharmaceutical Products. WHO Technical Report Series, No. 1010, 2018, Annex 318

10. 319

http://www.who.int/medicines/


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7. Analytical Method Validation, Appendix 4 in Supplementary Guidelines on Good 320

Manufacturing Practices: Validation. WHO Technical Report Series, No. 937, 2006, 321

Appendix 4. 322

323

FURTHER READING 324

325

1. Guidance for Organizations Performing In Vivo Bioequivalence Studies. WHO 326


328

2. Model Certificate of Analysis. WHO Technical Report Series, No. 1010, 2018, 329

Annex 4. 330

331

3. Good Practices for Pharmaceutical Quality Control Laboratories. WHO 332


334

4. WHO Good Manufacturing Practices for Pharmaceutical Products. WHO 335

Technical Report Series 986, 2014, Annex 2. 336

337

5. Determinação da Solubilidade Aplicada à Bioisenção de acordo com o Sistema de 338

Classificação Biofarmacêutica. Edition 5, Brazilian Pharmacopoeia, II supplementary, 339

2017. 340

341


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ANNEX 1 342

343

Header: 344

Logo of the laboratory/company issuing the certificate (if applicable) 345

Identification No. of the study: page X of Y 346

347

348

MODEL CERTIFICATE OF EQUILIBRIUM SOLUBILITY 349

EXPERIMENTS FOR BIOPHARMCEUTICS CLASSIFICATION 350

SYSTEM-BASED CLASSIFICATION OF ACTIVE 351

PHARMACEUTICAL INGREDIENTS FOR BIOWAIVER 352

353

Name and address of the laboratory issuing the study report: 354

355

356

Name of the API (international nonproprietary name (INN), brand name, etc.): 357

358

359

Certificates of analysis (CoAs) from manufactures provided: assay within specifications 360

<Yes/No> 361

362

363

Batch number: 364

365

Date received: Quantity received: 366

367

Date of manufacture (if available): 368

369

Expiry date/retest date: 370

371


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Name and address of the original manufacturer: 372

373

374

375

Telephone: 376

377

E-mail: 378

379

Information about the API 380

381

Chemical structure (please report here): 382

383

384

385

386

Nature of the drug (i.e. acid, basic, neutral, amphoteric): 387

388

Dissociation constants [i.e. pKa(s)]: 389

390

Molecular weight (g/mol): 391

392

Equilibrium solubility experiment 393

394

Apparatus: 395

396

397

Highest therapeutic dose: 398

399

Recorded temperature (target 37 °+ 1 °C): 400

401

Volume of the buffer: 402

403


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Sampling times: 404

405

Time to equilibrium: 406

407

Buffer composition (please indicate if different buffers from those recommended in the 408

Protocol to conduct equilibrium solubility experiments for the purpose of BCS-based 409

classification of APIs for Biowaiver where used): 410

411

412

Separations of samples (please indicate how and when samples were filtered, filter type and 413

pores size. If samples are centrifuged, the conditions of centrifugation should be recorded. If 414

separated through different methods, this should be justified): 415

416

417

418

419

Stability (report and discuss any problems with pH-related stability of samples): 420

421

422

423

Solubility method and conditions: 424

425

426

427

428

429

Brief summary of analytical methods including validation: 430

431

432

433

434

435

436

437


July 2018


Result of the preliminary solubility experiment 438

Theoretical

pH

Individual

pH

measurement

Final pH

before

correction

Adjusted

with (ml of

0.1 N HCL

or NaoH)a

Final pH

corrected

API

equilibrium

concentrati

on (mg/ml) b

Concentrati

on mean

(mg/ml) c

CV % d

Conc.

(mg/ml)

2 h

Conc.

(mg/ml)

4 h

Conc.

(mg/ml)

6 h

Conc.

(mg/ml)

12 h

Conc.

(mg/ml)

24 h

Conc.

(mg/ml)

48 h

Conc.

(mg/ml)

72 h

pH 1.2 1

2

3

pH 4.5 1

2

3

pH 6.8 1

2

3

Potential

additional

pH

1

2

3

439 440 a Amount of acid or base needed to adjust the measured pH. The measurement should be conducted in triplicates and, per each measurement, the corresponding pH values should be reported. 441 b Report here the three measurements registered at each Ph. 442 c Report here only the mean of the individual values reported in the previous column. 443 d Coefficient of variation. 444 445

446

447

448


page 20

Result of the pivotal solubility experiment 449

450

Theoretical

pH

Individual pH

measurement

Final pH

before

correction

Adjusted

with (ml of

0.1 N HCL

or NaoH)a

Final pH

corrected

Time to

equilibrium

APIs Weight Buffer

volume

API

equilibrium

concentratio

n (mg/ml) b

API

equilibrium

concentration

mean (mg/ml)c

CV % d

pH 1.2 1

2

3

pH 4.5 1

2

3

pH 6.8 1

2

3

Potential

additional

pH

1

2

3

451 452 a Amount of acid or base needed to adjust the measured pH. The measurement should be conducted in triplicates and, per each measurement, the corresponding pH values should be reported. 453 b Report here the three measurements registered at each pH. 454 c Report here only the mean of the individual values reported in the previous column. It is the mean solubility value for each pH. 455 d Coefficient of variation. 456 457 458 459 460 461 462 463 464 465 466


July 2018


Plot of solubility 467

468

To identify the pH of minimum solubility: plot concentration at saturation versus pH and provide a 469

graphical representation of the results. Include error bars on mean. 470

471

Example chart 472

473

474

475

Please report here the intermediate calculation for the DSV at (add additional pHs tested as

appropriate):

pH 1.2 Highest therapeutic dose (mg)/Solubility (mg/ml)] [Concentration mean] =

pH 4.5 Highest therapeutic dose(mg)/Solubility (mg/ml) [Concentration mean]=

pH 6.8 Highest therapeutic dose(mg)/Solubility (mg/ml)] [Concentration mean] =

476

Conclusion: is the highest single therapeutic dose (according to the approved originator 477

product labelling) soluble in 250 mL of buffer over the pH range of 1.2 - 6.8 at 37 ± 1 °C i.e., 478

in all buffers tested including buffers at pH 1.2, 4.5, and 6.8? 479

<Yes>/<No> 480

481

482

0

1

2

3

4

5

pH 1.2 pH 4.5 pH 6.8Equ

ilib

riu

m c

on

cen

trat

ion

m

ean

(

mg/

ml)

<API> solubility profile


page 22

Solubility classification (please refer to Multisource (generic) pharmaceutical products: 483

guidelines on registration requirements to establish interchangeability. WHO Technical 484

Report Series, No. 1003, 2017, Annex 6): 485

486

<High> / <Low> 487

488

Name of the head of laboratory or person authorized to approve the certificate: 489

________________________________________________________________________________ 490

Telephone: E-mail: 491

Signature: Date: 492

493

494

*** 495

protocol to conduct equilibrium …...working document qas/17.699/rev.2 page 2 schedule for the...

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