Contents

Contributors xxi

1 Introduction to Biopharmaceutics and its Role in Drug Development . . 1

1.1 Introduction to Biopharmaceutics 1

1.1.1 What is Biopharmaceutics? 1

1.1.2 Physical Pharmacy: Physical-Chemical Principles 2

1.1.2.1 Solubility 2

1.1.2.2 Hydrophilicity/Lipophilicity 2

1.1.2.3 Salt Forms and Polymorphs 2

1.1.2.4 Stability 3

1.1.2.5 Particle and Powder Properties 3

1.1.2.6 Ionization and p^a 3

1.1.3 Formulation Principles 4

1.1.4 Physiological/Biological Principles 4

1.1.4.1 Pharmacokinetics 4

1.1.5 Biopharmaceutics: Integration of Physical/Chemical and Biological/Pharmacokinetic Principles and Impact on Clinical Efficacy 6

1.1.5.1 Introduction to the Biopharmaceutics Classification System 6

1.1.5.2 Impact of Physical/Chemical Properties on Absorption and Transport 7

1.1.5.3 Strategies to Achieve Target Pharmacokinetic Profile 10

1.2 Role of Biopharmaceutics in Drug Development 14

1.2.1 Importance of Biopharmaceutics in the Overall Development Process 14

1.2.2 Discovery and Preclinical Development:

Candidate Selection 15

1.2.3 Preclinical Development: Preparation for Phase I Clinical Studies 16

1.2.4 Early Clinical Development 17

1.2.5 Advanced Clinical Development 19

1.2.6 Postapproval Considerations 20

1.2.7 Regulatory Considerations 21

1.3 Summary 21

2 Molecular and Physicochemical Properties Impacting

Oral Absorption of Drugs 26

2.1 Introduction 26

2.2 Molecular and Physicochemical Properties

Impacting Oral Absorption 27

2.2.1 Molecular Weight, Log P, the Number of H-Bond Donors and Acceptors, Polar Surface Area, and the Number of Rotatable Bonds 27

2.2.2 Chirality 29

2.2.3 Dissolution 29

2.2.4 Solubility 30

2.2.4.1 Definition of Solubility 30

2.2.4.2 Factors Contributing to Poor Aqueous Solubility 30

2.2.4.3 pH-Solubility Profile 31

2.2.4.4 Effect of Temperature on Solubility 34

2.2.4.5 Solubility in Gastric and Intestinal Fluids 35

2.2.4.6 Solubility as a Limiting Factor to Absorption . . 36

2.2.4.7 Solubility Determination 36

2.2.4.8 Solubility Prediction 38

2.2.5 Chemical Stability 38

2.2.6 Solid State Properties 39

2.2.6.1 Polymorphism 39

2.2.6.2 Amorphous Material 40

2.2.6.3 Particle Size 41

2.3 Physicochemical Properties and Drug Delivery Systems 41

2.4 Summary 43

3 Dissolution Testing 47

3.1 Introduction 47

3.2 Significance of Dissolution in Drug Absorption 47

3.3 Theories of Dissolution 49

3.4 Factors Affecting Dissolution 51

3.4.1 Factors Related to the Physicochemical Properties of the Drug Substance 52

3.4.1.1 Solubility 52

3.4.1.2 Particle Size 52

3.4.1.3 Solid Phase Characteristics 53

3.4.1.4 Salt Effects 53

3.4.2 Factors Related to Drug Product Formulation 53

3.4.3 Factors Related to Manufacturing Processes 54

3.4.4 Factors Related to Dissolution Testing Conditions 55

3.5 Roles of Dissolution Testing 55

3.6 In Vitro Dissolution Testing as a Quality Control Tool 56

3.6.1 Dissolution Method for Quality Control of Immediate-Release Dosage Forms 57

3.6.1.1 Dissolution Media 57

3.6.1.2 Apparatus and Test Conditions 58

3.6.2 Dissolution Method for Quality Control of Modified-Release Dosage Forms 58

3.6.2.1 Dissolution Media 58

3.6.2.2 Apparatus and Test Conditions 59

3.6.3 Limitations of Quality Control Dissolution Tests 59

3.7 Biorelevant Dissolution Testing 60

3.7.1 In Vivo-In Vitro Correlations 61

3.7.2 The Importance of BCS on Biorelevant

Dissolution Testing 61

3.7.3 Biorelevant Dissolution Methods 64

3.7.3.1 Biorelevant Dissolution Media for Gastric Conditions 65

3.7.3.2 Apparatus and Test Conditions for Simulating the Stomach 66

3.7.3.3 Biorelevant Dissolution Media for Intestinal Conditions 67

3.7.3.4 Apparatus and Test Conditions for Simulating Small Intestine 69

3.7.3.5 Biorelevant Methods for Extended-Release Dosage Forms 69

3.7.3.6 Remaining Challenges 69

3.8 Conclusions 70

4 Drug Absorption Principles 75

4.1 Drug Absorption and Bioavailability 75

4.2 Types of Intestinal Membrane Transport 76

4.2.1 Passive Diffusion 76

4.2.2 Carrier-Mediated Transport 78

4.2.2.1 Facilitated Diffusion 78

4.2.2.2 Active Transport 79

4.2.3 Paracellular Transport 79

4.2.4 Endocytosis 79

4.2.5 Which Absorption Path Dominates Drug Absorption? . . 80

4.3 Three Primary Factors Influence Drug Absorption 80

4.3.1 Membrane Permeability 81

4.3.1.1 Effective Permeability 81

4.3.1.2 Fraction of Drug Absorbed 81

4.3.1.3 Permeability and Absorption Rate Constant . . 82

4.3.2 Solubility 82

4.3.3 Dissolution of Solid Dosage Forms 83

4.4 Secondary Factors Influencing Drug Absorption 84

4.4.1 Biological Factors of Gastrio Intestinal Tract 84

4.4.1.1 Gastric Emptying Time 84

4.4.1.2 Surface Area 84

4.4.1.3 GI Transit Time 84

4.4.1.4 Intestinal Motility 85

4.4.1.5 Components, Volume, and Properties of Gastrointestinal Fluids 85

4.4.2 Dosage Factors Influencing Absorption 86

4.5 Evaluation of Oral Drug Absorption in Humans 86

4.5.1 Drug Absorption Assessment Using In Vivo Data 86

4.5.1.1 Estimation of Fraction of Drug Absorbed Using Experimental Intestinal Permeability

In Vivo 86

4.5.1.2 Estimation of Maximum Absorbable Dose Using In Vivo Absorption Rate

Constant and Drug Solubility 88

4.5.1.3 Estimation of MAD from Drug In Vivo Permeability in Human and Drug Solubility . . 89

4.5.2 Drug Absorption Assessment Using In Vitro Data 90

4.5.2.1 In Vitro Testing Conditions for Determining Drug Permeability in Caco-2 Cells and In Vitro/In Vivo Permeability

Correlation 90

4.5.2.2 Estimation of Fraction of Drug Absorbed

In Humans Using In Vitro Drug Permeability in Caco-2 Cells 92

4.5.2.3 Estimation of MAD in Human Based on In Vitro Data 93

4.5.3 Correlation of Oral Drug Bioavailability and Intestinal Permeability Between Rat and Human . . . 95

4.6 Summary 97

5 Evaluation of Permeability and P-glycoprotein Interactions:

Industry Outlook 101

5.1 Introduction 101

5.2 Anatomy and Physiology of the Small Intestine 104

5.3 Permeability Absorption Models 105

5.3.1 Physicochemical Methods 105

5.3.1.1 Lipophilicity (Log P/Log D) 105

5.3.1.2 Absorption Potential 105

5.3.1.3 Immobilized Artificial Membrane (IAM) 106

5.3.2 In Vitro Methods 106

5.3.2.1 Animal Tissue-Based Methods 107

5.3.2.2 Cell-Based Methods 109

5.3.3 In Situ Methods 111

5.3.4 In Vivo Methods 112

5.3.5 InSilico Methods 113

5.4 Comparison of PAMPA and Caco-2 Cells 114

5.4.1 Parallel Artificial Membrane Permeability Assay 114

5.4.1.1 PAMPA Study Protocol 115

5.4.2 Caco-2 Cells 115

5.4.2.1 Caco-2 Cell Culture 116

5.4.2.2 Caco-2 cells Study Protocol 116

5.4.3 PAMPA and Caco-2 Cell: Synergies 116

5.4.4 PAMPA and Caco-2 Cell: Caveats 123

5.4.4.1 Transporter- and Paracellular-Mediated Absorption 123

5.4.4.2 Incomplete Mass-Balance

Due to Nonspecific Binding 125

5.4.4.3 Inadequate Aqueous Solubility 125

5.4.4.4 Other Experimental Variability 126

5.5 P-gp Studies Using Caco-2 Cells 127

5.5.1 Experimental Factors Effecting Efflux Ratio 129

5.6 Conclusions 132

6 Excipients as Absorption Enhancers 139

6.1 Introduction 139

6.2 Basic Mechanisms in Transcellular and Paracellular Transport . . 140

6.2.1 Transcellular Transport 141

6.2.2 Paracellular Transport 142

6.2.3 Mechanisms of Action of Absorption Enhancers 142

6.2.3.1 Action on the Mucus Layer 143

6.2.3.2 Action on Membrane Components 143

6.3 Mucoadhesive Polymers as Absorption Enhancers 148

6.3.1 Theories of Mucoadhesion 148

6.3.2 Material Properties of Mucoadhesives 150

6.3.3 Classes of Mucoadhesive Polymers 152

6.3.3.1 Polyacrylates 152

6.3.3.2 Chitosan 156

6.3.3.3 N,N,N,-Trimethyl Chitosan Hydrochloride

6.3.3.4 Monocarboxymethyl Chitosan 161

6.3.3.5 Thiolated Polymers 162

6.3.3.6 Solid Dosage Form Design Based on TMC and Thiolated Polymers and Their In Vivo Evaluation 164

6.4 Conclusions 166

7 Intestinal Transporters in Drug Absorption 175

7.1 Introduction 175

7.2 ATP Binding Cassette Transporters 179

7.2.1 P-Glycoprotein (P-gp; ABCB1) 183

7.2.1.1 The Expression of P-gp 183

7.2.1.2 The Regulation of P-gp Expression 184

7.2.1.3 P-gp Mediated Drug Transport 185

7.2.1.4 The Substrate Specificity of P-gp 185

7.2.2 Multidrug Resistance-Associated Protein Family

7.2.2.1 The Expression of MRPs 188

7.2.2.2 The Regulation of MRP Isoform Expression . . 190

7.2.2.3 The Substrate Specificity of MRP's 190

7.2.3 Breast Cancer Resistance Protein (BCRP; ABCG2) 193

7.3 Solute Carrier Transporters 195

7.3.1 Proton/Oligopeptide Transporters (POT; SLC15A) 195

7.3.1.1 Peptide Transporter Mediated Transport 197

7.3.1.2 The Substrate Specificity of Peptide Transporters 198

7.3.1.3 The Regulation of Peptide Transporters 200

7.3.2 Organic Anion Transporters

7.3.3 Organic Cation Transporters (OCT, OCTN; SLC22A) . . 209

7.3.3.1 The Substrate Specificity of Organic Cation Transporters 210

7.3.3.2 Organic Cation Transporter Mediated

Transport 211

7.3.3.3 The Expression of Organic Cation

Transporters 211

7.3.3.4 The Regulation of Organic Cation

Transporters 212

7.3.4 Nucleoside Transporters

(CNT, SLC28A; ENT, SLC29A) 214

7.3.4.1 The Molecular and Structural Characteristics of Nucleoside Transporters 215

7.3.4.2 The Substrate Specificities of Nucleoside Transporters 217

7.3.4.3 The Expression of Nucleoside Transporters . . . 219

7.3.4.4 The Regulation of Nucleoside Transporters . . . 220

7.3.5 Monocarboxylate Transporters (MCT; SLC16A) 221

7.3.5.1 Molecular and Structural Characteristics of Monocarboxylate Transporters 222

7.3.5.2 The Substrate Specificity of Monocarboxylate Transporters 222

7.3.5.3 The Expression of Monocarboxylate Transporters 223

7.3.5.4 The Regulation of Monocarboxylate Transporters 224

7.4 Impact of Intestinal Transporters on Bioavailability 225

8 Bioavailability and Bioequivalence 262

8.1 Introduction 262

8.2 Bioavailability and Bioequivalence 262

8.2.1 Bioavailability and its Utility in Drug Development and Regulation 262

8.2.2 Bioequivalence and its Utility in Drug Development and Regulation 263

8.2.3 Bioavailability and Bioequivalence Studies: General Approaches 264

8.3 Pharmacokinetic Bioavailability and Bioequivalence Studies . . . 265

8.3.1 Bioavailability Studies: General Guidelines and Recommendations 265

8.3.2 Bioequivalence Studies: General Guidelines and Recommendations 267

8.3.2.1 Study Design 267

8.3.2.3 Subjects 268

8.3.2.4 Statistical Analysis of Bioequivalence 268

8.4 Bioequivalence: Challenging Topics 271

8.4.1 Drugs with Active Metabolites 271

8.4.2 Enantiomers vs. Racemates 273

8.4.3 Endogenous Substances 273

8.4.4 Highly Variable Drugs 274

8.4.4.1 Static Expansion of the BE Limits 274

8.4.4.2 Expansion of Bioequivalence Limits Based on Fixed Sample Size 275

8.4.4.3 Scaled Average Bioequivalence 275

8.5 Biowaivers 276

8.5.1 Solutions 276

8.5.2 Lower Strength 278

8.5.3 Biopharmaceutical Classification System 279

8.5.3.1 Biowaivers for BCS Class 2 Drugs with pH Dependent Solubility 280

8.5.3.2 Biowaivers for BCS Class 3 Drugs 280

8.6 Locally Acting Drugs 281

8.6.1 Topical Dermatological Products 281

8.6.2 Locally Acting Nasal and Oral Inhalation Drug

Products 283

8.6.2.1 Nasal Spray Products 284

8.6.2.2 Oral Inhalation Products 285

8.7 Conclusions 287

9 A Biopharmaceutical Classification System Approach to Dissolution: Mechanisms and Strategies 290

9.1 Introduction 290

9.2 Biopharmaceutical Classification System Approach to Dissolution 290

9.3 In Vitro-In Vivo Dissolution Correlation 292

9.4 Recent Climate: Pharmaceutical Quality Assessment 294

9.5 Discussion 296

9.5.1 BCS Class I and III Case Studies 296

9.5.1.1 Case Study 1: Fast Release (>85% Release in 15min) with Disintegration

Controlled Dissolution 298

9.5.1.2 CaseStudy2: <85% Release in 15 min with Disintegration/Erosion Controlled Dissolution 299

9.5.1.3 Case Study 3: Dissolution Mechanism not Dependent on Disintegration/Erosion 301

9.5.2 BCS Class II and IV Case Studies 302

9.5.2.1 Case Study 4: Liquid Filled (True Solution) Capsules 303

9.5.2.2 Case Studies 5, 6, and 7: Intrinsic Rate of Drug Solubilization Controlled Dissolution 303

9.5.2.3 Case Studies 8 and 9: Mixed Contribution of Formulation Colligative Properties and Intrinsic Rate of Drug Solubilization 306

9.5.2.4 Case Study 10: API with High Solubility at Gastric pHs 309

9.5.3 Controlled Release Dosage Form Case Study 310

9.5.4 Pharmaceutical Quality Assessment Implications of Dissolution 313

9.6 Conclusion 314

10 Food Effects on Drug Bioavailability: Implications for New and Generic Drug Development 317

10.1 Introduction 317

10.1.1 Objectives 317

10.1.2 Oral Bioavailability Defined 317

10.1.3 How Food Can Affect Drug Bioavailability 317

10.2 Food Interactions with Drug Substance 318

10.2.1 Pharmacokinetic Parameters Used to Characterize Food Effects on Drug Bioavailability 318

10.2.2 Prolonged Rate of Drug Absorption in the Presence ofFood 318

10.2.3 Decreased Drug Absorption in the Presence of Food . . . 319

10.2.3.1 Overview 319

10.2.3.2 Instability in Gastric Acids 319

10.2.3.3 Physical or Chemical Binding with Food Components 319

10.2.3.4 Increased First-Pass Metabolism and Clearance 320

10.2.4 Increased Drug Absorption in the Presence of Food . . . . 320

10.2.4.1 Inhibition of First-Pass Effect 320

10.2.4.2 Physicochemical and Physiological Effects . . . 321

10.2.4.3 Effects of Bile Release 322

10.2.4.4 Effects of Longer Gastric Residence Time . . . 322

10.2.5 Drug Absorption Unaffected by Food 322

10.2.6 FDA Guidance for Industry on Characterizing Food Effects in Drug Development 323

10.2.6.1 Objectives 323

10.2.6.2 Recommended Designs for Food-Effect Bioavailability Studies 323

10.2.6.3 Recommendations for Drug Product

Labeling 323

10.3 Food Interactions with Drug Product 324

10.3.1 Introduction 324

10.3.2 Issues with Modified-Release Drug Products:

Potential for Dose-Dumping 325

10.3.3 Issues with Modified-Release Drug Products: Formulation-Dependant Food Effects 326

10.3.3.1 In Vitro Drug Release Predictive of Food Effects 326

10.3.3.2 In Vitro Drug Release Profiles Not Predictive of Food Effects 326

10.3.4 Implications for Development of Generic Modified-Release Drug Products 327

10.3.4.1 Introduction 327

10.3.4.2 Role of In Vivo Fed Bioequivalence Studies . . 327

10.3.5 Implications for Development of Generic Immediate-Release Drug Products 328

10.3.5.1 BCS Class I Drugs 328

10.3.5.2 Label-Driven Criteria for Requesting Fed Bioequivalence Studies 329

10.3.6 Recommendations for Designing Fed Bioequivalence Studies 330

10.3.7 Food Effects and Generic Drug Product Labeling 331

10.3.8 Sprinkle Studies in New and Generic Drug Product Development 331

10.3.8.1 Sprinkle Studies in Development of New Modified-Release Capsules 331

10.3.8.2 Sprinkle Studies in Development of Generic Modified-Release Capsules 331

10.3.8.3 Example 332

10.4 Summary and Conclusions 332

11 In Vitro-In Vivo Correlation on Parenteral Dosage Forms 336

11.1 IVIVC Definition 336

11.2 Modified Release Parenteral Products 336

11.3 Factors to Consider for Meaningful IVIVC 337

11.3.1 Product Related Factors 337

11.3.2 Factors Affecting In Vitro Release 338

11.3.2.1 Accelerated In Vitro Release Testing 341

11.3.3 Mathematical Models of In Vitro Drug Release 341

11.3.4 Factors Affecting In Vivo Release 343

11.4 In Vitro-In Vivo Correlation 344

11.5 Microspheres 345

11.6 Liposomes 347

11.7 Emulsions 349

11.8 Hydrogels, Implants 350

11.9 Dendrimers 351

12 In Vitro-In Vivo Correlation in Dosage Form Development:

Case Studies 359

12.1 Introduction 359

12.2 IVIVC in Drug Product Development: A Four-Tier Approach . . . 360

12.3 Case Studies 363

12.3.1 Tier 1 - Discovery and Early Preclinical Development: Assessing Developability and Formulation Principles 363

12.3.2 Tier 2 - Preclinical Product Development: Selection of Meaningful Dissolution Method 367

12.3.3 Tier 3 - Full Development: Deconvolution of Human Pharmacokinetic Data and Comparison with

In Vitro Dissolution Data 372

12.4 Deconvolution and Convolution 372

12.4.1 Tier 4: Application of IVIVC in LCM 376

12.5 Conclusions 380

Index 383

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