Drug Bioavailability : Estimation of Solubility, Permeability, Absorption and Bioavailability (Methods and Principles in Medicinal Chemistry Vol.40) (2nd ed. 2008. XVI, 572 p. w. 220 b&w and 20 col. figs. 24 cm)

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Drug Bioavailability : Estimation of Solubility, Permeability, Absorption and Bioavailability (Methods and Principles in Medicinal Chemistry Vol.40) (2nd ed. 2008. XVI, 572 p. w. 220 b&w and 20 col. figs. 24 cm)

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Full Description

Drug Bioavailability In order to reach its intended site of action, the drug molecules in every pill that we swallow must first be absorbed, transported via the bloodstream and evade various mechanisms that eliminate drugs from the body. Those drug properties that determine, for example, its stability in the gut or its ease of uptake into the bloodstream, are therefore of central importance in drug development. In fact, many potentially useful drugs fail because of insufficient availability at the biological target site.

This second edition of the gold standard for industrial research is thoroughly revised in line with current trends in the field, with all contributions extensively updated or rewritten. No other publication offers the same level of treatment on this crucial topic.

In 22 chapters readers can benefit from the key working knowledge of today's leading pharmaceutical companies, including Pfizer, AstraZeneca, and Roche. Drug developers from industry and academia present all the factors governing drug bioavailability, complete with practical examples and real-life data.

Part I focuses on solubility and gastrointestinal absorption, while the second discusses in vitro and in vivo measurements of physicochemical properties, such as membrane permeability and solubility. Part III is devoted to metabolism and excretory mechanisms. The much revised and expanded Part IV surveys current in silico approaches to predict drug properties needed to estimate the bioavailability of any new drug candidate. The final part shows new drug development approaches as well as delivery strategies.

Indispensable for all those working in the pharmaceutical industry, pharmaceutical and medicinal chemists, and toxicologists.

Contents

List of Contributors XIX

Preface XXIII

A Personal Foreword XXV

1 Introduction: The Why and How of Drug Bioavailability Research 1
Han van de Waterbeemd and Bernard Testa

1.1 Defining Bioavailability 1

1.1.1 The Biological Context 1

1.1.2 A Pharmacokinetic Overview 3

1.1.3 Specific Issues 3

1.2 Presentation and Layout of the Book 4

References 6

Part One Physicochemical Aspects of Drug Dissolution and Solubility 7

2 Aqueous Solubility in Drug Discovery Chemistry, DMPK, and Biological Assays 9
Nicola Colclough, Linette Ruston, and Kin Tam

2.1 Introduction 10

2.1.1 Definition of Aqueous Solubility 11

2.1.2 Aqueous Solubility in Different Phases of Drug Discovery 12

2.2 Aqueous Solubility in Hit Identification 12

2.2.1 Aqueous Solubility from DMSO Solutions 13

2.2.1.1 Turbidimetric Methods 14

2.2.1.2 UV Absorption Methods 15

2.2.1.3 Alternative Detection Methodology 17

2.2.1.4 Application of DMSO-Based Solubility Assays 18

2.3 Aqueous Solubility in Lead Identification and Lead Optimization 18

2.3.1 Dried-Down Solution Methods 20

2.3.2 Solubility from Solid 21

2.3.3 Thermodynamic Solubility Assays with Solid-State Characterization 22

2.3.4 Solubility by Potentiometry 24

2.3.5 Application of Thermodynamic Solubility Data in LI and LO 26

2.4 Conclusions 28

References 28

3 Gastrointestinal Dissolution and Absorption of Class II Drugs 33
Arik S. Dahan and Gordon L. Amidon

3.1 Introduction 33

3.2 Drug Absorption and the BCS 34

3.3 Class II Drugs 36

3.4 GI Physiological Variables Affecting Class II Drug Dissolution 38

3.4.1 Bile Salts 38

3.4.2 GI pH 39

3.4.3 GI Transit 39

3.4.4 Drug Particle Size 40

3.4.5 Volume Available for Dissolution 41

3.5 In Vitro Dissolution Tests for Class II Drugs 41

3.5.1 Biorelevant Media 41

3.5.2 Dynamic Lipolysis Model 42

3.6 BCS-Based FDA Guidelines: Implications for Class II Drugs 43

3.6.1 Potential of Redefining BCS Solubility Class Boundary 43

3.6.2 Biowaiver Extension Potential for Class II Drugs 44

3.7 Conclusions 45

References 45

4 In Silico Prediction of Solubility 53
Andrew M. Davis and Pierre Bruneau

4.1 Introduction 54

4.2 What Solubility Measures to Model? 54

4.3 Is the Data Set Suitable for Modeling? 56

4.4 Descriptors and Modeling Methods for Developing Solubility Models 58

4.5 Comparing Literature Solubility Models 59

4.6 What Is the Influence of the Domain of Applicability? 63

4.7 Can We Tell when Good Predictions Are Made? 65

4.8 Conclusions 65

References 66

Part Two Physicochemical and Biological Studies of Membrane Permeability and Oral Absorption 69

5 Physicochemical Approaches to Drug Absorption 71
Han van de Waterbeemd

5.1 Introduction 73

5.2 Physicochemical Properties and Pharmacokinetics 74

5.2.1 DMPK 74

5.2.2 Lipophilicity, Permeability, and Absorption 74

5.2.3 Estimation of Volume of Distribution from Physical Chemistry 76

5.2.4 Plasma Protein Binding and Physicochemical Properties 76

5.3 Dissolution and Solubility 76

5.3.1 Calculated Solubility 78

5.4 Ionization (pKa) 78

5.4.1 Calculated pKa 79

5.5 Molecular Size and Shape 79

5.5.1 Calculated Size Descriptors 79

5.6 Hydrogen Bonding 80

5.6.1 Calculated Hydrogen-Bonding Descriptors 80

5.7 Lipophilicity 81

5.7.1 log P and log D 81

5.7.2 Calculated log P and log D 83

5.8 Permeability 84

5.8.1 Artificial Membranes and PAMPA 84

5.8.1.1 In Silico PAMPA 85

5.8.2 IAM, ILC, MEKC, and BMC 85

5.8.3 Liposome Partitioning 86

5.8.4 Biosensors 86

5.9 Amphiphilicity 86

5.10 Drug-Like Properties 87

5.11 Computation Versus Measurement of Physicochemical Properties 88

5.11.1 QSAR Modeling 88

5.11.2 In Combo: Using the Best of Two Worlds 89

5.12 Outlook 89

References 89

6 High-Throughput Measurement of Physicochemical Properties 101
Barbara P. Mason

6.1 Introduction 102

6.2 Positioning of Physicochemical Screening in Drug Discovery 102

6.3 ''Fit for Purpose'' Versus ''Gold Standard'' 103

6.4 Solubility 104

6.4.1 ''Thermodynamic'' Versus ''Kinetic'' 104

6.4.2 Methods of Measuring High-Throughput Solubility 106

6.4.3 Supernatant Concentration 106

6.4.4 Measuring Solubility Across a pH Range 107

6.4.5 Supernatant Concentration Methods from Solid Material 109

6.4.6 Precipitate Detection 109

6.4.7 Other Methods of Measuring Solubility 110

6.5 Dissociation Constants, pKa 110

6.5.1 Measuring pKa 111

6.5.2 pKa Measurements in Cosolvent Mixtures 112

6.5.3 pKa Measurements based on Separation 113

6.6 Lipophilicity 115

6.6.1 log P Versus log DpH 115

6.6.2 Measuring Lipophilicity 116

6.6.3 High-Throughput log D7.4 Measurements 117

6.6.4 High-Throughput log D7.4 Versus Shake-Flask log D7.4 117

6.6.5 Alternative Methods for Determining High-Throughput log DpH 118

6.7 Permeability 119

6.7.1 Permeability and Lipophilicity 121

6.7.2 Cell-Based Assays 121

6.7.3 Noncell-Based Assays: Chromatographic Methods 122

6.7.4 Noncell-Based Assays: Parallel Artificial Membrane Permeability Assay 122

6.7.4.1 Membrane Composition 123

6.7.4.2 Suggestions for PAMPA 123

6.7.4.3 Considerations in the Calculation of Permeability from PAMPA Data 124

6.7.5 Sink Conditions 125

6.7.6 Unstirred Water Layer 126

6.7.7 Surface Properties for the Determination of Permeability 126

6.8 Data Interpretation, Presentation, and Storage 126

6.9 Conclusions 127

References 127

7 An Overview of Caco-2 and Alternatives for Prediction of Intestinal Drug Transport and Absorption 133
Anna-Lena Ungell and Per Artursson

7.1 Introduction 134

7.2 Cell Cultures for Assessment of Intestinal Permeability 134

7.2.1 Caco-2 135

7.2.2 MDCK Cells 136

7.2.3 2/4/A1 Cells 137

7.2.4 Other Cell Lines 139

7.3 Correlation to Fraction of Oral Dose Absorbed 140

7.4 Cell Culture and Transport Experiments 141

7.4.1 Quality Control and Standardization 143

7.4.2 Optimizing Experimental Conditions: pH 144

7.4.3 Optimizing Experimental Conditions: Concentration Dependence 144

7.4.4 Optimizing Experimental Conditions: Solubility and BSA 145

7.5 Active Transport Studies in Caco-2 Cells 145

7.6 Metabolism Studies using Caco-2 Cells 146

7.7 Conclusions 147

References 148

8 Use of Animals for the Determination of Absorption and Bioavailability 161
Chris Logan

8.1 Introduction 162

8.1.1 ADME/PK in Drug Discovery 162

8.1.2 The Need for Prediction 163

8.2 Consideration of Absorption and Bioavailability 163

8.3 Choice of Animal Species 167

8.4 Methods 168

8.4.1 Radiolabels 169

8.4.2 Ex Vivo Methods for Absorption 169

8.4.2.1 Static Method 169

8.4.2.2 Perfusion Methods 170

8.4.3 In Vivo Methods 170

8.5 In Vivo Methods for Determining Bioavailability 171

8.5.1 Cassette Dosing 171

8.5.2 Semisimultaneous Dosing 172

8.5.3 Hepatic Portal Vein Cannulation 173

8.6 Inhalation 173

8.7 Relevance of Animal Models 174

8.7.1 Models for Prediction of Absorption 174

8.7.2 Models for Prediction of Volume 175

8.8 Prediction of Dose in Man 176

8.8.1 Allometry 176

8.8.2 Physiologically Based Pharmacokinetics 176

8.8.3 Prediction of Human Dose 177

8.9 Conclusions 179

References 179

9 In Vivo Permeability Studies in the Gastrointestinal Tract of Humans 185
Niclas Petri and Hans Lennernäs

9.1 Introduction 185

9.2 Definitions of Intestinal Absorption, Presystemic Metabolism, and Absolute Bioavailability 188

9.3 Methodological Aspects of In Vitro Intestinal Perfusion Techniques 190

9.4 Paracellular Passive Diffusion 193

9.5 Transcellular Passive Diffusion 196

9.6 Carrier-Mediated Intestinal Absorption 199

9.7 Jejunal Transport and Metabolism 202

9.8 Regional Differences in Transport and Metabolism of Drugs 208

9.9 Conclusions 209

References 210

Part Three Role of Transporters and Metabolism in Oral Absorption 221

10 Transporters in the Gastrointestinal Tract 223
Pascale Anderle and Carsten U. Nielsen

10.1 Introduction 223

10.2 Active Transport Along the Intestine and Influence on Drug Absorption 228

10.2.1 Peptide Transporters 232

10.2.2 Nucleoside Transporters 233

10.2.3 Amino Acid Transporters 234

10.2.4 Monosaccharide Transporters 234

10.2.5 Organic Cation Transporters 235

10.2.6 Organic Anion Transporters 235

10.2.7 Monocarboxylate Transporters 235

10.2.8 ABC Transporters 235

10.2.9 Bile Acid Transporters 237

10.3 Transporters and Genomics 237

10.3.1 Introduction to Genomics Technologies 237

10.3.2 Gene Expression Profiling Along the Intestine and in Caco-2 Cells 238

10.3.2.1 Profiling of the Intestinal Mucosa 238

10.3.2.2 Profiling of Caco-2 Cells 240

10.3.3 Intestinal Transporters and the Influence of Genotypes 242

10.4 Structural Requirements for Targeting Absorptive Intestinal Transporters 245

10.4.1 Strategies for Increasing Drug Absorption Targeting Transporters 245

10.4.2 Changing the Substrate: SAR Established for PEPT1 247

10.4.3 Methods for Investigating Affinity and Translocation 248

10.4.4 Quantitative Structure-Activity Relations for Binding of Drug to Transporters 249

10.5 Transporters and Diseased States of the Intestine 251

10.5.1 Intestinal Diseases 251

10.5.2 Basic Mechanisms in Cancer and Specifically in Colon Carcinogenesis 252

10.5.2.1 Basic Mechanisms 252

10.5.2.2 Colon Cancer 253

10.5.3 Transporters and Colon Cancer 253

10.5.3.1 Transporters as Tumor Suppressor Genes 255

10.5.3.2 Role of Transporters in the Tumor-Stroma Interaction 255

10.5.3.3 Role of Transporters in Intestinal Stem Cells 258

10.5.4 Role of PEPT1 in Inflammatory Bowel Disease 259

10.6 Summary and Outlook 260

References 261

11 Hepatic Transport 277
Kazuya Maeda, Hiroshi Suzuki, and Yuichi Sugiyama

11.1 Introduction 278

11.2 Hepatic Uptake 278

11.2.1 NTCP (SLC10A1) 279

11.2.2 OATP (SLCO) Family Transporters 279

11.2.3 OAT (SLC22) Family Transporters 281

11.2.4 OCT (SLC22) Family Transporters 284

11.3 Biliary Excretion 284

11.3.1 MDR1 (P-glycoprotein; ABCB1) 287

11.3.2 MRP2 (ABCC2) 287

11.3.3 BCRP (ABCG2) 289

11.3.4 BSEP (ABCB11) 290

11.3.5 MATE1 (SLC47A1) 290

11.4 Sinusoidal Efflux 290

11.4.1 MRP3 (ABCC3) 291

11.4.2 MRP4 (ABCC4) 291

11.4.3 Other Transporters 293

11.5 Prediction of Hepatobiliary Transport of Substrates from In Vitro Data 294

11.5.1 Prediction of Hepatic Uptake Process from In Vitro Data 294

11.5.2 Prediction of the Contribution of Each Transporter to the Overall Hepatic Uptake 295

11.5.3 Prediction of Hepatic Efflux Process from In Vitro Data 298

11.5.4 Utilization of Double (Multiple) Transfected Cells for the Characterization of Hepatobiliary Transport 299

11.6 Genetic Polymorphism of Transporters and Its Clinical Relevance 301

11.7 Transporter-Mediated Drug-Drug Interactions 305

11.7.1 Effect of Drugs on the Activity of Uptake Transporters Located on the Sinusoidal Membrane 305

11.7.2 Effect of Drugs on the Activity of Efflux Transporters Located on the Bile Canalicular Membrane 308

11.7.3 Prediction of Drug-Drug Interaction from In Vitro Data 309

11.8 Concluding Remarks 309

References 311

12 The Importance of Gut Wall Metabolism in Determining Drug Bioavailability 333
Christopher Kohl

12.1 Introduction 334

12.2 Physiology of the Intestinal Mucosa 334

12.3 Drug-Metabolizing Enzymes in the Human Mucosa 336

12.3.1 Cytochrome P450 336

12.3.2 Glucuronyltransferase 337

12.3.3 Sulfotransferase 337

12.3.4 Other Enzymes 337

12.4 Oral Bioavailability 341

12.4.1 In Vivo Approaches to Differentiate Between Intestinal and Hepatic First-Pass Metabolism 342

12.4.2 In Vitro Approaches to Estimate Intestinal Metabolism 344

12.4.3 Computational Approaches to Estimate and to Predict Human Intestinal Metabolism 345

12.5 Clinical Relevance of Gut Wall First-Pass Metabolism 347

References 347

13 Modified Cell Lines 359
Guangqing Xiao and Charles L. Crespi

13.1 Introduction 359

13.2 Cell/Vector Systems 360

13.3 Expression of Individual Metabolic Enzymes 363

13.4 Expression of Transporters 365

13.4.1 Efflux Transporters 365

13.4.2 Uptake Transporters 367

13.5 Summary and Future Perspectives 368

References 368

Part Four Computational Approaches to Drug Absorption and Bioavailability 373

14 Calculated Molecular Properties and Multivariate Statistical Analysis 375
Ulf Norinder

14.1 Introduction 377

14.2 Calculated Molecular Descriptors 377

14.2.1 2D-Based Molecular Descriptors 377

14.2.1.1 Constitutional Descriptors 378

14.2.1.2 Fragment- and Functional Group-Based Descriptors 378

14.2.1.3 Topological Descriptors 379

14.2.2 3D Descriptors 381

14.2.2.1 WHIM Descriptors 381

14.2.2.2 Jurs Descriptors 382

14.2.2.3 VolSurf and Almond Descriptors 383

14.2.2.4 Pharmacophore Fingerprints 384

14.2.3 Property-Based Descriptors 385

14.2.3.1 log P 385

14.2.3.2 HYBOT Descriptors 386

14.2.3.3 Abraham Descriptors 386

14.2.3.4 Polar Surface Area 386

14.3 Statistical Methods 387

14.3.1 Linear and Nonlinear Methods 388

14.3.1.1 Multiple Linear Regression 388

14.3.1.2 Partial Least Squares 389

14.3.1.3 Artificial Neural Networks 390

14.3.1.4 Bayesian Neural Networks 390

14.3.1.5 Support Vector Machines 390

14.3.1.6 k-Nearest Neighbor Modeling 392

14.3.1.7 Linear Discriminant Analysis 392

14.3.2 Partitioning Methods 393

14.3.2.1 Traditional Rule-Based Methods 393

14.3.2.2 Rule-Based Methods Using Genetic Programming 394

14.3.3 Consensus and Ensemble Methods 395

14.4 Applicability Domain 396

14.5 Training and Test Set Selection and Model Validation 398

14.5.1 Training and Test Set Selection 398

14.5.2 Model Validation 399

14.6 Future Outlook 400

References 401

15 Computational Absorption Prediction 409
Christel A.S. Bergström, Markus Haeberlein, and Ulf Norinder

15.1 Introduction 410

15.2 Descriptors Influencing Absorption 410

15.2.1 Solubility 411

15.2.2 Membrane Permeability 412

15.3 Computational Models of Oral Absorption 413

15.3.1 Quantitative Predictions of Oral Absorption 413

15.3.1.1 Responses: Evaluations of Measurement of Fraction Absorbed 417

15.3.1.2 Model Development: Data sets, Descriptors, Technologies, and Applicability 419

15.3.2 Qualitative Predictions of Oral Absorption 420

15.3.2.1 Model Development: Data sets, Descriptors, Technologies, and Applicability 420

15.3.2.2 An Example Using Genetic Programming-Based Rule Extraction 426

15.3.3 Repeated Use of Data Sets 427

15.4 Software for Absorption Prediction 427

15.5 Future Outlook 428

References 429

16 In Silico Prediction of Human Bioavailability 433
David J. Livingstone and Han van de Waterbeemd

16.1 Introduction 434

16.2 Concepts of Pharmacokinetics and Role of Oral Bioavailability 437

16.3 In Silico QSAR Models of Oral Bioavailability 438

16.3.1 Prediction of Human Bioavailability 438

16.3.2 Prediction of Animal Bioavailability 441

16.4 Prediction of the Components of Bioavailability 441

16.5 Using Physiological Modeling to Predict Oral Bioavailability 443

16.6 Conclusions 445

References 446

17 Simulations of Absorption, Metabolism, and Bioavailability 453
Michael B. Bolger, Robert Fraczkiewicz, and Viera Lukacova

17.1 Introduction 454

17.2 Background 454

17.3 Use of Rule-Based Computational Alerts in Early Discovery 456

17.3.1 Simple Rules for Drug Absorption (Druggability) 456

17.3.2 Complex Rules That Include Toxicity 473

17.4 Mechanistic Simulation (ACAT Models) in Early Discovery 474

17.4.1 Automatic Scaling of k'a 0 as a Function of Peff, pH, log D, and GI Surface Area 477

17.4.2 Mechanistic Corrections for Active Transport and Efflux 478

17.4.3 PBPK and In Silico Estimation of Distribution 481

17.5 Mechanistic Simulation of Bioavailability (Drug Development) 481

17.5.1 Approaches to In Silico Estimation of Metabolism 484

17.6 Regulatory Aspects of Modeling and Simulation (FDA Critical Path Initiative) 484

17.7 Conclusions 485

References 485

18 Toward Understanding P-Glycoprotein Structure-Activity Relationships 497
Anna Seelig

18.1 Introduction 498

18.1.1 Similarity Between P-gp and Other ABC Transporters 498

18.1.2 Why P-gp Is Special 500

18.2 Measurement of P-gp Function 500

18.2.1 P-gp ATPase Activity Assay 500

18.2.1.1 Quantification of Substrate-Transporter Interactions 503

18.2.1.2 Relationship between Substrate-Transporter Affinity and Rate of Transport 504

18.2.2 Transport Assays 506

18.2.3 Competition Assays 508

18.3 Predictive In Silico Models 508

18.3.1 Introduction to Structure-Activity Relationship 509

18.3.2 3D-QSAR Pharmacophore Models 509

18.3.3 Linear Discriminant Models 510

18.3.4 Modular Binding Approach 511

18.3.5 Rule-Based Approaches 512

18.4 Discussion 513

18.4.1 Prediction of Substrate-P-gp Interactions 513

18.4.2 Prediction of ATPase Activity or Intrinsic Transport 513

18.4.3 Prediction of Transport (i.e., Apparent Transport) 513

18.4.4 Prediction of Competition 514

18.4.5 Conclusions 514

References 514

Part Five Drug Development Issues 521

19 Application of the Biopharmaceutics Classification System Now and in the Future 523
Bertil Abrahamsson and Hans Lennernäs

19.1 Introduction 524

19.2 Definition of Absorption and Bioavailability of Drugs Following Oral Administration 527

19.3 Dissolution and Solubility 528

19.4 The Effective Intestinal Permeability (Peff) 535

19.5 Luminal Degradation and Binding 539

19.6 The Biopharmaceutics Classification System 541

19.6.1 Regulatory Aspects 541

19.6.1.1 Present Situation 541

19.6.1.2 Potential Future Extensions 543

19.6.2 Drug Development Aspects 543

19.6.2.1 Selection of Candidate Drugs 544

19.6.2.2 Choice of Formulation Principle 545

19.6.2.3 In Vitro/In Vivo Correlation 547

19.6.2.4 Food-Drug Interactions 549

19.6.2.5 Quality by Design 552

19.7 Conclusions 552

References 553

20 Prodrugs 559
Bernard Testa

20.1 Introduction 559

20.2 Why Prodrugs? 560

20.2.1 Pharmaceutical Objectives 560

20.2.2 Pharmacokinetic Objectives 561

20.2.3 Pharmacodynamic Objectives 564

20.3 How Prodrugs? 565

20.3.1 Types of Prodrugs 565

20.3.2 Hurdles in Prodrug Research 567

20.4 Conclusions 568

References 568

21 Modern Delivery Strategies: Physiological Considerations for Orally Administered Medications 571
Clive G. Wilson and Werner Weitschies

21.1 Introduction 571

21.2 The Targets 572

21.3 The Upper GI Tract: Mouth and Esophagus 573

21.3.1 Swallowing the Bitter Pill... 575

21.4 Mid-GI Tract: Stomach and Intestine 576

21.4.1 Gastric Inhomogeneity 576

21.4.2 Gastric Emptying 579

21.4.3 Small Intestinal Transit Patterns 581

21.4.4 Modulation of Transit to Prolong the Absorption Phase 582

21.4.5 Absorption Enhancement 582

21.5 The Lower GI Tract: The Colon 583

21.5.1 Colonic Transit 584

21.5.2 Time of Dosing 585

21.5.3 Modulating Colonic Water 586

21.6 Pathophysiological Effects on Transit 587

21.7 Pathophysiological Effects on Permeability 589

21.8 pH 589

21.9 Conclusions 590

References 590

22 Nanotechnology for Improved Drug Bioavailability 597
Marjo Yliperttula and Arto Urtti

22.1 Introduction 597

22.2 Nanotechnological Systems in Drug Delivery 599

22.2.1 Classification of the Technologies 599

22.2.1.1 Nanocrystals 599

22.2.1.2 Self-Assembling Nanoparticulates 600

22.2.1.3 Processed Nanoparticulates 601

22.2.1.4 Single-Molecule-Based Nanocarriers 601

22.2.2 Pharmaceutical Properties of Nanotechnological Formulations 601

22.2.2.1 Drug-Loading Capacity 601

22.2.2.2 Processing 602

22.2.2.3 Biological Stability 602

22.3 Delivery via Nanotechnologies 603

22.3.1 Delivery Aspects at Cellular Level 603

22.3.2 Nanosystems for Improved Oral Drug Bioavailability 606

22.3.3 Nanosystems for Improved Local Drug Bioavailability 606

22.4 Key Issues and Future Prospects 608

References 609

Index 613

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