(RP) Physicochemical Principles of Pharmacy. Alexander T Florence CBE, DSc, FRSE, FRPharmS. David Attwood PhD, DSc, CChem, FRSC. Pharmaceutical Press

Transcription

1 Physicochemical Principles of Pharmacy Alexander T Florence CBE, DSc, FRSE, FRPharmS The School of Pharmacy, University of London, UK David Attwood PhD, DSc, CChem, FRSC School of Pharmacy and Pharmaceutical Sciences University of Manchester, UK (RP) Pharmaceutical Press

2 Contents Preface About the authors Introduction xv xvii 1 1 Solids 1.1 Classincation of solids Crystalline solids - structure and properties Crystal structure Crystal form Polymarphism Multicomponent crystals Amorphous solids Dissolution of solid drugs Importance of particle size in the farmulation and manufacture of solid dosage farms Biopharmaceutical importance of particle size Wetting of powders Contact angle and wettability of solid surfaces Wettability of powders Sublimation Solid dispersions Eutectics and drug identification Physicochemical properties of drugs in solution 2.1 Concentration units Weight or volume concentration Molarity and molality Milliequivalents Mole fraction 2.2 Thermodynamics - abrief introduction Energy Enthalpy 22.3 Entropy Free energy

3 vi I Contents 2.3 Activity and chemical potential Activity and standard states Activity of ionised drugs Solvent activity Chemical potential Osmotic properties of drug solutions Osmotic pressure Osmolality and osmolarity Clinical relevance of osmotic effects Preparation of isotonic solutions Ionisation of drugs in solution Clinical relevance of drug ionisation Dissociation of weakly acidic and basic drugs and their salts The effect of ph on the ionisation of weakly acidic or basic drugs and their salts Ionisation of amphoteric drugs Ionisation of polyprotic drugs Microdissociation constants pk a values of proteins Calculation of the ph of drug solutions Buffer solutions Diffusion of drugs in solution ~~~ ~ 3 Drug stability 3.1 The chemical decomposition of drugs Hydrolysis Oxidation Isomerisation Photochemical decomposition Polymerisation 3.2 Kinetics of chemical decomposition in solution Classifyi ng reactions: the order of reaction Zero-order reactions First-order reactions Second-order reactions Third-order reactions Determination of the order of reaction Complex reactions 3.3 Solid dosage forms: kinetics of chemical decomposition 3.4 Factors influencing drug stability Liquid dosage forms Semisolid dosage forms Solid dosage forms 3.5 Stability testing and prediction of shelf-life Effect of temperature on stability

4 Contents I vii Other environmental factors affecting stability Protocol for stability testing The solubility of drugs Definitions Expressions of solubility Factors influencing solubility Structural features and aqueous solubility Hydration and solvation The effect of simple additives on solubility The effect of ph on the solubility of ionisable drugs Measurement of solubility The solubility parameter Solubility parameters and biological processes Solubility in mixed solvents Cyclodextrins as solubilising agents Solubility problems in formulation Mixtures of acidic and basic compounds Choice of drug salt to optimise solubility Drug solubility and biological activity Partitioning The partition coefficient Free energies of transfer Octanol as a nonaqueous phase Biological activity and partition coefficients: thermodynamic activity and Ferguson's principle Using 10gP The relationship between lipophilicity and behaviour of tetracyclines Sorption A chromatographie model for the biophase Calculating log P from molecular structures Drug distribution into human milk Surfactants Amphipathic compounds Surface and interfacial properties of surfactants Effects of amphiphiles on surface and interfacial tension Change of surface tension with surfactant concentration - the critical micelle concentration Gibbs adsorption equation The influence of the surfactant structure on surface activity Surface activity of drugs Insoluble monolayers

5 viii I Contents Pharmaceutical applications of surface film studies Adsorption at the solid-liquid interface Micellisation Water structure and hydrophobie bonding Theories of micelle formation Micellar structure Factors affecting the critical micelle concentration and micellar size Liquid crystals and surfactant vesicles Liquid crystals Liposomes, niosomes and surfactant vesicles 224 Properties of some commonly used surfactants Anionic surfactants Cationic surfactants Nonionic surfactants Solubilisation Determination of maximum additive concentration Location of the solubilisate Factors affecting solubilisation Pharmaceutical applications of solubilisation Emulsions, suspensions and other disperse systems Colloids and their classification Colloid stability Forces of interaction between colloidal particles Repulsion between surfaces with macromolecular stabilisers Emulsions Stability of o/w and w/o emulsions HLB system Multiple emulsions Microemulsions Structured (semisolid) emulsions Biopharmaceutical aspects of emulsions Preservative availability in emulsified systems Mass transport in oil-in-water emulsions Intravenous fat emulsions Emulsion rheology Suspensions Stability of suspensions Extemporaneous suspensions Suspension rheology Nonaqueous suspensions Electrostatics in aerosols Adhesion of suspension particles to containers Powder processing 273

6 Contents I Ix 6.5 Miscellaneous colloidal systems Applications of colloid stability theory to other systems Cell-cell interactions Adsorption of microbial cells to surfaces Blood as a colloidal system Foams Polymers and macromolecules Pharmaceutical polymers Definitions Polydispersity Polymer mixtures or blends Polymer solubility Water-soluble polymers General properties of polymer solutions Viscosity of polymer solutions Gel formation Syneresis Polymer complexes Binding of ions to macromolecules Interaction of polymers with solvents inc!uding water Adsorption of macromolecules Water-soluble polymers used in pharmacy and medicine Carboxypolymethylene (Carbomer, Carbopol) Cellulose derivatives Natural gums and mucilages Chitosan Dextran Polyvinylpyrrolidone Polyoxyethylene glycols (Macrogols) Bioadhesivity of water-soluble polymers Polymers as wound dressings Polymer crystallinity Water-insoluble polymers and polymer membranes Permeability of polymers Ion-exchange resins Silicone oligomers and polymers Some applications of polymerie systems in drug delivery Film coating Matrices Microcapsules and microspheres 319 ) Rate-limiting membranes and devices Eroding systems Osmotic pumps Transdermal delivery systems 325

7 I Contents Further reading Pharmaceutical nanotechnology Introduction 8.1 PartieIe size 8.2 Physicochemical characterisation of nanosystems 8.3 Nanoparticles in pharmacy Nanoparticles as drug carriers Application of nanopartieies in drug delivery 8.4 NanopartieIe manufacturing methods Solvent displacement Salting-out Emulsion-diffusion Emulsion-solvent evaporation Supercritical fluid technologies eoacervation and complexation techniques In situ polymerisation 8.5 Nanocrystal formation 8.6 Drug targeting with nanopartieies - particle flow 8.7 Aggregation 8.8 PEGylated nanoparticles 8.9 Nanoparticle diffusion 8.10 Regulatory challenges: characterisation Drug absorption and the oral route 9.1 Biologlcal membranes and drug transport Lipophilicity and absorption Permeability and the ph-partition hypothesis 9.1,3 Problems wlth the quantitative application of the ph-partition hypothesis 92 The oral route and oral absorption 92.1 Drugabsorptton from the gastrointestinal tract StrUeture of thegastrointestinal tract 92.3 Blle salts and fat absorption pathways Gastrlc emptying, motlllty'am volume of contents 9.3 Oral dosage forms The Biopharmaceutical Classiflcation System (ßeS) 9.4 Buccal and sublingual absorption Mechanismsof absorption

8 Contents I xi 10 Parenteral routes of drug administration Intravenous and intra-arterial administration Intramuscular and subcutaneous injection The importance of site of injection Vehicles Blood flow in muscles Formulation effects The case of insulin Transdermal delivery Routes of skin penetration Influence of the drug Influence of the vehicle Dilution of topical steroid preparations Transdermal medication: patches and devices Ultrasound and transdermal penetration Jet injectors Topical treatment ofthe nails: trans-ungual therapy Medication of the eye and the eye as a route for systemic delivery The eye Absorption of drugs applied to the eye Influence of formulation Systemic effects from eye-drops The ear (the aural route) Absorption from the vagina Delivery systems Inhalation therapy Physical factors affecting deposition of aerosols Experimental observations The nasal route Rectal absorption of drugs Intrathecal drug administration Further reading Physlcochemlcal drug Interactions and Incompatlblllties ph effects in vitro and in vive In vitro ph effects In vivo ph effects Dilution of mixed solvent systems Cation-anion interactions Polyions and drug solutions Chelation Other complexes Interaction of drugs with cyclodextrins lon-exchange interactions 433

9 xii Contents 11.7 Adsorption of drugs Protein and peptide adsorption Protein aggregation and interactions Drug interactions with plastics Protein binding Thermodynamics of protein binding Lipophilicity and protein binding Penetration of specialised sites Appendix: Drug interactions based on physical mechanisms 446 A: Interactions affecting absorption of drugs 446 B: Interactions involving protein binding Peptides, proteins and other biopharmaceuticals Structure and solution properties of peptides and proteins Structure of peptides and proteins Hydrophobicity of peptides and proteins Solubility of peptides and proteins The stability of proteins and peptides Physical instability Formulation and protein stabilisation Chemical instability Protein formulation and delivery Protein and peptide transport Lyophilised proteins Water adsorption PEGylation of peptides and proteins Routes of delivery A therapeutic protein and a peptide Insulin Calcitonin DNA and oligonucleotides DNA Oligonucleotides Therapeutic monoclonal antibodies Physical assessment of dosage forms 13.1 Dissolution testing of solid oral dosage forms Pharmacopoeial and compendial dissolution tests Flow-through systems 13.2 In vitro-in vivo correlations

10 Contents I xiii Index 13.3 Evaluation of suppositories and topical preparations Suppository formulations In vitra release from topical products and transdermal systems Rheological characteristics of products Adhesivity of dosage forms Gastro-retentive systems: buoyancy tests Evaluation of aerosols