Drug Stability for Pharmaceutical Scientists

Table of Contents

I. Principles of drug degradation (the solution kinetics and mathematical treatment): 1. Zero, first, second and third order reactions 2. Complex reactions (e.g. reversible reactions, parallel reactions, consecutive reactions, steady state, enzyme kinetics etc.) 3. Effect of temperature (e.g. Arrhenius, Q10-values, Collision theory, Transition state theory, Eyring equation etc.) 4. Effect of pH (Specific acid/base catalysis, pH-rate profiles) 5. Effect of buffer salts (General acid/base catalysis or buffer catalysis) 6. Ionic strength 7. Solvent effects (e.g. dielectric constant) 8. Surface active compounds (micelle effect) 9. Effect of complexation (e.g. cyclodextrins, metal ions and carbohydrates) 10. Effect of light, oxygen and other catalytic compounds. II. Degradation pathways Selected examples of drug degradation with examples and mathematical calculations. 1. Hydrolysis (aspirin, procaine, procainamide, acetaminophen, ß-lactam antibiotics, nitrogen mustards etc.) 2. Oxidation (morphine, epinephrine, vitamin C, vitamin A, hydrocortisone, polyunsaturated fatty acids (autoxidation) etc.; antioxidants) 3. Isomerization and racemization (ephedrine, tetracyclines, pilocarpine, vitamin A, thalidomide, etc.) 4. Photodegradation 5. Polymerization (ß-lactam antibiotics etc.) 6. Decarboxylation and elimination (p-aminosalicylic acid) 7. Dehydration (prostaglandins etc.) III. Drug degradation in semi-solid state 1. Ointments 2. Creams (o/w and w/o emulsions) 3. Gels IV. Drug degradation in solid state 1. Physical stability of drugs (crystallization of amorphous drugs, polymorph transitions, crystal growth, moisture absorption and vapor absorption, nitroglycerine) 2. Chemical stability (hydrolysis (aspirin), etc.) V. Stability of peptide and proteins VI. Stability testing 1. Stability testing during preformulation studies. 2. Stability testing of the final product 3. Regulations of stability testing (including ICH guidelines) Appendix

Authors

Thorsteinn Loftsson MS Pharm, MSc, PhD, Faculty of Pharmaceutical Sciences, Professor of Physical Pharmacy, University of Iceland, Reykjavik, Iceland. Dr. Thorsteinn Loftsson is a Professor of Physical Pharmacy at the University of Iceland in Reykjavik. He received his MS Pharm degree from University of Copenhagen and his MS and PhD degrees from the Department of Pharmaceutical Chemistry at the University of Kansas. Dr. Loftsson has authored or co-authors over 200 papers in peer-reviewed journals, numerous book chapters and 20 patents and patent applications. His main research areas include the pharmaceutical applications of cyclodextrins, marine lipids, prodrugs and soft drugs. He has conducted over 100 lectures and is a Fellow of the American Association of Pharmaceutical Scientists (AAPS). Dr. Loftsson is also a member for the editorial board of Journal of Pharmaceutical Sciences, International Journal of Pharmaceutics, Journal of Pharmacy and Pharmacology, die Pharmazie and Journal of Drug Delivery Science and Technology (formerly STP Pharma Sciences).