DEVELOPMENT AND ASSESSMENT OF MINOCYCLINE SUSTAINED RELEASE CAPSULE FORMULATIONS By Tinotenda Chipo Victoria Sachikonye A Thesis Submitted to Rhodes University in Fulfillment of the Requirements for the degree of MASTER OF SCIENCE (PHARMACY) February 2010 Faculty of Pharmacy Rhodes University Grahamstown South Africa ABSTRACT The use of minocycline for the treatment of a broad range of systemic infections and for severe acne has been associated with vestibular side effects. The severity of side effects may lead to poor adherence to therapy by patients. The use of sustained release formulations of minocycline that display slow dissolution of minocycline following administration may be beneficial in reducing the incidence and severity of side effects. Therefore, sustained release capsule dosage forms containing 100 mg minocycline (base) were manufactured and assessed for use as sustained release oral dosage forms of minocycline. \ Minocycline sustained release capsules were manufactured based on matrix technologies using hydroxypropylmethyl cellulose (HPMC) and Compritol® as release retarding polymers. The rate and extent of minocycline release from the capsules was evaluated using USP Apparatus 1 and samples were analysed using a validated High Performance Liquid Chromatographic (HPLC) method with ultraviolet (UV) detection. Differences in the rate and extent of minocycline release from formulations manufactured using HPMC or Compritol® were influenced by the concentration of polymer used in the formulations. The rate and extent of minocycline release was faster and greater when low concentrations of polymer were used in formulations. The effect of different excipients on the release pattern(s) of minocycline and particularly their potential to optimise minocycline release from experimental formulations was investigated. The use of diluents such as lactose and microcrystalline cellulose (MCC) revealed that lactose facilitated minocycline release when HPMC was used as the polymer matrix. In contrast, the use of lactose as diluent resulted in slower release of minocycline from Compritol® based formulations. The addition of sodium starch glycolate to HPMC based formulations resulted in slower release of minocycline than when no sodium starch glycolate was used. Compritol® based formulations were observed to release minocycline faster following addition of sodium starch glycolate and Poloxamer 188 to experimental formulations. In vitro dissolution profiles were compared to a target or reference profile using the difference and similarity factors, f1 and {2 , and a one way analysis of variance (ANOVA). In addition, the mechanism of minocycline release was elucidated following fitting of dissolution data to the Korsmeyer-Peppas, Higuchi and Zero order models. Minocycline release kinetics were best described by the Korsmeyer-Peppas model and the values of the release exponent, n, revealed that drug release was a result of the combined effects of minocycline diffusion through matrices and erosion of the matrices. These in vitro dissolution profiles were better fit to the Higuchi model than to the Zero order model. Two formulations that displayed a fit to the Zero order model were identified for further studies as potential dosage forms for sustained release minocycline. II ACKNOWLEDGEMENTS I hereby express my sincere gratitude to the following people: My supervisor Prof R. B. Walker for his guidance and continuous motivation throughout the duration of my studies. ProfR. B. Walker, in his capacity as Head and Dean, and the staff of the Faculty of Pharmacy for the use of the facilities in the Faculty. Mr T. Samkange, Mr L.H. Purdon and Mr T. C. Nontyi for technical assistance throughout the course of this study. The Mandela Rhodes Foundation for financial support and for the opportunity to attend leadership courses and participate in the mento ring programme during the course of my postgraduate studies. Aspen Pharmacare (Port Elizabeth, South Africa) for the donation of minocycline hydrochloride and various excipients, and Gattefosse Corp. (Paris, France) for the donation of lipid excipients. My colleagues in the Biopharmaceutics Research Laboratory for their support and motivation throughout the course of this study. My late parents, Mr M.I. and Mrs G. Sachikonye for the values they instilled in me that have made me the person I am today. My siblings, Tonderai, Sarah and Mwazvita, for their encouragement and for believing in me. My aunt and uncle, MrS. and Mrs F. Mutepfa, for their support throughout the duration of my studies. Nyasha Chigwamba, for his support and encouragement throughout the period of this study. I give all the glory to the Lord God Almighty for it is only by His grace that I have made it thus far in my academic career and in my life. iii STUDY OBJECTIVES Minocycline, a second generation tetracycline antibiotic is prescribed for a broad range of systemic infections [1]. In addition, minocycline is used for the management and treatment of severe acne that is unresponsive to treatment with other tetracycline antibiotics [ 1]. Chronic use of minocycline is associated with vestibular side effects, the severity of which may cause patients to default on treatment [2-4]. The incidence and severity of side effects bas been shown to be greater when dissolution of m.inocycline following administration is rapid [5]. The vestibular side effects associated with rapid dissolution of the API may be reduced by the administration of a sustained release formulation, thereby potentially promoting adherence to therapy by the patient. The objectives of this study were: 1. To develop and validate a stability-indicating, simple, sensitive and selective High Performance Liquid Chromatographic (HPLC) method with the necessary accuracy and precision for the quantitation of minocycline in aqueous solutions and in pharmaceutical dosage forms. 2. To investigate the use of hydrophilic and lipophilic polymers for the development of minocycline (100 mg base) sustained release dosage forms that released at least 80% according to a zero order kinetic model for 12 hours. 3. To assess and evaluate the rate and extent of minocycline release from the formulations using an appropriate dissolution method. 4. To study the dissolution kinetics and release mechanisms of minocycline from manufactured capsule dosage forms. lV TABLE OF CONTENTS ABSTRACT ACKNOWLEDGEMENTS iii STUDY OBJECTIVES iv LIST OF FIGURES X LIST OF TABLES xii CHAPTER ONE 1 MINOCYCLINE HYDROCHLORIDE 1 1.1 INTRODUCTION 1 1.2 PHYSICO-CHEMICAL PROPERTIES 2 1.2.1 DESCRIPTION 2 1.2.2 SOLUBILITY 2 1.2.3 DISSOCIATION CONSTANT (PKA) 3 1.2.4 PARTITION COEFFICIENT 4 1.2.5 PH OF SOLUTION 4 1.2.6 M ELTING RANGE 4 1.2.7 INFRA-RED ABSORPTION SPECTRUM 5 1.2.8 ULTRA-VIOLET ABSORPTION SPECTRUM 5 1.2.9 NUCLEAR MAGNETIC RESONANCE SPECTRUM 8 1.3 SYNTHESIS 9 1.3.1 S YNTHETIC PROCEDURE/PATHWAY 9 1.3 .2 STRUCTURE ACTIVITY RELATIONSHIP 12 1.4 STABILITY 13 1.4.1 TEMPERATURE 13 1.4.2 PH 13 1.4.3 OXIDATIVE DEGRADATION 14 1.4.4 STRUCTURAL REARRANGEMENT OF TETRACYCLINE ANTffiiOTICS 14 1.5 CLINICAL PHARMACOLOGY 15 1.5.1 M ODE OF ACTION 15 1.5 .2 SPECTRUM OF ACTIVITY 15 1.5.3 INDICATIONS 16 1.5 .4 R OLE OF MINOCYCLJNE IN NEUROLOGY 16 1.5.5 RESISTANCE 17 1.5.6 CONTRAINDICATIONS 18 1.5.7 DRUG INTERACTIONS 18 1.5.8 ADVERSE REACTIONS 18 1.5.9 HIGH RISK GROUPS 19 1.6 PHARMACOKINETICS 19 1.6.1 D OSAGE 19 1.6.2 ABSORPTION 20 1.6.3 DISTRIBUTION 20 1.6.4 METABOLISM 20 1.6.5 ELIMINATION 21 1.7 CONCLUSIONS 21 v CHAPTER TWO 23 THE DEVELOPMENT AND VALIDATION OF AN HPLC METHOD FOR THE ANALYSIS OF MINOCYCLINE 23 2.1 INTRODUCTION 23 2.1.1 OVERVIEW 23 2.1.2 PRINCIPLES OF HPLC 23 2.2 LITERATURE REVIEW 26 2.3 EXPERIMENTAL 28 2.3.1 REAGENTS 28 2.3.2 PREPARATION OF STOCK SOLUTIONS 28 2.3.3 PREPARATION OF BUFFER SOLUTIONS 28 2.3.4 PREPARATION OF MOBILE PHASE 29 2.3.5 HPLCSYSTEM 29 2.4 METHOD DEVELOPMENT AND OPTIMISATION 29 2.4.1 INTRODUCTION 29 2.4.2 COLUMN SELECTION 30 2.4.3 lN DETECTION 33 2.4.4 CHOICE OF INTERNAL STANDARD 34 2.4.5 MOBILE PHASE SELECTION 34 2.4.5.1 Effect of organic modifier 36 2.4.5.2 Effect of buffer molarity 37 2.4.5.3 Effect of buffer pH 38 2.4.6 MOBILE PHASE SELECTED 39 2.4.7 CHROMATOGRAPHIC CONDITIONS 41 2.4.8 CONCLUSIONS 41 2.5 METHODVALIDATION 42 2.5.1 INTRODUCTION 42 2.5.2 LINEARITY AND RANGE 42 2.5.3 PRECISION 43 2.5.3.1 Repeatability 43 2.5.3.2 Intermediate precision 44 2.5.3.3 Reproducibility 44 2.5.4 ACCURACY 45 2.5.5 LIMITS OF QUANTITA TION (LOQ) AND DETECTION (LOD) 46 2.5.6 SPECIFICITY AND SELECTIVITY 48 2.5.7 STRESS STUDIES 48 2.5.7.1 Photostability studies 49 2.5.7.2 Temperature stress studies 49 2.5.7.3 Acid degradation studies 49 2.5.7.4 Oxidation studies 50 2.5.7.5 Alkali degradation studies 50 2.5.7.6 Results and discussion 50 2.6 ASSAY OF CYCLIMYC~-50 AND CYCLJMYCIN®-100 CAPSULES 53 2. 7 CONCLUSIONS 53 VI CHAPTER THREE 54 FORMULATION DEVELOPMENT AND ASSESSMENT OF MINOCYCLINE SUSTAINED -R ELEASE CAPSULE DOSAGE FORMS 54 3.1 INTRODUCTION 54 3.2 ORAL MODIFIED-RELEASE DRUG DELIVERY SYSTEMS 54 3.2.1 M ATRIX SYSTEMS 55 3.2.2 RESERVOIR SYSTEMS 56 3.2.3 OSMOTIC SYSTEMS 58 3.3 MINOCYCLINE MODIFIED-RELEASE DOSAGE FORMS 60 3.4 PHARMACEUTICAL CAPSULES 62 3.4.1 TWO-PIECE HARD CAPSULES 62 3.4.1.1 Manufacture of hard gelatin capsules 62 3.4.1.2 Capsule properties 63 3.4.1.3 Capsule sizes 64 3.4.2 ALTERNATIVES TO HARD GELATIN CAPSULES 64 3.4.2.1 Hydroxypropyl methylcellulose (HPMC) capsules 65 3.4.2.2 Starch capsules 65 3.4.3 CAPSULE FILL MATERIALS 66 3.4.3.1 Solids for capsule filling 66 3.4.3.2 Liquid and semi-solid