Formulation and Ocular Bioavailability of Certain Drugs from Ophthalmic Preparations Thesis presented by Ghada Saad Ahmed El-Moursy B. Pharm. Mansoura University (2007) Submitted in Partial Fulfillment for the Master Degree in Pharmaceutical Sciences (Pharmaceutics) Under the Supervision of Prof. Dr. Abd El-Gawad H. Abd El-Gawad Professor of Pharmaceutics Faculty of Pharmacy, Mansoura University Prof. Dr. Osama Abd EL-Azeem Soliman Professor of Pharmaceutics Faculty of Pharmacy, Mansoura University - 1 -
The complicated anatomical structure of the eye and precorneal factors are the main factors that may hinder the absorption of drugs from eye surface and so decrease their bioavailability. Precorneal factors include blinking, tear formation, tear turn over, and flow through nasolacrimal duct. Numerous strategies were developed to increase the bioavailability of ophthalmic drugs by prolonging the contact time between the preparations containing drug and the corneal/conjunctival epithelium. These strategies are including viscosity enhancers, penetration enhancers, nanoparticles, usage of mucoadhesive polymers, and other controlled systems, like ocuserts. The main objective of this thesis, is to formulate certain ophthalmic preparations including eye gels, ocuserts, microemulsions and in-situ gelling systems using different polymers. In-vitro release characteristics and accelerated stability study of the prepared formulations were of prime interest in this investigation. Also, in-vivo study of the selected formulae was performed to examine the ocular bioavailability of the investigated drugs in the eye tissues. In this thesis, two drugs were selected; the first drug was desloratadine (antihistaminic agent) and the second one was gatifloxacin (antibacterial agent). To fulfill these goals, this thesis includes the following two parts: Part I: Formulation and Evaluation of Desloratadine Ophthalmic Preparations. Part II: Formulation and Evaluation of Gatifloxacin Ophthalmic Preparations. Part I Formulation and Evaluation of Desloratadine Ophthalmic Preparations This part consists of four chapters and deals with formulation, evaluations of the ophthalmic formulations containing desloratadine. In addition, accelerated stability of desloratadine from different ophthalmic formulae and the effect of the drug on the decongesion time of inflamed rabbits eyes were studied. Furthermore, the ocular bioavailability of the drug was investigated. - 2 -
Chapter 1 Formulation and In-vitro Evaluation of Desloratadine Ophthalmic Preparations The work in this chapter involved the formulation of desloratadine in different ophthalmic preparations including eye gels, microemulsions, and ocuserts using different polymers such as; hydroxypropyl methylcellulose, methylcellulose, sodium carboxymethyl cellulose, and sodium alginate. The characterizations of the prepared formulae were performed through the determination of drug content, ph, viscosity, and transmission electron microscopy (TEM) for microemulsions. Furthermore, in-vitro release through cellophane membrane in phosphate buffer of ph 7.4 at 37 o C was investigated. Then, the kinetic analysis of the release data was done. From the obtained results it was clear that: 1) The prepared ophthalmic preparations showed that the drug content was complied with pharmacopial limits, ph values tolerated by the eye, and acceptable viscosity limits. 2) Regarding the percentage of the drug release from different formulations, it was found that, the drug release is affected by the polymer types and dosage forms. 3) The nature of polymers utilized affected drug release in the following order: HPMC > Sod. CMC > MC. 4) Ocuserts exhibited a significantly higher release of desloratadine with the corresponding gels of the same polymers due to the difference in their viscosities upon exposure to the release conditions, as the higher the viscosity the slower drug release rate. 5) Microemulsions of desloratadine were successfully prepared employing isopropyl myristate as oil phase, tween 80 as surfactant, and propylene glycol as cosurfactant in different ratios, which was suggested depending on pseudoternary phase diagram. 6) The drug from microemulsions released slowly as it was located in the internal oil phase. 7) Images of microemulsions by transmission electron microscopy showed that all the prepared microemulsions have distinct shapes which are perfectly spherical with solid dense surfactant and co-surfactant cores surrounded by evenly distributed thin coat that may be comprised of oils. - 3 -
8) Regarding the results of the release kinetic analysis: the drug release mechanism from the different ophthalmic formulations was a combination of two mechanisms Higuchi model followed by first-order model, in which one is more predominant than the other. Chapter 2 Stability Study of Desloratadine in Ophthalmic Preparations The purpose of work in this chapter was, to study the effect of different storage temperatures on the physical and chemical stability of desloratadine in ophthalmic formulations. The stability study was carried out on the formulations prepared in chapter 1. The tested formulations were stored at different temperatures (30 o C, 35 o C, and 40 o C) for six months. The tested formulations were evaluated initially and at specified time intervals (1, 2, 3, 4, 5 and 6 months) for their physical characteristics, ph, viscosity, in-vitro release and drug content. The obtained results revealed that: 1) The decomposition rate of desloratadine followed first-order degradation kinetics. 2) The prepared formulations exhibited the highest physical and chemical stability up to six months of storage at 30 C, 35 C and 40 C except formulae containing MC polymer showed the least stable formulations. 3) The stability of the tested formulae could be arranged in the following order; ocuserts > eye gels > microemulsions. 4) The nature of polymers utilized affected drug stability in the following order: HPMC > Sod. CMC > MC. 5) The most stable formula for ocusert was HPMC & Sod. Alg formula (25.77 months), for eye gel was HPMC formula (24.33 months) and for microemulsion was Sod. CMC formula (23.45 months) at 25 o C. 6) The most stable formulae were selected for further study of the effect of desloratadine ophthalmic formulations on the treatment of allergic conjunctivitis. - 4 -
Chapter 3 Effect of Desloratadine Ophthalmic Formulations on the Treatment of Allergic Conjunctivitis The purpose of work in this chapter was to study the effect of the selected ophthalmic formulations containing desloratadine on the inflamed rabbits eyes after instillation of histamine solution and determine the average of decongestion time. These formulae were selected on the basis of in-vitro drug release and stability data. The selected formulae were HPMC eye gel, HPMC/Sod. Alg ocusert and Sod. CMC microemulsions, in addition to the control formula, drug suspended in water (0.05% w/v). The obtained results can be summarized as follow: 1) Desloratadine, as antihistaminic drug, could treat the histamine induced ocular surface redness in the rabbits eyes successfully. 2) The average currance times of the inflamed rabbits eyes treated with the tested formulations which containing 0.05% of desloratadine are markedly influenced by the formulation type (eye gels, ocuserts or microemulsions). 3) The tested formulae regarding to their effect on the currancy time can be arranged in the following order; microemulsions > ocuserts > eye gels. Chapter 4 Ocular Bioavailability of Desloratadine from Different Ophthalmic Preparations in Rabbits Eyes This chapter deals with the study of the effect of polymers and dosage form on the uptake of desloratadine by eye tissues and aqueous humor of rabbits, at different time intervals after application of the selected ophthalmic preparations. The selected formulae were HPMC eye gel, HPMC/Sod. Alg ocusert and Sod. CMC microemulsions, in addition to the control formula, drug suspended in water (0.05% w/v). Then, the drug concentration in each tissue was determined by high performance liquid chromatography (HPLC) assay. From the obtained results it was clear that: 1) The peak time for maximum drug concentration (T max ) from tested formulations in eye tissues and aqueous humor after application on rabbits eyes was 2 hrs for all tested formulations. While, T max for control preparation was 1 hr. - 5 -
2) All selected formulations provided the higher C max of the drug in cornea followed by conjunctiva, iris-ciliary body then aqueous humor. 3) The ocular bioavailability of the drug in all eye tissues and aqueous humor from the tested formulations, was found to be in the following order; microemulsion > ocusert > eye gel > control. Part II Formulation and Evaluation of Gatifloxacin Ophthalmic Preparations This part consists of two chapters and deals with the formulation, in-vitro and in-vivo evaluation of ophthalmic formulations containing gatifloxacin. Chapter 1 Formulation and In-vitro Evaluation of Gatifloxacin from Different Ophthalmic Preparations The work in this chapter involved the formulation of gatifloxacin in different ophthalmic preparations including in-situ gelling systems, microemulsions, and ocuserts using different polymers. The physical characteristics of the prepared formulae were performed through the determination of drug content, ph, viscosity, and transmission electron microscopy (TEM) for microemulsions. Furthermore, in-vitro release through cellophane membrane in phosphate buffer of ph 7.4 at 37 o C was investigated. Then, the kinetic analysis of release data was done. The obtained results can be summarized as follow: 1) The prepared ophthalmic preparations showed drug content that complied with pharmacopeial limits, ph values tolerated by the eye, and acceptable viscosity limits. 2) Regarding the percentage of the drug release from different formulations, it was found that, the drug release is varied with the polymer types and dosage forms. 3) According to the result of in-situ gelling systems: a) The combined solutions which were free flowing liquid at the room temperature would convert to gels after administration, which could ensure suitable gel strength and prevent rapid drainage from the eye and so improve the bioavailability of the drug. b) The in-situ gelling systems produced sustained drug release over 12 hrs. - 6 -
4) Regarding to the release data, the tested formulations were arranged in the following order; in-situ gelling systems > ocuserts > microemulsions. 5) Regarding to the results of the release kinetic analysis: the drug release mechanism from the different ophthalmic formulations was a combination of two mechanisms Higuchi model followed by first-order model, in which one is more predominant than the other. Chapter 2 Ocular Bioavailability of Gatifloxacin from Different Preparations in Rabbits Eyes Ophthalmic This chapter deals with the study of the effect of polymer type and dosage form on the uptake of gatifloxacin by eye tissues and aqueous humor of rabbits, at different time intervals after application of the selected ophthalmic preparations. The selected formulae were sodium alginate & carbopol 940 in-situ gelling system, polyvinyl alcohol & carbopol 940 ocusert and sodium carboxymethyl cellulose microemulsion, in addition to the control formula, Tymer drops (0.3% w/v). The drug concentration in each tissue was determined by high performance liquid chromatography (HPLC) assay. From the obtained results it was clear that: 1) The peak time for maximum drug concentration (T max ) from tested formulations in eye tissues and aqueous humor after application on rabbits eyes was 2 hrs for all tested formulations. 2) All selected formulations provided the higher C max of the drug in conjunctiva followed by cornea, iris-ciliary body then aqueous humor. 3) The ocular bioavailability of the drug in all eye tissues and aqueous humor from the tested formulations, was found to be in the following order; in-situ gelling systems > microemulsions > ocuserts > control. - 7 -