Preparation and evaluation of reverse-phase evaporation and multilamellar niosomes as ophthalmic carriers of acetazolamide

 
Ahmed S. Guinedi, Nahed D. Mortada, Samar Mansour^*, Rania M. Hathout

Department of Pharmaceutics, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt.

Abstract

    Niosomes have been reported as a possible approach to improve the low corneal penetration and bioavailability characteristics shown by conventional ophthalmic vehicles. Niosomes formed from Span 40 or Span 60 and cholesterol in the molar ratios of (7:4), (7:6), and (7:7) were prepared using reverse-phase evaporation and thin film hydration methods. The prepared systems were characterized for entrapment efficiency, size, shape and in vitro drug release. Stability studies were carried out to investigate the leaching of the drug from niosomes during storage. The intraocular pressure (IOP) lowering activity of acetazolamide niosomal formulations in rabbits was measured using ShiÆtz tonometer. Histological examination for the corneal tissues of rabbits receiving niosomal formulations was carried out for assessment of the ocular irritancy of niosomes. The results showed that the type of surfactant, cholesterol content and the method of preparation altered the entrapment efficiency and drug release rate from niosomes. Higher entrapment efficiency was obtained with multilamellar niosomes prepared from Span 60 and cholesterol in a 7:6 molar ratio. Niosomal formulations have shown a fairly high retention of acetazolamide inside the vesicles (approximately 75%) at a refrigerated temperature up to a period of three months. Each of the tested acetazolamide niosomes prepared by either method produced a significant decrease in IOP compared to the solution of free drug and plain niosomes. Multilamellar acetazolamide niosomes formulated with Span 60 and cholesterol in a 7:4 molar ratio were found to be the most effective and showed prolonged decrease in IOP. Histological examination of corneal tissues after instillation of niosomal formulation for 40 days showed slight irritation in the substantia propria of the eye which is reversible and no major changes in tissues were observed.

Keywords: Acetazolamide; Niosomes; Non-ionic surfactant vesicles; Ocular irritancyy; Ophthalmic; Stability

*Corresponding author:

E- mail: samar_holayel@yahoo.com

              samarmansour@asu-pharmacy.edu.eg

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Preparation, Freeze drying and Physical Stability

of Chloramphenicol Liposomes

Mohamed S. El-Samaligy, Omaima N. El-Gazayerly and Samar Mansour

Pharmaceutics Department, Faculty of Pharmacy,

Cairo University, Cairo, Egypt.

Abstract:

Chloramphenicol-entrapped multilamellar liposomes were prepared using the thin film hydration method. The effects of cholesterol molar ratio, and charge inducing agents on encapsulation efficiency values and in-vitro drug release of multilamellar liposomes were studied. Freeze dried liposomal products were prepared with or without cryoprotectants.  Results showed that incorporation of stearylamine resulted in an increased entrapment of chloramphenicol, whereas incorporation of dicetyl phosphate decreased the drug entrapment efficiency.  In-vitro release studies revealed that incorporation of cholesterol into multilamellar liposomal formulations decreased drug permeability from liposomes. Positively-charged chloramphenicol multilamellar liposomes gave rise to a slow release rate compared to neutral liposomes whereas negatively-charged chloramphenicol liposomes showed a rapid release rate. Physical stability studies showed that lyophilized cake of liposomes without cryoprotectants was compact and difficult to reconstitute, compared to fluffy easily reconsistituted cakes upon using cryoprotectants.  Chloramphenicol retained in freeze-dried liposomes without cryoprotectants was 62.0% compared to 95.6% using 3 grams trehalose as cryoprotectant per gram lipid in positively-charged multilamellar liposomes.  Physico-chemical stability studies showed superior potentials of the lyophilized product after reconstitution in comparison to a solution product.

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Liposomes as an Ocular Delivery System for Acetazolamide: In Vitro and In Vivo Studies

Ahmed S. Guinedi, Nahed D. Mortada, Samar Mansour ^*, Rania M. Hathout

Department of Pharmaceutics, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt

Abstract

            Development of topically effective controlled release ophthalmic acetazolamide liposomal formulations would be a promising drug delivery system for the treatment of glaucoma. Reverse-phase evaporation and lipid film hydration methods were used for the preparation of reverse-phase evaporation (REVs) and multilamellar (MLVs) acetazolamide liposomes consisting of egg phosphatidylcholine (PC) and cholesterol (CH( in different molar ratios, viz: PC:CH (7:2), (7:4), (7:6), and (7:7) with or without stearylamine (SA) or dicetyl phosphate (DP) as positive and negative charge inducers respectively. The prepared liposomes were evaluated for their entrapment efficiency and in vitro release. Multilamellar liposomes entrapped greater amounts of drug than reverse- phase evaporation vesicles of the same composition. Drug loading was increased by inclusion of cholesterol as well as stearylamine. Highest percent of entrapment efficiency was observed with the positively charged multilamellar liposomes consisting of PC:CH:SA (7:7:1) reaching a value of 48.27%. The in-vitro drug release from the prepared liposomes was found to be dependent upon lipid bilayer composition and the method of preparation. Drug release showed an inverse relationship to drug loading as it decreased upon inclusion of cholesterol as well as stearylamine. Stability study was carried out to investigate the leak out of the drug from liposomes during storage. The results indicate that approximately 89%, 77% and 69% of acetazolamide was retained in positive, negative and neutral multilamellar liposomal formulations up to a period of three months at a refrigerated temperature. The intraocular pressure (IOP) lowering activity in mmHg of selected acetazolamide liposomal formulations in rabbits was determined and compared to that of the solution of free drug using a ShiÆtz tonometer. All the tested acetazolamide liposomal formulations prepared by either method significantly lowered the intraocular pressure compared to the solution of free drug. Multilamellar acetazolamide liposomes revealed more prolonged effect than reverse-phase evaporation liposomes of the same composition. The positively charged and neutral liposomes exhibited higher lowering in IOP and a more prolonged effect than the negatively charged ones. The positive multilamellar liposomes composed of PC:CH:SA (7:4:1) molar ratio showed the maximal response which reached a value of  – 7.8±1.04 mmHg after three hours of topical administration.

Keywords:  Acetazolamide, Multilamellar liposomes, Reverse- phase evaporation liposomes

*Correspondence to:

Samar Mansour Holayel, Ph.D.