Research paper
Preparation and in vitro characterization of amifostine biodegradable microcapsules

https://doi.org/10.1016/S0939-6411(03)00148-6Get rights and content

Abstract

The purpose of this project was to develop sustained release microcapsules of amifostine. The microcapsules were prepared using solvent evaporation technique. The effect of several formulation variables on the characteristics of the microcapsules was studied. The formulation variables studied were drug loading, polymer (polylactide-co-glycolide) (PLGA) concentration, and the amount of gelatin in the initial aqueous phase. The drug loading was studied at three different levels (5, 10, and 25 mg); the PLGA concentration was studied at two levels (500 and 1000 mg); and the amount of gelatin used ranged from 2 to 14 mg. In general, the microcapsules were less than 155 μm in diameter with median size between 50 and 80 μm. While the use of higher amounts of PLGA significantly increased the median size of the microcapsules, using higher amounts of amifostine had no significant effect, irrespective of the amount of PLGA. The use of gelatin, within the range 2–14 mg, did not show any significant effect on the particle size distribution. Scanning electron microscopy (SEM) of the microcapsules revealed that all nine formulations yielded spherical particles. The use of 500 mg PLGA with 10 or 25 mg amifostine yielded microcapsules with porous surfaces. The surface pores, however, were not present in microcapsules prepared using 1000 mg PLGA. The efficiency of encapsulation decreased significantly from 63 to 24% when the amount of amifostine increased from 5 to 25 mg in the formulations using 500 mg PLGA. Similarly, the efficiency of encapsulation decreased from 87 to 23% when the amount of PLGA was doubled to 1000 mg. An increase in the amount of amifostine in the formulation using 500 mg PLGA also resulted in a significant increase in initial drug release (from 20 to 62%) within the first hour. These results were consistent with the porous morphology of these microcapsules. In general, all batches of microcapsules showed 24–96 h sustained drug release.

Introduction

Amifostine, also known in the literature as ethiofos, ethyol (MedImmune, Gaithersburg, MD, USA), or WR-2721, is an organic thiophosphate, which has been extensively studied as a cytoprotective agent [1], [2], [3]. It has been studied as a protector of normal tissue against the damaging effects of ionizing radiation and/or chemotherapy and was approved by the United States Food and Drug Administration in 1997. Amifostine's current indicated use in clinical practice is limited to that of reduction in the cumulative renal toxicity associated with repeated administration of cisplatin in patients with advanced ovarian or non small cell lung cancer [4], [5]. Amifostine, however, continues to be evaluated as a cytoprotector in a variety of other clinical settings involving radiotherapy and/or chemotherapy [6], [7]. Even if amifostine were shown to be successful in these trials, its clinical use is likely to remain severely limited due to the following facts: (1) amifostine in its presently available formulation must be administered intravenously in order to be effective [8]; (2) serious adverse effects of amifostine such as hypotension, nausea, and vomiting are significantly augmented upon intravenous route of administration [9], [10]; (3) amifostine does not cross the blood–brain-barrier even when administered systemically; and (4) amifostine in its present formulation is not effective when administered orally [11], [12]. Most, if not all, of the above-mentioned barriers to amifostine use can, however, be overcome by utilizing alternative formulation strategies, which are based upon modern techniques in drug delivery including microencapsulation using biodegradable polymers [12]. The most widely investigated biodegradable polymers are aliphatic polyesters based on lactic acid and glycolic acid. The copolymers of these two acids have attracted much attention because the biodegradation rate of the copolymer is easily controlled by altering their ratios [13], [14], [15]. These polymers have been used with numerous drugs and have been shown to be biocompatible [16].

The long-term objective of this project is to develop orally active amifostine microcapsules. In our previous report [17], we demonstrated that amifostine microcapsules prepared by the solvent evaporation technique using high molecular weight PLGA (RG506) released the drug in 3 days. However, these microcapsules had very low efficiency of encapsulation. Now we report on increasing the efficiency of encapsulation of amifostine by modifying the method of preparation.

Section snippets

Materials

The copolymer poly(dl-lactic/glycolic acid), PLGA 50:50 (RG 502; inherent viscosity 0.2 dl/g) was obtained from Boehringer Ingelheim (Germany). The surfactant l-α phosphatidylcholine was obtained from Avanti Polar-lipids Inc. (Birmingham, AL, USA). Amifostine, polyvinyl alcohol (PVA), gelatin (Type A), chloroform, and dichloromethane were obtained from Sigma Chemical Co. (St. Louis, MO, USA).

Experimental design

Three samples were prepared where the PLGA amount was fixed at 500 mg while the amount of amifostine

Results and discussion

Six different formulations (A–F) were prepared, following a partial factorial design, to study the combined effects of the amount of PLGA and amifostine on the microcapsules characteristics. In an effort to improve the efficiency of encapsulation of amifostine, three additional formulations (G–I) were also prepared by incorporating 2, 7, or 14 mg gelatin within the amifostine aqueous phase. All microcapsules were evaluated for total drug content, i.e. efficiency of encapsulation, particle size

Acknowledgements

The authors wish to thank Dr. Nikhil Sarkar and Ms. Raisa Moiseyev from the LSU School of Dentistry for the SEM analysis. This work was funded in part by the NIH/NIGMS grants #GM08008 and GM08008-32S1.

References (18)

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