87 Progress in Rubber, Plastics and Recycling Technology, Vol. 32, No. 2, 2016 The Potential Use of Natural Rubber in Pharmaceutical Closures *Author for correspondence, e-mail: trangrriv@yahoo.com © Smithers Information Ltd., 2016 The Potential Use of Natural Rubber in Pharmaceutical Closures Nguyen Ngoc Bich, Nguyen Thi Hue Trang,* Nguyen Duy Luan, and Huynh Van Son Rubber Research Institute of Vietnam, 236 bis Nam Ky Khoi Nghia Street, District 3, Ho Chi Minh City, Vietnam Received: 3 June 2013, Accepted: 30 March 2015 SUMMARY Current manufacturing techniques could produce natural rubber closures that meet all criteria standardized by pharmacopeias except the ultraviolet absorbance limit in the range of 220-360 nm for the closures’ leachate. The type and the dosage of the rubber compounds’ ingredients affected the ultraviolet absorbance of the leachate, while rinsing the closures in water with ultrasonic waves and ozone did not. Intensive washing of the rubber coagulum and deproteinization of the rubber latex using bromelain reduced ultraviolet absorbance of the leachate significantly. Further purification of natural rubber latex is necessary to enable the use of natural rubber in pharmaceutical closures. Keywords: Natural rubber, Pharmaceutical closures, Leachables, Ultraviolet absorbance INTRODUCTION Elastomeric pharmaceutical closures should not react with, absorb, or release harmful impurities into the drug product. The possibility of rubber closures to leach chemicals into drug compositions was noticed at early as in 1964 [1]. Vulcanization accelerators and antioxidants were found in the drug composition [2]. Other leachables may include formaldehyde [3] and hydrogen sulfide [4]. Leachables mostly came from vulcanization activators and accelerators as well as antioxidants [5, 6]. Leachables are not a challenge only for natural rubber (NR); however the problem is more serious in the case of NR because of non-rubber constituents in the NR latex. In addition, NR closures have been observed to release allergic proteins into drug products [7]. This weakness