1. World Health Organization. Model list of essential medicines. 17th ed. 2011. Available from http://whqlibdoc.who.int/hq/2011/a95053_eng.pdf. Accessed February 13, 2013.
2. World Health Organization. Model list of essential medicines for children. 3rd ed. 2011. Available from http://whqlibdoc.who.int/hq/2011/a95054_eng.pdf. Accessed February 13, 2013.
3. World Health Organization. Guidelines on the pharmacological treatment of persisting pain in children with medical illnesses. 2012. Available from http://whqlibdoc.who.int/publications/2012/9789241548120_Guidelines.pdf. Accessed February 13, 2013.
4. International Narcotics Control Board. Single convention on narcotic drugs 1961 as amended by the 1972 protocol. Available from http://www.incb.org/documents/Narcotic-Drugs/1961Convention/convention_1961_en.pdf. Accessed February 13, 2013.
5. A first comparison between the consumption of and the need for opioid analgesics at country, regional, and global levels;Seya;J Pain Palliat Care Pharmacother,2011