1. European Medicines Agency (EMA) Review of codeine-containing medicines 2012 http://www.ema.europa.eu/docs/en_GB/document_library/Referrals_document/Codeine_containing_medicinal_products/Procedure_started/WC500133297.pdf
2. Current practice and recent advances in pediatric pain management;Chiaretti;Eur Rev Med Pharmacol Sci,2013
3. Tramadol as an analgesic for mild to moderate cancer pain;Leppert;Pharmacol Rep,2009
4. Tramadol. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in acute and chronic pain states;Lee;Drugs,1993
5. Pharmacokinetics of oral tramadol drops for postoperative pain relief in children aged 4 to 7 years-a pilot study;Payne;Anesth Prog,2002