Williams RE, Bosnic N, Sweeney CT, Duncan AW, Levine KB, Brogan M, Cook SF. Prevalence of opioid dispensings and concurrent gastrointestinal medications in Quebec. Pain Res Manag. 2008;13(5):395-400.
Urrutia I, Aguirre U, Sunyer J, Plana E, Muniozguren N, Martinez-Moratalla J. Changes in the prevalence of asthma in the Spanish cohort of the European Community Respiratory Health Survey (ECRHS-II). Arch. Bronconeumol. 2007 Aug;43(8):425-30.