Background Case reports of suspected adverse drug reactions (ADRs) are common in the medical literature, but there is a high variation in their characteristics, quality and relevance.

Purpose The aim of the study is characterise the publications of adverse drug reactions (ADRs) published as letters to the editor (LE) in four Spanish medical journals.

Materials and methods Systematic literature survey was realised. The authors evaluated all case reports of adverse drug reactions published as LE during 2 years (since April 2006 to March 2008) in four Spanish medical journals (Medicina Clínica, Revista Clínica Española, Atención Primaria and Anales de Medicina Interna). Reports were excluded if the event was due to medicinal plants or drug abuse, or if the publication was a cases serie. The evaluation of the cases selected for the study was realised by a group of experts made up of three physicians, a pharmacologist and a pharmacist. Main outcome measures are number of suspected adverse reactions and the following characteristics: therapeutic group of the implied drug, seriousness of the reaction, notification to the pharmacovigilance system, year of commercialisation, and previous knowledge of the reaction.

Results A total of 771 LE were reviewed and 93 corresponded to suspected ADRs, 20 cases were excluded and finally The authors evaluated 73 publications corresponding to 79 patients and 97 active principles. About active principles implied:39, 2% were nervous system drugs; 22, 8 were antineoplastic and immunomodulating drugs (18, 6%); and 11, 4% were alimentary tract and metabolism drugs. About the seriousness of the ADRs: 44% were serious; 37% were moderate; 16% were mild; and only two cases (3%) were mortal reactions. Nine LE had been notified to the Spanish pharmacovigilance system, and nine active principles corresponded to a drug of recent commercialisation (less than 5 years from its approval). These new active principles were: telithromycin, erlotinib, ezetimibe (two cases), dutasteride, pioglitazone, tenofovir, inhaled iloprost and pregabalin. Analysing previous knowledge of the reaction: 54, 4% were well-known reactions, 31, 6% were anecdotal events, and 13, 9% were unknown reactions.

Conclusions The drugs which are used for treat nervous system pathologies and antineoplastic and immunomodulating drugs are highly associated with ADRs. However it does not represent the real percentage of adverse effects of these groups as the main percentage remains underreported. It is necessary more information about new drugs, and a better collaboration between health professionals and the Spanish pharmacovigilance system.