Background Gastrointestinal tract resection (GIR) results in a range of physiological changes that affect the absorption of nutrients, water, and electrolytes. These changes may also affect the absorption of orally medication reducing its effect. The highly heterogeneous of GIR patients makes individual monitoring necessary to ensure an optimal clinical effect.

Purpose To determinate the incidence of patients with GIR and the proportion of patients with oral medication, which absorption may be affected after GIR.

Materials and methods Observational prospective study of patients undergoing gastrointestinal surgery in a third-level hospital. All patients undergoing general surgery during October 2010 were collected, selecting those with GIR. Demographics (age, sex), before and after admission pharmacological treatment (drug, dosage, drug formulation) and surgery information (site of resection) were collected. A bibliographic research was made to establish how GIR could affect the clinical efficacy of drugs.

Results Out of 249 patients undergoing surgery (106 women, 57,6 years (16-90)), 35 (14%) had GIR (mean age 58 years (24-84)). 15 (42,8%) had total/partial colectomy, 14 (40%) partial gastrectomy, 3 (8,6%) rectum resection, 2(5,7%) small bowel resection and 1 (2,9%) oesophagectomy. 7 (20%) patients were treated with oral medication which pharmacological effect may be reduced after GIR: 1(14.7%) had small bowel resection and received hydrochlorothiazide, 6(85.7%) had gastrectomy: one received Metformin which decreases B12 levels and 2 received enalapril and cotrimoxazole respectively which absorption may be decreased. Other 3 patients received drugs formulations which couldn't be absorbed because of the gastrectomy. To avoid a decrease in pharmacological effect patients medication was switched to a correct formulation or to an active substance with an appropriate absorption site.

Conclusions There were few patients treated with drugs affected by GIR, however, they should be closely monitored. There is limited and scarce updated literature regarding clinical outcome of drug efficacy in these patients. The authors should keep in mind those patients with GIR and poor pharmacological response.