Background Alterations in laboratory parameters can be associated with adverse drug reactions (ADRs). Therefore, monitoring parameters may enable early detection and treatment of ADRs.

Purpose To assess the association between laboratory parameters and ADRs in Internal Medicine at a tertiary hospital.

Materials and methods Prospective observational study of hospitalised patients in a section of internal medicine department during February and March 2011. Every day, a pharmacist recorded drug prescriptions and the following parameters: Na, K, Ca, serum creatinine, glomerular filtration rate (GFR), INR, glucose, haemoglobin, platelets, ALT, AST, bilirubin, GGT, alkaline phosphatase, TSH, T4 and blood digoxin. The causal association between parameters outside the reference range and drugs was analysed using the modified Karch–Lasagna scale.

Results 52 patients (65.4% men) were included; median age 74 years; median hospital stay 7 days. A mean of 2.94 parameters per patient were outside the reference range. An association with drugs was observed in 25.5% of patients. Reduction in GFR, 27.0% (associated with diuretics (41.7%), ACE inhibitors (33.3%), angiotensin II receptor blockers (ARB) (16.6%) and antidiabetics drugs (8.3%)); hypokalaemia, 22.6% (associated with diuretics (50.0%), fluid without potassium (37.5%) and salbutamol (12.5%)); hyperkalaemia, 14.5% (associated with ACE inhibitors (60.0%) and ARB (40.0%)); INR out of range, 10.8% (associated with interactions (66.7%)); hyperglycaemia, 8.4% (associated with corticosteroid (66.7%) and antidiabetic drugs (33.3%)); low blood digoxin during admission, 5.3%; and others, 10.8%. No ADRs led to prolonged hospital stay. In terms of causality, ADRs were classed as possible (52.9%), probable (44.1%) and definite (2.9%).

Conclusions 25.5% of alterations in laboratory parameters were probably or possibly associated with drugs. The most common alterations were as follows: decrease in GFR associated with the use of diuretics, ACE inhibitors and ARB; hypokalaemia due to diuretics; and hyperkalaemia due to ACE inhibitors and ARB. There were no severe ADRs, as these were detected early.