“…Maintenance of its blood level between 10-20 µg/mL is important to obtain a maximum bronchodilator effect; its serious side effects take place over 20 µg/mL; its efficacy falls below 10 µg/mL of blood concentrations. Besides having a narrow therapeutic range, alteration of its pharmacokinetic characteristics due to individual variations, drugs, diet and habits such as smoking and alcohol has led to requirement of a simple, sensitive and reproducible assay method for determination of theophylline and its metabolites (1,2). Biological samples such as urine plasma, serum and tissue have been used in determination of theophylline for doping control investigations, clinical pharmacokinetic experiments and human liver metabolism studies (3).…”