Bromide as a marker to measure adherence to drug therapy

Objective: Several methods have been described to measure adherence to prescribed drug therapy. However, most of these have been shown to be inaccurate. Bromide is an anion that is readily absorbed in the gut and has an elimination half-life of about 12 days. In the present study, we investigated the pharmacokinetic properties of bromide with the objective to use it as a measure of drug adherence. Methods: Three groups of each 8 healthy volunteers took 15, 24 or 30 mg potassium bromide, respectively, daily for 20 weeks. Serum concentrations of bromide were measured every two weeks. Results: There was a linear relationship between the daily dosage taken and the mean increase of bromide concentration. In every group considerable inter-individual variability was seen. Correction for body weight resulted in an improved correlation between daily bromide dose and increase in concentration (r=0.78, p < 0.01). Conclusions: Unfortunately, the inter-individual variability in clearance of bromide was considerable. This limits the use of bromide to primarily measuring adherence in individual patients during long term follow-up. Bromide appears to be a potentially useful marker to be added to drugs for assessment of individual adherence to long term drug therapy. This needs to be investigated in various patients, particularly for patients with relatively asymptomatic diseases (e.g. hypertension).