Background Deterioration in renal function occurs with ageing and can affect drug pharmacokinetics, decreasing elimination. Furthermore, the narrow therapeutic range (TR) of digoxin increases the vulnerability of the elderly to toxicity by cardiac glycosides.
Purpose To optimise digoxin dose regimens for geriatric patients living in a nursing home (NH) by therapeutic drug monitoring (TDM).
Material and methods Transversal study conducted in a NH, in all patients treated with digoxin, between January and April 2012. TR was established as 0.5–1.2 ng/mL in older people.
Data were obtained from: the inpatient dispensing programme (Silicon) and electronic medical records (Ianus). Pharmacokinetic data were estimated using a Bayesian approach (PKS).
Variables collected: age, sex, creatinine, digoxin treatment data (initial and recommended dose) and trough level (Cmin) before and after the recommendations. Drug concentrations were analysed with Architect i1000SR. Estimated glomerular filtration rate (GFR) was calculated using the MDRD-4 equation. Categorical variables were reported as frequency and percentage, while continuous variables were reported as mean±SD.
Results Digoxin was used in 13 (7.0%) patients (30.8% men) with a median age of 83.5 ± 6.1 years, from a total population of 185 institutionalised patients.
The mean values for daily dose of digoxin and GFR were 0.176 ± 0.059 mg and 83.64 ± 29.09 mL/min/1.73, respectively.
During this period, 20 Cmin of digoxin were analysed in 13 inpatients. The mean digoxin Cmin was 0.9 ± 0.6 ng/mL. 46.2% were within the therapeutic range when the first measure was made. Supratherapeutic levels were found in 3 (23.1%) patients and infratherapeutic in 4 (30.8%) patients.
Medicine adjustment recommendations were provided in all patients with a Cmin outside of the TR: concerning dose (14.3%), frequency (71.4%) or both (14.3%). Following this recommendation, the target was reached in 71.4% of patients while 28.6% were lost to follow-up.
Conclusion Initial concentrations were out of the therapeutic range in more than half of patients, suggesting that TDM of digoxin is highly recommended in this group of patients.
In order to assure the optimal dose regimen of cardiac glycosides, hospital pharmacists have an important role. Therapeutic digoxin monitoring is an instrument to ensure quality of care in terms of effectiveness and safety.
No conflict of interest.
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