The evaluation of digoxin therapeutic drug monitoring after training of healthcare workers in aAuniversity hospital

The Evaluation of Digoxin Therapeutic Drug Monitoring After Training of Healthcare Workers in a University Hospital Şeyma Öncü, Dokuz Eylul University School of Medicine, Department of Medical Pharmacology, Izmir, Turkey Objective Therapeutic drug monitoring (TDM) is the interpretation of the measured serum drug concentration with drug and patient characteristics. It can be useful when it is done in appropriate indications and at appropriate times, not as a routine application. Our previous retrospecive study evaluating the appropriateness of serum digoxin concentration (SDC) measurements revealed errors in the timing of blood specimen collection in 98% of the tests. The aim of this study is to evaluate the appropriateness of the TDM and the factors involved in inappropriate test-ordering, after training health personnel in digoxin therapeutic drug monitoring. Methods This is a training-based quasi-experimental study. The residents and nurses of the Cardiology Clinic were trained first in December 2017, and refresher training courses were carried out every month throughout the study. The medical data of the inpatients receiving digoxin therapy were recorded prospectively, between January and December 2018. The appropriateness of the physicians' orders for TDM was evaluated in terms of the right indication, blood collection at the right time and interpretation of the results. Furthermore, factors affecting SDC and toxicity of digoxin were examined. The results are presented by descriptive statistics, student's t-test, Kruskal Wallis, Mann Whitney U, chi-square and logistic regression. P<0.05 accepted as statistically significant. Results A total of 232 TDM were ordered for 121 patients (age: 71.0±12.6 years, 56.2% women). Of these orders, 55.6% were considered appropriate: 88.4% for indication and 62.9% for blood collection timing. An SDC test was not ordered in 49 patients, where 14 (28.6%) were determined to have an indication. There was a significant correlation between inappropriate order for TDM and the more advanced age, female gender, impairment of renal function tests, high levels of serum BNP, being in the Coronary Intensive Care Unit and the number of medications used (p<0.05). Proportion of inappropriate was at the lowest in the first three month period of the study and it was gradually increased in the following three month periods (%25.0, %42.5, %47.3 ve %52.2 respectively, p=0.006). SDC (mean 1.10 ± 0.69 ng/mL) was found subtherapeutic in 14%, therapeutic in 77.7%, toxic in 8.3% of the patients. Change in digoxin therapy was made in 39.7% of this patients. There was a significant correlation between being older than 70 years, female gender, impairment of renal function tests, low level of serum sodium and SDC. There were at least one medication use causing increase in SDC in 31.4% of the patients. Conclusion Approximately a one-half decrease in inappropriate tests compared with our previous study results imply that education has a positive effect on physician behaviour. However, physicians' concerns due to increased risk factors for the patient still play a role in inappropriate test-ordering. The decrease in the effect of education over time is a sign that more permanent solutions are needed.