Digoxin therapeutic drug monitoring: an audit and review

The measurement and assessment of digoxin concentrations are often performed poorly. We have conducted an audit to assess the appropriateness of digoxin therapeutic drug monitoring in Christchurch Hospital.

One hundred consecutive requests for digoxin concentrations in Christchurch Hospital inpatients were assessed. The case notes and hospital medication records were reviewed to determine the indication for testing, the appropriateness of the sampling time and of the subsequent alteration to dosing.

In 53% of requests no clear indication for digoxin therapeutic drug monitoring (TDM) could be determined. In the remainder, 'suspected toxicity' accounted for 31% and 'therapeutic failure' for 16%. Samples were inappropriately taken within eight hours post-dose in 32% of requests. In 19% of cases, the samples did not reflect steady-state conditions. In 5% of occasions, the subsequent decision regarding dose adjustment was felt to be clearly inappropriate, and there was uncertainty regarding appropriateness in some other cases. Overall, in only 29% of requests was TDM performed appropriately with regard to indication, sampling and subsequent dose alteration.

At Christchurch Hospital, the practice of TDM for digoxin is often inappropriate. It would seem that medical staff education is required to improve this practice.