An evaluation of a clinical pharmacokinetic service for serum digoxin levels

The appropriateness of requests by physicians for serum digoxin measurements (SDMs) and the appropriateness of responses by physicians to a reported SDM were evaluated with and without the contribution of a pharmacy-based clinical pharmacokinetic service (CPS). Also, for each patient, the difference between dosage regimens that had been established by means of SDMs and those regimens that would have been estimated by the method of Dobbs et al. was analyzed. This prospective evaluation involved two 3-week phases and included inpatients. During phase I the CPS was intact, while during phase II it was discontinued. There was a significant increase from phase I (23.4%) to phase II (36.4%) in the rate of inappropriate action or inaction with respect to requesting SDMs. There was also a significant increase from 9.7 to 24.6% in the rate of inappropriate dosage adjustments in response to a reported SDM. There was a statistically significant difference between the digoxin dosages estimated by the method of Dobbs et al. and the actual dosage regimen established with SDMs. The disparity between the CPS approach and the Dobb et al. method was such that 23.4% of digoxin dosage regimens determined with the guidance of SDMs did not result in an estimated steady-state level within the therapeutic range when those regimens were applied to the Dobbs et al. method. Thus, the pharmacy-based CPS improved the appropriateness of physician utilization of SDMs. Also, sole use of the Dobbs et al. method as an example of a noninvasive approach to digoxin dosing is not a reasonable alternative in a tertiary care institution.