Therapeutic drug monitoring (TDM) in psychiatry, and adherence to orienting therapeutic ranges (OTRs) of medications in particular, is regarded as useless by many psychiatrists.
To evaluate the hypothesis that pre-medicated patients requiring acute psychiatric inpatient treatment have plasma levels below OTR and have actual plasma that are below the level expected from their dosing regimen.
Included were all patients who were consecutively admitted for acute inpatient treatment in June 2005 and who had been treated with medications (N=161) for which OTRs are available. A determination was done of all plasma levels and their comparison to their OTRs, and to the expected plasma levels, based on known preadmission dosing regimen and average pharma-cokinetic data.
A significantly higher-than-chance fraction of medicated patients who had to be admitted for acute inpatient treatment had plasma levels below OTR. Of 149 patients for which OTRs are available, 105 (70.5%) were below OTR, 37 (24.8%) were within OTR, and 7 (4.7%) were above OTR. Of 161 (100%) admissions, 99 (61.5%) had actual plasma levels that were below the expected individual plasma level, and 62 (38.5%) were at or above the expected plasma level, 23 (14.3%) out of them had a plasma level of 0.
Failure to reach the orienting therapeutic level (OTR) of a psychiatric medication increases the risk of hospitalization.