Table 2 Rates of undetectable and subtherapeutic serum levels among patients within 12 months prior to initiating therapeutic drug monitoring of clozapine or LAI antipsychotics.

From: Undetectable or subtherapeutic serum levels of antipsychotic drugs preceding switch to clozapine

Patient group

Undetectable/subtherapeutic, combined

Undetectable

Clozapine patients, n (%, 95% CI)

38 (10.8, 7.7–14.5)

19 (5.4, 0.65–17.7)

LAI patients, n (%, 95% CI)

188 (17.9, 15.7–20.4)

91 (8.7, 4.9–13.5)

  1. Subtherapeutic patients were defined as a person with at least one subtherapeutic sample of antipsychotic drug (and metabolite, if applicable) in a TDM sample during the observation period, despite indicated dose in the submitted requisition form. Subtherapeutic levels were defined as a serum concentration below 50% of the lower reference range boundary. Undetectable was defined as absence/below Lower Limit Of Detection (LLOD) of the prescribed drug (both drug and metabolite if applicable) ordered for TDM by the physician, in the respective patient’s blood sample submitted for concentration analysis. Reference ranges and prescribed doses relative to lower recommended therapeutic dose in schizophrenia were adapted from the AGNP 2017 consensus guidelines19.
  2. LAI long-acting injectables, TDM therapeutic drug monitoring.
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