Table 3 Frequency of various oral antipsychotics analysed in blood samples during the whole observation period prior to initiating therapeutic drug monitoring of clozapine in patients with undetectable or subtherapeutic versus therapeutic TDM events.

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

Antipsychotic drug

Undetectable/subtherapeutic, n (%)

Therapeutic, n (%)

p

Total samples

226 (100)

1138 (100)

–

Amisulpride

1 (0.4)

43 (3.9)

n.a.

Aripiprazole

19 (8.4)

102 (9.0)

0.90

Chlorprothixene

2 (0.9)

22 (1.9)

n.a.

Flupentixol

3 (1.3)

10 (0.9)

n.a.

Haloperidol

6 (2.7)

20 (1.8)

n.a.

Levomepromazine

3 (1.3)

14 (1.2)

n.a.

Olanzapine

62 (27.4)

367 (32.3)

0.16

Perphenazine

13 (5.8)

34 (3.0)

0.06

Quetiapine

52 (23.0)

263 (23.1)

1.0

Risperidone

22 (9.7)

112 (9.8)

1.0

Sertindole

10 (4.4)

14 (1.2)

0.003

Ziprasidone

20 (8.9)

49 (4.3)

0.007

Zuclopenthixol

13 (5.8)

88 (7.7)

0.33

  1. Subtherapeutic samples were defined as a TDM sample indicating subtherapeutic levels of antipsychotic drug (and metabolite, if applicable) 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, above minimum therapeutic doses. 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 minimum therapeutic doses were adapted from the AGNP 2017 consensus guidelines19.
  2. TDM therapeutic drug monitoring.
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