Severe neutropenia unrelated to clozapine in patients receiving clozapine.

BACKGROUND: Clozapine is known to cause agranulocytosis. Mandatory monitoring schemes are aimed at reducing the risk of agranulocytosis and of the consequences of agranulocytosis. All cases of agranulocytosis occurring in people prescribed clozapine are assumed to be caused by clozapine. METHODS: In a previous study, we examined a cohort of patients listed on our hospital database as having had clozapine-induced agranulocytosis and applied specific criteria to identify those with confirmed clozapine-related, life-threatening agranulocytosis. In this study, we examine the cases not meeting these specific criteria. RESULTS: In the original study, 9 of 23 cases met the criteria for clozapine-induced, life-threatening agranulocytosis. Of the 13 remaining cases for whom data were available, 5 were probably caused by clozapine but were not life-threatening. Three cases were the result of concomitant cancer chemotherapy. Three were anomalous results probably related to measurement error. For the remaining two cases, the cause was not identified. CONCLUSION: Not all cases of agranulocytosis occurring in people taking clozapine are caused by clozapine. The widely used threshold criterion-based diagnosis overestimates the risk of agranulocytosis. True clozapine-related agranulocytosis is best identified by pattern-based criteria: rapid fall in neutrophil counts over around 2 weeks to below 0.5 × 109/L for two consecutive days (unless clozapine is stopped very early or granulocyte colony stimulating factor is given) where other possible causes (benign ethnic neutropenia, cancer chemotherapy) can be ruled out.

Distinctive pattern of neutrophil count change in clozapine-associated, life-threatening agranulocytosis.

The wider use of clozapine is limited by the risk of agranulocytosis and the associated requirement for monitoring of neutrophil counts. We searched local electronic patient records for cases of agranulocytosis occurring during clozapine treatment during the period 2007-2020. We found 23 episodes recorded as agranulocytosis in clozapine patients. Of these, nine met pre-defined criteria and were considered episodes of life-threatening agranulocytosis (LTA). These episodes of clozapine-induced LTA exhibited a distinct pattern of continuous and rapid neutrophil count decline to zero or near zero. Mean time for neutrophils to fall from ANC > 2 to ANC <0.5 × 109/L was 8.4 days (range 2-15 days). Each event was also characterised by a prolonged nadir and delayed recovery (range 4-16 days). Non-LTA episodes were, in contrast, brief and benign. We conclude that an important proportion of cases of agranulocytosis identified in people prescribed clozapine are not life-threatening and may not even be clozapine-related. Monitoring schemes should aim to identify true clozapine-induced LTA as opposed to threshold-defined nominal agranulocytosis. Genetics studies might benefit from examining associations with clozapine-induced LTA rather than with recorded cases of agranulocytosis or neutropenia.

Changes in Brain Glutamate on Switching to Clozapine in Treatment-Resistant Schizophrenia.

It has been suggested that the antipsychotic clozapine may modulate brain glutamate, and that this effect could contribute to its efficacy in treatment-resistant schizophrenia (TRS). The aim of this study was to examine the effects of clozapine on brain glutamate in TRS longitudinally. This study examined individuals with TRS before and 12 weeks after switching from a non-clozapine antipsychotic to treatment with clozapine as part of their normal clinical care. Proton magnetic resonance spectroscopy (1H-MRS) measured concentrations, corrected for voxel tissue content, of glutamate (Glucorr), and glutamate plus glutamine (Glxcorr) in the anterior cingulate cortex (ACC) and right caudate nucleus. Symptoms were monitored using the Positive and Negative Syndrome Scale (PANSS). Of 37 recruited patients (27 men, 39.30 years old, 84% clozapine naïve), 25 completed 1H-MRS at both timepoints. 12 weeks of clozapine was associated with a longitudinal reduction in Glucorr in the caudate (n = 23, F = 7.61 P = .01) but not in the ACC (n = 24, F = 0.02, P = .59). Percentage reduction in caudate Glucorr was positively correlated with percentage improvement in symptoms (total PANSS score, n = 23, r = .42, P = .04). These findings indicate that reductions in glutamate in the caudate nucleus may contribute to symptomatic improvement during the first months of clozapine treatment.