COVID-19 infection causes a reduction in neutrophil counts in patients taking clozapine

COVID-19 infection causes a reduction in neutrophil counts in patients taking clozapine

J Psychiatry Neurosci 2021;46(2):E232-E237 | PDF

Siobhan Gee, MPharm, PGDip, PhD; David Taylor, MSc, PhD

Background: Monitoring of white cell counts during clozapine treatment leads to cessation of therapy if levels fall below predetermined values. Reductions in white cell counts, driven by lower levels of lymphocytes, have been observed with coronavirus disease 2019 (COVID-19). Neutropenia during COVID-19 has not been reported. We present data for 56 patients who were taking clozapine and had COVID-19.

Methods: We included patients who were taking clozapine at the time they tested positive for COVID-19. We compared absolute neutrophil counts, lymphocyte counts and white cell counts between baseline and the first week of infection, and baseline and the second week of infection.

Results: We observed reductions in absolute neutrophil counts (p = 0.005), lymphocyte counts (p = 0.003) and white cell counts (p < 0.001) between baseline and the first 7 days of COVID-19. All cell counts had returned to baseline levels by days 8 to 14. Six patients experienced neutropenia (absolute neutrophil counts < 2.0 × 109/L) and of those, 4 underwent mandatory cessation of clozapine. For 3 patients, clozapine treatment had been established for more than 6 months with no previous neutropenia, neutrophil levels returned to baseline within 2 weeks and no further neutropenia was observed on restarting treatment.

Limitations: This was a retrospective chart review; larger cohorts are required. Clozapine plasma levels were largely not measured by clinicians.

Conclusion: These data strongly suggest that mild neutropenia in the acute phase of COVID-19 in patients who are well established on clozapine is more likely to be a consequence of the virus than of clozapine treatment.


Submitted Nov. 12, 2020; Revised Dec. 2, 2020; Accepted Dec. 2, 2020.

Acknowledgments: The authors thank to Alexandra Lumley-Jones (South West London and St. George’s NHS Foundation Trust), Marwa Mohammed (Camden and Islington NHS Foundation Trust), Georgina Ell (Central and North West London NHS Foundation Trust), Deborah Baidoo and Sarwjit Vatti (West London NHS Foundation Trust), who collected data for this study. They also acknowledge the North East London NHS Foundation Trust; East London NHS Foundation Trust; Oxleas NHS Foundation Trust; Barnet, Enfield and Haringey Mental Health Trust; and Surrey and Borders Partnership NHS Foundation Trust for their support and contribution toward recruitment, coordination and communication between participating trusts.

Affiliations: From the Pharmacy Department, South London and Maudsley NHS Foundation Trust, Denmark Hill, London, United Kingdom (Gee, Taylor); and the Institute of Pharmaceutical Sciences, King’s College London, Franklin Wilkins Building, Stamford Street, London, United Kingdom (Gee, Taylor).

Availability of data and materials: The datasets generated during the current study are not publicly available because of restrictions on sharing patient data outside individual NHS trusts. Data are available from the authors upon reasonable request and with permission of the relevant individual NHS trusts.

Ethics approval and consent to participate: Ethics approval and consent was provided by drug and therapeutics committees or information governance committees at individual NHS trusts. Data were collated and analyzed by South London and Maudsley NHS Foundation Trust; drug and therapeutics committee study approval code: DTC/2020/101

Funding disclosure: None declared.

Competing interests: D. Taylor has received research grants from Janssen, Lundbeck and Recordati, and personal fees from Mylan, Janssen, Sunovion and Recordati. No other competing interests declared.

Contributors: S. Gee and D. Taylor designed the study. S. Gee acquired and analyzed the data. S. Gee and D. Taylor wrote the article, which S. Gee reviewed. Both authors approved the final version to be published and can certify that no other individuals not listed as authors have made substantial contributions to the paper.

Content licence: This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY-NC-ND 4.0) licence, which permits use, distribution and reproduction in any medium, provided that the original publication is properly cited, the use is non-commercial (i.e. research or educational use), and no modifications or adaptations are made. See: https://creativecommons.org/licenses/by-nc-nd/4.0/

DOI: 10.1503/jpn.200208

Correspondence to: S. Gee, South London and Maudsley NHS Foundation Trust, Pharmacy Department, Denmark Hill, London, United Kingdom, SE5 8AZ; siobhan.gee@slam.nhs.uk