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Drug toxicity: Idiosyncratic Reactions

Drug toxicity: Idiosyncratic Reactions

Idiosyncratic drug reactions represent abnormal chemical responses that vary significantly among individuals, ranging from extreme sensitivity to low doses to insensitivity to high doses. These reactions often occur due to the drug's covalent binding with serum proteins, forming a foreign hapten that triggers an immunotoxicological response. The variability in drug reactions has a strong pharmacogenetic foundation, with genetic differences crucial in how individuals metabolize drugs. For...

Chronopharmacokinetics: Circadian Rhythms and Influence on Drug Response

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Nonlinear Pharmacokinetics: Dependence of Elimination Half-Life and Dose Clearance

Nonlinear Pharmacokinetics: Dependence of Elimination Half-Life and Dose Clearance

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Related Experiment Video

Updated: May 31, 2026

Self-Administration of Drugs in Mouse Models of Feeding and Obesity

Self-Administration of Drugs in Mouse Models of Feeding and Obesity

Published on: June 8, 2021

Morning pseudoneutropenia during risperidone treatment.

Gurinder Singh¹, Sreekant Kodela

¹Greater Manchester West NHS Trust, Royal Bolton Hospital, Bolton, Manchester, BL4 0JR, UK.

BMJ Case Reports

|June 21, 2011

Summary

Neutropenia, a low neutrophil count, can occur with risperidone. This case shows diurnal variation, suggesting afternoon blood tests are crucial before changing antipsychotic medication.

Area of Science:

Pharmacology
Hematology
Clinical Medicine

Background:

Risperidone is an atypical antipsychotic.
Neutropenia is a known side effect.
Low absolute neutrophil count (ANC) may prompt drug discontinuation.

Purpose of the Study:

To report a case of risperidone-induced neutropenia with diurnal variation.
To highlight the importance of timing for neutrophil count assessment.

Main Methods:

Case report of a young man on risperidone.
Monitoring of absolute neutrophil count (ANC).
Observation of diurnal variation in ANC.

Main Results:

The patient developed neutropenia while on risperidone.

Related Experiment Videos

Last Updated: May 31, 2026

Self-Administration of Drugs in Mouse Models of Feeding and Obesity

Self-Administration of Drugs in Mouse Models of Feeding and Obesity

Published on: June 8, 2021

Neutrophil counts exhibited significant diurnal variation.

Normal neutrophil counts were observed later in the day.

Conclusions:

Diurnal variation in neutrophil counts can occur in patients on risperidone.
Afternoon ANC measurements are essential before altering risperidone therapy.
Avoid premature discontinuation of risperidone based solely on morning counts.