Prolonged sedation due to accumulation of conjugated metabolites of midazolam
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T M Bauer1, R Ritz, C Haberthür
1Division of Intensive Care, University Hospital, Basel, Switzerland.
Abstract:
Midazolam is a short-acting benzodiazepine routinely used in intensive-care medicine. Conjugates of its main metabolite, alpha-hydroxymidazolam, have been shown to accumulate in renal failure but have not previously been related to the prolonged sedative effects commonly observed in critically ill patients. We report five patients with severe renal failure who had prolonged sedation after administration of midazolam. In all five patients, the comatose state was immediately reversed by the benzodiazepine-receptor antagonist flumazenil. Serum concentration monitoring showed high concentrations of conjugated alpha-hydroxymidazolam when concentrations of the unconjugated metabolite and the parent drug were below the therapeutic range. In-vitro binding studies showed that the affinity of binding to the cerebral benzodiazepine receptor of glucuronidated alpha-hydroxymidazolam was only about ten times weaker (affinity constant 16 nmol/L) than that of midazolam (1.4 nmol/L) or unconjugated alpha-hydroxymidazolam (2.2 nmol/L). Conjugated metabolites of midazolam have substantial pharmacological activity. Physicians should be aware that these metabolites can accumulate in patients with renal failure.
Insights
Conjugated midazolam metabolites accumulate in renal failure, causing prolonged sedation in critically ill patients. Flumazenil reversed these effects, highlighting the active nature of these metabolites.
Area of Science:
- Pharmacology
- Intensive Care Medicine
- Nephrology
Background:
- Midazolam is a common sedative in intensive care.
- Its metabolite, alpha-hydroxymidazolam, accumulates in renal failure.
- The clinical significance of this accumulation for prolonged sedation was unclear.
Purpose of the Study:
- To investigate the role of midazolam metabolites in prolonged sedation in patients with renal failure.
- To assess the pharmacological activity of conjugated midazolam metabolites.
- To inform clinical practice regarding midazolam use in renal impairment.
Main Methods:
- Case series of five patients with severe renal failure receiving midazolam.
- Clinical observation of sedation duration and response to flumazenil.
- Serum concentration monitoring of midazolam and its metabolites.
- In-vitro receptor binding studies of conjugated alpha-hydroxymidazolam.
Main Results:
- Patients with renal failure experienced prolonged sedation after midazolam administration.
- Flumazenil (a benzodiazepine antagonist) rapidly reversed the sedative effects.
- High serum concentrations of conjugated alpha-hydroxymidazolam were found, even when parent drug levels were low.
- Conjugated metabolites exhibited significant binding affinity to the benzodiazepine receptor.
Conclusions:
- Conjugated metabolites of midazolam possess significant pharmacological activity.
- Accumulation of these active metabolites in renal failure contributes to prolonged sedation.
- Clinicians should exercise caution when administering midazolam to patients with impaired renal function.