What evidence exists that describes the duration of action of induction agents used for intubation (primarily etomidate, ketamine, propofol, midazolam) based on patient's body weight and total dose administered. Please include all references found, including any case reports describing duration of sedative effect.

Comment by InpharmD Researcher

Evidence describing the duration of action of induction agents based on body weight and total dose appears limited. For midazolam, pharmacokinetic studies demonstrate that obesity prolongs the half-life, suggesting a risk of accumulation with large or repeated doses. A case report of etomidate overdose (250 mg over 43 minutes) resulted in unconsciousness lasting approximately 5–6 hours, while a case series of ketamine overdoses in children (5 to 100 times the intended dose) produced prolonged sedation lasting 3 to 24 hours. Pharmacokinetic study of propofol confirmed that while a single bolus yields brief hypnosis due to rapid redistribution, large cumulative doses during prolonged infusion can lead to a prolonged terminal elimination half-life (mean 1411 minutes) that extends duration of effect.

etomidate, ketamine, propofol, midazolam weight obesity overweight dose pharmacokinetics duration length of action sedation induction

Background

A comprehensive review on pharmacotherapy optimization for rapid sequence intubation (RSI) in the emergency department highlights important considerations regarding weight-based dosing (see Table 1). RSI medications in obese patients are often underdosed, particularly etomidate and succinylcholine, although the clinical consequences of this underdosing remain unclear. Given the critical importance of achieving full induction and paralysis during RSI, underdosing may carry greater risk than overdosing. In emergent settings, total body weight (TBW) can be used for dosing when calculating ideal or adjusted body weight is not feasible, with suggested maximum doses considered to avoid excessive exposure. However, for induction agents that predispose to hypotension, dosing based on adjusted body weight may be appropriate. Additionally, clinicians should anticipate a potentially prolonged duration of paralysis when large doses of neuromuscular blocking agents are required in obese patients. Further studies are needed to define optimal weight-based dosing strategies for RSI medications in this population.[1]

Though not specific to RSI dosing, literature emphasizes midazolam’s lipophilicity, which seems to demonstrate a higher volume of distribution without significant impact on total clearance in obese patients versus non-obese patients. A recent review on the subject describes a pharmacokinetic study from 1984 that reported a prolonged half-life with the use of midazolam in obese versus non-obese patients. (5.94 ± 0.85 versus 2.27 ± 0.3 hours respectively; p<0.001). A second pharmacokinetic study observed an increase in the central and peripheral volume of distribution as the actual body weight increased, but clearance remained unaffected. As the authors have observed a potential risk of accumulation, they recommend ideal or actual body weight for initial dosing and calculating continuous infusions, with small supplemental doses to achieve desired effects. However, caution is warranted when extrapolating these recommendations, as the cited studies provide general guidance and were not conducted in RSI settings. [2], [3], [4]

A 2021 review provides a comprehensive overview of the pharmacokinetic and pharmacodynamic properties of etomidate and its analogs, with a focus on ABP-700. The paper highlights the limited recent pharmacokinetic and pharmacodynamic studies on etomidate, necessitated by its decreased popularity due to adrenal suppression concerns. Etomidate is characterized by ultra-rapid hypnotic action and swift recovery. A continuous infusion causes loss of consciousness within 6 minutes. The effect of a single bolus on loss of eyelash reflex and electro-encephalographic activity were noted to be affected regardless of dose. Further discussions are limited. [5]

A 1983 case report describes an incidence of etomidate overdose via continuous infusion in a 67-year-old patient. The patient required intermittent positive pressure ventilation of lungs after successful resuscitation from cardiac arrest. She was sedated with etomidate 35 mg/hour, but was inadvertently given 250 mg of etomidate over 43 minutes. The patient was deeply unconscious, but no other complications occurred. The patient responded to painful stimuli after one hour, and was rousable after 5 hours. By 6 hours, she was fully conscious, alert, and able to communicate. [6]

A 1999 study analyzed the clinical manifestations and outcomes of inadvertent ketamine overdoses in children treated in emergency departments. This investigation involved a synthesis of cases identified through electronic mail subscription lists or reported to the Institute for Safe Medication Practices. The report meticulously examined cases where children received 5 to 100 times the intended dose of ketamine, with administration occurring via intramuscular or intravenous routes. Each case was scrutinized to detail the clinical manifestations, outcomes, and causes of the overdose, providing insights into the safety margins and potential complications arising from such dosing errors. In the series, nine cases were documented where healthy children experienced prolonged sedation lasting between 3 to 24 hours. Four of these children encountered brief respiratory depression shortly after administration of the drug, necessitating assisted ventilation in two instances. Notably, two of the children without immediate respiratory difficulties were intubated as a precautionary measure by physicians. Despite the significant dosing errors, no adverse neurological outcomes were reported upon discharge or longer-term follow-up where available. The findings suggested a potentially wide margin of safety for ketamine overdoses, although the report emphasized the need for caution as more serious outcomes could not be entirely excluded given the small and self-reported sample size. [7]

A 1992 study provides relevant pharmacokinetic data on propofol that directly inform how body weight and total dose influence duration of action. 12 critically ill, mechanically ventilated patients (predominantly male, mean age 58 years, mean weight 66.9 kg) received propofol by continuous infusion at a mean rate of 2.58 mg/kg/h for an average of 85.6 hours, after which blood concentrations were sampled for up to 42 hours. The results demonstrated that propofol’s elimination follows a triphasic pattern, with mean half‑lives of 1.81 minutes (rapid redistribution), 70.9 minutes (elimination), and 1411 minutes (slow terminal phase). Importantly, the median total body clearance was 2.11 L/min, consistent with shorter infusions, indicating that even after large cumulative doses, clearance mechanisms remain robust and weight‑based dosing remains reliable. The rapid 50% drop in concentration within the first 10 minutes after stopping the infusion explains why a single induction dose (typically 1.5–2.5 mg/kg based on lean body weight) yields a brief duration of hypnosis (5–10 minutes), while the prolonged terminal half‑life becomes clinically relevant only after prolonged administration or very large total doses, emphasizing that both body weight (as a determinant of distribution volume) and cumulative dose are critical factors in predicting propofol’s overall duration of effect. [8]

Literature Review

A search of the published medical literature revealed 2 studies investigating the researchable question:

Level of evidence

C - Multiple studies with limitations or conflicting results Read more→

Please see Tables 1-2 for your response.

Pharmacokinetic & pharmacodynamic properties of pretreatment, induction, and neuromuscular blocking agents
Medication	Mechanism of action	Dosing	Onset of action	Duration of action	Adverse effects	Considerations for use
Pretreatment agents
Atropine	Anticholinergic	Adults 0.01 mg/kg IV up to 0.5–1 mg; Pediatrics 0.02 mg/kg IV; max dose 0.5 mg, use TBW	Variable, >2 min	1 h	Tachycardia, flushing, vomiting, urinary retention, constipation	Use: -pediatric patients under the age of 1 years receiving succinylcholine
Lidocaine	Sodium channel blocker (Vaughan-Williams Class 1B antiarrhythmic)	1.5 mg/kg IV, use IBW	Immediate, max effect 1–2 min	15 min	Hypotension, bradycardia	Use: -no clear indication for use
Fentanyl	Opioid receptor agonist	1–2 μg/kg IV, max 200 μg, use adj BW^⁎⁎	Immediate, max effect 2–3 min	60 min	Hypotension, respiratory depression	Use: -no clear indication for use
Induction agents
Etomidate	Indirect GABA agonism	0.3 mg/kg IV, max 40 mg, use adj BW	Immediate, 5–15 s	5–15 min	Adrenal suppression, myoclonus, nausea & vomiting	Use: -hemodynamic instability
Ketamine	NMDA antagonism	1–2 mg/kg IV, 4–6 mg/kg IM, max 200 mg IV or 500 mg IM, use adj BW	30–90 s	10–30 min IV 25–45 min IM	Hypertension, tachycardia, myocardial ischemia, nystagmus, increased oral secretions, emergence phenomena	Use: -reactive airway disease -caution if hemodynamic instability Avoid: -severe hypertension -cardiac ischemia -excess oral secretions -severe eye injury or need for eye exam
Propofol	GABA agonism	1–2 mg/kg IV, max 200 mg, use adj BW	Immediate, 15–30 s	5–10 min	Hypotension, bradycardia	Use: -seizure -head injury Avoid: -hemodynamic instability
Midazolam	GABA agonism	0.1–0.3 mg/kg IV or IM adj BW, recommend non-weight-based dose of 5–10 mg	1–3 min IV 5–15 min IM	10–30 min^⁎	Hypotension (dose dependent)	Use: -seizure -no IV access (use IM) Avoid: -hemodynamic instability
Neuromuscular blocking agents (NMBA)
Succinylcholine	Depolarizing neuromuscular junction blockade	1.5 mg/kg IV, use TBW	30–45 s	5–15 min	Hyperkalemia, malignant hyperthermia	Use: -need a neurological exam after intubation Avoid: -hyperkalemia -history malignant hyperthermia -upregulation of acetylcholine receptors^⁎⁎⁎
Rocuronium	Non-depolarizing neuromuscular junction blockade	1–1.2 mg/kg IV, max 150 mg, use IBW	45–60 s	45–120 min		Use: -succinylcholine not appropriate -longer duration of paralysis necessary
Vecuronium	Non-depolarizing neuromuscular junction blockade	0.1 mg/kg IV, max 15 mg, use IBW	Delayed, 2–4 min	40–60 min		Use: -longer duration of paralysis necessary -longer shelf life necessary (e.g. prehospital)
IV = intravenous; IM = intramuscular; Min = minutes; TBW = total body weight; Adj BW = adjusted body weight; IBW = ideal body weight; GABA = gamma-aminobutyric acid; NMBA = neuromuscular blocking agent. ⁎Effects may be longer in patients with severe hepatic impairment. ⁎⁎For all agents, adjusted body weight should only be utilized in the setting of obesity, total body weight should be used otherwise. ⁎⁎⁎Spinal cord injury, burn or crush injury >24 h, sepsis >7 days, muscular dystrophy, demyelinating neuromuscular disease, severe immobility.

References:
[1] [1] Engstrom K, Brown CS, Mattson AE, Lyons N, Rech MA. Pharmacotherapy optimization for rapid sequence intubation in the emergency department. Am J Emerg Med. 2023;70:19-29. doi:10.1016/j.ajem.2023.05.004

Etomidate-overdose by continuous infusion
Design	Case report
Case presentation	A 1983 case report describes an incidence of etomidate overdose via continuous infusion in a 67-year-old patient. The patient required intermittent positive pressure ventilation of lungs after successful resuscitation from cardiac arrest. She was sedated with etomidate 35 mg/hour, but was inadvertently given 250 mg of etomidate over 43 minutes. The patient was deeply unconscious, but no other complications occured. The patient responded to painful stimuli after one hour, and was rousable after 5 hours. By 6 hours, she was fully conscious, alert, and able to communicate. Unfortunately, the patient died 6 days later due to a second cardiac arrest.
Study Author Conclusions	N/A

References:
[1] [1] Chalmers P. Etomidate-overdose by continuous infusion. Anaesthesia. 1983;38(5):506. doi:10.1111/j.1365-2044.1983.tb14045.x