Pharm 101: Midazolam

Class

Benzodiazepine

Pharmacodynamics
  • Benzodiazepine drug:
    • Binds to GABA-A receptor in neuronal membranes in CNS (y subunit of the pentamer). This receptor is a chloride ion channel.
    • Enhances inhibitory effect of GABA through hyperpolarisation
    • This increases frequency of chloride channel opening
Pharmacokinetics
  • Various routes of administration: PO, IV, IM, PR, IN, buccal
  • Water soluble therefore intramuscular injection possible
  • Poor oral bioavailability
  • Crosses the blood brainer barrier easily at body pH
  • Highly protein bound
  • Hepatic metabolism and renal excretion (56%)
  • Short elimination half-life of 1.5-2.5 hours
Clinical uses (and organ level effects)
  • Sedative-hypnotic
  • Anticonvulsant
  • Anxiolytic
  • Antiemetic
  • Reduced sensitivity to CO2
Adverse effects
  • Excess sedation
  • Respiratory depression:
    • Can be profound even at therapeutic doses in patients with pulmonary disease
    • Effects are dose-related
    • Depression of medullary respiratory centre is usual cause of death in overdose
  • Cardiovascular depression:
    • May occur at normal dose in hypovolaemic states and heart failure
    • Toxicity causes depression of both myocardial contractility and vascular tone leading to circulatory collapse
Precautions/contraindications
  • As above, caution in patients with respiratory or cardiovascular disease due to depressant effects on these organ systems
  • All benzodiazepines are liver metabolised and thus dose may need to be reduced in liver disease
Further Reading

Pharmacology 101

Top 200 drugs

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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