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
Pharm 101 700

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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