Benzodiazepines Flashcards
What do Benzodiazepines do?
Anxiolysis Sedation Anticonvulsant action Spinal cord mediated skeletal muscle relaxation Anterograde Amnesia
What do we use benzodiazepines for?
Pre-Op sedation
Conscious Sedation
Short Procedures such as regional anesthesia placement
Theoretically can be used for induction of anesthesia
Specific uses
MOA of Benzodiazepines
GABA Molecule
GABAa- pentameric
2 alpha subunits, 2 beta units and 1 gamma
What subunit of benzo causes sedation
alpha-1
5 subunits
What subunit of benzo causes anxiolysis?
Alpha-2
GABA Agonist
binds to GABAa increasing affinity of receptors for GABA
What change opens in GABA channels
Cl, increased frequency of cl channel opening, increased Cl conductance
What occurs with increased Cl conductance
post synaptic membrane hyperpolarization. More resistance to excitation= drug effect we are looking for
Generalizations about Benzos
Highly lipid soluble, protein bound
Higher margin of safety
Fewer/less serious drug interactions (compared to others)
Anticonvulsant, increased seizure threshold in LAST
Depresses swallowing reflex and upper airway activity
synergistic with other CNS depressants
HPA suppression, inhibit platelet aggregation (unsure if clinically relevant)
LAST
Local Anesthetic Systemic Toxicity
Anticonvulsant Characteristics of Benzos
Decreased alpha activity
Increased low voltage rapid beta activity
Unable to produce isoelectric EEG
Benzos in Elderly
Increased sensitivity due to pharmacokinetics, dose dependent
Aging/liver disease effect on glucuronidation
Structure of Midazolam
Substituted imidazole ring makes drug stable in aqueous solution, accounts for rapid metabolism
Water soluble, no preservative, painless injection
Pharmacokinetics of Midazolam (PO)
rapid GI absorption (50% reaches systemic circulation= substantial hepatic first pass)
Hepatic/small intestine metabolism
What enzyme breaks down Midazolam
P450 CYP3A4-> active, inactive metabolites, cleared by kidneys
Midazolam Elimination Time
Elimination 1/2 time 1.9 hours (can be 2x in elderly d/t decreased hepatic BF/Enzyme activity
Midazolam DOA
short (15-80 mins) d/t lipid distribution from brain to inactive tissue sites
Pharmacodynamics of Midazolam (CNS)
decreases CMRO2/CBF
Cerebral vasomotor response to CO2 stays in tact, does NOT prevent increase in ICP with DL, NO neuroprotective qualities
Pharmacodynamics of Midazolam (Respiratory)
DD (0.15 mg/kg) decreases ventilation d/t decreased hypoxic drive
Pharmacodynamics of Midazolam (CV)
decreases SVR (coudn increase CO in CHF) enhanced CV changes with other induction drugs in hypovolemic patients, does not attenuate CV response to DL
MIdazolam IV Dose
1-2.5 mg adults
Midazolam PO Dose
0.5mg/kg q30 mins prior to induction= reliable sedation anxiolysis without delayed wakening
Dose of Midazolam for Paradoxical Vocal Cord Motion Treatment
0.5-1mg