Benzodiazepines

Definition: Benzodiazepines are a class of medications that act as central nervous system depressants.
Mechanism of Action:
- Bind to the GABA A receptor in the central nervous system.
- Different binding sites compared to barbiturates.
- They cause anterograde amnesia.
- Function as GABA A agonists similar to IV anesthetics.
- Instead of keeping the chloride channel open like barbiturates, they increase the frequency of chloride channel openings, leading to neuronal hyperpolarization.

Composed of:
- A benzene ring.
- A seven-member diazepine ring.
Substitutions at various positions on the rings influence potency and biotransformation information.
Solubility Properties:
- Imidazole ring of Midazolam increases water solubility.
- Diazepam and Lorazepam are water-insoluble, often due to propylene glycol, contributing to IV pain during administration.
  - Diazepam more than Lorazepam

Uses: Primarily for premedication, sedation, and induction.
Dosage:
- Premedication IM: 0.07 - 0.15 mg/kg.
- IV Sedation: 0.1 - 0.15 mg/kg.
- Induction IV Dose: 0.1 - 0.4 mg/kg.
** pH Dependence**:
- At acidic pH: Imidazole ring opens, increasing water solubility.
- At physiologic pH: Imidazole ring closes, increasing lipid solubility, allowing it to cross the blood-brain barrier.
Active Metabolite: One hydroxymidazolam.
- More potent (0.5 times) and prolongs effects in patients with renal failure.
- Rapidly conjugated to an inactive compound.
Cardiovascular Effects:
- Sedation dosage shows minimal cardiovascular effects.
- Induction dosage results in:
  - Decreased blood pressure.
  - Decreased systemic vascular resistance (SVR).
Respiratory Effects:
- Sedation dosage shows minimal respiratory effects.
- Induction dosage can lead to respiratory depression, particularly concerning in COPD patients due to heightened sensitivity.
Central Nervous System Effects:
- Causes anterograde amnesia.
- Displays anticonvulsant properties.
- Produces anxiolysis.
- Lacks analgesic effects and isoelectric EEG.
- Facilitates spinally mediated skeletal muscle relaxation; effective as an antispasmodic (used in conditions like cerebral palsy).

Uses: Employed for premedication and sedation.
Dosage:
- Premedication Oral Dose: 0.2 - 0.5 mg/kg.
- Sedation IV Dose: 0.04 - 0.2 mg/kg.
Elimination Half-Life: Approximately 43 hours due to intrahepatic recirculation.
Applications:
- Effective as an anticonvulsant.
- Prevents emergence delirium associated with ketamine.
- Acts as an antispasmodic by reducing skeletal muscle tone at spinal neuron level.

Properties: An ultra-short-acting benzodiazepine with high affinity for GABA A receptor.
Usage Guidelines: After reconstitution, must be discarded within eight hours.
Metabolism: Rapidly metabolized by nonspecific esterases due to ester link; associated with:
- Lower respiratory depression.
- Fast onset and quick recovery.
Contraindications: Should not be used in patients with a history of severe hypersensitivity reactions to dextran 40.

Function: A competitive antagonist of the GABA A receptor and a reversal agent for benzodiazepine effects.
Properties:
- High affinity but short duration of action (30-60 minutes).
- Requires redosing to prevent resedation.
Initial Dosage: 0.2 mg IV; titrate up to 0.1 mg every minute as needed.
Side Effects:
- Postoperative use may worsen anxiety and does not elevate sympathetic nervous system tone.
- In cases of chronic benzodiazepine use, cessation can precipitate withdrawal symptoms (e.g., seizures) and can reverse sedative effects more prominently than amnestic effects of benzodiazepines.