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BENZODIAZEPINES PREOPERATIVE MEDICATIONS. DENNIS STEVENS MSN, CRNA, ARNP OCTOBER 2005 FLORIDA INTERNATIONAL UNIVERSITY PHARMACOLOGY OF ANESTHESIOLOGY NURSING NGR 6173. OBJECTIVES. Discuss the principal pharmacologic effects of benzodiazepines.

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benzodiazepines preoperative medications
BENZODIAZEPINESPREOPERATIVE MEDICATIONS

DENNIS STEVENS MSN, CRNA, ARNP

OCTOBER 2005

FLORIDA INTERNATIONAL UNIVERSITY

PHARMACOLOGY OF ANESTHESIOLOGY NURSING

NGR 6173

objectives
OBJECTIVES
  • Discuss the principal pharmacologic effects of benzodiazepines.
  • Explain mechanism of action associated with benzodiazepines and their interaction with the CNS.
  • Compare the unique chemical structure of midazolam and how it differs at various pH levels.
  • Discuss the pharmacokinetic properties specific to benzodiazepines.
  • Explain the effects on organ systems of benzodiazepines.
  • State the clinical indications of midazolam and diazepam.
  • Discuss the action and dosing regime of flumazenil.
references
REFERENCES

Morgan, G.E., Mikhail, M.S., and Murray, M.J. (2002).

Clinical Anesthesiology. (3rd Ed.) New York, NY:

McGraw-Hill.

Nagelhout, J.J. and Zaglaniczny, K.L. (2005). Nurse Anesthesia. (3rd Ed.) St. Louis, MO: Elsevier-Saunders.

Stoelting, R.K. (1999). Pharmacology & Physiology in Anesthetic Practice. (3rd Ed.) Philadelphia, PA:

J.B. Lippincott Company.

clinical considerations
CLINICAL CONSIDERATIONS
  • Benzodiazepines exert five principal pharmacologic effects:
    • Sedation
    • Anxiolysis
    • Anticonvulsant actions
    • Spinal cord-mediated skeletal muscle relaxation
    • Anterograde amnesia
  • Benzodiazepines have replaced barbiturates for preoperative medication and production of sedation during monitored anesthesia care
mechanism of action
MECHANISM OF ACTION
  • Benzodiazepines interact with specific receptors in the central nervous system
  • Benzodiazepine-receptor binding enhances the inhibitory effects of various neurotransmitters
  • Facilitates GABA receptor binding which increases the membrane conductance of chloride ions
  • Causes a change in membrane polarization that inhibits normal neuronal function
  • Receptor occupancy
  • Receptor subtypes
structure activity relationships
STRUCTURE-ACTIVITY RELATIONSHIPS
  • Benzodiazepines are similar structurally and share many active metabolites
  • Benzodiazepine refers to the portion of the chemical structured composed of a benzene ring fused to a seven-membered diazepine ring
  • Substitutions at various positions on these rings affect potency and biotransformation
  • Benzodiazepines differ markedly in speed that they are metabolized and eliminated
pharmacokinetics
PHARMACOKINETICS
  • Absorption:
    • Commonly administered orally, intramuscularly, and intravenously
    • Diazepam and lorazepam are well absorbed from the GI tract, peak plasma levels usually achieved in 1 and 2 hours
    • IM injection of diazepam is painful and unreliable
    • Oral midazolam popular for pediatric premedication
      • Intranasal: (0.2-0.3 mg/Kg)
      • Buccal: (0.07 mg/Kg)
      • Sublingual: (0.1 mg/Kg)
      • Premedication IM: (0.07-0.15 mg/Kg)
      • Sedation IV: (0.01-0.1 mg/Kg)
pharmacokinetics10
PHARMACOKINETICS
  • Distribution:
    • Diazepam quite lipid-soluble and rapidly penetrates the blood brain barrier
    • Midazolam water-soluble at low pH and at physiologic pH increase in its lipid solubility
    • Moderate lipid solubility of lorazepam
    • Redistribution fairly rapid for the benzodiazepines
    • Benzodiazepines highly protein-bound
biotransformation and excretion
BIOTRANSFORMATION AND EXCRETION
  • Rely on the liver for biotransformation into water-soluble glucuronide end products
  • Phase I metabolites of diazepam are pharmacologically active
  • Elimination half-life: time necessary to eliminate 50% of a drug from the body after its rapid IV injection
  • Long elimination half-life for diazepam
  • Lorazepam shorter elimination half-life
  • Midazolam shortest elimination half-life
  • Metabolites of benzodiazepine biotransformation are excreted chiefly in the urine
effects on organ systems
EFFECTS ON ORGAN SYSTEMS
  • Cardiovascular:
    • Minimal cardiovascular depressant effects
    • Arterial blood pressure, cardiac output, and peripheral vascular resistance usually decline slightly and heart rate sometimes rises
    • Midazolam tends to reduce blood pressure and peripheral vascular resistance more than diazepam
effects on organ systems13
EFFECTS ON ORGAN SYSTEMS
  • Respiratory:
    • Benzodiazepines depress the ventilatory response to CO2
    • Ventilation must be monitored in all patients receiving IV medications
  • Cerebral:
    • Reduce CMRO2, cerebral blood flow, and intracranial pressure
    • Effective in preventing and controlling grand mal seizures
    • Provides antianxiety, amnesic, and sedative effects
    • Possesses mild muscle-relaxant properties
    • No direct analgesic properties
drug interactions
DRUG INTERACTIONS
  • Cimetadine binds to cytochrome P-450 and reduces the metabolism of diazepam
  • Erythromycin inhibits midazolam metabolism and causes prolongation and intensification of its effects
  • Heparin displaces diazepam from protein-binding sites and increases free drug concentration
  • Combination of opioids and diazepam markedly reduces arterial blood pressure and peripheral vascular resistance
  • MAC of volatile anesthetics reduced as much as 30%
  • Ethanol, barbiturates, and other CNS depressants potentiate sedative effects
midazolam clinical uses
MIDAZOLAM: CLINICAL USES
  • Most commonly used benzodiazepine for preoperative medication and IV sedation
  • Provides amnesia
  • Potent anticonvulsant for the treatment of grand mal seizures
  • Administration:
    • PO: 0.5 mg/Kg
    • IV: 0.01-0.1 mg/Kg
    • IM: 0.05-0.10 mg/Kg
  • Doses of 1.0-2.5 mg IV effective for sedation during regional anesthesia and brief therapeutic procedures
  • Administered as a supplement for maintenance of anesthesia
diazepam clinical uses
DIAZEPAM: CLINICAL USES
  • Diazepam dissolved in organic solvents and is associated with pain on injection and thrombophlebitis
  • Popular drug for preoperative medication of adults, management of delirium tremens, and treatment of local anesthetic-induced seizures
  • Produces anterograde amnesia
  • Skeletal muscle relaxant
  • Preoperative: PO 10-15 mg
  • Extensively bound to plasma protein
flumazenil
FLUMAZENIL
  • An imidazobenzodiazepine, specific and competitive antagonist of benzodiazepines at benzodiazepine receptors
  • Useful in the reversal of sedation and overdose
  • Prompt onset (< 1 minute)
  • Slow titration of 0.2 mg doses IV (up to 1 mg)
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