Anesthesia Pharmacology Flashcards
The anesthesia provider should do the following 5 things prior to induction?
- Perform and document a thorough pre anesthesia assessment and evaluation
- Obtain and document informed consent for the planned anesthetic from the patient or legal guardian
- Formulate a patient specific plan for anesthesia care
- Implement and adjust the plan based on the patient’s physiologic response… intervene to maintain optimal physiologic condition
- Monitor, oxygenate, ventilate, CV, temp NMBs, positioning
Pharmacodynamics
- The action of the drug on the body
- “Relationship between the concentration of the drug and the magnitude of effect”
- Nature of the drug (racemic, oral, IV)
- receptors and binding sites
- therapeutic index
Pharmacokinetics
- The effects of the body on the drug
- “Relationship between the drug dose and the time course of drug levels in the bloodstream”- for anesthesia- At the receptor site of desired action*
- binding, permeability, elimination, distribution
Agonists
Cause desired action at the receptor
Antagonists
Have affinity for receptor but NO efficacy
-No action at the receptor
Competitive Antagonism
- shifts agonist-concentration effect curve to the right
- tend to bind at the same site as agonists
Non-competitive antagonists
- May bind irreversibly to the receptor
- Lowers the number of active receptors available
- less effect seen
- tend to bind to another (allosteric) site which changes the desired receptor site
ED/C50 and ED/C95
The dose (concentration) of drug needed to obtain 50% or 95% of the maximal effect
During anesthesia induction, why do we give 2-3 times the ED95 of drugs?
-to achieve rapid onset, knowing it will take a longer time for the effect-site concentration to drop low enough for the effect of that drug to wear off
Potency
- function of affinity for the receptor and function at the receptor
- high affinity with low potency= low potency
- low affinity with higher potency= HIGH potency
Therapeutic Index
Toxic Dose (TD50)/ Effective dose (ED50)
- high TI indicates relatively safe drug
- anesthesia drugs have low TI- less safe
Dissociation constant
- describes the propensity for a drug-receptor complex to break apart
- relatively more important for anesthesia drugs
Clearance
Rate of elimination/ plasma drug concentration
-clearance by an organ is equal to the extraction capability of the organ X the blood flow to the organ
First order Clearance
- clearance of drugs with first order kinetics is constant regardless of plasma concentration
- constant T1/2, 50% decrement per time interval
Zero order Clearance
- clearance of drugs with zero order kinetics is not constant and depends upon plasma concentration
- constant elimination, units eliminated/time (EtOh)
T 1/2 life
- varies directly with the Vd and inversely with clearance
- higher Vd= takes longer to clear
- higher clearance= shorter 1/2 life
Phase 1 metabolism
converts parent drug to more polar substance (hydrophobic to hydrophilic)
Phase 2 metabolism
conjugate drug with polar moiety making it more water soluble and excretable
CYPS: p450, p2D, P3A
response for most drug metabolism
Enzyme induction
- stimulation of drug metabolizing enzymes in the liver, usually phase 1 enzymes