Pharmacology for anaesthesia Flashcards
(40 cards)
Define pharmacokinetics.
The relationship between drug dose, concentration in bodily fluids and tissues, and time
What the body will do with a given drug
Give 4 routes of drug administration.
Oral, sublingual, rectal, inhalational, transdermal, transmucosal, subcutaneous, intramuscular, and intravenous
Which 4 processes make up pharmacokinetics?
Absorption
Distribution
Metabolism
Excretion
Define absorption.
The processes by which a drug moves from the site of administration to the bloodstream.
Give 3 factors that affect volume distribution.
Lipid solubility
Protein binding
Ion binding- electrical charge
Molecular weight- smaller easy to cross membrane
Define Volume of distribution.
Apparent volume into which a drug has mixed-distributed throughout the body.
Give 2 factors that affect absorption.
- Physical properties of drug- Solubility, Diluent, Binders, Formulations
- Dose
- Site/Route.
How do you calculate volume of distribution?
VD = Total quantity of drug / Plasma concentration in steady state
Define terminal half life.
Time required for the plasma concentration to decrease by 50% during the terminal phase of decline
Define clearance.
Represents the volume of blood or plasma from which the drug is completely eliminated in unit time (ml/min)
What is pharmacokinetic modeling used for?
Used to analyze drug distribution and elimination as well as complex patient situations to describe and predict drug behavior.
What is the one compartment model?
The rate of drug elimination is assumed to be proportional to the amount of drug in the body (X) at any time (t), it decreases exponentially with time and is consistent with first-order kinetics (dX/dt = k X)
What is two compartment model?
Each phase follows exponential first-order processes
A-rapid distribution
B- elimination of the drug
Which compartment model is most important in anaesthesia?
Three compartment model
It divides the body into three compartments: a central compartment (usually representing plasma) and two peripheral compartments representing tissues that are either highly or scarcely perfused by blood.
What is zero order elimination?
A constant amount of drug is eliminated per time unit (Thiopentone, Phenytoin, Salicylates, Theophyllin, alcohol)
Define pharmacodynamics.
Relationship between a drug’s mechanism of action and the biochemical and physiologic response produced in the body.
What does the drug do to the body.
What is Minimal Alveolar Concentration (MAC)?
The concentration at which 50% of subjects do not produce a reaction to a standard stimulus.
What does the anesthesia triad include?
Hypnosis—-Analgesia—Paralysis
What are intravenous anaesthetics used for?
Hypnosis- During Induction & maintenance.
What are the properties of an ideal IV anaesthetic agent? (4)
- Rapid onset + rapid recovery
- Storability: Long shelf-life at room temperature
- Pleasant effect during the induction phase
- Safety following extravasation or inadvertent intra-arterial injection
- Analgesic at sub-anaesthetic concentrations
- Minimal cardiovascular and respiratory depression
Give 4 examples of IV anaesthetic drugs.
Barbiturates (thiopental, methohexitone)
Non-barbiturates (propofol, ketamine, etomidate)
What properties should an ideal IV anaesthetic agent not have? (4)
- toxic effects
- emetic effects
- pain on injection
- histamine release or hypersensitivity reaction
- interference with other drugs
- stimulation of porphyria
- unpleasant experiences in the peri-operative phase
Name the 3 IV anaesthetic drugs most commonly used in Malawi.
Thiopentone
Ketamine
Propofol
What are the key pharmacological properties and cautions of Thiopentone?
Class: Barbiturate
MOA: Prolongs GABA-dependent Cl⁻ channel opening
Onset: Rapid (one arm-brain circulation time)
Duration: Short (due to redistribution)
Effects: Antiepileptic, mild muscle relaxation, causes hypotension, histamine release
Cautions: Unsafe in porphyria
Formulation: Alkaline solution (pH ~10.5)
Note: Long half-life with repeated doses or infusion
