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Flashcards in Pharmacodynamics (DONE) Deck (14):

What determines the therapeutic dose of a drug, the manner of its administration and its frequency of administration?

Trial and error between dosage regimen and desired/adverse effects
Regimen refined and optomised


What is the rational approach to determine dosing regimen?

Dosage regimen> exposure to drug within body> desired and adverse effects
Use pharmacokinetics and pharmacodynamics to inform regimen design


Drug input-response phases (PK and PD)

Pharmacokinetic phase: relationship between drug input (adjustable) and concentration with time
Adjustable factors include dose, dosage form, frequency and route
Pharmacodynamic phase: relationship between concentration and effects produced with time
NB effects are both desired and adverse


Achieving the therapeutic window- PK and PD

PK will provide information on the dosage regimen to achieve a given window of plasma drug concentrations
PD will provide information on the effect likely to be achieved with regards to a given window of plasma drug concentrations


Effects of drugs

Stimulation e.g. adrenaline stimulates heart
Depression e.g. quinidine depresses heart
Irritant e.g. counterirritants increase blood flow to site of injury
Replacement e.g. insulin in diabetes
Cytotoxicity e.g. antibiotics, chemotherapeutics


Classification of response to drug

Clinical- subjective vs objective
Surrogate endpoint


Chemical actions of drug within body

Drug acts extracellularly- conforms to simple chemical equations
e.g. antacids neutralise gastric secretions


Protein interactions with drugs

Interaction with endogenous protein i.e. receptor theory: antagonize, block or inhibit; activate; unconventional mechanisms
Receptor interaction determines selectivity of drug and also provides quantitative relationship between dose and response


Effects of receptors, enzymes and structural proteins on drugs

Cell surface and intracellular receptors- mediate signal transduction e.g. ACh, insulin etc,
Enzymes- catalyse substrate to product
Structural proteins e.g. tubulin


What are the definitions of pharmacokinetics and pharmacodynamics?

Pharmacokinetics is the relationship between dose and concentration but relationship changes with time
Pharmacodynamics is the relationship between concentration and effect but relationship does not change with time


Concentration-effect rule

If concentration and effect relationship does not change with time in a drug's PD relationship, then for the same concentration, effect will be the same independent of time


Efficacy and potency definitions

Efficacy is the maximum effect of a drug
Potency affords comparison between a set of drugs and indicates the doses of drugs required to produce the same effect


Physical actions of drug within body and examples

Mass: bulk forming laxative e.g. Fybogel
Adsorptive: charcoal, kaolin
Osmotic activity: mannitol (brain swelling)
Radioactivity: radioisotopes in radiotherapy


Emax and EC50 definitions

Emax is the maximum possible response of the system to drug
EC50 is the concentration of drug that produces half the maximal response