Flashcards in Pharmacokinetics - ADME Deck (55)
What is the pharmacokinetic process?
Getting the drug to the site of action
What is the pharmacodynamic process?
Producing the correct pharmacological effect
What four events happen as part of the pharmacokinetic process?
What is drug absorption?
movement of the unchanged drug from site of administration to systemic circulation
What is Tmax?
time taken for a drug to reach peak concentration in the body
comes earlier if absorption if the drug is more rapid
What is Cmax?
peak concentration of the drug in the body
affected by increases in dosage
What is AUC?
the amount of the drug that reaches the systemic circulation
What is bioavailability?
the amount of a drug that reaches systemic circulation and is available for action
What is the therapeutic range of a drug?
the area where drug concentration if safe and active
above = toxicity
below = ineffective
What are the factors that effect the bioavailability of oral absorption if drugs?
- physiological barriers
- gastrointestinal effects
- first pass metabolism
What type of drugs are absorbed through diffusion?
Non-ionised drugs (weak acids/bases, changes in pH change ability to diffuse)
Lipophilic drugs (must be lipid-soluble to diffuse through lipid membranes)
What must drugs resemble in order to be absorbed by active transport?
What is the main gastrointestinal factor that influences drug absorption?
- speed of gastric absorption
- affected by food/drink/illnesses
What illnesses can affect GI motility?
- Coeliac disease (gives rise to malabsorption)
- Migraine (reduces the rate of stomach emptying)
What is the first pass metabolism?
the metabolism of a drug before it can reach the systemic circulation
i.e. a drug could be fully metabolised before reaching the blood, e.g. insulin (reason for IV administration)
Why are other routes of drug absorption used?
- absorption rate can be changed with different formulation
- drugs with small volumes
- blood flow differences
- avoiding the first pass metabolism
Name four sites of drug administration, other than oral
What is drug distribution?
the reversible transfer of a drug between blood and extravascular fluids/tissues in order for it to become active
What factors can influence drug distribution?
Plasma protein binding
What is plasma protein binding?
when drugs bind to plasma proteins such as albumin, nullifying their effects
What can affect the amount of a drug that is bound to plasma proteins?
- renal failure
- other drugs (by displacement)
Name three parameters of the therapeutic range
Apparent volume of distribution (Vd)
What is apparent volume of distribution?
theoretical volume needed to contain the total amount of a drug in the blood plasma if the drug was present in the same concentration throughout the body (L/Kg)
What is caused by a greater Vd?
greater ability of a drug to diffuse to/through membranes
What is clearance?
volume of fluid from which a drug is completely removed over a period of time (ml/min)
What does renal clearance depend on?
- urine flow rate
What does hepatic clearance depend on?
- biliary excretion
What is the half-life of a drug?
time taken for the drug concentration to decline by half its current value
What does T1/2 depend on?
- apparent volume of distribution