Pharmacokinetics Flashcards
What does pharmacodynamics describe
the interaction of drugs and their receptors (including affinity and efficacy) and the tissue distribution of the receptor
What does pharmacokinetics describe
the factors that determine the concentration of the drug at the target receptor
What does relationship between administered dose and concentration at the target site depend upon
absorption,
distribution,
metabolism
excretion
How does plasma concentration of a drug vary over time for:
a) a single iv bolus dose
b) oral dose
a) initially high then decreases
b) initially increases to a peak as drug is absorbed, before decreasing as metabolism and excretion increase
What is the range the plasma conc of a drug must be within
therapeutic window - higher than minimum effective conc. but lower than the minimum toxic conc
Do you want the therapeutic window to be wide
yes this is ideal
How is the therapeutic window reflected in dosing strategies
An effective dosing strategy will maintain the plasma concentration within
the therapeutic window for as long as necessary
What kind of chemicals are local anaesthetics
Where do they act? What does this mean?
weak bases
intracellular side of the Nav channels
They must cross the plasma membrane to access the intracellular compartment.
How do local anaesthetics cross into the intracellular compartment
in their un-ionised form (D)
Why does the chemistry of inflammation affect the transport of local anaesthetics
Local inflammation decreases tissue pH (higher H+
concentration).
This shifts the equilibrium to favour DH+
Local anaesthesia is delayed or even prevented
Which form of a weak base/acid is more likely to cross the PM
un-ionised form is usually more lipid soluble so diffuses readily, whereas
the ionised form cannot cross the membrane
Name 2 subgroups in the SLC superfamily
organic anion transporters (OATs)
organic cation transporters (OCTs).
Name a SRC that is a drug target itself
SERT (transports serotonin)
Name members of the SRC superfamily that are a) highly selective and b) less selective
a) SERT
b) OCT, OAT - can transport a wide range of structurally diverse molecules
Describe the ABC superfamily
Give an example
ATP-binding cassette superfamily use ATP to drive drug efflux from cells.
MDR1 (P-glycoprotein, P-gp) is a particular example. They may be important drug resistance.
What are SLC and ABC superfamilies particularly important for in pharmacokinetics
absorption from the small intestine, excretion into the bile or urine, and transport across
the blood-brain barrier
What is the only time a drug does not have to cross a barrier to reach the plasma
iv
What is the fastest and most certain route of drug administration
When would this be useful
iv
if the drug has a small therapeutic window
Why might you use a slow iv administration of a drug over a fast administration
A rapid bolus injection can produce a very high plasma
concentration, initially in the right side of the heart and pulmonary circulation. Slow i.v.
infusion avoids this high peak plasma concentration while still avoiding uncertainly inherent
in absorption from other sites
Disadvantages of iv drug administration (3)
injection or infusion requires a
skilled practitioner, and inconvenience to the patient. There is also risk of infection
What are disadvantages of subcut. or intramuscular injections
rate of absorption can be unpredictable and inconsistent. These
injections can also be painful.
What is the rate of absorption dependant on for subcutaneous/ intramuscular injections
diffusion through the tissue and removal by local
blood flow, as long as the drug can cross the capillary endothelium
How does absorption differ between intramuscular and subcit injections
Blood flow to
the muscle is higher than to the skin, so absorption from intramuscular is often more rapid
than for subcutaneous. Exercise increases muscle blood flow, increasing absorption.
Why is oral administration the most common route for drug administration
cheap and easy to administer (self administering)