pharmokinetics pharmacology Flashcards
what is the difference btwn pharmakinetics and pharmacodrynamics?
PK: what the body does to the drug (effect of the body on teh drug)
PD: effect of the drug on the body / target organ
what are the 4 parts to PK
- absorption
- distribution
- metabolism
- elimination
why does obesity affect PK? (3 things)
increased blood volume, increased adipose tissue and increased cardiac output
what is absorption
process by which the drug proceeds from its site of administration to the site of measurement (usually in the plasma, but sometimes in the breath/urine)
what are some drug factors / body factors affecting drug absorption?
Drug factors: Molecular size, particle size, degree of ionisation, lipid/water solubility (*), physical/chemical structure, dosage forms, formulation (bound to another carrier?)
Body factors:
Surface area (an inc means increased absorption0, vascularity, pH (*), food, gastric emptying, disease, secreted substances, presence of P-glycoprotein
what is distribution
process of reversible transfer of drugs to and from the site of measurement `
apparent volume of distribution
is the volume that contains the total amount of drug administered at a concetration equal to that present in the plasma
is the extent to whcih a drug partitions btwn blood and tissue compartments
Vd = dose / concentration of drug in plasma
what does it suggest of the apparent voluem of distribution is more than the total ovluem of water in a human body (35L)?
means that the drug must be in a compartment other than the plasma compartment
How does loading dose relate to the apparent volume of distribution
loading dose is usually given to compensate for the distribution into the tissues
Doseloading = Vd x Csteady state
metabolism
is the conversion of one chemicla species to another, via the addition of functional groups (often OH) and often inactivates the drug, but not walways
what is the purpose of metabolism
makes the drugs more solune so it can leave via the hepatobiliary system and the lungs. this process occurs in the liver
what is systemic clearance
hypothetical volume of blod which teh drug can be irreversible eliminated per unit time, describing hte drug elimination process
clearance = dose x bioavailblity
over area under the curve (L/h)
what are the two forms of elimiantino
renal excretion and enterohepatic circulation
what is enterohepatic circulation (and recirculation)
give an example - morphine
recycling of drugs, biliary acids and bilirubin in bile btwn the lvier and GI tract.
drug undergoes glucuronidation in the lvier, then passes out as bile in the GI tract, where it can either continue to excretion or be degluconated back to the activae drug form by B glucuronidase.
e.g.: morphine, gets caught up in this circulation and is gluconrinated into morphine glucuronide in the liver, and then excreted in the bile, entering the GI tract and cleaved back into morphine by the gut glora, and then into the liver, meaning that it takes a very long time to be administered. on the graph, shos secondayry peak, which corresponds to morphine glucorinide being converted back and reabsorbed.
what is bioavailbility (F)
the proportion of administered drugs which reaches the circulation in its original form and the rate at which this occurs. drugs with low F are most likely to broken down via first pass metabolisatin
