Excretion Flashcards
what organs are involved in the elimination of drugs in the system
Kidney, Liver, Lungs, intestinal tracts, and other (milk, sweat, tears, etc)
breifly describe the renal excretion (kidneys)
it receives 20% of cardiac output, glomerular capillaries highly porous and permeable, which allows for filtration of undound drugs is a non-saturable and non-selective process.
what kind of drugs are eliminated by the Renal system?
Polar drugs, and drug metabolites
Describe active tubular secretion, and which bodily system its connected with?
occurs with Renal excretion, and its where transporters in proximal tubules actively pump a minority of drug types into urine, its also saturable.
describe tubular reabsorption, and which bodily system its connefcted with?
occurs with Renal extractions, and its where active tranporters present in distal tubules reabsorb some filtered drugs from provisinal urine. Lipid-soluble un-ionized drugs are reabsorbed passively (diffuse out of tubule back into bloodstream)
What mathematical method can be used to describe the elimination process
half-life, which is the time required for the drug to decrease by 50%. Its a result of the 1-step-first-order process
*it does not depend on dose of drug concentration
After how many half lifes is a drug usually eliminated from the body
4-5 half-lifes
what two factors much be considered through drug administration, related to half-lifes and blood concentration
the minimum toxic concentration be avoided, and the minimum effective concentation should be maintained.
when dealing with substantial half-life concentrations, with continuous administration, which method of administration is best?
and IV drop allows a slow and long administration
does the time taken to achieve a steady state depend on the rate at which the drug is administered?
no
describe the ratio between chronic dosing, and rate of administration
the steady state plasma drug concentration (Css) is directly proportional to the rate of drug administered. there fore if double the rate of admin then you double the Css
how can Css be reached more rapidly?
if the initial dose is larger than the subsequent doses (called a loading dose)
what happens if the excretion rhythm is decreases (eg. renal failure)
then the drug-half like increases, therefore you must decrease the dose of increase he dosing interval.
how can you alternate the new time interval (mathematical equation used in definition)
you can do this based on serum creatinine.
the new interval is the usual interval multiplied by (the patient creatinine divided by the normal creatinine)
how much of a drug is eliminated in 5 half lives? in 10 half-lifes?
- 5= 97%
2. 10=99.9%
how can you minimize the differece between peak and through drug concentrations?
by giving smaller doeses more frequently
where do we want the drug through concentration to remain?
above minimum effective concentrations (MEC) and peak levels below minimum toxic concentration (MTC)
what is enterohepatic recycling?
its when some conjugated drugs can be deconjugated by gut bacteria -> reabsorbed into the blood
what is hepatic excretion?
the drugs that are conjugted via phase 2 metabolism are excreted into the bile (active transport )-> into the gut -> feces
what can cause adverse effects, in relation to a therapeutic margi?
Essentially all drugs have more than one effect in the body, and too much can be toxic. The adverse effects can be due to excessive receptor stimulation, or stimulation of other receptors.
what is ment when a drug is said to have a wide theraputic margin
?
it referes to the drugs that produce toxicity at doses much higher than those required for desired effect.
what kind of drug are barbiturates?
theres are drugs that produce toxicity at doses close to those required for therapeutic effect to have a narrow therapeutic margin.
what is clearance? and what is its purpose?
(volume/unit time/Kg body weight) its the apparent complete removal of drug from a certain volume of plasma per unit of time per unit of body weight.
and it gives and indication of efficiency of elimination of drug from plasma.
what routes are involved in total systematic clearance?
elimination of drug via liver, kidney, others (all)
what are the application purposes of clearance?
its used to clinically to calculate dosing rate and maintenance doses to maintain a target drug concentration(TC).
dosing rate =CL (clearance rate) x TC (target concentration)
how do you calculated maintenance dose?
MD= (dosing rate/F) * dosing interval F= bioavailability
