4 - Excretion Flashcards
Which drugs are excreted renally?
Hydrophilic drugs
Which drugs are excreted through the bile?
Steroids, morphine
What are other routes for excretion besides renal and biliary?
- Skin
- Lung
What is renal clearance?
Volume of plasma that is freed of the drug per unit time
What is the formula for renal clearance (Clr)?
Excretion rate of drug / [drug]plasma
What is the formula for excretion rate of a drug?
[drug]urine * F (bioavailability)
What can be determined if you know the renal clearance of a drug?
Nothing, need to compare it to something
How is GFR (glomerular filtration rate) determined?
1) PAH (para-aminohippuric acid) - no longer used b/c some secretion by proximal tubules
2) Inulin *best one b/c not secreted or reabsorbed and is filtered by kidneys, so a good reflection of GFR
3) Creatinine *2nd best b/c some secretion occurs, so it will overestimate GFR slightly, but still used
What can be determined about the possible excretion mechanism if renal clearance and inulin clearance are relatively similar?
Only filtration is occurring
What can be determined about the possible excretion mechanism if renal clearance is greater than inulin clearance?
- Drug is being secreted into the urine
- Filtration is also occurring
What can be determined about the possible excretion mechanism if renal clearance is lower than inulin clearance?
- Drug is reabsorbed
- Filtration is also occurring
How are drugs secreted into the tubules? What can be done about this?
Through transporters, so they can be blocked
___ of a drug can be altered to increase/decrease elimination of the drug
pH
What can be concluded if the biliary clearance of a drug is very high (around 500 mL/min)?
There must be a transporter, likely an ATP transporter, bringing the drug into bile
MW < 300 = ____ excretion
Urinary
MW > 300 = ______ excretion
Biliary
Describe the enterohepatic recirculation
Liver (glucuronidation) -> common bile duct -> small intestine -> superior mesenteric vein -> portal vein -> liver
What are some examples of drugs excreted in bile?
- Morphine
- Digitoxin
- Bile acids
- Steroids
What can happen if a women taking birth control is simultaneously taking an antibiotic?
Concentration of birth control can be decreased
What are pharmaceutical equivalents? Give an example
- Drug products w/ same active ingredient, same strength/concentration, same dosage form, and same route of administration
- Ex: erythromycin stearate from 2 different manufacturers
What are pharmaceutical alternatives? Give an example
- Drug products w/ same therapeutic moiety but as different salts, esters, or complexes (dosage form)
- Ex: erythromycin stearate and erythromycin ethylsuccinate; tablet vs capsule
What are bioequivalent drug products?
Pharmaceutical equivalents that have similar bioavailability when given in the same molar dose and studied using similar experimental conditions
Can excipients affect the solubility of their active ingredient?
Yes
Which concentrations should be looked at when comparing 2 drugs?
Concentrations after steady state has been reached
Clinically, __ half lives is enough for drug to be considered eliminated
3
In the lab, __ or even ___ half lives are needed for a drug to be considered eliminated
5 or even 10
What are the units for renal clearance?
mL/min
What is creatinine?
End-product of metabolism
___% of cardiac output flows into kidney
25%
