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Lecture 5 Excretion - Coggle Diagram
Lecture 5
Excretion
Clearance
Volume of plasma from which drug is completely removed per unit of time (
mL/min (/kg)
)
Measure of efficiency of drug elimination
Influenced by 4 factors
Blood flow
Reduced blood flow = less drug delivered to organ = reduced clearance
Eg. hepatic clearance = hepatic blood flow X arteriovenous drug concentration difference
Liver function
Reduced liver function = decreased polar metabolites = reduced clearance
Kidney function
Decreased kidney function = decreased renal clearance
Drug properties
Increased lipophilicity = decreased clearance (
reabsorption
)
High nonionized:ionized ratio = decreased clearance (
reabsorption
)
Larger size = decreased renal clearance
Calculated by Cl = rate of elimination / plasma concentration
Half-life
Time required for blood concentration of drug to be reduced by 50%
Half-life = 0.693 Vd / clearance
Renal excretion
Glomerular filtration
Drug enters renal tubule dissolved in plasma filtrate
Impacted by plasma protein binding
Drug bound to PP not filtered, only free drug
Passive process
Pathway
Afferent arteriole (
free drug
)
Glomerular capillaries
Bowman's capsule
Nephron tubule
Efferent arteriole (
bound drug
, not filtered)
Peritubular capillaries
Proximal nephron tubule via
active transport
Active tubular secretion
Active process using
cation/anion transporters
Secreted by
proximal tubular cells
Passive tubular reabsorption
Lipophilic non-ionized drugs reabsorbed
Pathway
Nephron tubule
Peritubular capillaries
Passive process
Net removal = amount filtered + amount secreted - amount reabsorbed