Excretion

Question 0

Breast milk excretion

Answer 0

Most drugs present in maternal blood detectable in milk, usually no problem
Anti thyroid-> thyroid suppression of infant
Sulphonamides-> haemolytic anaemia
Anticoagulants-> coagulation problem
ACEis-> profound hypertension

Question 1

Routes of excretion

Answer 1

Expired air-> drugs with high vapour pressure
Urine-> water soluble drugs/ metabolites small 25% of drugs
Bile-> water soluble drugs/metabolites big
Sebum/sweat-> very minor
Breast milk

Question 2

Biliary excretion

Answer 2

Active transport process for large highly polar compounds
Generally minor route for unmetabolised drugs
Major route for some metabolites-> Glucuronides
Alternative route of excretion for polor drugs in patients with renal impairment -> enterohepatic re circulation-> prolonged drug action or localisation of drug action

Question 3

Glomerular excretion

Answer 3

All unbound drug and metabolites freely filtered

Protein bound drugs not filtered however binding is weak and readily reversible

Question 4

Active tubular secretion, excretion

Answer 4

Separate mechanism for acids and bases
Acids-> uric acid, steroid conjugates, penicillins, methotrexate
cation-> OCT-> proximal cell-> efflux transport-> tubular fluid
Bases-> histamine, cimetidine, digoxin
anion-> OAT-> proximal cell-> efflux transport-> tubular fluid
Compete for secretion

Question 5

Passive tubular reabsorption

Answer 5

Tubule behaves like a typical lipid barrier
Reabsorption dependent on pH, pKa, lipid solubility
High conc gradient for reabsorption deceased if urine flow increased
Used in overdoes treatment if reabsorption important in drug excretion

Question 6

Renal clearance

Answer 6

Volume of blood which is cleared per minute of the amount of drug appearing in the urine at that time
Cl=UxV/P
V-> volume of urine per minute
GFR= 125 ml/min RPF=650
125-> drug is filtered only or filtered the reabsorbed and secreted to the same extent
drug is filtered and reabsorbed
> 125-> drug is filtered and secreted
Drugs which are eliminated mainly by urinary route-> decreased dose in renal impairment to remain in therapeutic window

Question 7

Renal function at the extremities of age

Answer 7

Renal function inefficient in new borne, coupled with inefficient metabolism
Matures by two years
Plateaus at 20-30
Then declines by 2-3% per year 
80yrs-> 50% of renal function