Excretion Flashcards
Main routes of excretion
- Expired air
- Urine
- Bile
- Sebum/sweat
- Breast milk
Typical drugs excreted by air
Drugs with high vapour pressure e.g. halothane
typical drugs excreted in urine
Water-soluble drugs/metabolites, MW <350
Typical drugs excreted in bile
Water-soluble drugs, MW >350
Drugs that present a problem in breast milk excretion
- Antithyroid drugs: Thyroid suppression in infant
- Sulphonamides: haemolytic anaemia
- Anticoagulants: Coagulation problems
- ACE inhibitors: Profound hypotension
Characteristics of bile excretion
- Active transport for highly-polar compounds over 350
- Minor route for unmetabolized drugs, major route for metabolites
- May serve as alternative rout of excretion of polar drugsin patients with renal impairment
Effect of enterohepatic recycling
- Prolongation of drug action - ezetimimbe
-
Localisation of drug action
- Loperamide; useful since antidiarrhoea, stays in GI
- Budesonide; limits systemic side effects
Drugs that are renally excreted EXAM
- Aminoglycosides
- Some cephalosporins
- Some penicillins
- methotrexate
- Digoxin
- Lithium
Which drugs are and are not glomerurally filtered
- All unbound drugs & metbaolites freely filtered
- Protein-bound drugs are not filtered, but does not impede excretion as binding is weak and readily reversible
How are weak acids secreted in renal tubules
Organic Anion transporters
How are weak bases secreted in renal tubules
Organic cation transporter
Important factor in methotrexate excretion
Is a weak acid; ensure patient is not on other weak acid drugs(NSAID, salicylate) competing for OAT
Would lead to build up and toxicity
Characteristics of passive renal reabsorption(distal)
- Tubule behaves like lipid barrier
- Reabsorption dependant on pH, pKa, lipid solubility
- Concentration gradient for reabsorption decreased if urine flow rate increases
How would one treat an acid/base drug overdose
Acid drugs(barbiturates, salicylate) - Alkaline diruesis
Basic drugs(amphetamine, quinine) - acid diuresis
Consequence of renal impairment in exretion
May reduce elimination/ lead to accumulation/toxicity
e.g digoxin
