Where are the various sites of metabolism within the body? (HINT: there’s 7)
Drug metabolism mainly occurs in the liver in 2 phases, what are the 2 phases? Describe them.
Phase I Metabolism
- generally oxidation, reduction or hydrolysis (introduce/reveal reactive chemical group, “functionalisation”)
- products are often more reactive
Phase II Metabolism
- synthetic, conjugative reactions
- hydrophilic, inactive compounds usually generated
What are the types of reactions which occur in (i) phase I (ii) phase II? List as many as you can.
(i) oxidation, reduction, hydrolysis, hydration, dethioacetylation, isomerisation
(ii) glucuronidation/glucosidation, sulfation, methylation, acetylation, amino acid conjugation, glutathione conjugation, fatty acid conjugation, condensation
What is the mixed function oxidase system (CYP450s)? What does it consist of? What does it require?
Microsomal ER enzymes - liver, kidney, lung, intestine etc
Consists of :
- cytochrome P450, NAPDH-CYP450 reductase and a lipid
Requires: molecular oxygen and NADPH
Many enzymes are capable of metabolising drugs and there is overlapping of substrate specificities, what is there potential for?
Competition and saturation
With regards to drug metabolism, what are there issues of?
Variation/induction/inhibition
How are drugs eliminated? What types of drugs are excreted more easily?
- hydrophilic drugs are eliminated more readily than lipophilic drugs
What do the possible sources of excretion include?
Explain biliary excretion.
Transfer of drugs from plasma to bile
- organic cation transporters (OCTs)
- organic anion transporters (OATs)
- P-glycoproteins (P-GP)
It is concentrated in bile then delivered to intestines
- hydrophilic drug conjugates
- hydrolysis of conjugate can occur: reabsorption of liberated drug or enterohepatic circulation
What types of drugs does the glomerulus filter?
- not filtered if drug bound to plasma albumin
Describe tubular secretion/
OATs and OCTs
If the renal tubule is freely permeable, how much of the drug is reabsorbed?
99%
What is the effect of urinary pH on excretion of weak acids/bases?
- Weak bases more rapidly excreted if urine is acidic
How does ion trapping work?
What is zero order kinetics?
What is first order kinetics?
What is the eqn for the apparent volume of distribution of a drug?
Total amount drug in the body / blood plasma conc of drug
units = L or L/kg
What is the clearance (CL) of a drug?
The sum of all routes of elimination
e.g. metabolism + excretion
units = L/h
What doe t1/2 depend on? What is the eqn?
What is the (i) Vd (ii) CL of aspirin?
(i) 10.5 L
(ii) 39 L/h
What is the (i) Vd (ii) CL of salicylic acid?
(i) 11.9 L
ii) 3.6 L/h (dose dependent
How does age affect metabolism?
How does disease affect metabolism?
How does genetic variation affect metabolism?