Pharmacokinetics 2 Flashcards
1
Q
What is the volume of distribution Vd
A
- How far a drug is distributed impacts on plasma conc for a given dose
- Vd is defined as the volume of fluid required to contain the total amount of drug in the body (D) at the same conc as that present in the plasma (Cp)
2
Q
How do we calculate plasma conc
A
3
Q
What factors control distribution
A
- Physiochemical features of the drug : size and pka
- Pharmacological properties: binding of molecule to particulat protein
- Blood flow in the organ/tissue
- Barriers of organ/tissue
4
Q
Name the phases of drug metabolism
A
5
Q
Describe phase I of drug metabolism
A
- Change the structure of drug molecule
- Via oxidation, reduction or hydrolysis
6
Q
Describe phase II of drug metabolism
A
- Involves the formation of a covalent bond
- Results in H2O soluble conjugate (excretion)
- Products of phase II are mainly inactive
7
Q
Name some factors which effect drug metabolism
A
- Food interactions: grapefruit juice reduces first pass effect
- Genetic influence: poor metabolisers, extensive metaboliser, ultra rapid metabolisers
- Excretion route: in fluid e.g. sweat urine, in solids e.g. faeces, in gases
8
Q
Describe the process of renal excretion
A
- Total renal excretion = GF + TS - reabsorbtion
9
Q
What is enterohepatic cycling
A
- Drugs that conjugate with glucoronic acid enter the bile duct
- These conjugates are too polar (ionised) and remain in the gut
- They are then broken down by enzymes releasing the parent molecule
- Reabsorbed and processed by the liver once more
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