Pharmacology Flashcards
In regards to pharmacology, what is the body considered as ?
One compartment
What is the magnitude of the drug effect associated to ?
The amount of drug available on the plasma/ blood.
What does passive diffusion depend on ?
Depends on the ability of drug (physiochemical characteristics) crossing lipid bilayer membrane
What does active diffusion require ?
Require transporter/carrier for the uptake of drug across cell membrane
What is the major mechanism of drug delivery ?
Passive diffusion
What does rate of diffusion depend on ?
- surface area
- thickness of membrane
- molecular size and lipid solubility (diffusion constant)
What are the names of the transporters that low lipid soluble (hydrophilic) drugs use ?
Organic anion transporters (OATs)
Organic cation transporters (OCTs)
Which drugs will cross the lipid belayers by passive diffusion ?
Un-ionised only drugs
What’s the pH of the mouth ?
7.4
What is the pH of the stomach
1.5
What’s the pH of the small intestine ?
5.3
What factors affect ionisation ?
- pH (i.e. concentration of H+ ions)
- pKa of drug
(pH at which 50% of molecules are in each state)
What will the precise degree of ionisation be determined by ?
The pKa and exact pH
What factors influence G.I absorption ?
- G.I. motility
- G.I. secretions & enzymes
- drug-food/supplement interactions
What are the advantages of G.I absorption ?
- Large surface area for passive diffusion
- Range of pH environments promote uptake of weak acids/bases
- Richly vascularised (high blood supply)
- Long tract and long dwell time
- Some active transport (e.g. Levodopa taken up by phenylalanine transporter)
- Small intestine is a major site for drug absorption
What is bioavailability ?
A measure of the proportion of the dose absorbed compared to I.V dose
What is time to peak (t max) ?
Time to peak (tmax): time required to reach maximum drug concentration in plasma (is a measure of rate of absorption)
What is the major site or drug absorption ?
Small intestine
What does the rate of absorption depend on ?
- Vascularisation of site of absorption
- Characteristics of formulation/dosage forms
- lipid solubility of the drug
- pH of the site of absorption
The free or bound drug is in ___________ equilibrium ?
Dynamic
What plasma proteins do acidic and neutral drugs bind to ?
Albumin (warfarin)
What plasma proteins do basic drugs bind to ?
Beta-globulins (quinine)
What does high binding of drugs to place proteins cause ?
Less drugs available for target action
How do drugs bind to plasma proteins ?
Reversibly
What affects the kinetics of drug distribution ?
- the blood supply
- lipid solubility
- tissue depots
What does volume of distribution (Vd) indicate ?
the theoretical distribution of drugs in various fluid and tissue compartments
