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Pharm1Pkin
Pharm1 Pharmacokinetics
Question | Answer |
---|---|
What is clearance? | The removal of a drug in units of volume/time. |
Intensity of effect related... | To drug concentration at receptor sites. |
Duration of action related to... | How long drug conc. at receptor site remains high enough to provide response. |
One-compartment model easiest to use, and many drugs follow this scheme. | Assumes a single compartment which is in equilibrium which accounts for drug in plasma, and various tissues. |
Two (or more) compartment models more difficult to model. | Seen when drug moves into tissues and is handled at different rates than central plasma compartment. |
Two compartment model... | Involves both distributive and elimination phases normally.I |
Describe log plot of two compartment model: | Log plot does not give a single straight line, but instead shows two phases. |
What is zero-order kinetics? | The rate is independent of the concentration. |
What happens if a process (ex.- elimination) is dependent on a carrier or enzyme that may become saturated? | Rate now no longer dependant on concentration, but instead becomes constant, at least until concentration falls below saturation. (Zero-order kinetics) |
Bioavailability: | Percentage of a drug or drug product that enters the general systemic circulation. Includes not only amount entering body, but also rate of entry. |
What is the volume of distribution? | The volume of distribution, Vd, is the apparent or “virtual” volume into which a drug distributes. |
Can Vd be larger than the total plasma volume in the body? | heparin = 5 liters (plasma only) chlordiazepoxide = 28 liters (extracellular water) imipramine = 1600 liters(highly lipid soluble) |
Knowledge of the Vd is also important in estimating the... | Loading dose. |
About how many half-lives to reach steady-state? | Five. |
Drugs with a t1/2 less than 6 hours require a <blank> to use them in repeated doses. | Very wide therapeutic window. |
Drugs with narrow therapeutic windows should be given by... | Continuous infusion. |
First pass may be saturable, and like all liver metabolism may increase due to... | Enzyme induction. |
High Extraction Ratio: | ClH controlled by blood flow rate, Strong first-pass effect, Plasma protein binding may facilitate clearance |
Low Extraction Ratio: | ClH controlled by intrinsic clearance, Biotransformation limited by diffusion, Plasma protein binding reduces clearance, Sensitive to enzyme inhibition and induction |
Rate of renal excretion = | Rate of filtration + Rate of secretion – Rate of reabsorption |
For Biliary Excretion: | ClB = (Conc. in bile / Conc. In plasma) Bile flow |
What is normal bile flow? | Bile flow normally 0.5 – 0.8 ml/min. |