Pharmacokinetics 4 Flashcards
If the rate of drug elmination is independent of plasma concentration (Cp) is this first-order or zero-order kinetics?
Zero order kinetics.
It means the enzymes are all saturated and as soon as an enzyme has acted on one substrate it will then begin to act on many other free substrate molecules. If all enzymes are constantly going through many substrate molecules at the same time, then the rate of product production (metabolism) will be the same until the enzymes outnumber the substrate.
The upper boundary and lower boundary of the therapeutic window are?
Upper: Maximum Safe Concentration (MSC)
Lower: Minimum Effective Concentration (MEC)
The elimination phase is known as the?
(a) Alpha-phase
(b) ß-phase
(b) ß-phase
Describe the difference between the one-compartment and two-compartment model.
The one-compartment model takes into consideration the Oral dose, its oral absorption, different entry of IV to the system in comparison to Oral route, its volume of distribution, metabolism and excretion.
The two-compartment model does all this but also considers the bi-directional interchange of the drug between the tissues and Vd
Km is used to denote what concentration of drug?
The concentration at which a drug goes from first-order to zero-order kinetics.
Is the t1/2 of a drug proportional or inversely proportional to the Vd?
Proportional.
n.b. They are both constants for any given drug and patient.
Cp approaches Css asymptotically or linearly?
Asymptotically.
What is the formula for loading dose?
Vd * Cp = QL
Rate of drug elimination is calculated by what formula?
Cp * CL
s.t.
Cp is plasma concentration (mg/L)
CL is volume cleared per time (L/hr)
What is the qualitative definition of CL (clearance)?
The volume of plasma that is cleared per unit of time.
Is the t1/2 of a drug proportional or inversely proportional to the CL?
Inversely proportional.
What are the two qualities of a drug’s pharmacokinetics that will determine whether it will adcversely affect renal dz and hepatic dz pts?
Low therapeutic index (LD50/ED50)
Fraction of the drug is excreted unchanged.
Means that in hepatic & renal pts that they will have a build up of the drug (due to decreased elmination) and these minor changes in concentration will be very bad, due to the low therapeutic index.
The distribution phase is also known as the?
(a) Alpha-phase
(b) ß-phase
(a) Alpha-phase
How many t1/2 does it usually take until Cp approaches Css?
4 to 5.
