PK

Question 1

what is PK and PD

Answer 1

Pharmacokinetics (PK): How the body processes the drug

Pharmacodynamics (PD): How drugs affect the body

Question 2

Secondary PK Parameters:

Answer 2

1. Elimination half life (t1/2)
   * t1/2= ln(2) x V/CL
2. Elimination Rate constant (k)
   * k=CL/V
3. Fraction excreted unchanged (fe)

Question 3

Primary PK Parameters:

Answer 3

1. Clearance (CL)
Volume of plasma from which a substance is completely removed per unit time (L/h, L/h/kg)
* Proportionality constant between the rate of drug elimination and the drug concentration (-dA/dT=CL x C)

2. Volume of Distribution (V)
* Apparent volume into which the drug is distributed to provide the same concentration as it is currently is in blood plasma (L/kg)

3. Bioavailability(F)
* The rate and extent to which the active ingredient or active moiety is absorbed from a drug product and becomes available at the site of action

4. Absorption rate constant (ka)
* The fractional rate of absorption. Rate of absorption = ka x Aa (amount of drug present in the compartment)
* Affected by blood flow at absorption site, exercise, etc

5. Distribution rate constant (kT)
* kT=(Q/VT)/KPb (See rate of distribution)

Question 4

PK parameters whose values depend on primary PK parameters and dose of drug

Answer 4

Area under curve (AUC) (Dose/CL)
Cmax (Dose/V)
Amount excreted unchanged

Question 5

3 ways of transport across membrane

Answer 5

1. passive transcelllular
2. facilitated transcellular
3. paracellular

Question 5

different drusg ahve different pk profiles in individuals.
PK profile is affected by

Answer 5

Physicochemical properties (Polarity, Lipophilicity, Acidic/basic, Molecular weight)
PK properties (% metabolised, % renally cleared, % binding, High/low Eh, Large/small V)
Route of administration

Question 6

what law for passive diffusion

Answer 6

ficks law of diffusion

Question 7

what affects absorption rate?

Answer 7

physiochemical factors(size, lipophilicity, charge, solubility)
physiological factors(total absorptive area, blood flow, permeability, transporters, drug metabolising enzyme)

Question 8

factors that affect bioavailability

Answer 8

AUC
CL
Dose

Question 9

Rate limited Gi absorption

Answer 9

dissolution&raquo_space; absorption
dissolution &laquo_space;absorption

Question 10

enteric coat purpose

Answer 10

protects from stomach acid

Question 11

BCS(biopharmaceuticals classification system)

Answer 11

class 1: high sol, high per
class 2: low sol, high per
class 3: high sol, low per
class 4: low sol, low per

most drugs in class 1 and 2

Question 12

usually ka is slower or faster than k

ka is absorption rate while k is elimination rate

Answer 12

ka»k

if it goes the other way, its the flip-flop phenomeneme

Question 13

physiological factors that affects distribution

Answer 13

1. membrane characteristics (thickness and porosity)
2. carrier-mediated transport
   * equilibrating transporters
   * concentrating transporters

Question 14

how to calculate V?

Answer 14

V = Dose(mg)/Co

Question 15

is there a way to measure appareatness?

Answer 15

Kp: tissue to plasma equilibrium distribution ratio (Ct/C)

V = Vp + VtKp