Equations and Symbols

Question 1

Henserson-Hasselbalch Equations

Answer 1

For Acids:
pH - pKa = log([A-]/[AH])

For Bases:
pKa - pH = log([BH+]/[B])

Question 2

Half Life =

Answer 2

t1/2 = 0.693 / Ke

Ke = elimination rate constant

Question 3

Elimination Following IV Bolus

Answer 3

Ct = C0(0.5)^n
or
At = A0(0.5)^n
A = amount of drug in body (mass)

Question 4

Rate of Elimination

Answer 4

RoE = Cp . CL
CL = clearance

RoE = A . Ke

A = amount of drug in body (mass)

Question 5

Clearance =

Answer 5

Ke . Vd

Question 6

Steady State Kinetics

Answer 6

During Accumulation:
Ct = Css(1 - 0.5^n)
During Elimination
Ct = Css(0.5)^n

Css = C0 as it is concentration at ‘time zero’ (conc when administration stops)

Question 7

Volume of Distribution =

Answer 7

Vd = D / Cp

D = dose (mass)

Question 8

Loading Dose (IV) =

Answer 8

LD = Cp . Vd

Question 9

A

Answer 9

Amount of drug in body (mass)

Question 10

AUC

Answer 10

Area Under Curve of plasma concentration

Question 11

C

Answer 11

Concentration in plasma at any time

Question 12

C0

Answer 12

Cp at time zero (following IV Bolus, or Css Stop)

Question 13

Css

Answer 13

Cp at steady-state

Question 14

Ct

Answer 14

Cp at specific time

Question 15

CL

Answer 15

volume of blood cleared of drug in unit time (L/min, or L.min/kg)

Question 16

D

Answer 16

Dose (mass)

Question 17

F

Answer 17

Fraction (usually given to you as %)

Question 18

Ke

Answer 18

Elimination rate constant (time^-1)

Question 19

LD

Answer 19

Loading Dose (mass or mass/weight)

Question 20

pKa

Answer 20

pKa = -log(Ka)

Acid dissociation constant

Question 21

t

Answer 21

Time (usually time after drugs administration)

Question 22

t1/2

Answer 22

Half life (eg hours)

Question 23

Vd

Answer 23

Volume of Distribution

Volume or volume/kg

Question 24

Ka

Answer 24

Association constant

Question 25

Kd

Answer 25

Dissociation constant

Question 26

pA2

Answer 26

aka pKant

pA2 = -log (Kantagonist)

Question 27

Kant

Answer 27

Antagonist dissociation constant (Schild plot - Dose Ratios)

Question 28

Dose Ratio =

Answer 28

DR = Dx/D1

D1 is EC50 of dose-response curve of agonist
Dx is the Ec50 of dose-response curve of agonist in presence of antagonist

Plot DRs on Schild Plot to get Kant (x-axis intercept)

Question 29

pH =

Answer 29

pH = -log([H+])

if pKa = pH, 50% dissociation

Question 30

Theraputic Ratio =

Answer 30

TR = MTC / MEC

Question 31

IV Cpss =

Answer 31

Cpss(IV) = maintenance dose rate (mass.time) / CL

Question 32

F =

Answer 32

is essentially the fractional oral bioavailability

F = AUC(oral) / AUC(IV)

Question 33

Per Os Cpss

Answer 33

Cpss(oral) = (F . D) / (CL . Dose Interval)

Question 34

LD(Oral) =

Answer 34

LD (oral) = (Vd . Cp) / F

Question 35

Ligand Efficiency (LE) =

Answer 35

LE = dG / N
or
LE = 1.4(-log IC50) / N

dG = delta G, Gibbs free energy

Question 36

Henderson-Hasselbalch equations

Answer 36

For acids:
pH - pKa = log ([A-] / [AH])

For bases
pKa - pH = log ([BH+] / [B])