Equations and Symbols Flashcards
Henserson-Hasselbalch Equations
For Acids:
pH - pKa = log([A-]/[AH])
For Bases:
pKa - pH = log([BH+]/[B])
Half Life =
t1/2 = 0.693 / Ke
Ke = elimination rate constant
Elimination Following IV Bolus
Ct = C0(0.5)^n
or
At = A0(0.5)^n
A = amount of drug in body (mass)
Rate of Elimination
RoE = Cp . CL CL = clearance
RoE = A . Ke
A = amount of drug in body (mass)
Clearance =
Ke . Vd
Steady State Kinetics
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)
Volume of Distribution =
Vd = D / Cp
D = dose (mass)
Loading Dose (IV) =
LD = Cp . Vd
A
Amount of drug in body (mass)
AUC
Area Under Curve of plasma concentration
C
Concentration in plasma at any time
C0
Cp at time zero (following IV Bolus, or Css Stop)
Css
Cp at steady-state
Ct
Cp at specific time
CL
volume of blood cleared of drug in unit time (L/min, or L.min/kg)
D
Dose (mass)
F
Fraction (usually given to you as %)
Ke
Elimination rate constant (time^-1)
LD
Loading Dose (mass or mass/weight)
pKa
pKa = -log(Ka)
Acid dissociation constant
t
Time (usually time after drugs administration)
t1/2
Half life (eg hours)
Vd
Volume of Distribution
Volume or volume/kg
Ka
Association constant
Kd
Dissociation constant
pA2
aka pKant
pA2 = -log (Kantagonist)
Kant
Antagonist dissociation constant (Schild plot - Dose Ratios)
Dose Ratio =
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)
pH =
pH = -log([H+])
if pKa = pH, 50% dissociation
Theraputic Ratio =
TR = MTC / MEC
IV Cpss =
Cpss(IV) = maintenance dose rate (mass.time) / CL
F =
is essentially the fractional oral bioavailability
F = AUC(oral) / AUC(IV)
Per Os Cpss
Cpss(oral) = (F . D) / (CL . Dose Interval)
LD(Oral) =
LD (oral) = (Vd . Cp) / F
Ligand Efficiency (LE) =
LE = dG / N
or
LE = 1.4(-log IC50) / N
dG = delta G, Gibbs free energy
Henderson-Hasselbalch equations
For acids:
pH - pKa = log ([A-] / [AH])
For bases
pKa - pH = log ([BH+] / [B])
