Formulae

Question 1

Rate of Transport

Answer 1

P x SA x (Chigh-Clow) / x

P = Permeability
SA = Surface Area
Chigh-Clow = drug concentration difference across membrane
X = membrane thickness

Question 2

Partition Coefficient (PC)

Answer 2

[Drug]octanol / [Drug]buffer

higher PC = higher lipophilicity

LogP = LogPC

Question 3

Henderson-Hasselbalch Equation

Answer 3

ACIDS: pH = pKa + log[ionized/un-ionized]

BASES: pH = pKa + log[un-ionized/ionized]

Question 4

Volume of Distribution (Vd)

Answer 4

“Apparent volume”

Amount (dose) / concentration in blood

• at one given time
• *for a large Vd, levels in the blood are LOWER meaning that a lot are in tissues
• **Plasma proteins DECREASE the Vd because they keep drugs in the vascular compartment

Question 5

Michaelis-Menten Equation (Rate of Elimination)

Answer 5

When drug C < Km: first-order kinetics
Vmax x C / Km
or Vmax / Km if C &laquo_space;Km

When drug C&raquo_space; Km: zeroth order kinetics
Vmax only

Question 6

Clearance (CL)

Answer 6

Rate of drug elimination / concentration of drug in the blood

• higher = greater efficiency of drug removal
• *constant for a drug in a person

Dose (IV) / AUC

AUC is directly proportional to the dose

Question 7

Half Life

Answer 7

0.693 x Vd / CL

INDEPENDENT of dose

Higher CL = shorter half life

Question 8

Fractional Occupancy

Answer 8

[DR]/[Rt] = [D]/[D]+Kd

*Rt = number of receptors

Question 9

Graded Dose Response Curves

Answer 9

E/Emax = [D]/[D]+Kd

E = efficacy
Emax = maxima efficacy

Question 10

Therapeutic Index

Answer 10

TD50/ED50

*Larger therapeutic index = safer drug

Question 11

Cheng Prusoff Equation

Answer 11

Ki = IC50 / 1+[S]/Kd

[S] = concentration of agonist
Kd = agonist binding affinity