Rate of diffusion =

(C₁-C₂) x (permeability coefficient x area) / thickness

Thus, diffusion increases:

1. When difference in C₁ and C₂ is great

2. Area over which diffusion occurs is increased

3. Thickness of membrane is decreased

V_d = Total amount of drug in body / plasma [drug]

Units = vol

Pharmacodynamics: The actions of drugs on body (drugs can make you DY --> acting on body)

Pharmacokinetics: Actions of body on drug

CL = (rate of drug elimination) / [plasma]

Units = vol/t

T_1/2 = (0.7 x V_d) / CL

Dosing rate_ss = (CL x target plasma [drug]) / bioavailability

Loading dose = (V_d x target [drug]_­) / bioavailability

1. Increasing concentrations after administration:

First half life = 50%

Second half life = 75%

Third half life = 87.5%

Fourth half life = 93.75%

2. Decline in [drug] after cessation of administration:

First half life = 50%

Second half-life = 25%

Third half-life = 12.5%