Equations

Question 1

Dosing rate

Answer 1

Dosing rate = CL x CSS

Question 2

Clearance

Answer 2

CL = rate of elimination/ concentration

Question 3

Systemic clearance

Answer 3

CL = CLrenal + CLhepatic + CLother

Question 4

extraction ratio

Answer 4

CL = Q[(CA – CV)/ CA] = Q x E

where E is referred to as the extraction ratio.

where Q is the blood flow to the organ.

Answer 5

Vd = Amount of drug in body / C (Blood concentration )

Question 6

elimination half life

elimination constant

Answer 6

CL / Vd = (ml/min) / ml = 1/min = elimination constant (Ke)

Ke= 0.7/ t 1

Question 7

clearance in a multicompartment model

Answer 7

CL = dose / AUC

Question 8

bioavailability (F)

Answer 8

F x Dosing rate = CL x Css

Question 9

dosing rate

Answer 9

dose / T

Question 10

steady state concentration

dose

Answer 10

* Css = (F x Dose) / (CL x T)

Dose = (Css x CL x T) / CL x T F

Question 11

IV infusion concentration steady state

Answer 11

Css = infusion rate / total body clearance

Question 12

Loading dose

Answer 12

Loading dose (LD) = (Css x Vd) / F

Question 13

zero order elimination kinetics

Answer 13

LD = (Vd x Css)/F

Css = (Km x DR)/(Vm- DR)

DR = (Css x (Vm – DR))/ Km

• Km is the dose that produces 50% of the maximal elimination rate
• Vm is the maximum rate of the process

Question 14

HH equation for weak base

Answer 14

pH = pKa + log [B]/[BH+]

[Unprotonated]/[Protonated]

nonionized / ionized

Question 15

Michaelis-Menton kinetics.

Answer 15

V = Vmax[S]/(Km+[S])

Question 16

If the drug is filtered but not secreted or reabsorbed the renal clearance will be about 120 ml/min in normal subjects

Answer 16

(CLr = GFR)

Question 17

If the renal clearance is less than 120 ml/min then drug show net reabsorption

Answer 17

(CLr < GFR)

Question 18

If the renal clearance is greater than 120 ml/min then tubular secretion must be contributing to the elimination process.

Answer 18

(CLr > GFR)

Question 19

Rising phase of effect

Answer 19

Abs > Met + Exc

Question 20

Falling phase of drug results

Answer 20

Met + Exc > Abs

Question 21

Therapeutic Index

Answer 21

MTC/MEC

• MTC (minimal toxic concentration)
• MEC (minimal effective concentration)

Question 22

Fick’s law

Answer 22

Diffusion rate = -DAK (C out-C in) / X

• The diffusion coefficient (D): inversely related to the size of the drug.
• partition coefficient (K): reflects the lipid solubility of the drug (oil:H20)
• Surface area (A): larger surface area promotes diffusion.
• Membrane thickness (X): The thinner the membrane the quicker the diffusion.
• Concentration gradient (C out-C in): larger gradients promote drug diffusion.
• Ionization (affects K): is a major determinant of the ability of a drug to cross membranes. It is dictated by the environment (pH) of the bodily fluid in which the drug is dissolved in.

Question 23

weak acid HH

Answer 23

pH = pKa + log [A-] / [HA]

unprotonated / protonated

ionized / non-ionized

Question 24

Volume of Distribution

Answer 24

Vd = amount of drug administered / plasma drug concentration