Pharmacokinetic Equations-Segars

Question 1

Equation for “amount of drug absorbed”

Answer 1

Amount of drug absorbed=(S) (F) (dose)

S=salt factor
F=bioavailability factor

Question 2

Equation for “Dose of different dosage form”:

Answer 2

Dose of different dosage form=amount (mg) absorbed from current form / (S) (F) of new dosage form

Question 3

Equation for “Concentration in plasma (Cp)”:

Answer 3

Concentration in plasma (Cp)=(S) (F) (Dose) / Vd

Question 4

Equation for “Loading dose”:

Answer 4

Loading dose=(Vd) (Cp) / (S) (F)

Question 5

Equation for “Supplemental loading dose”:

Answer 5

Supplemental loading dose=(Vd) (Cpdesired - Cpinitial) / (S) (F)

Question 6

Equation for “Clearance (Cl)”:

Answer 6

Clearance (Cl)=(S) (F) (Dose/tau) / Cpss avg

Question 7

Equation for “Maintenance dose”:

Answer 7

Maintenance dose=(Cl) (Cpss avg) (tau) / (S) (F)

Question 8

Equation for “Elimination rate constant”:

Answer 8

Elimination rate constant (Kel)=(Cl) / (Vd)

Question 9

Equation for “Half-life”:

Answer 9

Half-life (t1/2)=0.693 / (Kel)

Question 10

Equation for “Creatinine clearance (eGFR)”:

Answer 10

[(140-age) x IBW in kgs / (72 x SCr)

Multiply by 0.85 if pt is female

Question 11

Equation for “Ideal body weight”

Answer 11

Female: 45 kg + (2.3 kg x (height in inches - 60 inches)
-2.3 kg for every inch OVER 5 ft + base weight of 45 kg

Male: 50 kg + (2.3 kg x (height in inches - 60 inches)
-2.3 kg for every inch OVER 5 ft + base weight of 50 kg

Question 12

Equation for “adjusted body weight”:

Answer 12

Adjusted body weight= (0.4 x (ABW - IBW) + IBW