Pharmacology principles and equations

Question 1

Equation for volume of distribution

Answer 1

Vd = amount of drug given IV / concentration in plasma

Question 2

Equation for clearance

Answer 2

Cl = rate of elimination / plasma concentration 
Cl = 0.7 x Vd / t1/2 
Cl = K x Vd 
*K = elimination constant, 0.7 / t1/2

Question 3

Equation for Loading Dose

Answer 3

LD = Css x Vd 
*Css = concentration desired at steady state

Question 4

Equation for Maintenance Dose

Answer 4

MD = Css x Cl

*concentration at steady state x clearance

Question 5

Effects of competitive inhibitors

Answer 5

increase Km, no change of Vmax
can be overcome by increasing substrate
decrease potency of the drug

Question 6

Effects of noncompetitive inhibitors

Answer 6

decrease Vmax, no change of Km
cannot be overcome by increasing substrate
decrease efficacy of the drug

Question 7

of half-lives and percent of desired plasma concentration of drug

Answer 7

1 - 50%
2 - 75%
3 - 87.5%
4 - 94%

Question 8

Inducers of Cyp450

Answer 8

Guinness, Coronas, and PBRs Induce Chronic Alcoholism

Griseofulvin, Carbamazepine, Phenytoin, Barbituates, Rifampin, St. John’s wort, Chronic Alcoholism

Question 9

Inhibitors of Cyp450

Answer 9

CRACK AMIGOS

Ciprofloxacin, Ritonavir (all protease inhibitors), amiodarone, cimetidine, ketoconazole, acute alcohol, macrolides (erythromycin, clarithromycin), isoniazid, grapefruit juice, omemprazole, sulfonamides

Question 10

Renal clearance of a substance

Answer 10

Urine concentration x urine flow rate / plasma concentration

Question 11

Renal plasma flow

Answer 11

Urine PAH x urine flow rate / plasma PAH

Question 12

Renal blood flow

Answer 12

RPF / (1 - Hct)

Question 13

Filtration fraction

Answer 13

GFR / RPF

-normal is around 20%

Question 14

Filtered load

Answer 14

GFP x plasma concentration

Question 15

Excretion rate

Answer 15

urine flow rate x urine concentration