Time and Elimination Rate

Excretion-the final elimination fom the body’s

-Drugs may be eliminated from the systemic circulation by different pathways such as through * Urine * Bile * Intestine * Saliva * Alveolar air * Sweat * Milk

Kidney –
Nephron

Glomurelar filtration-

Refer to book

Order of rxn-it refers to the way in w/c the conc of a drug or reactant influences the rate of chemical rxn

1st order reaction
-causes constant percentage of the drug to be lost per unit time
-An elimination rate constant can be describe
-Ke( elimination rate constant) the unit is t ½
-One the log plot, the slope is equal to- ke/2.303
-The factor 2.303 converts from natural log to base 10 log units
-Half-life-is the period of time required for the conc of a drug to decrease by 1/2
-This is a constant and is related to ke drugs that hav 1st order kinetics
-T1/2 = 0.693/ke
1st order elimination rate -rate constant X Plasma conc X vol. of distribution.
-K(1/2 min) X P(mg/ml) X Va(ml)=mg/ml

Elimination rate – rate of removal of a drug in units of weight per unit time

| First order | Zero order | | 500mg(20%/hr) | 1000mg(20%/hr) | 500mg(100mg/hr) | 1000(100mg/hr) | 1 | 400 | 800 | 400 | 900 | 2 | 320 | 740 | 300 | 800 | 3 | 256 | 640 | 200 | 700 | 4 | 204.8 | 512 | 100 | 600 | 5 | | | | 500 | 6 | | | | | 7 | | | | | 8 | | | | | 9 | | | | | 10 | | | | | | | | | |

1st oreder elimintation - half life is constant * Lower risk of toxicity * Very predictable

Zero order elimination - half life is not constant * As the amount of the drug inc, the time for half life inc.
Clearance of a drug is different from the elimination rate

Clearance=rate of removal of drug(mgmin)plasma conc of drug(mgml)

Clearance is the volume of fluid cleared of a drug per unit time

Type equation here.
For 1st order reaction
Vd,t1/2,Ke areinterelated

Clearance = elimination rate/plasma