1. First Order & Zero Order Reaction

2. Rate The rate of a chemical reaction of process
Is the velocity with which the reaction occurs.
For drug A (decreasing)
-dA/dt
For Drug B (increasing)
+dB/dt

3. Rate Constant

5. Zero order reactions
Amount of drug A is decreasing at a constant rate for each time interval
-dA/dt=-k0
k0= is the zero order rate constant and is expressed in units of mass/time
Equation:
At=A0-k0 t
Ct=C0-k0 t

6. At=A0-k0 t A A0
Slope=-k0 t

7. Drug Concentration (mg/ml) 100 2 95 4 90 6 85 8 80 10 75 12 70
Time
(hr)
Drug Concentration (mg/ml)
100 2 95 4 90 6 85 8 80 10 75 12 70
5mg/ml
5mg/ml
5mg/ml
5mg/ml
5mg/ml
5mg/ml

8. First order Half life
The time required for the amount to decrease by one half life
It is constant
no matter what the initial concentation of a drug is

10. C0 =100mg/ml at t=0
C =90mg/ml at t=4hr
90=-k0(4)+100
K0 =2.5mg/ml hr

11. The amount of drug A is decreasing at a rate that is proprotional to the amount of drug remaining.
-dA/dt=K A
At=A0e-kt
Ct=C0e-kt

12. Half life
t1/2
The period of time required for the amount or concentration of a drug to decrease by one half.

13. Not constant
The zero order t1/2 is proportional to the initial amount or concentration of the drug and is inversely proportional to the zero order rate constant k0
t1/2= 0.5A0 k0

14. Time
(hr)
Drug Concentration (mg/ml)
100 4 50 8 25 12
12.5 16
6.25 20
3.13 24
1.56

15. First order
The amount of drug eliminated over a certain time period increases as the amount of drug in the body increases.
The amount of drug eliminated per unit of time decreases as the amount of drug in the body decreases
But the fraction of a drug remain constant

16. Zero order
The amount of drug eliminated for each time interval is constant ,regardless of the amount in the body.
In other words the amount of drug in the body does not change with the amount or concentration of the drug in the body. but the fraction removed varies

17. First Order Elimination
Fraction of drug eliminated over preceding hour
Amount of drug eliminated (mg)
Amount of drug in the body (mg)
time
0.15 -
1000
150
850 1
127
723 2
109
614 3 92
522 4 78
444 5 67
377 6

19. Fraction of drug eliminated over preceding hour
Amount of drug eliminated (mg)
Amount of drug in the body (mg)
time -
1000
0.15
150
850 1
0.18
700 2
0.21
550 3
0.27
400 4
0.38
250 5
0. 60
100 6

20. First order