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PHARMACOKINETIC DESCRIPTION OF PLASMA LEVELS OF DRUGS - INTRAVENOUS BOLUS INJECTION |
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NB Assuming one - compartment model applies.
C
- Co .
e
or
Ab - Dose
. e
Variables from plasma data:
- t ½
- k (hr-1)
- t½ = 0.693 / k
- slope = -k / 2.303
- Vd : Co = dose / Vd
- Co : Cl = k . Vd
- Co : Cl = Vd . (0.693 / t½)
Dose = Cl x AUC
Dose
OR
Dose
________
= k . Vd Vd = ________
AUC
AUC . k
Calculation of IV bolus dose
Variables from urine data (Refer to Prac. 1)
(a) Excretion rate method:
Rate of excretion = Cl
x C
if Cl
then rate of excretion
C
Problems
(b) Sigma-minus method (R&T Appendix C)
Cumulative amount of drug excreted
Problems
Fraction of dose entering the systematic circulation that is excreted unchanged (fe).
Ie. fe = Xu
/ Dose for IV
NB
fe = Cl / Cl = ke / k
Cl
and ke can be readily obtained.
The following urinary excretion data are obtained following intravenous administration of a 100mg dose:
|
Time (hr) |
Urine Volume (ml) |
Drug Concentration |
|
0-1 |
200 |
1.85 |
|
1-3 |
150 |
2.86 |
|
3-5 |
300 |
0.70 |
|
5-9 |
700 |
0.20 |
If the volume of distribution is 100 litres, calculate the half-life, K; ke; renal clearance; the half-life in case of anuria, or in the case of 50 percent renal function; plasma concentration at t = 3; and percent biotransformation in normal subjects.
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g/ml)