Bio pharmaceutics and Pharmacokinetics. It ia a part of MDR(Multiple Dosage Regimen)

1. Presented by:
Imran Ahammad Chowdhury

2. A loading dose is an initial
higher dose of a drug that may be
given at the beginning of a course
of treatment before dropping
down to a lower maintenance
dose.
LOADING DOSE

3. Drugs with long half-life require a loading
dose to more rapid attain steady state plasma
concentration. It is clinically desirable to
achieve rapid therapeutic drug levels by using
a loading dose.

4. If a rapid dose is given too rapidly, the drug
may initially give excessive high
concentration in the plasma (central
concentration), which then decrease as drug
equilibrium reached.

5. CALCULATION:
The time required for the drug to accumulate to a steady-state
plasma level is dependent mainly on its elimination half-life.
The time needed to reach 90% of C ∞
av is approximately 3.3
half-lives, and the time required to reach 99% of C ∞
av is equal
to approximately 6.6 half-lives. For a drug with a half-life of 4
hours, it will take approximately 13 and 26 hours to reach 90%
and 99% of C ∞
av, respectively.
For drugs absorbed rapidly in relation to elimination
(k a >> k) and are distributed rapidly, the loading
dose D L can be calculated as follows:

6. For extremely rapid absorption, as when the product of k a is
large or in the case of IV infusion, e –k
a becomes approximately
zero and 1st equation reduces to :
The loading dose should approximate the amount of drug contained in the body at
steady state. The dose ratio is equal to the loading dose divided by the maintenance
dose.
As a general rule, the dose ratio should be equal to 2.0 if the selected
dosage interval is equal to the elimination half-life. shows the plasma level–
time curve for dosage regimens with equal maintenance doses but different
loading doses. A rapid approximation of loading dose, D L, may be
estimated from:
Where, C ∞
av is the desired plasma drug concentration, S is the salt form
of the drug, and F is the fraction of drug bioavailability

7. IMPORTANCE OF LOADING
DOSE
1. To attend quick plasma level.
2. Attain quick action.
3. The main importance of loading dose is
average plasma concentration at steady state as
quickly as possible.
4. In some cases loading dose helps to get
therapeutic effect quickly.

8. THANK YOU