The amount of drug required in a sustained release dosage form to provide a sustained drug level (C_{SS}) in the body is determined by

* the pharmacokinetic parameters of the drug (V_{d}, K_{E}, CL),

* the desired therapeutic concentration of the drug (C_{SS})and

* the intended duration of action (T).

Total dose (D_{tot} ) required = Initial dose or loading dose (Di) + Maintenance dose (Dm)

D_{tot} = Di + Dm

Calculation of initial dose

At the desired therapeutic concentration (C_{SS}) the body contains( C_{SS} x V_{d}_{ }) amount of drug.

If Di amount of drug is administered as loading dose then (FxDi ) amount of drug will be absorbed in the body where F is the oral bioavailability of drug

Therefore, F Di = C_{SS} x V_{d}

Calculation of maintenance dose

The Di dose will raise the plasma concentration of the drug to C_{SS} and will reach the peak. After C_{SS} is reached the elimination rate from the body will be maximum and the elimination rate will be K_{E} x V_{d} x C_{SS}. An ideal maintenance dose will supply drug at a rate in which the drug is eliminated from the body.

Therefore, the rate of delivery from the maintenance dose = elimination rate (R_{output})

i.e. R_{output} = K_{E} x V_{d} x C_{SS}. = CL x C_{SS}. where the clearance value of the drug, CL = K_{E} x V_{d}.

If the intended duration of action = T then the amount of drug required for maintenance dose D_{m} can be calculated from the equation:

## Comments

Eswar GsnkRao

Mon, 06/16/2014 - 16:07

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## The amount of drug required

_{SS}) in the body is determined by_{d}, K_{E}, CL),_{SS})and_{tot}) required = Initial dose or loading dose (Di) + Maintenance dose (Dm)_{tot}= Di + DmCalculation of initial dose_{SS}) the body contains( C_{SS}x V_{d}_{ }) amount of drug._{SS}x V_{d}Calculation of maintenance dose_{SS}and will reach the peak. After C_{SS}is reached the elimination rate from the body will be maximum and the elimination rate will be K_{E}x V_{d}x C_{SS}. An ideal maintenance dose will supply drug at a rate in which the drug is eliminated from the body._{output})_{output}= K_{E}x V_{d}x C_{SS}. = CL x C_{SS}. where the clearance value of the drug, CL = K_{E}x V_{d}._{m}can be calculated from the equation:_{m}= R_{output}x TRef:

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Regards

ESWAR :-)