How is the "dose" calculation done for a 'controlled release formulation'?

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Eswar GsnkRao's picture

The amount of drug required in a sustained release dosage form to provide a sustained drug level (CSS) in the body is determined by
* the pharmacokinetic parameters of the drug (Vd, KE, CL),
* the desired therapeutic concentration of the drug (CSS)and
* the intended duration of action (T).
Total dose (Dtot ) required = Initial dose or loading dose (Di) + Maintenance dose (Dm)
Dtot = Di + Dm
Calculation of initial dose
At the desired therapeutic concentration (CSS) the body contains( CSS x Vd ) 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 = CSS x Vd
Calculation of maintenance dose
The Di dose will raise the plasma concentration of the drug to CSS and will reach the peak. After CSS is reached the elimination rate from the body will be maximum and the elimination rate will be KE x Vd x CSS. 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 (Routput)
i.e. Routput = KE x Vd x CSS. = CL x CSS. where the clearance value of the drug, CL = KE x Vd.
If the intended duration of action = T then the amount of drug required for maintenance dose Dm can be calculated from the equation:
FxDm = Routput x T



ESWAR :-) 

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