Dose of a drug in any sustained release dosage form can be calculated by Robison and Eriksen method:

DT = DL + DM ------------ 1.        DL = Di  - KO TP---------------------- 2.      KO = DI KE ---------- 3.

KE = O.693/ t1/2 ----------------- 4.   DM = KO TP --------- 5.

DT = Total required dose of the drug, DL = Loading dose,  Dm = Maintenance dose,  DI = Initial dose of the drug used to determine CMAX / TMAX , KO = Zero order constant, Tp = TMAX, KE = Elimination rate constant.

DI of each drug is written in their respective monographs in Matriandale and Drug facts and comparison.

Reference: http://onlinelibrary.wiley.com/doi/10.1002/jps.2600551118/abstract

Thanks for your valuable answer RAHUL GUPTA sir. This is surely going useful in my work.

Agree with Prof. Rahul Gupta. Also refer  as per followings:

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.              or,

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.

For more detail use this link: http://www.pharmainfo.net/answers/formulation-development/how-dose-calculation-done-controlled-release-formulation.