I would like to know the approaches or any formulas that are in use for calculating the drug concentration in a specific area of the prepared buccal/ocular films (assuming uniform thickness and drug distribution). For instance, in a film prepared with a concentration of 1% w/v of active. How to calculate the area of film that should be cut so that each film contains a dose of 5 mg. Thank you.
First calculate the volume of the solution you need to prepare the film. Then prepare the film and weight the film using an accurate digital balance. Say the weight of the prepared film is for example Z mg. Then cut 1*1 cm2 of the film and weight it. Say the weight is W mg.
Through the 1 % w/v say 1 mg film contains d mg drug.
1cm2 film= W mg
Therefore, (1 cm2) film = (W*d) mg drug.
Now, if you need a film with 5 mg of drug, cut a 5/(W*d) cm2 of the film.
or:
Area of the film which contain 5 mg of drug= [5 mg drug]*[(1 mg film)/(d mg drug)]*[(1 cm2 film)/(W mg film)]=X cm2
Note that if during the preparation of the film there is a loss in the drug, you should reconsider the assumption of 1 % w/v .
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