Role of Dosage Forms

The means by which drug molecules are delivered to sites of action within the body

• Accurate dosing- ideally pre-metered dose of the API
• Protection and shelf life- coated tablets, sealed ampoules (moisture ingression)
• Protection from gastric juice- enteric coating
• Masking tase and odour
• Placement of drugs directly within tissues
• Sustained release medication
• Controlled release medication (4/day --> 2/day)
• Insertion of drugs into body cavities
• Use of desired vehicle for insoluble drugs- e.g. emulsions 

Excipients

• all other components in the formulation other than the API
• each component requires safety evaluation 
• each component physiologically and chemically inert
• moral/religious complications eg gelatin

• aid processing of the system during manufacture and accurate dose control 
• control absorption rate
• protect, support or enhance bioavailability, stability or acceptability
• assist in product identification 
• enhance overall safety and efficacy during storage and use

Dose Control

• aspirin tablet 300mg API- difficult to make tablet as poor flow/compressability 
• drugs with lower doses eg alfacalcidol and ethinyl estradiol dificult to blend uniformly 

• rapid drug delivery to site of action
• drug action onset is rapid
• less drug in systemic circulation
• significantly lower doses required compared to oral route