Page 18 - controlled drug delievery

II- Biological Factors
3- Safety margin

• A controlled release system can reduce side effects by --------
• Safety margin of the drug is commonly estimated by its

therapeutic index (TI)
TI = TD50% /ED50%

TD50% = Median toxic dose, ED50% = Median effective dose

• Drugs with a TI> 10 are safe for SR/CR formulation.

• Drugs with TI< 10 are poor candidates because of high toxicity
risk in case of dose dumping or premature release e.g.
Phenobarbital, Digoxin.