Sustained vs. immediate release
In order to avoid high peak plasma drug levels after repeated oral administration, sustained release tablets were developed. Besides the avoidance of toxic high peak concentrations, sustained release tablets also prolong the duration of drug action.
Examples of drugs available as sustained release tablets (or retard tablets) are theophylline, nifedipine, and verapamil.
Another novel utilization of enteric coating can be seen with Pentasa® (mesalazine) granules. The enteric coating of the granules is resistant to the 5.5 pH found in the duodenum, but dissolves in distal ileum when the pH reaches 7.5. Since this drug is used to treat ulcerative colitis, this design allows the drug to be active where it is most needed.
See how different dosage forms and regimens will effect serum concentrations by clicking here.
What is the advantage of diclofenac 100 mg as a slow release tablet compared to diclofenac as a normal tablet in an equal dose of 100 mg?
Extra info: Slow release formulations are designed to lead to longer and more stable exposure.