Kindly explain me the difference between sustained release & extended release in drugs?

Same thing: Those are just marketing terms to indicate a medication that only needs to be taken once or twice a day rather than 3 to 4 times daily. Some brands will use "xl" or "la" to denote longer acting drugs. If there's any concern, ask your doctor or pharmacist about your specific situation & medications.

Same thing.: Different name for same thing. Different manufacturers use different terms. There are many synopnyms: sustained-release (sr), sustained-action (sa), extended-release (er, xr, xl), timed-release (tr), controlled-release (cr), modified release (mr), or continuous-release (contin).

What's In a name: The terms extended release and sustained release are generalizations and are virtually interchangable. Er, sr, xr, cr, xl are all suffixes attached to drug names to indicate that the medication is delivered over a period of time (usually 12 to 24 hours) instead of being immediately available to your body. This is achieved in various ways. Naming is just a preference of the manufacturer.