immediate-release

The tablet coating breaks down immediately in the body and instantaneously disintegrates to make the drug available for absorption and subsequent pharmacologic action.
It goes into the system quickly and start acting. The advantage is that it starts working quickly but often the disadvantage is that the effect does not last longer than a few hours.

(Examples of the medication: Analgesics for moderate to severe pain)
• oxycodone/paracetamol
• hydrocodone/paracetamol

Therapeutic concentration range is the dosage range or serum concentration usually expected to achieve the desired therapeutic effect.
This does not mean that patients may not achieve benefit at concentrations below the minimum threshold, or not experience adverse effects if kept within the range.

(Comparison)
• controlled-release: Released into the body in specified amounts over a specified period of time. It is designed to release the drug's active ingredient gradually over the day.
• extended-release: Released over prolonged time periods.
• short-acting: Peaks and falls in the bloodstream quickly. The patients might feel irritable when it wears off (rebound effect).
• long-acting: Works in phases. Part of them release into the bloodstream immediately and the rest throughout the day.

Cf. osmotic-controlled release oral delivery system