A technician is selecting the correct dosage form for a metoprolol product the prescriber has marked as needing twice-daily dosing with a rapid onset, while a separate metoprolol product on the shelf is labelled for once-daily dosing. Which property most accurately distinguishes an immediate-release tablet from an extended-release tablet of the same drug?
- AThe immediate-release tablet contains a larger total dose per unit because it must cover the whole day in one tablet.
- BThe immediate-release tablet must always be enteric coated so it dissolves only in the small intestine.
- CThe extended-release tablet works faster because its coating dissolves instantly on contact with stomach acid.
- DThe extended-release tablet is formulated to release drug gradually so the active ingredient is absorbed over a prolonged period, allowing less frequent dosing. Correct
Why A is wrong: Tempting because extended-release products are often dosed once daily, suggesting they hold less drug; in fact the extended-release unit usually holds the larger total daily dose released slowly, so this is reversed.
Why B is wrong: Tempting because enteric coating is a real release-modifying feature, but enteric coating delays release rather than defining immediate release, and most immediate-release tablets are not enteric coated.
Why C is wrong: Tempting because patients may assume a 'stronger' once-daily tablet acts quickly, but extended-release products are engineered for slow, prolonged release, not instant onset, so this is the opposite of their design.
Why D is correct: Correct: extended-release (modified-release) formulations are designed to slow dissolution or diffusion so plasma levels are sustained, which is why such products can be dosed less frequently than their immediate-release counterparts.