Magnesium oxide and Dex/AMP duration of effect
Magnesium oxide is an antacid that can act as a gastrointestinal alkalinizing agent, which may increase amphetamine blood levels. [1]
A clinically established increase in “how long” (duration) Amfexa lasts from magnesium oxide has not been quantified in dose–response studies in the available prescribing-label evidence, so a reliable numeric estimate of additional duration is not available. [1]
Mechanism relevant to amphetamine exposure
Amphetamines show exposure changes with body pH. [2]
Urinary alkalinizing agents increase the non-ionized fraction and are associated with reduced renal elimination, which can increase amphetamine exposure. [3]
Gastrointestinal alkalinizing agents (antacids) can potentiate amphetamine action by increasing blood levels. [1]
Does magnesium oxide make Amfexa “last longer”?
No prescribing information provides a specific duration extension (for example, “X more hours”) from magnesium oxide coadministration with amphetamine/dexamfetamine products. [1]
The main documented concern is higher systemic exposure, not a predictable, measured prolongation of duration. [1]
How much longer (quantified effect)
A numeric estimate of “by how much longer” is not established in authoritative labeling that specifically addresses magnesium oxide with dexamfetamine/amphetamine products. [1]
Clinical management implications
Coadministration of amphetamine products with gastrointestinal alkalinizing agents such as antacids should be avoided due to potential increased blood levels. [1]
If magnesium oxide is required for another medical indication, timing separation and monitoring for increased stimulant effects are typically used in practice, but a specific evidence-based separation interval and quantified duration change are not provided in the cited authoritative labeling. [1]