Is Vyvanse (lisdexamfetamine) effected by urine alkalinity?

Excretion is. The percent of dose excreted as unchanged drug varies greatly depending upon urinary ph and urine flow. At low ph as much as 70% of the dose may be excreted as amphetamine in 24 h, whereas as little as 1% may be excreted within 24 h at alkaline ph (j. Pharm. Pharmacol. 21:241-258 (1969).