Vyvanse (lisdexamfetamine) states it's not effected by food since it's broken down in the small intestine. is it's efficacy changed by urine ph or frequent urination?

No: Urine ph or frequency will not effect efficacy of vyvanse (lisdexamfetamine).

Efficacy is not: Affected but excretion of amphetamine is after covalent bond between Dextroamphetamine and l-lysine is broken. The percent of dose excreted as unchanged drug varies greatly depending upon urinary ph & 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).