FYI, here are the pharmacokinetics of hyoscyamine for safe doses below 1500 micrograms:

"Following parenteral administration of hyoscyamine sulfate, the drug has an onset of action of 2–3 minutes; peak pharmacologic action occurs within 15–30 minutes and persists for up to 4 hours. Following oral administration of hyoscyamine sulfate conventional tablets, the drug has an onset of action of 20–30 minutes. When hyoscyamine sulfate conventional tablets are chewed or administered sublingually or when the drug is administered orally as an elixir or solution, the drug has an onset of action of 5–20 minutes. Oral administration of the sublingual tablets results in similar pharmacologic effects as sublingual administration, although the onset may not be as rapid. Pharmacologic action peaks within 30–60 minutes and persists for about 4 hours when hyoscyamine sulfate is administered orally as conventional tablets, elixir, or solution or sublingually as conventional tablets or when conventional tablets are chewed. Following oral administration of hyoscyamine sulfate extended-release capsules, the drug has an onset of action of about 20–30 minutes; pharmacologic action peaks within 40–90 minutes and persists for about 12 hours."