Hyoscyamine (Hyoscyamine Sulfate) - Description and Clinical Pharmacology

Rx only

DESCRIPTION

Hyoscyamine Sulfate Extended-Release Tablets, USP contain 0.375 mg of hyoscyamine sulfate in a formulation designed for oral b.i.d dosage.

Hyoscyamine sulfate is one of the principal anticholinergic/antispasmodic components of belladonna alkaloids. The empirical formula is (C₁₇H₂₃NO₃)₂•H₂SO₄•2H₂O and the molecular weight is 712.85. Chemically, it is benzeneacetic acid, alpha-(hydroxymethyl)-, 8-methyl-8-azabicyclo [3.2.1.] oct-3-yl ester, [3(S)-endo]-, sulfate (2:1), dihydrate with the following structure:

Each tablet also contains as inactive ingredients: calcium phosphate dibasic, ethylcellulose, lactose monohydrate, magnesium stearate, microcrystalline cellulose and stearic acid.

CLINICAL PHARMACOLOGY

Hyoscyamine sulfate inhibits specifically the actions of acetylcholine on structures innervated by postganglionic cholinergic nerves and on smooth muscles that respond to acetylcholine but lack cholinergic innervation. These peripheral cholinergic receptors are present in the autonomic effector cells of the smooth muscle, the cardiac muscle, the sinoatrial node, the atrioventricular node, and the exocrine glands. At therapeutic doses, it is completely devoid of any action on autonomic ganglia. Hyoscyamine sulfate inhibits gastrointestinal propulsive motility and decreases gastric acid secretion. Hyoscyamine sulfate also controls excessive pharyngeal, tracheal, and bronchial secretions.

Hyoscyamine sulfate is absorbed totally and completely by oral administration. Once absorbed, hyoscyamine sulfate disappears rapidly from the blood and is distributed throughout the entire body: the half-life of hyoscyamine sulfate is 2 to 3½ hours. Hyoscyamine sulfate is partly hydrolyzed to tropic acid and tropine but the majority of the drug is excreted in the urine unchanged within the first 12 hours. Only traces of this drug are found in breast milk. Hyoscyamine sulfate passes the blood brain barrier and the placental barrier.

Hyoscyamine Sulfate Extended-Release Tablets, USP releases 0.375 mg hyoscyamine sulfate at a controlled and predictable rate for 12 hours. The mean peak plasma concentration occurred at 4.20 hours. The mean (±SEM) apparent plasma elimination half-life is 7.47 hours (±0.60). Tablets may not completely disintegrate and may be excreted by some patients.