Buscopan Mechanism of Action

Sugar-coated tablet: BUSCOPAN Tablets contain a medicine called "hyoscine butylbromide". This belongs to a group of medicines called "antispasmodics".
Injection: Pharmacology: Mechanism of Action: BUSCOPAN (hyoscine butylbromide) is an antispasmodic agent which relaxes the smooth muscle of the gastrointestinal, biliary and urinary (parenteral formulation) tracts. It is believed to act predominantly at the parasympathetic ganglia in the walls of the viscera of these organs. Structurally, BUSCOPAN exists as a quaternary ammonium compound and as a single positively charged cation throughout the entire pH range.
Pharmacokinetics: Absorption and distribution: After intravenous administration, hyoscine butylbromide is rapidly distributed (t_1/2α = 4 min, t_1/2β = 29 min) into the tissues. The volume of distribution (Vss) is 128 L (corresponding to approx. 1.7 L/kg). Because of its high affinity for muscarinic receptors and nicotinic receptors, hyoscine butylbromide is mainly distributed on muscle cells of the abdominal and pelvic area as well as in the intramural ganglia of the abdominal organs. Plasma protein binding (albumin) of hyoscine butylbromide is approximately 4.4%. Animal studies demonstrate that hyoscine butylbromide does not pass the blood-brain barrier, but no clinical data to this effect is available. Hyoscine butylbromide (1 mM) has been observed to interact with the choline transport (1.4 nM) in epithelial cells of human placenta in vitro.
Metabolism and elimination: The main metabolic pathway is the hydrolytic cleavage of the ester bond. The half-life of the terminal elimination phase (t_1/2γ) is approximately 5 hours. The total clearance is 1.2 L/min.
Clinical studies with radiolabeled hyoscine butylbromide show that after intravenous injection 42 to 61% of the radioactive dose is excreted renally and 28.3 to 37% faecally.
The portion of unchanged active ingredient excreted in the urine is approximately 50%. The metabolites excreted via the renal route bind poorly to the muscarinic receptors and are therefore not considered to contribute to the effect of the hyoscine butylbromide.