Singapore Drugs Database

Indication

Used in the management of chronic obstructive pulmonary disease (COPD).

Mechanism of Action

Tiotropium is a muscarinic receptor antagonist, often referred to as an antimuscarinic or anticholinergic agent. Although it does not display selectivity for specific muscarinic receptors, on topical application it acts mainly on M3 muscarinic receptors located in the airways to produce smooth muscle relaxation, thus producing a bronchodilatory effect.

Pharmacokinetics

Absorption

Bioavailability is 19.5% following administration by inhalation. Oral solutions of tiotropium have an absolute bioavailability of 2-3%.

Distribution

* 32 L/kg

Metabolism

The extent of biotransformation appears to be small. This is evident from a urinary excretion of 74% of unchanged substance after an intravenous dose to young healthy volunteers. Tiotropium, an ester, is nonenzymatically cleaved to the alcohol N–methylscopine and dithienylglycolic acid, neither of which bind to muscarinic receptors. In vitro experiments with human liver microsomes and human hepatocytes suggest that a fraction of the administered dose (74% of an intravenous dose is excreted unchanged in the urine, leaving 25% for metabolism) is metabolized by cytochrome P450–dependent oxidation and subsequent glutathione conjugation to a variety of Phase II metabolites. Via inhibition studies, it is evident that CYP450 2D6 and 3A4 are involved in the metabolic pathway that is responsible for the elimination of a small part of the administered dose.

Elimination

Clearance

* 880 mL/min [young healthy volunteers receiving IV administration] * Renal cl=326 mL/min [COPD patients (70 years)]

Toxicity

No mortality was observed at inhalation tiotropium doses up to 32.4 mg/kg in mice, 267.7 mg/kg in rats, and 0.6 mg/kg in dogs. These doses correspond to 7,300, 120,000, and 850 times the recommended human daily dose on a mg/m2 basis, respectively.

Active Ingredient/Synonyms

Tiotropium | Tiotropium |