Dicyclomine Half-Life
The elimination half-life of dicyclomine is approximately 1.8 hours based on initial plasma measurements, with a secondary elimination phase showing a somewhat longer half-life when measured up to 24 hours after dosing. 1
Pharmacokinetic Profile
The FDA-approved drug label provides the definitive pharmacokinetic data for dicyclomine:
- Primary elimination half-life: approximately 1.8 hours when plasma concentrations were measured for 9 hours after a single oral dose 1
- Secondary elimination phase: somewhat longer half-life detected in subsequent studies when plasma concentrations were followed for up to 24 hours, indicating biphasic elimination kinetics 1
- Peak plasma concentrations: 60-90 minutes after oral administration 1
- Volume of distribution: approximately 3.65 L/kg for a 20 mg oral dose, suggesting extensive tissue distribution 1
Elimination Pathways
Dicyclomine is primarily eliminated through renal excretion:
- Urinary excretion: 79.5% of the administered dose 1
- Fecal excretion: 8.4% of the dose 1
- The metabolism of dicyclomine has not been systematically studied according to the FDA label 1
Clinical Implications
The relatively short half-life of dicyclomine has important dosing implications:
- Multiple daily doses are required to maintain therapeutic effect, as the drug is rapidly eliminated from plasma 1
- The biphasic elimination pattern (initial rapid phase followed by slower secondary phase) means that the clinically relevant terminal half-life is longer than the initial 1.8-hour measurement 1
- Rapid absorption and elimination result in peak effects within 1-1.5 hours, with relatively short duration of action requiring frequent dosing intervals 1
Important Caveat
The presence of a secondary elimination phase with a longer half-life suggests that simple first-order kinetics may not fully describe dicyclomine's elimination, and accumulation with multiple dosing may differ from predictions based solely on the 1.8-hour half-life 1. This biphasic pattern is consistent with the drug's extensive tissue distribution (large volume of distribution of 3.65 L/kg) 1.