Half-Life of Metoclopramide (Reglan)
The half-life of metoclopramide (Reglan) is 5 to 6 hours in individuals with normal renal function. 1
Pharmacokinetic Profile
Metoclopramide is rapidly and well absorbed after oral administration with:
- Absolute oral bioavailability of 80% ± 15.5%
- Peak plasma concentrations occurring at 1-2 hours after a single oral dose
- Volume of distribution of approximately 3.5 L/kg
- Plasma protein binding of about 30%
- Elimination half-life of 5-6 hours in adults with normal renal function 1
The onset of pharmacological action varies by route of administration:
- Intravenous: 1-3 minutes
- Intramuscular: 10-15 minutes
- Oral: 30-60 minutes
The pharmacological effects typically persist for 1-2 hours regardless of administration route. 1
Factors Affecting Half-Life
Renal Function
- Renal impairment significantly affects metoclopramide clearance
- Reduction in creatinine clearance correlates with reduced plasma clearance, renal clearance, and non-renal clearance
- Patients with renal impairment experience an increased elimination half-life 1
Age
- In pediatric patients, particularly neonates and young infants, half-life can be significantly longer
- In one study, a 3.5-week-old infant showed a half-life of 23.1 hours after the first dose 1
- Pediatric cancer patients (ages 7-14 years) showed a mean elimination half-life of 4.4 hours (range 1.7-8.3 hours) 1
Clinical Implications
The 5-6 hour half-life of metoclopramide has important implications for dosing:
- For oral administration, metoclopramide is typically dosed every 6-8 hours, aligning with its half-life
- In adjunctive therapy for migraine treatment, metoclopramide is administered 20-30 minutes before or with other medications 2
- The relatively short half-life means that metoclopramide is generally not intended for long-term use
- Oral preparations are recommended for 4-12 weeks of therapy
- Parenteral administration should be limited to 1-2 days 3
Elimination
Approximately 85% of an orally administered dose appears in the urine within 72 hours, with about half present as free or conjugated metoclopramide. 1 The clearance of metoclopramide (0.53 ± 0.19 L/kg/h) approaches liver plasma flow, suggesting that its clearance is probably limited by liver blood flow rather than liver metabolic capacity. 4
Understanding the half-life of metoclopramide is essential for appropriate dosing and minimizing adverse effects, particularly when used in patients with renal impairment or in pediatric populations.