Metformin Formulations
Metformin is supplied in two primary oral formulations: immediate-release (IR) tablets for twice-daily dosing and extended-release (XR) tablets for once-daily dosing. 1
Available Strengths and Forms
According to FDA labeling, metformin hydrochloride tablets are available in the following strengths 2:
- 500 mg tablets: White to off-white, round, biconvex, film-coated
- 850 mg tablets: White to off-white, round, biconvex, film-coated
- 1000 mg tablets: White to off-white, oval, biconvex, film-coated with score line
These are supplied in bottles of 60,90,100,500, or 1000 tablets 2.
Formulation Differences
Immediate-Release (IR)
- Requires twice-daily dosing with meals
- Reaches peak plasma concentrations more rapidly
- Standard first-line formulation historically used in clinical trials 1
Extended-Release (XR)
- Allows once-daily dosing
- Slower absorption with delayed peak plasma concentrations
- Improved gastrointestinal tolerability compared to IR formulation 1
- Particularly useful for patients experiencing GI side effects (bloating, abdominal discomfort, diarrhea) with IR formulation 1
Clinical Equivalence
Both formulations demonstrate equivalent glycemic efficacy with similar A1C reduction, weight effects, and cardiovascular benefits 3, 4. The extended-release formulation provides similar total drug exposure at equivalent daily doses but with better patient compliance due to once-daily dosing 3, 5.
Storage Requirements
Store at 20°C to 25°C (68°F to 77°F), with excursions permitted to 15°C to 30°C (59°F to 86°F). Dispense in tight, light-resistant containers with child-resistant closures 2.
Key Clinical Consideration
The choice between IR and XR should prioritize the extended-release formulation when gastrointestinal side effects limit tolerability or when once-daily dosing would improve medication adherence. Both formulations can be safely titrated gradually to minimize GI symptoms 1.