Metformin VS Metformin XR

Drug availability in Hospital Keningau:

• Metformin HCl 500mg Tab
• Metformin 500mg Extended Release (ER) Tablet

Pharmacokinetics:

• Pharmacokinetic studies demonstrate that maximum metformin concentrations are reached within about 7 hours after administration with ER formulations.
• Immediate-release (IR) maximum concentrations are seen within about 2-3 hours.
• The slower absorption with ER formulations allows for convenient once-daily dosing, which can improve adherence, particularly in patients taking multiple medications.

Efficacy:

• No significant changes in terms of efficacy between both formulation
• A randomized, double-blind, parallel trial comparing metformin IR 500 mg twice daily vs ER 1000 mg or ER 1500 mg once daily, A1c changes were similar among all three groups at 24 weeks.

GI Side Effects:

• Adherence and tolerability are often limited by the gastrointestinal (GI) side effects of metformin, such as diarrhea, nausea, and bloating.
• There was  a more than two-fold difference in the frequency of any GI adverse event during the first year of treatment (19.8 vs. 9.23% for immediate-release metformin vs. metformin-XR, respectively; p = 0.0414).
• The predominant GI adverse event in these cohorts was diarrhea, which was reported in 13.50 and 3.08% of the immediate-release metformin and metformin-XR cohorts, respectively (p = 0.0169).
• Likewise, a multisite retrospective analysis study found that GI side effects were reduced in patients transitioned from IR to ER metformin (26.34% vs 11.71%, P = .0006)

Recommendation:

• In view of efficacy, there is no significant differences in terms of efficacy between both agents.
• However in view of GI side effects and compliant issues, may consider to change to Metformin XR

References

• http://www.medscape.com/viewarticle/845753
• http://www.medscape.com/viewarticle/475277_4
• Ali, S., & Fonseca, V. (2012). Overview of metformin: special focus on metformin extended release. Expert opinion on pharmacotherapy, 13(12), 1797-1805.