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Table 3 Percentage of fractional ionization of metformin after oral administration in different organs/tissues calculated using the Henderson–Hasselbalch equation

From: Actions of metformin and statins on lipid and glucose metabolism and possible benefit of combination therapy

Human body pH Metformin chemical form Absorption
[B] [HB+] [H2B2+]
Oral cavity 7 0 99.99 0.01
Stomach 2 0 7.36 92.64 10%
Jejunum + ileum 8 0 100 0 60%
Duodenum 6.25 0 99.93 0.07 20%
Plasma/liver 7.4 0 99.99 0.01
  1. The pH in the different organs/tissues/plasma leads to different forms of metformin. Neutral metformin, which is a base, will only be dominant at very high pH. The monoprotonated conversion of metformin with a stabilized cation (equally distribution between the nitrogen atoms) occurs in a neutral environment (pH ≈ 7). Biprotonation of metformin appears by a decreasing pH value