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

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

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	–

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

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