Biguanides plasma levels

Metformin has an absolute oral bioavailability of about 50-60% of the dose after oral application of a single dose. Deconvolution analysis showed that after a short lag-time, the available remainder of the oral dose was absorbed at an exponential rate over about 6 h (Tucker et al., 1981). The bioavailability of phenformin seems to be more variable but also in the range of about 50% (Beckmann, 1968 Travis and Sayers, 1970). In general, absorption of biguanides is slower than their elimination, hence the plasma levels follow flip-flop kinetics (Pentikainen et al., 1979). 

Metformin is the only biguanide available in the United States. It enhances insulin sensitivity of both hepatic and peripheral (muscle) tissues. This allows for increased uptake of glucose into these insulin-sensitive tissues. Metformin consistently reduces A1C levels by 1.5% to 2%, FPG levels by 60 to 80 mg/dL, and retains the ability to reduce FPG levels when they are very high (>300 mg/dL). It reduces plasma triglycerides and low-density lipoprotein (LDL) cholesterol by 8% to 15% and modestly increases high-density lipoprotein (HDL) cholesterol (2%). It does not induce hypoglycemia when used alone. 

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