Pharmacokinetics, Safety, and Tolerability of Metformin in Healthy Elderly Subjects

Age-related physiological changes are known to alter the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs. Metformin is commonly used as first-line medication for management of diabetes in elderly patients. However, the PK and PD of metformin have not been sufficiently studied in elderly subjects. Here, 12 elderly subjects, aged 65 to 85 years, and 20 younger healthy volunteers were orally administered 750 mg of metformin 2 hours after dinner, followed by administration of a second dose (500 mg) 12 hours later. An oral glucose tolerance test (OGTT) was performed 2 hours after the second dose, with 75 g of glucose administered. Blood samples were collected at specific time points after the second metformin dose for the assessment of PK and the glucose-lowering effect of metformin. Elderly subjects exhibited 1.7 and 2.0 times higher average C_maxand AUC_∞than the younger subjects, respectively (P =.007 and.001, respectively), and t_1/2was comparable between the elderly and younger subjects. However, relative glucose level changes from baseline after metformin administration tended to be lower in elderly subjects. Systemic exposure to metformin was elevated by 50% or more in elderly subjects, whereas the glucose-lowering effect was similar compared to younger subjects after 2 doses of metformin.