Bioavailability Of Type 2 Diabetes Medication

Liquid formulations of oral hypoglycemics can be useful for patients unable or unwilling

to swallow large tablets each day, but only if the two forms of the drug are bioequivalent.

Metformin liquid and tablets: a common medication for type 2 diabetes

Metformin is the usual first line oral type 2 diabetes medication for obese patients who fail to achieve adequate blood sugar control using diet and exercise. Metformin is often taken at high daily doses and the large 500 mg or 850 mg tablets can be hard to swallow, particularly for people who become anxious when swallowing pills. Liquid metformin provides an easy-to-swallow alternative, but is it equivalent to tablets in terms of bioavailability?

Studying the pharmacokinetics of metformin

Pharmacokinetic studies of metformin reveal that it is eliminated from the body extremely rapidly by the kidney. It is scarcely metabolised and shows negligible levels of binding to plasma proteins. At the same time, its absorption from the gut is slow. Bioavailability of the active drug ingredient therefore requires multiple, frequent dosing.

Bioequivalence of liquid metformin and tablets

Evidence shows that the liquid form of metformin is exactly bioequivalent to the tablet form. A trial comparing dosing with a 500mg tablet, an 850 mg tablet, an 850 mg dose of liquid metformin, all taken without food, showed no significant difference in terms of bioavailability or the timing of peak blood concentration.

Improving bioavailability of metformin medication for diabetes

Although no difference in bioavailability has been observed between liquid metformin or tablets, a 14% higher bioavailability was noted in patients who took a 500 mg tablet compared to an 850 mg tablet. In addition, bioavailability was almost 25% lower when the tablets were taken with food. The peak blood concentration of metformin was also delayed by over 35 minutes in patients who swallowed the tablet with a meal.

Patients taking metformin as a diabetes type 2 medication experience uncomfortable gastrointestinal irritation if they do not swallow the tablets when eating. Further studies are required, but if it were possible for patients to tolerate taking metformin without food, this could increase bioavailability significantly. Whether the liquid form of metformin would be more easily tolerated than tablets under these conditions would also require further investigation.

Reference: Sambol NC et al. Food intake and dosage level, but not tablet vs solution dosage form, affect the absorption of metformin HCl in man. Br J Clin Pharmacol 1996: 42; 510-512

by: Jan Peterson

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