Contraindicated Combinations: Iodinated contrast materials: Depending on the renal function, Metformin must be discontinued 48 hours before the test or from the time of the test and may not be reinstituted until 48 hours afterwards (see Contraindications and Precautions).
Concomitant Use Not Recommended: Alcohol: The risk of lactic acidosis is increased in acute alcohol intoxication, particularly in case of fasting or malnutrition, hepatic insufficiency.
Avoid consumption of alcohol and alcohol-containing medicinal product.
Combinations Requiring Precautions for Use: Medicinal products with intrinsic hyperglycaemic activity (e.g. glucocorticoids and tetracosactides (systemic and local routes), beta-2-agonists, Danazol, Chlorpromazin at high dosages of 100 mg per day and diuretics.
More frequent blood glucose monitoring may be required, especially at the beginning of treatment. If necessary, adjust the Metformin dosage during therapy with the respective medicinal product and upon discontinuation.
Diuretics especially loop diuretics: They may increase the risk of lactic acidosis due to their potential to decrease renal function.
Organic cation transporters (OCT): Metformin is a substrate of both transporters OCT1 and OCT2.
Co-administration of Metformin with: Substrates/inhibitors of OCT1 (such as Verapamil) may reduce efficacy of Metformin.
Inducers of OCT1 (such as Rifampicin) may increase gastrointestinal absorption and efficacy.
Substrates/inhibitors of OCT2 (such as Cimetidine, Dolutegravir, Crizotinib, Olaparib, Daclatasvir, Vandetanib) may decrease the renal elimination of Metformin and thus lead to an increase Metformin plasma concentration.
Inhibitors of both OCT1 and OCT2 (such as Crizotinib, Olaparib) may alter efficacy and renal elimination of Metformin.
Therefore, caution is advised when these drugs are co-administered with Metformin and a dose adjustment may be considered, particularly in patients with renal impairment.