Betaxolol and glucose-insulin relationships: studies in normal subjects taking glibenclamide or metformin

1. The potential interaction between selective beta 1-adrenoceptor blockers and sulphonylureas or biguanides was studied by comparing the beta 1-adrenoceptor antagonist betaxolol with placebo in 12 normal subjects taking glibenclamide or metformin in a single-blind crossover group study. 2. After a 4 day run-in period on no treatment, six subjects took glibenclamide 2.5 mg twice daily, and six subjects took metformin 850 mg twice daily from day 5 to day 19. All subjects took betaxolol 20 mg daily from day 10 to day 13, and placebo from day 5 to day 10 and from day 13 to day 19. 3. Plasma glucose and insulin concentrations were measured fasting and 60 min after a standard breakfast for 3 successive days during each study treatment; plasma potassium, sodium and betaxolol concentrations were also measured. 4. Fasting glucose, insulin and potassium concentrations did not differ significantly between betaxolol and placebo treatment periods in either glibenclamide- or metformin-treated groups. Post-prandial glucose and insulin concentrations were lower and higher, respectively, relative to fasting concentrations but there was no significant difference between any of the treatment periods. Glibenclamide produced significant increases in insulin concentrations compared with drug-free periods (P less than 0.01). Plasma potassium and sodium concentrations were not affected by any of the treatments. 5. Plasma betaxolol concentrations were adequate for beta 1-adrenoceptor blockade. 6. This study suggests that selective beta 1-adrenoceptor blockade with betaxolol does not change fasting or post-prandial glucose-insulin relationships during simultaneous treatment with either the sulphonylurea glibenclamide or the biguanide metformin.