The haemoglobin‐oxygen dissociation curve: in vivo and in vitro effects of five beta‐adrenoceptor antagonists and lignocaine.

1 The effects of several β-adrenoceptor antagonists and lignocaine on blood oxyhaemoglobin dissociation curves have been studied in healthy non-smoking subjects. 2 The P(O2) at 50% saturation (P(50)) did not significantly change after oral propranolol 80 mg (single dose, and following 2 weeks' administration of 80 mg twice daily), or following separate intravenous injection of propranolol (0.2 mg/kg), practolol (1 mg/kg), atenolol (0.2 mg/kg) and SL 75212 (0.15 and 0.6 mg/kg). 3 Increases in P(50) were found after the addition of propranolol 100 and 500 μg/ml, and lignocaine 5 μg/ml to whole blood, but incubation with propranolol at 1000 ng/ml or less, or sotalol 5 and 500 μg/ml and 5 mg/ml resulted in no significant change in P(50). 4 These results suggest that to increase P(50) with propranolol requires plasma propranolol concentrations far in excess of concentrations normally achieved, and that the therapeutic effect of propranolol in patients with ischaemic heart disease cannot be attributed to an increase in P(50).