Effect of protriptyline, 10 mg daily, on chronic hypoxaemia in chronic obstructive pulmonary disease

A daily dose of 20 mg of protriptyline can improve daytime arterial blood gas tensions in chronic obstructive pulmonary disease (COPD). Its usefulness is limited by anticholinergic side-effects. This study examined whether a daily dose of 10 mg of protriptyline improved daytime arterial oxygen tension (PaO2) and quality of life in patients with stable mild or moderate hypoxaemia caused by COPD. Twenty six patients were randomized to receive protriptyline or placebo in a double-blind parallel-group trial for 12 weeks, following a run-in period of 4 weeks, in order to assess the stability of hypoxaemia. Patients with a change in PaO2 of > 0.7 kPa during the run-in were excluded. Spirometry, quality of life and dyspnoea score were measured at randomization and after 12 weeks, whilst arterial blood gas tensions were also measured 2 and 6 weeks after randomization. No improvement in arterial blood gas tensions, spirometry values, dyspnoea score, or quality of life was found in either the protriptyline or the placebo group. The majority of patients receiving protriptyline experienced anticholinergic side-effects, which necessitated the withdrawal of the drug in one patient. We conclude that there was no evidence that a daily dose of 10 mg of protriptyline had a significant effect on daytime arterial oxygen tension in stable mild and moderate hypoxaemia caused by COPD. Despite the low dose, anticholinergic side-effects occurred in most patients.