Pharmacotherapies for obstructive sleep apnoea: where are we now?

Obstructive sleep apnoea (OSA) is common, causes considerable morbidity and probably contributes to mortality particularly through associated cardiovascular disease. The physical therapy of continuous positive airway pressure (CPAP) is extremely effective in the majority of patients but most patients would prefer an alternative. Intuitively, OSA should be amenable to pharmacotherapy. The upper airway of affected individuals can be narrowed but is patent during wakefulness. Collapse of the airway during sleep occurs when negative intra-luminal pressure generated by inspiratory effort exceeds the tone of the upper airway dilators. This mismatch may be in part due to respiratory drive instability but the state-dependent fall in drive to the airway dilator muscles is the biggest factor in most patients. Various drugs have been investigated as treatment for OSA. Acetazolamide, theophylline, nicotine, opioid antagonists and medroxyprogesterone have been used to increase respiratory drive. Clonidine has been tested with the aim of reducing rapid eye movement sleep when OSA is often most severe. Various antidepressants have been used to suppress rapid eye movement sleep and to preferentially activate the upper airway dilators. The drug trials have often been of poor design and none has included more than a few patients. Most of the drugs have been found to be ineffective and those that have worked for some patients (acetazolamide and protriptyline) have produced intolerable adverse effects. There have been recent advances in the understanding of the neurotransmitters involved in the control of sleep and the upper airway motor neurones, offering the possibility of novel approaches to the drug treatment of OSA for those patients who cannot tolerate or do not benefit from CPAP. It seems likely that a better understanding of the mechanisms of OSA in individual patients and tailoring of drug therapy will be the way forward.