Clinical pharmacokinetics of bambuterol

Bambuterol, a biscarbamate ester prodrug of the beta 2 adrenergic agonist terbutaline, has been approved for the treatment of asthma in 28 countries. It is available in 10 and 20mg (25 and 50 mumol) tablets as the hydrochloride salt. Bambuterol is stable to presystemic elimination and is concentrated by lung tissue after absorption from the gastrointestinal tract. The prodrug is hydrolysed to terbutaline primarily by butyrylcholinesterase, and lung tissue is capable of this metabolic pathway. It is also oxidatively metabolised to products which can be hydrolysed to terbutaline. Peak terbutaline plasma concentrations occur 3.9 to 6.8 hours after bambuterol ingestion, and the peak: trough terbutaline concentration ratio is lower than that after ingestion of terbutaline. Older patients have a greater area under the plasma concentration-time curve for terbutaline over a dose interval at steady-state. Whether genetic variations in the expression of butyrylcholinesterase alter therapeutic response remains to be determined. The efficacy of bambuterol has been demonstrated to last for 24 hours after ingestion; once-daily administration in the evening is recommended. Maximum therapeutic benefit requires more than 1 week of treatment. Except for the suppression of plasma butyrylcholinesterase, the adverse effect profile of bambuterol is essentially that of a beta 2 agonist and is best correlated with circulating terbutaline concentration in plasma. Plasma butyrylcholinesterase activity returns to control values approximately 2 weeks after discontinuation of treatment with bambuterol. This new drug provides oral beta 2 agonist therapy in a more convenient form than was available previously, and may have a better therapeutic: toxic ratio than terbutaline.