How safe is terbutaline for asthmatics?

Studies, drug reference describe risks

Terbutaline (aka Brethine) is used "off label" as a preterm labor drug. However, its original use was in treating asthma. Several studies of asthmatics question whether the use of beta-adrenergics like terbutaline has contributed to the increased heart failure and mortality among asthma patients.

A 1995 study found an association between the use of beta-adrenergics for respiratory illnesses and the incidence of idiopathic (of unknown origin) dilated cardiomyopathy in these same patients (American Journal of Epidemiology, Vol. 142, pp. 395-403). Patients diagnosed with respiratory illnesses were compared with neighborhood controls. The study's authors reported: "The results of this study suggest, but do not prove, that use of beta-agonists has an etiologic role in idiopathic dilated cardiomyopathy."
A 1998 study (The Lancet, Vol. 352, pp. 1081-1082) compared the death rate among asthmatics treated with salmeterol (a long-lasting inhalant) and bambuterol (a long-acting oral drug that is slowly hydroloysed into terbutaline in the body). The study found "an excess of non-fatal "cardiac failure" in the bambuterol group during the first month and a lower but increased incidence in the second to sixth months, whereas there was no excess in the salmeterol group."
A 1998 study (Chest, Vol 114, pp. 380-387) of eight stable asthmatics found that a 14-day maintenance dose of inhaled terbutaline increased their cardiac output beyond the initial IV dose of terbutaline. In other words, their hearts did not develop a tolerance to terbutaline. "Lack of cardiovascular tolerance to maintenance doses of aerosolized Beta-2-agonists may be important in increased morbidity if excessive amounts of these drugs are administered during asthma exacerbation," the study concluded.
If asthmatics must take terbutaline, a drug reference offers some advice: "Whichever of these drugs you take (albuterol or terbutaline), use only the inhaled form. Do not take the tablets, capsules or liquids. Because these drugs are swallowed, the drug is distributed throughout your body, increasing the risk of adverse effects. An inhaler deposits most of the drug in the lungs, where it is needed."
-- Worst Pills, Best Pills: A Consumer's Guide to Avoiding Drug-Induced Death or Illness, by Sidney M. Wolfe, M.D., et al., New York, 1999, Public Citizen Foundation, Inc., Pocket Books.

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