Enhancement of cardiotoxic effects of beta-adrenergic bronchodilators by aminophylline in experimental animals

Cardiotoxic Effects in Rats and Rabbits Treated with Terbutaline Alone and in Combination with Aminophylline

Studies were conducted to determine the myocardial effects of a selective beta-adrenoceptor agonist, terbutaline, administered alone and in combination with aminophylline in the 4-to 5-month-old, 500-600 g (heavy) rat and the rabbit, using electrocardiographic and histopathological methods. Terbutaline given at high (5.0 mg/kg) and low (0.1 mg/kg) doses was not arrhythmogenic in the heavy rat; however, dose-dependent myocardial lesions were observed. Terbutaline given at the same doses to heavy rats pretreated with aminophylline was arrhythmogenic and produced severe cardiac lesions. Rats administered aminophylline at a dose of 18.75 mg/kg had plasma theophylline levels of 15-22 μg/ml; these concentrations are similar to the recommended human therapeutic levels, i.e., 10-20 μg/ml. The administration of terbutaline in conjunction with aminophylline did not seem to affect the plasma levels of theophylline. No arrythmias were detected in rabbits given terbutaline alone or in combination with aminophylline and no deaths occurred.

Diagnosis and management of asthma in older adults

Despite comprehensive guidelines established by the European Global Initiative for Asthma and the U.S. National Asthma Education and Prevention Program on the diagnosis and management of asthma, its mortality in older adults continues to rise. Diagnostic and therapeutic problems contribute to older patients being inadequately treated. The diagnosis of asthma rests on the history and characteristic pulmonary function testing (PFT) with the demonstration of reversible airway obstruction, but there are unique problems in performing this test in older patients and in its interpretation. This review aims to address the difficulties in performing and interpreting PFT in older patients because of the effects of age-related changes in lung function on respiratory physiology. The concept of "airway remodeling" resulting in "fixed obstructive" PFT and the relevance of atopy in older people with asthma are assessed. There are certain therapeutic issues unique to older patients with asthma, including the increased probability of adverse effects in the setting of multiple comorbidities and issues surrounding effective drug delivery. The use of beta 2-agonist, anticholinergic, corticosteroid, and anti-immunoglobulin E treatments are discussed in the context of these therapeutic issues.

Caffeine induces Ca2+ release by reducing the threshold for luminal Ca2+ activation of the ryanodine receptor

Caffeine has long been used as a pharmacological probe for studying RyR (ryanodine receptor)-mediated Ca(2+) release and cardiac arrhythmias. However, the precise mechanism by which caffeine activates RyRs is elusive. In the present study, we investigated the effects of caffeine on spontaneous Ca(2+) release and on the response of single RyR2 (cardiac RyR) channels to luminal or cytosolic Ca(2+). We found that HEK-293 cells (human embryonic kidney cells) expressing RyR2 displayed partial or 'quantal' Ca(2+) release in response to repetitive additions of submaximal concentrations of caffeine. This quantal Ca(2+) release was abolished by ryanodine. Monitoring of endoplasmic reticulum luminal Ca(2+) revealed that caffeine reduced the luminal Ca(2+) threshold at which spontaneous Ca(2+) release occurs. Interestingly, spontaneous Ca(2+) release in the form of Ca(2+) oscillations persisted in the presence of 10 mM caffeine, and was diminished by ryanodine, demonstrating that unlike ryanodine, caffeine, even at high concentrations, does not hold the channel open. At the single-channel level, caffeine markedly reduced the threshold for luminal Ca(2+) activation, but had little effect on the threshold for cytosolic Ca(2+) activation, indicating that the major action of caffeine is to reduce the luminal, but not the cytosolic, Ca(2+) activation threshold. Furthermore, as with caffeine, the clinically relevant, pro-arrhythmic methylxanthines aminophylline and theophylline potentiated luminal Ca(2+) activation of RyR2, and increased the propensity for spontaneous Ca(2+) release, mimicking the effects of disease-linked RyR2 mutations. Collectively, our results demonstrate that caffeine triggers Ca(2+) release by reducing the threshold for luminal Ca(2+) activation of RyR2, and suggest that disease-linked RyR2 mutations and RyR2-interacting pro-arrhythmic agents may share the same arrhythmogenic mechanism.

Left ventricular diastolic dysfunction in patients with bronchial asthma with long-term oral beta2-adrenoceptor agonists

BACKGROUND

Long-term administration of oral beta(2)-adrenergic receptor agonists (beta(2)-AG) in patients with bronchial asthma (BA) causes disastrous events such as sudden death and heart attack. However, long-term effects of beta(2)-AG on cardiac function have not been previously quantified.

METHODS

Seventy-four patients with BA with regular long-term use of oral beta(2)-AG (group A) and 69 patients with BA without beta(2)- AG (group B) were examined in medical records of outpatient clinics from 1985 to 1999. In the prospective study, echocardiography was performed in 48 consecutive patients from January to April 1999. There were 26 patients with regular oral use of beta(2)-AG (group a) and 22 patients without beta(2)-AG (group b). Twenty-one age-matched normal volunteers without heart or pulmonary diseases were used as control subjects (group c). Oral beta(2)-AG was withdrawn from remedies in 11 patients of group a, and echocardiographic studies were repeated 2 weeks after its cessation.

RESULTS

Events related to heart failure were more frequently seen in group A than in group B (14% vs 1%, P <.01). The echocardiographic study showed that indexes of left ventricular diastolic but not systolic function were significantly deteriorated in group a, along with a markedly reduced level of plasma norepinephrine concentration (P <.05 vs groups b and c). When heart rate was adjusted to 90 beats/min during isoproterenol infusion, left ventricular diastolic function remained deteriorated in group a (P <.05 vs groups b and c). In 11 patients of group a, the cessation of beta(2)-AG for 2 weeks resulted in an improvement of left ventricular diastolic function and in an increase of plasma norepinephrine level (P <.01).

CONCLUSIONS

Long-term use of oral beta(2)-AG impaired left ventricular diastolic function in patients with BA, and the cessation of beta(2)-AG reversed diastolic pump performance to the normal level.

Efficacy of IV theophylline in children with severe status asthmaticus

STUDY OBJECTIVE

To determine whether adding IV theophylline to an aggressive regimen of inhaled and IV beta-agonists, inhaled ipratropium, and IV methylprednisolone would enhance the recovery of children with severe status asthmaticus admitted to the pediatric ICU (PICU).

DESIGN

A prospective, randomized, controlled trial. Asthma scoring was performed by investigators not involved in treatment decisions and blinded to group assignment.

SETTING

The PICU of an urban, university-affiliated, tertiary-care children's hospital.

PATIENTS

Children with a diagnosis of status asthmaticus who were admitted to the PICU for < or = 2 h and who were in severe distress, as indicated by a modified Wood-Downes clinical asthma score (CAS) of > or = 5.

INTERVENTIONS

All subjects initially received continuous albuterol nebulizations; intermittent, inhaled ipratropium; and IV methylprednisolone. The theophylline group was also administered infusions of IV theophylline to achieve serum concentrations of 12 to 17 microg/mL. A CAS was tabulated twice daily.

MEASUREMENTS AND RESULTS

Forty-seven children (median age, 8.3 years; range, 13 months to 17 years) completed the study. Twenty-three children received theophylline. The baseline CASs of both groups were similar and included three subjects receiving mechanical ventilation in each group. All subjects receiving mechanical ventilation and theophylline were intubated before drug infusion. Among the 41 subjects who were not receiving mechanical ventilation, those receiving theophylline achieved a CAS of < or = 3 sooner than control subjects (18.6 +/- 2.7 h vs 31.1 +/- 4.5 h; p < 0.05). Theophylline had no effect on the length of PICU stay or the total incidence of side effects. Subjects receiving theophylline had more emesis (p < 0.05), and control patients had more tremor (p < 0.05).

CONCLUSIONS

Theophylline safely hastened the recovery of children in severe status asthmaticus who were also receiving albuterol, ipratropium, and methylprednisolone. The role of theophylline in the management of asthmatic children in impending respiratory failure should be reexamined.

Enhancement of acute myocardial lesions by asthma drugs in rats

Asthma morbidity and mortality have risen significantly in the last 10 years. The reasons for the increase are multifactorial. One proposed explanation is possible myocardial toxicity arising from the use of beta-agonists alone or in combination with methylxanthines. Previous studies have shown that beta-agonists given alone and beta-agonist/methylxanthine combinations given at higher than recommended clinical doses induced dose-related cardiotoxicity and sudden death in rats. The objective of the present study was to determine whether or not beta-agonists given alone and in combination with methylxanthines at recommended clinical doses also induce cardiotoxicity and sudden death in rats. The beta-agonists, isoproterenol hydrochloride (15 micrograms/kg), fenoterol hydrobromide (40 micrograms/kg), and terbutaline hemisulfate (0.4 mg/kg) were given in single sc doses separately and concurrently with the methylxanthines aminophylline hydrate (20 mg/kg) and caffeine (40 mg/kg), which were given up to a susceptible animal model, the heavy Sprague-Dawley rat. beta-agonist-induced myocardial toxicity (necrosis) was observed. The toxicity was enhanced by aminophylline resulting in the sudden death (most likely due to ventricular fibrillation) of some animals. A decrease in serum iron levels was observed in rats of all beta-agonist and/or methylxanthine-treated groups.

Lack of arrhythmogenicity of aminophylline in dogs

This study was designed to determine if doses of aminophylline up to 10 mg/kg given i.v. would produce ventricular arrhythmias in seven healthy dogs anaesthetized with fentanyl-droperidol-pentobarbital. Arrhythmias were sought by inspection of ECGs before and after attempts at provoking them with 5 micrograms/kg boluses of epinephrine given i.v., or by programmed electrical stimulation. After cumulative doses of 10 mg aminophylline/kg body weight, producing an estimated plasma concentration of greater than 30 micrograms/ml, no ventricular ectopia other than escape depolarizations were observed. We were unable to document an arrhythmogenic effect of aminophylline when given rapidly by the i.v. route. It is possible that the anaesthetic regimen reduced the arrhythmogenic property of aminophylline, or that arrhythmias might be produced in either obese or ill dogs; but it is unlikely that chronic administration of aminophylline would be more arrhythmogenic.

Electrophysiologic Study of the Effects of Aminophylline and Metaproterenol on Canine Myocardium

Aminophylline and beta-adrenergic agonists are widely used in the treatment of obstructive lung diseases. It has been suggested that combined aminophylline and beta-agonist therapy may promote the development of atrial and ventricular arrhythmias. The effects of these agents in combination on myocardial conduction and tissue refractoriness have not been documented. We evaluated the electrophysiologic effects of intravenous aminophylline and inhaled metaproterenol on canine myocardium. Aminophylline produced significant decreases from baseline in the AH interval (85 +/- 6.5 [SD] to 63 +/- 4.1 ms [p less than 0.02]), Wenckebach cycle length (WCL) (226 +/- 8.7 to 182 +/- 5.8 ms [p less than 0.02]), and ventricular effective refractory period (VERP) (166 +/- 6.0 to 148 +/- 4.9 ms [p less than 0.01]). Metaproterenol produced similar results, except metaproterenol significantly decreased the atrial effective refractory period (AERP) from 152 +/- 6.6 to 130 +/- 3.2 ms (p less than 0.02), an effect not seen with aminophylline alone. Metaproterenol also produced significantly greater reductions in AH interval and WCL, as well as a greater increase in heart rate than aminophylline did. When compared with aminophylline alone, combined metaproterenol and aminophylline therapy produced significantly greater reductions in the AH interval (63 +/- 4.1 versus 48 +/- 1.2 ms for combined therapy [p less than 0.01]), HV interval (32 +/- 1.2 versus 28 +/- 2.0 ms for combined therapy [p less than 0.02]), WCL (182 +/- 5.8 versus 150 +/- 7.1 ms for combined therapy [p less than 0.02]), and VERP (148 +/- 4.9 versus 132 +/- 2.0 ms for combined therapy [p less than 0.02]). We conclude that both aminophylline and metaproterenol significantly enhance AV nodal and His-Purkinje conduction. Metaproterenol produced significant changes in both atrial and ventricular tissue refractoriness. Metaproterenol produced significantly greater changes than aminophylline alone, and inhaled metaproterenol combined with intravenous aminophylline produced greater changes in AV nodal and His-Purkinje conduction and ventricular refractoriness than did aminophylline alone in a canine model.

Asthma deaths

Deaths from asthma seem to be increasing in spite of considerable improvements in drug treatment and management plans. There are many hypotheses to explain this, but little emphasis has been placed on the possibility that confidence in better drug treatments may modify patients' behavior so as to place them at greater risk of illness. It is well recognized that excessive confidence in bronchodilator inhalers and nebulizers can make patients stay away from hospitals too long during acute attacks. It is also very possible that prevention of symptoms by use of antiasthma drugs could allow patients to spend more time in environments containing antigens or other agents that provoke asthma, resulting in more serious and long-lasting bronchial inflammation and reactivity.

Respiratory arrest in near-fatal asthma

BACKGROUND AND METHODS

The majority of asthma-related deaths occur outside the hospital, and therefore the exact factors leading to the terminal event are difficult to ascertain. To examine the mechanisms by which patients might die during acute exacerbations of asthma, we studied 10 such patients who arrived at the hospital in respiratory arrest or in whom it developed soon (within 20 minutes) after admission.

RESULTS

The characteristics of the group were similar to those associated in the literature with a high risk of death from asthma, including a long history of the disease in young to middle-aged patients, previous life-threatening attacks or hospitalizations, delay in obtaining medical aid, and sudden onset of a rapidly progressive crisis. Extreme hypercapnia (mean [+/- SD] partial pressure of arterial carbon dioxide, 97.1 +/- 31.1 mm Hg) and acidosis (mean [+/- SD] pH, 7.01 +/- 0.11) were found before mechanical ventilation was begun, and four patients had hypokalemia on admission. Despite the severe respiratory acidosis, no patient had a serious cardiac arrhythmia during the resuscitation maneuvers or during hospitalization. We observed systemic hypertension and sinus tachycardia in eight patients, atrial fibrillation in one, and sinus bradycardia in another. In both patients with arrhythmia the heart reverted to sinus rhythm immediately after manual ventilation with 100 percent oxygen was begun. The median duration of mechanical ventilation was 12 hours, and all patients had normocapnia on discharge from the hospital.

CONCLUSIONS

We conclude that at least in this group of patients, the near-fatal nature of the exacerbations was the result of severe asphyxia rather than cardiac arrhythmias. These results suggest that undertreatment rather than overtreatment may contribute to an increase in mortality from asthma.

Unexpected, unexplained sudden death in young asthmatic subjects

The clinical course of asthma in four patients younger than 25 years was considered. Three died unexpectedly of their disease, and the fourth was successfully resuscitated after cardiopulmonary arrest. None of these patients met the criteria for status asthmaticus in the period preceding their death. The time course of the illness from apparent wellness to death was documented as seconds to minutes. No obvious cause of the severe disease was found at postmortem in two patients or by clinical analysis in all four. Patients with bronchial asthma may die with this disease unexpectedly, rapidly and with no obvious cause for the severity of this process.

Cardiotoxic effects of the combined use of caffeine and isoproterenol in the minipig

Beta agonists such as isoproterenol are widely used in the treatment of acute asthmatic attacks. It would not be unexpected that some patients receiving isoproterenol might have ingested caffeine as an over-the-counter drug or beverage. This study explores the possible interaction between these two drugs. Anesthetized minipigs were injected with 0.5 mg/kg caffeine iv followed by a 10-min infusion of 1 microgram/kg.min isoproterenol. Heart rate, EKG, respiration, and blood pressure were recorded continuously and the animals were sacrificed at 72 h. The two drugs in combination produced subtle changes in heart rate and blood pressure with significant alteration in the EKG tracing (premature ventricular contractions and extrasystoles). These changes persisted for 8 to 24 h. At autopsy both gross and microscopic lesions were noted in 10 of the 13 minipig hearts receiving the combination of drugs. This was not true of the six minipigs given only caffeine or the eight minipigs receiving only the infusion of isoproterenol. No changes in EKG tracings or pathologies were noted with caffeine and only two of eight animals infused with isoproterenol showed any lesions. Results indicate that doses of caffeine equivalent to that expected from drinking a cup of coffee appear to increase the toxicity of isoproterenol to a point that EKG changes and myocardial pathologies are observed.

Salbutamol induced hypokalaemia: the effect of theophylline alone and in combination with adrenaline

1. We have previously shown that salbutamol induced hypokalaemia, like adrenaline induced hypokalaemia, is the result of stimulation of a membrane bound beta 2-adrenoreceptor linked to Na+/K+ ATPase. We have also demonstrated that adrenaline induced hypokalaemia is potentiated by therapeutic concentrations of theophylline. 2. In a single-blind study of 14 normal volunteers, we infused salbutamol in doses used in clinical practice and examined the effects of the addition of theophylline alone or combined with (-)-adrenaline on plasma potassium levels, heart rate and blood pressure. The combinations studied were (i) salbutamol + vehicle control adrenaline infusion + placebo theophylline; (ii) salbutamol + vehicle control adrenaline infusion + theophylline; (iii) salbutamol + adrenaline + theophylline. 3. In a randomised, balanced placebo controlled design oral slow release theophylline or placebo was given for 9 days. Subjects were studied twice on the active limb (days 7 and 9) and once on the placebo limb (day 9) and the procedure was identical on each of the 3 study days except for the solutions administered. 4. Theophylline increased salbutamol induced hypokalaemia and in some individuals profound hypokalaemia (less than 2.5 mmol l-1) was observed with these relatively low doses of salbutamol and theophylline. Adrenaline did not further increase the magnitude of the fall in potassium observed. Combining theophylline with salbutamol increased the tachycardia resulting from the salbutamol infusion. Salbutamol infusion caused a fall in diastolic and rise in systolic blood pressure on all 3 study days and this was not altered by either theophylline or adrenaline alone or together.(ABSTRACT TRUNCATED AT 250 WORDS)

Death from bronchial asthma

There is now incontrovertible evidence that there is a progressive and strikingly increased mortality from bronchial asthma in the US. The increase is more dramatic in the older age groups, but younger age groups are not spared. The exact cause or causes of this increased mortality are not known, and it is even possible (although not likely) that the increase is artifactual. This increased death rate is in sharp contrast to the general medical perception that major advances in the management of bronchial asthma have occurred. Perhaps they have, but if so, more patients are dying during this period of advances than were dying before. The most prudent course would be to assume that the excess deaths are iatrogenic in origin and to act accordingly. Even if this assumption is flawed, acting on it would improve the management of patients with bronchial asthma. If it is true that the major purpose of risk-benefit analysis is to improve patient outcome rather than merely analyze risk-benefit balance, then a series of proposals can be generated to grapple with this problem in bronchial asthma.

Guide to therapy with theophylline for the treatment of obstructive lung disease

During the last 10-15 years, therapy with theophylline for the treatment of obstructive lung disease has been rationalized because of increased investigation into drug pharmacokinetics and metabolism and the introduction of new techniques for measuring drug concentration in plasma. Orally administered sustained-release preparations of theophylline have recently been introduced as therapy following the development of new technology. Such preparations allow more effective use of theophylline through increased patient compliance and the maintenance of more stable plasma theophylline concentrations.

Aminophylline toxicity

Aminophylline therapy has undergone change in the past decade. With the changes in usage and dosage forms, the frequency of toxicity in the pediatric population, especially in adolescents, has increased dramatically. Two distinct patterns, chronic and acute, have been recognized and treatment methods for both are changing. Table 4 summarizes the emerging state-of-the-art therapy for aminophylline toxicity. Judging from the activity seen in the literature, investigation into aminophylline toxicity will continue to be a priority. We will see a greater understanding of the disease process and a refining of the therapeutic process. The ultimate goal is the elimination of mortality and the minimization of morbidity from aminophylline toxicity.

Supraventricular tachycardia in patients with cystic fibrosis

Reports on arrhythmias in cystic fibrosis (CF) patients are limited. Four CF patients treated at our center had recurrent supraventricular tachycardia (SVT). Three had cor pulmonale, as evidenced by echocardiogram, and all had baseline tachycardia. Twenty-four hour Holter monitoring in three patients showed ectopic atrial pacing and premature atrial and ventricular contractions in one patient, rare PVCs in another, and SVT in all three. All patients had significant bronchospasm requiring the use of theophylline, prednisone, and frequent daily doses of beta-2 adrenergic agonists; two also used nebulized atropine. Average theophylline level for the group was 13.4 micrograms/ml during SVT. There was no correlation between pulmonary obstruction and the frequency of SVT. Factors such as cor pulmonale, ectopy, hypoxia, infection, intensive combination bronchodilator therapy, and corticosteroids probably interacted to precipitate SVT. Altered autonomic responses and a myocardial infiltrative process noted in some patients with CF may also play a role in causing arrhythmias.

Cardiac arrhythmias during the combined use of beta-adrenergic agonist drugs and theophylline

We studied 15 nonsmoking, clinically stable asthmatic subjects aged 27 to 39 years to evaluate the potential cardiotoxic effects of combined use of a beta-adrenergic agonist drug and theophylline in the treatment of asthma. Subjects underwent a one-week washout period followed by two one-week periods of study receiving either oral terbutaline or sustained-release theophylline during week 1 and both drugs during week 2. Thirty-six-hour Holter monitoring was performed at the end of each period of study. No significant increase in the total number of ventricular premature beats was noted, although the average heart rate increased significantly between each period of study. Although not statistically significant, the number of individuals with multiform or complete and repetitive ventricular premature beats increased from one at baseline to three during each period of study, including one subject with ventricular tachycardia on combined therapy. These data suggest that combined therapy with theophylline and a beta-adrenergic agonist in young, otherwise healthy asthmatic subjects does not lead to an increase in the total number of ectopic beats but may increase the degree of complexity of ventricular premature beats.

Ventricular arrhythmias during treatment for acute asthma

A double-blind, randomized study was performed to determine the occurrence of ventricular arrhythmias in acute asthma patients treated with epinephrine, aminophylline, or both in combination. Sixty patients were studied with Holter monitoring during the 90-minute study period. There was no statistical difference among the study groups in frequency or grade of ventricular arrhythmia. Combination treatment of acute asthma with these drugs is as safe as treatment with either alone.

Theophylline poisoning. Pharmacological considerations and clinical management

The recent marketing of slow release preparations of theophylline and new indications for the use of the drug have resulted in a marked increase in the sale of theophylline products. This phenomenon combined with the drug's highly variable pharmacokinetics has led to an increase in the number of theophylline intoxications. The morbidity and mortality rates associated with theophylline intoxication are significant. Therefore it is essential that clinicians are aware of the pathophysiology, clinical presentation and treatment of this poisoning. Theophylline intoxication mainly affects the gastrointestinal, cardiovascular and central nervous systems. Signs and symptoms range from mild gastrointestinal upset to serious central nervous system manifestations such as seizures, a symptom often associated with a bad prognosis. Theophylline serum concentrations are very useful for making decisions regarding treatment. However, their interpretation should take into account several factors such as the age of the patient and the type of intoxication (acute versus chronic). Prevention of gastrointestinal absorption should be the principal objective of treatment of an oral theophylline poisoning. The repetitive administration of activated charcoal not only prevents theophylline absorption but also increases its rate of Once absorbed, external methods such as haemodialysis and haemoperfusion can significantly accelerate the elimination of the drug from the body. Finally, the rapid suppression of seizures and cardiac arrhythmias are essential to prevent severe neurological sequelae and death. Since theophylline intoxication can be potentially life-threatening, its administration should be monitored with regular measurements of the serum theophylline concentration, especially in the very young and the very old.

Adrenergic bronchodilators: pharmacology and toxicology

Advances in the understanding of catecholamine metabolism and adrenergic receptor biochemistry have permitted the development of a number of potent and relatively selective sympathomimetic drugs that are active after oral administration as well as when administered by injection or inhalation. Their toxicity derives solely from their effect as adrenergic agonists, and their appropriate use is based on understanding their pharmacology.

Bitolterol mesylate: a beta-adrenergic agent. Chemistry, pharmacokinetics, pharmacodynamics, adverse effects and clinical efficacy in asthma

Bitolterol, (3-4 diester colterol) is a new beta 2-adrenergic agonist. Since it in itself is biologically inactive, bitolterol is considered a pro-drug. When administered it is activated within the lung by esterase hydrolysis to the active compound colterol catecholamine N-t-butyl-arterenol). In preclinical and clinical studies to date, bitolterol has proved to be an effective bronchodilator for adult and pediatric patients with chronic stable asthma and for some with chronic obstructive pulmonary disease. Bitolterol has been compared with other beta 2 agents, including isoproterenol, metaproterenol and albuterol. There is no evidence for cardiotoxicity when bitolterol is used in combination with theophylline in human studies. It is effective for control of exercise-induced asthma.

Arrhythmias in patients with chronic obstructive pulmonary disease

Cardiac arrhythmias are commonly associated with chronic obstructive lung disease and these arrhythmias can impair arterial blood oxygenation. The etiology of the arrhythmias is multifactorial. The treatment of the arrhythmias is largely the treatment of the deranged physiology and the underlying pulmonary disease. The association of arrhythmias with chronic obstructive lung disease portends a poor prognosis.

Concomitant bitolterol mesylate aerosol and theophylline for asthma therapy, with 24 hr electrocardiographic monitoring

A higher incidence of fatal asthma after increased use of combined inhaled beta 2-agonists and theophylline has been attributed to additive cardiac toxicity of these agents. This study had three major objectives: first, to evaluate the efficacy and safety of a new long-acting beta 2-agonist, bitolterol mesylate, given as metered-dose aerosol in a regular "round-the-clock" asthma medication regimen; second, to compare the efficacy and safety of bitolterol with those of sustained-release theophylline alone and of the combination of bitolterol and theophylline; third, to use 24 hr Holter monitoring to evaluate cardiac toxicity of the three medication regimens. This was a 6 wk double-blind study of regular, daily medication in 36 young non-steroid-dependent and 37 older steroid-dependent stable asthmatic patients. All patients had two 24 hr Holter ECG monitorings during the 2 wk baseline period when all patients received theophylline only and four further 24 hr Holter monitorings during the double-blind period. All Holter recordings from the study groups showed no significant abnormalities in any treatment group. Pulmonary function studies were performed on 4 study days in the 6 wk double-blind period. The largest increase in bronchodilator effect was obtained with combined medication and the smallest with theophylline alone. Mean duration of action was markedly longer in the combined treatment group (greater than 7 hr) than with bitolterol mesylate aerosol or theophylline alone (greater than 5 and greater than 4 hr, respectively) in the non-steroid-dependent patients. Degree of bronchodilation and duration of action was less in the steroid-dependent patients in all treatment groups. There is no evidence from cardiac monitoring that therapeutic doses of bitolterol mesylate or theophylline alone or in combination have cardiotoxic effects.