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Therapeutic Theophylline Levels and Adverse Cardiac Events
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IN RESPONSE:
We appreciate Dr. Raggi's comments on the potential for normally therapeutic theophylline levels to produce significant cardiac disturbances. This risk has been reported by many investigators. In a separate study, Bittar and colleagues [1] reported that among elderly patients receiving theophylline, those with serum concentrations between 10 and 20 mg/L had an 3.7-fold greater risk for cardiac disturbances than did patients of similar age with nondetectable serum theophylline concentrations. In an in vitro study, Lin and coworkers [2] found that theophylline has specific arrhythmogenic effects on human atrial tissue. Although their data suggest that theophylline has direct actions on cardiac membrane depolarization, other theories of theophylline-induced cardiotoxicity include the drug's ability to antagonize the cardioprotective effects of endogenous adenosine (for example, coronary artery dilation) as well as its ability to stimulate plasma catecholamine activity and to increase myocardial oxygen demand. These findings provide consistent evidence that adverse cardiac events may occur not only in patients with theophylline intoxication [3] but also in patients whose levels are within the therapeutic range.
Michael Shannon, MD, MPH
Children's Hospital; Harvard Medical School; Boston, MA 02115
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
