Clinical study
Prescription of QT-prolonging drugs in a cohort of about 5 million outpatients

https://doi.org/10.1016/S0002-9343(02)01455-9Get rights and content

Abstract

Purpose

Many drugs prolong the QT interval and increase the risk of torsade de pointes. Concurrent use of two or more of these drugs can further increase the risk, but the prevalence of concurrent prescription of QT-prolonging drugs is not known.

Methods

Using the administrative claims database of a national pharmaceutical benefit manager, we conducted a retrospective cohort study in 4,825,345 subjects aged 18 years or older. After identifying 50 drugs with QT-prolonging potential, and an additional 26 drugs that inhibit the metabolic clearance of QT-prolonging drugs, we measured the frequency of overlapping prescriptions for two or more of these drugs in the outpatient setting in 1999.

Results

Nearly 1.1 million subjects (22.8%) filled 4.4 million prescriptions for QT-prolonging drugs. Of these, 103,119 subjects (9.4%) filled overlapping prescriptions for two or more of the drugs or for a QT-prolonging drug and another drug that inhibits its clearance; 7249 subjects (0.7%) filled overlapping prescriptions for three or more of these drugs. Twenty-two percent of subjects who filled overlapping prescriptions were aged 65 or older; 74% were women. Antidepressants were involved in nearly 50% of the cases.

Conclusion

Concurrent prescription of QT-prolonging drugs is common in the outpatient setting, and antidepressants are involved in half of these cases. Large pharmaceutical claims databases are useful for detecting potentially harmful prescribing behaviors, but better clinical evidence on medication safety is needed before such a system can be implemented fully.

Section snippets

Study sample

We accessed the outpatient prescription claims database of AdvancePCS (Irving, Texas, and Scottsdale, Arizona), the largest pharmaceutical benefit manager in the United States. Health insurance carriers contract with Advance- PCS to manage their formularies and adjudicate their prescription drug claims. AdvancePCS maintains a computerized pharmacy system that records data on each prescription drug dispensed to its beneficiaries. More than 98% of the prescription drug claims are submitted and

Results

The mean (± SD) age of patients was 47.7 ± 16.3 years, and almost 60% were women (Table 1). The population was geographically diverse, with representation from all 50 states, the District of Columbia, Puerto Rico, and two U.S. territories. Of the 4.8 million patients, 1,097,871 (22.8%) filed claims for at least one QT-prolonging drug in 1999. Their mean age was 49.0 ± 16.0 years, and nearly two thirds were women (Table 1).

Nearly half (47.4%) of all patients with a claim for a QT-prolonging

Discussion

The findings of this population-based study suggest that drugs with the potential for QT prolongation, particularly antibiotics and antidepressants, are prescribed and dispensed frequently in the outpatient setting. Nearly 10% of patients who filled prescriptions for QT-prolonging drugs filled them in combination with another drug of concern; more than 25% of patients who filled a prescription for a QT-prolonging antidepressant filled an overlapping prescription for another drug of concern, as

Acknowledgements

The authors thank Damon Seils for editorial assistance and manuscript preparation, and O. Diana Bell for technical assistance.

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    This research was supported by Centers for Education and Research on Therapeutics (CERTs) cooperative agreement U18 HS10385, formerly between the Agency for Healthcare Research and Quality (AHRQ) and Georgetown University Medical Center, now between AHRQ and the University of Arizona Health Sciences Center. Drs. Curtis, Dans, Hutchison, Østbye, Schulman, Woosley, Wright, and Yasuda are supported in part by the CERTs program in Arizona. Drs. Allen LaPointe, Al-Khatib, and Califf are supported in part by the CERTs program at Duke University Medical Center.

    *

    Dr. Sendersky is now with the Department of Health Economics and Outcomes Research, Novartis Pharmaceuticals Corporation, East Hanover, New Jersey.

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