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*Department of Anesthesiology, University of Washington School of Medicine, Seattle, WA;
Department of Pharmacology, Rush Medical College, Chicago, IL;
Pharmaconsultant, Inc., Palatine, IL; and
Department of Veterans Affairs and the Departments of Anesthesiology and Medicine (adjunct, Pulmonary and Critical Care), University of Washington School of Medicine, Seattle, WA
Address correspondence and reprint requests to Sanjay M. Bhananker, MD, FRCA, Department of Anesthesiology, Harborview Medical Center, 325 9th Avenue, Seattle, WA 98104. Address electronic mail to: sbhanank{at}u.washington.edu.
| Abstract |
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| Introduction |
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Based on wholesale sales reports, rocuronium is the most commonly used intermediate acting muscle relaxant in the United States (U.S.) (Table 1). Studies from France and Norway have suggested a frequent rate of anaphylaxis with rocuronium (8,11,12). When interpreting these results, the frequency of use of different NMBDs in clinical anesthesia (the denominator data) must be considered. This is estimated from a market share survey for the various NMBDs (6). Some authors suggest that the incidence of anaphylactic reactions to rocuronium merely reflects its market share (clinical use), (13,14) but it remains uncertain whether these reports represent the experience of the larger anesthesiology community.
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The diagnosis of anaphylaxis is confirmed by a variety of tests, including serum tryptase levels, skin testing (intradermal or prick test), or detection of specific immunoglobulin E by radioimmunoassay. Skin testing is often considered the standard procedure, (15,16) but the prevalence of sensitivity to NMBDs based on skin testing or presence of specific immunoglobulin E can be as frequent as 9.3% (17). A study concerning allergy testing by Garvey et al. (10) in Denmark does not suggest a more frequent incidence of sensitivity to rocuronium, and mast cell activation patterns do not differ significantly between rocuronium and vecuronium during skin testing (18). Skin testing is fraught with difficulties and can result in frequent false-positive results (16,19).
Allergy testing provides one avenue for assessing the incidence of adverse reactions to a medication, but correlations with clinical adverse reactions can be highly variable. One important source for drug safety reporting is the Food and Drug Administration (FDA) Adverse Event Reporting System (AERS). We hypothesized that the AERS could be used to determine whether there had been an unusually large number of anaphylaxis or anaphylactoid reactions to rocuronium and whether the reports from France and Norway correlated with reports from the U.S. domestic market.
| Methods |
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We searched for all AERs for the drugs rocuronium and vecuronium, and then searched specifically on the terms considered to represent possible anaphylaxis, including "anaphylactic reaction," "anaphylactic shock," and "anaphylactoid reaction." Duplicate reports or duplicate use of the terms were eliminated. These terms are from the Medical Dictionary for Regulatory Activity (Northrop Grumman Mission Systems, Reston, VA) "Preferred Terms" (PT) for indexing adverse drug reactions. Searches were conducted using proprietary software created by Corel Corporation (Ottawa, Canada) for Pharmaconsultants, Inc. (Palatine, IL) to facilitate searching the FDA records. The proportion of all adverse events that were anaphylactic reactions were compared using a
2 test for rocuronium versus the second most commonly used intermediate-acting muscle relaxant, vecuronium. We then assessed the frequency of reports of anaphylaxis in the U.S. versus outside of the U.S., using
2 test or Fishers exact test as appropriate.
The market share for the various NMBDs for the U.S. for the years 19992002 was requested from IMS Health (Fairfield, CT). The market share for the various NMBDs over the years was used to estimate the relative usage of the various intermediate-acting NMBDs in the U.S..
| Results |
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The frequency of reports of anaphylaxis to vecuronium was similar to that for rocuronium in the U.S.. An incidence of 1 case of anaphylaxis per 1,008,000 vials of rocuronium sold in the U.S., and 1 case per 1,107,250 vials of vecuronium was noted. Reports of anaphylaxis to rocuronium were more common than that for vecuronium in the non-U.S. reports (P < 0.001).
| Discussion |
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Although early reports from Norway suggested a frequent incidence of anaphylaxis to rocuronium, an analysis by an expert panel of the Norwegian Medicines Agency reviewed the data and indicated that there was no evidence to support a more frequent rate of anaphylaxis with rocuronium than with other NMBDs (20). This contrasted with earlier Norwegian concerns about the drug that led the Norwegian Medicines Agency in 2000 to recommend use of rocuronium only if there was a clear positive indication. At the same time, a prospective monitoring plan was put in place to assess whether there was a true increased incidenceand the answer appears to be no. These data corroborate the U.S. experience and demonstrate the potential reporting bias of AERS.
It is also possible that the non-U.S. practitioners have observed a large number of anaphylactic reactions to rocuronium because they use rocuronium for tracheal intubation (for the larger dose and rapid administration) as opposed to the U.S. providers who may be using rocuronium to maintain intraoperative muscle relaxation (tracheal intubation with succinylcholine). Alternatively, more rapid tracheal intubation by providers in high-reporting areas could be causing bronchospasm during light anesthesia and subsequent hypotension as a result of decreased venous return. The lack of immunoglobulin E specific antibodies in the Garvey et al. study (10) certainly raises the possibility that some of the reports of apparent anaphylaxis actually represent a confluence of relatively common clinical findings (hypotension, vasodilation, and bronchospasm) that do not have an immunologic basis.
Drug reporting is inherently biased because people may be more likely to report things if they have heard that others have a similar problem. Spontaneous reports are rarely complete. Because the underlying population of patients exposed to the drug (the denominator data) is unknown, one can not estimate the risk or incidence of an adverse reaction (21). Although the market share can be used to estimate the relative frequency of use of a NMBD in a year, the lack of data on wasted drug, expired drug, or drug inventory makes this estimate unreliable. The highest peak in the reporting of adverse reactions to a drug generally occurs in the second year after its approval, a phenomenon known as the Weber effect, (22) and the reporting peaks periodically. Although we did not analyze the reactions by the year of origin, it is conceivable that the peak in non-U.S. reports of adverse reactions to rocuronium may be a part of this phenomenon.
We used the three terms considered to represent possible anaphylaxis, including "anaphylactic reaction," "anaphylactic shock," and "anaphylactoid reaction." To investigate the possibility that U.S. reporters used the terms "hypotension" or "bronchospasm" when non-U.S. reporters might have used an anaphylaxis term, we also performed searches on these two terms and found no difference between U.S. and non-U.S. reporters for either rocuronium or vecuronium.
Because there is no truly accurate denominator for our data, we compared the incidence of anaphylaxis reports to the total number of reports for a drug. This is similar to the technique used in the ASA Closed Claims Database studies, using the total number of reports as a denominator (23,24).
Because the MedWatch program is open to any observer, more than one drug name may be entered into the database for an identical chemical substance and be assigned a separate Individual Safety Report number. For example, a physician might make a MedWatch report and list rocuronium as a suspected drug and describe the reaction observed as bronchospasm. A nurse or patient relative might report the same event listing the suspected drug as Zemuron and the adverse event as wheezing. As a result, the database must be searched for each commonly used drug name and the results combined. This combined list may include duplicate reports of the same event. The database organization calls up each drug reaction PT, which also lists the name entered in the search so that a single report with one unique Individual Safety Report number may appear more than once if a MedWatch Report lists, for example, anaphylaxis, hypotension, or drug hypersensitivity. When this duplication occurs all of the listings are grouped together and counted as one report rather than three. We cannot be absolutely sure that we eliminated all duplicates, but the cases identified were reviewed individually, and cases that appeared to be identical were removed.
The AERS has come under recent criticism because of its failure to detect the increased risk of cardiovascular incidents with cyclooxygenase-2 inhibitors (25). For less common events, the "signal to noise" ratio should be clearer and the AERS system is considered critical for detecting such events during the post-marketing period. The widely differing results in reported anaphylaxis-like reactions is difficult to explain and suggests the need for prospective monitoring of outcomes to ascertain the safety of widely used drugs while also making sure that relatively safe drugs are not lost to the market.
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Disclosure: Michael Bishop and James ODonnell receive unrestricted grant funding from Organon, Inc.
Presented, in part, at the annual meeting of the American College of Clinical Pharmacology, Phoenix, Arizona, October 35, 2004.
Accepted for publication March 29, 2005.
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