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Good Samaritan Regional Medical Center Phoenix, AZ 85018
In the July 1999 issue of AJR, Yee et al. [1] present evidence that despite years of seemingly contrary experience with double-contrast barium enemas, glucagon administration is not helpful in the performance of CT colonography. In explaining this apparent contradiction, the authors themselves make the point that CT colonography is a rapid examination, typically completed (i.e., data fully acquired) in 5-10 min, whereas Lappas et al. [2] indicate glucagon does not begin to show a clinical effect until 8 min after IV administration.
Although this delay might account for why, in the protocol used by the authors, glucagon was not found helpful, the more interesting question is whether glucagon might be a helpful adjunct to CT colonography when attempts are made to optimize its effect. It is not difficult to administer glucagon, wait 8 min, and then begin CT colonography. This procedure would allow completion of CT while the glucagon effect is maximized.
Yee et al. [1] do not claim optimal distention of the colon without glucagon. In fact, they conclude by indicating that without glucagon "the descending and sigmoid colons were the segments in which inadequate distention was most common." They simply claim that glucagon does not improve matters. One can only conclude that glucagon is not helpful in this clinical context when the examination is performed in a way that would optimize any possible benefit the drug might have. Actually scanning the patient while the effect of the drug is at its peak is surely a prerequisite for such a determination.
References
San Francisco Veterans Affairs Medical Center University of California, San Francisco San Francisco, CA 94121
We thank Dr. Levatter for his interest in our article that concluded that glucagon administration before CT colonography does not improve colonic distention [1]. However, we disagree with his comment regarding the need to wait 8 min for the optimal effect of IV glucagon. One of the desired effects of glucagon for CT colonography is optimal colonic distention with decreased spasm. We and others have noted the onset of the antiperistaltic effect of glucagon within 1 min of IV administration. In the study by Lappas et al. [2], the effect of IV glucagon or placebo on patient discomfort was seen in a highly select group of 36 patients who experienced significant pain during double-contrast barium enema. The results of this study showed that patients who received glucagon had greater relief of discomfort starting at 8 min into the examination compared with that of the placebo group. More important, the level of patient discomfort did not show any correlation with the presence of colonic spasm.
Other published reports on glucagon and its effects during barium enema give us little reason to expect a measurable improvement of colonic distention after waiting 8 min before the onset of scanning. In a study of the glucagon and secretin effects on motor activity of the distal colon, Chowdhury and Lorber [3] found a prompt reduction of 84% of the food-induced motor activity of the distal colon. This reduction occurred in less than 1 min after IV administration of only 20% of the usual clinical dose of glucagon. During 90 min of ongoing glucagon infusion, no further decrease in the inhibition of motor activity occurred. This early onset of maximum action is not surprising because the plasma half-life of glucagon is only 3-10 min. On the basis of published reports [1] on the clinical application of glucagon, we believe that Dr. Levatter's argument against our seemingly contrary experience with double-contrast barium enemas does not hold. Evaluating all publications on the various possible effects of glucagon such as reduction of colonic spasm, increased ileocecal reflux, increased lesion sensitivity, reduction of procedure length, and decrease of patient discomfort, the extent of conflicting data and opinions becomes obvious. A general agreement on a decrease in patient discomfort after glucagon administration exists. However, results on the ability of glucagon to resolve or prevent spasm are inconsistent, with almost as many authors finding a measurable effect as those who do not. We would like to emphasize that our observations are consistent with most published clinical studies examining the effect of glucagon on colonic distention, and not contradictory as Dr. Levatter believes. It is important to note that these studies involved patients who were undergoing a double-contrast barium enema procedure that typically required 17 ± 6 min [4].
In conclusion, it remains hypothetical that waiting 8 min after IV glucagon injection before CT might improve colonic distention, but available data, in our opinion, do not justify a separate study of late glucagon response for improved performance of CT colonography.
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  B. M. Preston Rethinking the Use of Glucagon: Consider the Cost Am. J. Roentgenol., February 1, 2001; 176(2): 546 - 547. [Full Text] [PDF]
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