American Scientist

To the Editors:

Robert S. Gable's essay "The Toxicity of Recreational Drugs" (Macroscope, May-June) provides information that has significant societal relevance at the present time. I would, however, point out that Dr. Gable's determination of the ethanol (ethyl alcohol, or "alcohol") content of several beverages is inaccurate.

Specifically, Dr. Gable says that "approximately 33 grams of ethyl alcohol" would allow a normal, healthy 70-kilogram adult to "achieve a relaxed affability." He adds, "This effective dose can come from two 12-ounce beers, two 5-ounce glasses of wine or two 1.5-ounce shots of 80-proof vodka." I assume that fluid ounces are intended in these measurements. Of these three beverages, the only one whose alcohol concentration is specified is vodka, which at 80 proof contains 40 percent alcohol by volume, or 40 milliliters of alcohol per 100 milliliters of vodka.

The number of grams of alcohol in two 1.5-fluid ounce shots of vodka is essentially 28 grams, about 15 percent less than the 33 grams reported by Dr. Gable. The amount can be calculated using dimensional analysis, or the unit-factor method, as shown in the diagram below. In this calculation, the units of fluid ounces (fl oz) of vodka, milliliters (mL) of vodka, and mL alcohol "cancel" each other via the operation of division, so that the desired unit of grams (g) of alcohol" remains.

Similar calculations for two 12-fluid-ounce beers containing five percent alcohol by volume (or 0.05 milliliters of alcohol per 1 milliliter of beer) and two 5-fluid-ounce glasses of wine containing 12 percent alcohol by volume  (or 0.12 milliliters of alcohol per 1 milliliter of wine) yield 28 grams of alcohol as well.

I would submit that the "effective dose" of approximately 33 grams of alcohol specified by Dr. Gable would be obtained from approximately 2.4 shots of vodka at 1.5-fluid ounces each, 2.4 beers at 12 fluid ounces each or 2.4 glasses of wine at 5 fluid ounces each. Therefore, approximately 24 shots of vodka would be nearly equivalent to the 330-gram median lethal dose of alcohol cited by Dr. Gable.

I would emphasize that the quantitative fine-tuning of Dr. Gable's presentation that is offered here does not minimize the timely message of his essay.

Dominick A. Labianca
Brooklyn College
The City University of New York

Dr. Gable responds:

Dr. Labianca's "quantitative fine-tuning," as he described his comments, provides a valuable opportunity to emphasize the variability in ethanol content among common alcohol beverages. My statement that "approximately 33 grams of ethyl alcohol … can come from two 12-ounce beers, two 5-ounce glasses of wine, or two 1.5-ounce shots of 80-proof vodka" was a rough approximation. Dr. Labianca's letter, noting that the 80-proof vodka will yield only 28 grams (not 33 grams) of alcohol, is gratefully received, and I regret my imprecision.

However, in my view, 33 grams of alcohol is not an unreasonable general estimate for two containers of beer or malt beverage. Many of these drinks have alcohol greater than the 5 percent by volume that I mentioned as a sample in my article. The published range of alcohol concentration for theses beverages is 2.92 to 15.66 percent. Wine is often over 12 percent. The commonly seen label for table wine that states "alcohol 12.5% by volume" can legally represent a range from 11 to 14 percent. The legal range for sherries is 17 to 20 percent. Thus, the alcohol in these beverages, for the quantities I mentioned, can be considerably greater than 33 grams.

Given the variability within various categories of legal alcohol beverages, users of illicit substances should be even more wary of a potential overdose. Dr. Labianca's letter has usefully prompted attention to this hazard.