The Effect of Metronidazole on the Human Taste Threshold to Alcohol

Summary A method is described for measuring the taste threshold to alcohol in a sample of 163 subjects whose average age was 27 years. The subjects taste ascending concentrations of alcohol in water from 0.25% up to 64% absolute alcohol. Five mls of each concentration is tasted for 20 seconds, spat out, and then the subject washes out his mouth with the diluent water. Alcohol is detected as a sweet taste at a concentration of 4.2±S.E. 0.24% alcohol. The sweet taste changes to a burning taste at a mean concentration of 21.2±S.E. 1.22% alcohol. The frequency distributions for the sweet and burning tastes of alcohol depart significantly from the unimodal normal shape. During the 20 seconds while alcohol is maintained in the mouth for appreciation of its taste, the concentration of the 4% solution falls to 2%, and the concentration of the 20% solution falls to 16%. The taste threshold for metronidazole was tested in the same subjects and found to be 149±S.E. 17 mg/litre; the frequency distribution curve is unimodal in shape but negatively skewed. The taste threshold for PTC in the same subjects was bimodal with modes at 20 and 1300 mg/litre. Oral administration of 600 mg of metronidazole as 200 mg tablets over a period of 14 hours, caused no change in the taste threshold to alcohol during the following 6 days. Administration of 800 mg metronidazole over a period of 20 hours, caused a significant elevation of both sweet and burning taste thresholds to alcohol which reached its maximum on the second day after the last tablet had been taken. The taste threshold returned to its pre‐metronidazole level on the fourth day. The alcohol taste threshold was raised at concentrations of metronidazole equivalent to those excreted in the saliva. The taste threshold to alcohol is a measurable human physiological characteristic. In humans, and by implication in rats, taste threshold to alcohol is appreciated through pereipheral receptors and specific afferent taste discharges, and the taste mechanism is the primary regulator of alcohol intake. The finding of a taste threshold distribution curve with more than one mode provides evidence that there may be a genetic basis to variations in alcohol taste threshold. The action of metronidazole on the alcohol taste threshold suggests that this drug may exert psychotherapeutic effects on alcohol consumption in man not only through peripheral taste receptiors but also through central taste pathways.