Cotinine excretion and daily cigarette smoking in habituated smokers

A sensitive and specific radioimmunoassay of cotinine, a major metabolite of nicotine, was developed using an antiserum raised against ∓‐1‐(β‐aminoethyl)‐cotinine coupled to bovine serum albumin (BSA) and l25 I‐cotinine derivative. Inhibition studies with related compounds of cotinine revealed that the antiserum was not only specific for both the pyrrolidine and the pyridine ring but also highly reactive to the side chain attached to the latter ring for preparing the antigen and the labeled derivative of cotinine. The minimum detectable amount of cotinine was 1 ng. Urinary cotinine was extracted with chloroform and the mean recovery of cotinine added to nonsmoker's urine was 81 ± 10 (SEM) percent. The intra‐assay and the inter‐assay coefficients of variation were 17% and 28%. Urinary excretion of cotinine was high in habituated smokers before smoking and increased slightly after smoking three cigarettes. There was no correlation between urinary cotinine excretion and pH or urine flow after smoking. Daily urinary excretion of cotinine in smokers tended to relate roughly to daily cigarette consumption although excretion varied even among the smokers who consumed approximately equal numbers of cigarettes. There was no urinary excretion of cotinine in nonsmokers. Successive determinations of the daily cotinine excretion in 7 smokers revealed that the excretion correlated well with cigarette consumption on the corresponding days. We suggest that the measurement of urinary cotinine excretion provides a good index of cigarette smoking.