ASSESSMENT OF THE ANTITUSSIVE EFFICACY OF CODEINE IN COUGH ASSOCIATEDWITH COMMON COLD

Codeine is generally accepted as the standard antitussive against whic h new antitussive medications are compared. This presents a problem be cause the support for codeine's antitussive activity comes from studie s on cough in animals, and chronic and induced cough models in man, wh ereas antitussives are almost exclusively used for the treatment of co ugh associated with acute upper respiratory tract infection (URTI). Th e aims of this study were twofold. Firstly, to study the antitussive e fficacy of codeine in cough associated with URTI and, secondly, to val idate a sound meter as tool for quantifying cough. The efficacy of cod eine was assessed in a double-blind, stratified, placebo-controlled, p arallel-group, clinical trial using three different measures of cough: cough sound-pressure levels (CSPLs) measured on a sound meter; subjec tive scores of cough severity; and cough frequency recorded by means o f a microphone connected to an ink-pen recorder. A group of 82 subject s (51 females and 31 males; mean age 23.5 years, range 18-46 years) wi th cough owing to acute URTI were included in the study. The study too k place on two separate study days. On study day 1 cough measurements were made before and 90 min after treatment with a single dose of eith er 50 mg codeine or matched placebo in capsule form. The same three me asures of cough were repeated 2-5 days later (study day 2). On study d ay 1 a highly significant (P < 0.0001) decrease in all three measures of cough was found after treatment with both placebo and codeine yet t here was no significant difference between the treatment groups. A hig hly significant (P < 0.0001) decrease in the three measures of cough w as also found between days 1 and 2. The results demonstrate that codei ne is no more effective than placebo in reducing cough associated with acute URTI, as measured by CSPLs, cough frequency or subjective sympt om scores. This result might be explained on the basis of two central pathways for cough; a reflex pathway via the brain-stem which is sensi tive to codeine and a voluntary pathway via the cortex which is unaffe cted by codeine. The results also demonstrate that the sound-level met er appears to be a potentially useful investigative tool for the asses sment of cough and antitussive efficacy.