The opioid analgesics
are among the most effective drugs available for the suppression of cough. This
effect is often achieved at doses below those necessary to produce analgesia.
The receptors involved in the antitussive effect appear to differ from those
associated with the other actions of opioids. For example, the antitussive
effect is also produced by stereoisomers of opioid molecules that are devoid of
analgesic effects and addiction liability .
mechanism of cough is complex, and little is known about the specific mechanism
of action of the opioid anti-tussive drugs. It appears likely that both central
and peripheral effects play a role.
The opioid derivatives
most commonly used as antitussives are dextromethorphan,
codeine, levopropoxyphene, and
noscap-ine (levopropoxyphene and noscapine are not available in theUSA).
They should be used with caution in patients taking mono-amine oxidase
inhibitors (see Table 31–5). Antitussive prepara-tions usually also contain
expectorants to thin and liquefy respiratory secretions. Importantly, due to
increasing reports of death in young children taking dextromethorphan in
formula-tions of over-the-counter “cold/cough” medications, its use in children
less than 6 years of age has been banned by the FDA. Moreover, because of
variations in the metabolism of codeine, its use for any purpose in young
children is being reconsidered.
the dextrorotatory stereoisomer of a methylated derivative of levorphanol. It
is purported to be free of addictive properties and produces less constipation
than codeine. The usual antitussive dose is 15–30 mg three or four times daily.
Itisavailableinmanyover-the-counterproducts.Dextromethorphan has also been
found to enhance the analgesic action of morphine and presumably other μ-receptor agonists.
However, abuse of its purified (powdered) form has been reported to lead to
serious adverse events including death.
Codeine, as noted, has
a useful antitussive action at doses lower than those required for analgesia.
Thus, 15 mg is usually sufficient to relieve cough.
the stereoisomer of the weak opioid ago-nist dextropropoxyphene. It is devoid
of opioid effects, although sedation has been described as a side effect. The
usual antitussive dose is 50–100 mg every 4 hours.