How can eye drops or nasal sprays be toxic?

Answer: Most eye drops and nasal sprays contain tetryzoline (tetrahydrozoline), a sympathomimetic that can be lethal when ingested.

eye drops tetrahydrozoline

The primary ingredient of eye drops such as Visine is tetrahydrozoline hydrochloride. The drug is very effective at decreasing eye redness because of its action as a vasoconstrictor. Non steroidal nasal sprays work using the same mechanism, as constricting blood vessels in the nose can decrease the mucus output.

Tetrahydrozoline is an agonist at the alpha-2 adrenergic receptor, a G-protein coupled receptor that is coupled with Gi. As an agonist, it will mimic the action of norepinephrine release.

When locally applied to the eye or into the nasal cavity at the recommended doses, tetrahydrozoline does not pass significantly into the bloodstream. However, when used improperly, such as by oral ingestion, the drug can act on the alpha-2 adrenergic receptors producing symptoms such as decreased heart rate, respiratory depression, and low blood pressure. These symptoms can lead to a circulatory system shock, which may be lethal. Although there is no immediate cure for the symptoms, close medical assistance can minimize the risk to the person.

There are reports in the news of people who have committed murder using tetrahydrozoline, such as a recent case in South Carolina (US wife accused of 'fatally poisoning husband with eyedrops')