|Trade names||Rohto Relief, Visine Original, others|
|Main uses||Swelling of the whites of the eyes|
|Side effects||Dilated pupils, blurry vision, irritation of the eyes|
|Onset of action||Within minutes|
|Duration of action||Up to 8 hrs|
|Chemical and physical data|
|Molar mass||200.285 g·mol−1|
|3D model (JSmol)|
|Melting point||117–119 °C (243–246 °F)  256–257 °C (493–495 °F) for HCl-salt|
|Solubility in water||Very soluble in water and ethanol, slightly soluble in chloroform and insoluble in diethylether mg/mL (20 °C)|
|(what is this?)|
Tetryzoline, also known as tetrahydrozoline, is a medication used to improve swelling of the whites of the eyes. It is available alone and in combination as an over-the-counter eye drop. Effects begin within minutes and may last for up to 8 hours. Long term use may worsen the condition.
Common side effects include dilated pupils, blurry vision, and irritation of the eyes. Other side effects may include redness of the eyes, headache, palpitations, and trouble sleeping. It works by causing blood vessels to contract by activation α-adrenergic receptors.
Tetryzoline eye drops may cause blurred vision, eye irritation and dilated pupils. Tetryzoline is not suitable for prolonged use as its vasoconstrictive effects within the eye eventually decrease or stop. If tolerance to the drug has developed, ceasing its use may cause a rebound effect and increase redness of the eyes — a vasodilatory effect.
Intranasal use of tetryzoline may cause transient burning, stinging, or dryness of the mucosa and sneezing. Prolonged intranasal use often causes opposite effects in the form of rebound congestion with effects such as chronic redness, swelling and rhinitis. Prolonged use thus may result in overuse of the drug.
Overdose most often causes slow heart rate. Respiratory depression, low blood pressure, constricted pupils, hypothermia, brief episodes of high blood pressure, drowsiness, headaches and vomiting may also occur. In serious cases some of these effects may result in circulatory shock. Most often overdoses occur in children who have ingested the drug.
There is no antidote for tetryzoline or other similar imidazoline analogue poisoning, but the symptoms can be alleviated and with treatment, death is rare.
Mechanism of action
Tetryzoline is an alpha agonist for alpha-2 receptor and imidazoline receptor I-1 agonist. Mainly due to its alpha-2 agonism it can constrict conjuctival blood vessels of the eye when taken in the form of eye drops. This relieves the redness of the eye caused by minor ocular irritants. To treat allergic conjunctivitis, tetryzoline can be combined in a solution with antazoline.
The half-life of tetryzoline in healthy people is about 6 hours and it is excreted unchanged in urine, at least in part. In one study 10 people were given two drops of 0.5 mg/ml tetryzoline eye drops (0.025–0.05 mg) at 0, 4, 8 and 12 h. Within a 24 h time window since the last dose, tetryzoline blood serum concentration of the subjects was 13.0–210.0 ng/ml and urine concentration was 11–400 ng/ml. Both reached their maximum about 9 h post last dose. These levels correspond to normal ocular use of tetryzoline. Higher concentrations may indicate misuse of the drug or poisoning.
Society and culture
An urban legend suggests that tetryzoline can cause violent diarrhea if given orally, such as by putting a few drops of Visine in an unsuspecting person's beverage. However, the actual results of the prank may be worse, varying from severe nausea and vomiting to seizures or a coma. Diarrhea is not a side effect.
In late August 2018, a South Carolina woman was charged with murdering her husband by putting eye drops containing tetryzoline in his drinking water. An autopsy found high concentrations of tetryzoline in his body.
In 2018 an elderly woman in Pewaukee, Wisconsin died in an apparent overdose or suicide, and years later police charged her caregiver with murder, alleging that the death was caused by a water bottle laced with Visine.
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