Known brand names include No current brand name; marketed as generic ondansetron tablets and injection (the original brand was Zofran).
An antiemetic that blocks serotonin 5-HT3 receptors. It prevents nausea and vomiting from cancer chemotherapy, radiation therapy, and surgery. It comes as tablets and as an IV or IM injection.
Ondansetron blocks 5-HT3 receptors, a type of serotonin receptor found on nerve endings in the gut and in a vomiting control area of the brain. Chemotherapy seems to make cells in the small intestine release serotonin. That serotonin can stimulate nearby nerves through these receptors and set off the vomiting reflex, which the drug blocks. It is not certain whether it acts mainly in the gut, the brain, or both, and unlike many older anti-nausea medicines, it does not block dopamine.
Taken over several days, it can slow movement through the large bowel, and constipation is a known side effect. Larger IV doses lengthen the QT interval on a heart tracing, which the label links to a risk of dangerous heart rhythm changes. Combined with other drugs that act on serotonin, it can contribute to serotonin syndrome.
Ondansetron prevents nausea and vomiting caused by cancer chemotherapy, by radiation treatment to the whole body or the belly, and by surgery. The first dose is usually given before chemotherapy, radiation, or surgery starts. After surgery, the injection can also treat nausea and vomiting that start in someone who did not get a preventive dose, to stop further episodes.
It comes as tablets taken by mouth and as an injection into a vein or a muscle. The injection is approved from 6 months of age for chemotherapy and from 1 month for surgery, while the tablets have been shown to work in children 4 years and older only for moderately strong chemotherapy. It is not routinely given before surgery to people who are unlikely to have nausea afterward.
Headache is the side effect people notice most, followed by constipation, diarrhea, tiredness, drowsiness, and fever. The label treats a dangerous heart rhythm change as serious, along with serotonin syndrome when it is combined with other serotonin drugs. It also warns about reduced blood flow to the heart, mostly during or right after IV use, and about serious allergic reactions. Because it can hide the signs of a blocked or swollen bowel after belly surgery or during chemotherapy, those problems can be missed.
A clinician may order these while someone is taking it.
Sources: [1]