Alosetron clears quickly: its half-life is about 1.5 hours, so most of a dose is out of your bloodstream within 8 to 10 hours.
Because it clears so fast, alosetron does not accumulate over days when you take it on a regular twice-daily schedule, and steady levels are reached almost immediately. Your liver breaks the drug down and your kidneys remove most of what is left in urine. Liver disease slows that process and raises drug levels, which is why alosetron is not used in severe liver impairment. Medicines that block the CYP1A2 enzyme also slow clearance, and fluvoxamine should not be taken with alosetron at all. The bowel effects, including slowed stool transit, can last longer than the drug itself.
Taking alosetron consistently
Common questions
How long does Alosetron stay in your system?
Alosetron leaves your blood quickly. Its elimination half-life is about 1.5 hours, so most of a dose is cleared within about 8 to 10 hours, and it does not build up over days on a steady twice-daily schedule. Your liver breaks it down and your kidneys clear most of it in urine. Effects on urgency and stool frequency can outlast the drug, and constipation may take several days to ease after you stop. Clearance slows with liver disease or with medicines that block CYP1A2, such as fluvoxamine, which should not be taken with alosetron. Call your clinician about new or worsening constipation or any rectal bleeding, and stop the drug until you are seen.