Ondansetron metabolism and pharmacokinetics

Area of Science:

• Pharmacology
• Drug Metabolism
• Clinical Pharmacokinetics

Background:

• Hepatic oxidative metabolism is the primary route (>95%) for ondansetron clearance.
• Ondansetron acts as a competitive antagonist of the 5-hydroxytryptamine (5-HT3) receptor.
• Excreted metabolites of ondansetron contribute minimally to its overall activity.

Purpose of the Study:

• To characterize the pharmacokinetic profile of ondansetron.
• To investigate factors influencing ondansetron clearance and half-life, including age, gender, hepatic function, and enzyme inducers.
• To establish the relationship between ondansetron plasma concentration and antiemetic efficacy.

Main Methods:

• Plasma clearance and volume of distribution measurements in various volunteer and patient populations.
• Analysis of ondansetron half-life in relation to age and hepatic function.
• Assessment of ondansetron absorption and its correlation with emesis control.

Main Results:

• Ondansetron plasma clearance averages 0.45 L/h/kg and is generally consistent across young adults and chemotherapy patients.
• Clearance decreases with age, increasing half-life from 3.5 to 5.5 hours in older adults.
• Hepatic insufficiency significantly reduces clearance and prolongs half-life; enzyme inducers may enhance clearance.

Conclusions:

• Ondansetron pharmacokinetics are influenced by age, hepatic function, and potentially enzyme inducers.
• Despite intersubject variability, ondansetron's safety profile and established efficacy support current dosing regimens.
• No routine dose adjustments for ondansetron are recommended based solely on age or gender.