Adults

For chemotherapy-induced nausea and vomiting: 8 mg orally 30 minutes before chemotherapy, then 8 mg orally every 8 hours for 1-2 days. For post-operative nausea and vomiting: 16 mg orally one hour before anesthesia, or 8 mg orally one hour before anesthesia, followed by two further 8 mg doses at 8-hour intervals.

Elderly

No specific dose adjustment is required in elderly patients, but monitoring is advised. For patients aged 75 years or older, the initial IV dose should not exceed 8 mg.

Renal_impairment

No dose adjustment is necessary for patients with impaired renal function.

Onset

30 minutes (oral)

Excretion

Approximately 5% of the dose is excreted unchanged in urine; the remainder is excreted as metabolites via urine and feces.

Half life

Approximately 3-6 hours in adults, longer in elderly and hepatic impairment.

Absorption

Rapidly and extensively absorbed from the gastrointestinal tract, undergoes first-pass metabolism. Bioavailability is approximately 50-70%.

Metabolism

Extensively metabolized in the liver by cytochrome P450 enzymes (CYP2D6, CYP3A4, CYP1A2).

Tramadol

May reduce the analgesic effect of tramadol; concomitant use should be avoided.

Apomorphine

Concurrent use is contraindicated due to reports of profound hypotension and loss of consciousness.

CYP3A4 inducers (e.g., Rifampin)

May reduce ondansetron exposure; clinical significance generally not considered major.

QT-prolonging drugs (e.g., Amiodarone, Sotalol)

Increased risk of QT prolongation; use with caution.