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Drug Information
Pharmacokinetics
| Indication
& Dosage | Action
| Interactions Adverse
Effects & Precautions |
Brands available in Market
Following oral administration, ondansetron is rapidly absorbed with peak plasma concentration of around 0.03 to 0.04 micrograms per mL being reported about 1.5 to 2 hours after an oral dose of 8 mg. The absolute bioavailability is about 60%, due mainly to hepatic first-pass metabolism. It is extensively distributed in the body; results in vitro suggest that about 70 to 75% of the drug in plasma is protein bound. It is cleared from the systemic circulation predominantly by hepatic metabolism, with less than 5% of a dose being excreted in urine unchanged: clearances of around 6 mL per minute per kg have been reported in young, healthy subjects. In elderly subjects, bioavailability may be somewhat higher (65%) and clearance lower (4 to 5 mL per minute per kg), presumably due to reduced hepatic metabolism. The terminal elimination half-life is about 3 hours in younger subjects, prolonged to 5 hours in the elderly. These differences are not considered sufficient to warrant dosage adjustment; however, in patients with severe hepatic impairment, in whom bioavailability may approach 100% and clearance is markedly slowed, with elimination half-lives of 15 to 32 hours, dosage restriction is advisable.
Indication
& Dosage
IV
MANAGEMENT OF NAUSEA, VOMITING ASSOCIATED WITH CANCER CHEMOTHERAPY OR
RADIOTHERAPY: Highly emetrogenic regimens: 8mg by slow IV injection
mimmediately before chemotherapy. Followed by 2 further IV doses of 8 mg
ecach 2 or 4 hrs apart or a constant infusion of of 1 mg/hr for upto 24
hrs. OR A single dose of 32mg in 50-100ml of normal saline infused over
15 min just before chemotherpy. A single IV doses of dexamethassone
sodium phosphate 20mg before chemotherapy increases the effect of
ondansetron. To prevent delayed emesis, continue ondansetronorally 8 mg
12 hrly for upto 5 days. IV: Children: A single IV DOSE OF 5mg/m2 just
before chemotherapy followed by 4mg orally b.i.d. if necessary
POSTOPERATIVE NAUSEA, VOMITING: Adult: A single dose of 4mg slow IV
injection at induction.
Oral
POSTOPERATIVE NAUSEA, VOMITING: 8mg i hr before induction & 2
further doses of 8mg at 8hr intervals.
Action
Antagonises 5HT3 receptor present peripherally on vagal nerve
terminals and centrally in the chemoreceptor trigger zone. Ondansetron
probably acts at both sites to prevent vomiting due to cancer
chemotherapy and radiotherapy.
Induces or inhibitors of hepatic Cytochrome P450 drug metabolising enzymes : May chage the clearance and hence half-life of ondansteron but on the basis of available data there is no need to adjust the dose of ondasteron.
Adverse Effect & Precautions
Well tolerated drug,
headache, constipation, dizziness, allergic reactions.
Precaution: Hepatic impairment.
Pregnancy: Safety not established.
Pregnancy: Use with caution.
Man: May be given.
