Uses and Administration
Ondansetron/Emitino/Zofran is a 5-HT3-receptor antagonist with antiemetic activity. It is used in the management of nausea and vomiting induced by cytotoxic chemotherapy and radiotherapy. It is also used for the prevention and treatment of postoperative nausea and vomiting.
Ondansetron/Zofran in Kenya is given by intramuscular or slow intravenous injection as the hydrochloride, by mouth as the hydrochloride or base, or rectally as the base. Doses are expressed in terms of the base. Ondansetron hydrochloride 4.99 mg is approximately equivalent to 4 mg of ondansetron base.
For highly emetogenic chemotherapy the following dose schedules appear to be equally effective in preventing acute emesis:
a single dose of 8 mg by slow intravenous or intramuscular injection immediately before treatment
8 mg by slow intravenous or intramuscular injection immediately before treatment, either followed by a continuous intravenous infusion of 1 mg/hour for up to 24 hours, or by a further two doses of 8 mg two to four hours apart
a single dose of 32 mg given by intravenous infusion over at least 15 minutes immediately before treatment
a 16-mg suppository rectally, given 1 to 2 hours before treatment
The efficacy of ondansetron/Emitino in Kenya in highly emetogenic chemotherapy may be enhanced by intravenous administration of dexamethasone sodium phosphate 20 mg before chemotherapy.
For preventing acute emesis with less emetogenic chemotherapy and radiotherapy:
8 mg may be given as a slow intravenous or intramuscular injection immediately before treatment
16 mg rectally can be given 1 to 2 hours before treatment
8 mg can be given by mouth 1 to 2 hours before treatment followed by 8 mg 12 hours later
To protect against delayed emesis these regimens are followed by ondansetron 8 mg by mouth twice daily, or 16 mg rectally once daily, for up to 5 days after the end of a course of chemotherapy.
For children a recommended dose is 5 mg/m2 body-surface intravenously immediately before chemotherapy, followed by 4 mg orally 12 hours later. A dose of 4 mg orally twice daily may be continued for up to 5 days after the end of chemotherapy.
To prevent postoperative nausea and vomiting in Kenyan adults, the following doses may be given:
16 mg by mouth an hour before anaesthesia
8 mg by mouth an hour before anaesthesia followed by 2 further doses of 8 mg at 8-hour intervals
a single dose of 4 mg by intramuscular or slow intravenous injection at induction of anaesthesia
For the treatment of postoperative nausea and vomiting a single 4-mg dose by intramuscular or slow intravenous injection is recommended.
Children aged 2 years and over may be given 100 micrograms/kg by slow intravenous injection, up to a maximum dose of 4 mg, both for the prevention and treatment of postoperative nausea and vomiting.
In patients with moderate or severe hepatic impairment the manufacturers have recommended that the total daily dose of ondansetron should not exceed 8 mg.
Adverse Effects and Precautions of Ondansetron in Kenya
Ondansetron and other 5-HT3 antagonists may cause headache, a sensation of flushing or warmth, and constipation. A transient rise in liver enzymes has occasionally occurred. There have been rare reports of immediate hypersensitivity reactions, including anaphylaxis. Chest pain, hypotension, tachycardia, and bradycardia have been reported rarely. Dizziness and transient visual disturbances such as blurred vision have been reported during rapid intravenous administration.
5-HT3 antagonists should generally not be used in patients who have had a hypersensitivity reaction to a member of this drug class. They should be used with care in patients with signs of subacute intestinal obstruction or ileus. Ondansetron should be given in reduced doses to patients with moderate to severe hepatic impairment.
Incompatibility of Zofran and other drugs in Kenya
Ondansetron hydrochloride and dexamethasone sodium phosphate were not compatible when high concentrations were combined in polypropylene syringes.1 Lower concentrations (up to 640 micrograms/mL of ondansetron and 400 micrograms/mL of dexamethasone phosphate) were stable in 50 mL containers of infusion fluid for 30 days under refrigeration. Compatibility has been reported for 24 hours in plastic syringes at 4 degrees or 23 degrees with a variety of other drugs,2 and with several antineoplastics (cytarabine, dacarbazine, doxorubicin, etoposide, or methotrexate) in PVC infusion bags for 48 hours at room temperature.3
Interactions of Emitino with other Kenyan Drugs
Rifampicin pretreatment reduced the area under the plasma concentration-time curve of oral ondansetron by 65% and of intravenous ondansetron by 48% in healthy subjects.1 Use of rifampicin, or other potent inducers of cytochrome P450 isoenzyme CYP3A4, with ondansetron may reduce antiemetic efficacy.