Ondansetron

INDICATIONS AND USAGE Ondansetron Injection, USP is a 5-HT 3 receptor antagonist indicated for the prevention of: nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy. ( 1.1 ) postoperative nausea and/or vomiting. ( 1.2 ) 1.1 Prevention of Nausea and Vomiting Associated with Initial and Repeat Courses of Emetogenic Cancer Chemotherapy Ondansetron Injection, USP is indicated for the prevention of nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy, including high-dose cisplatin. Ondansetron Injection, USP is approved for patients aged 6 months and older. 1.2 Prevention of Postoperative Nausea and/or Vomiting Ondansetron Injection, USP is indicated for the prevention of postoperative nausea and/or vomiting. As with other antiemetics, routine prophylaxis is not recommended for patients in whom there is little expectation that nausea and/or vomiting will occur postoperatively. In patients in whom nausea and/or vomiting must be avoided postoperatively, Ondansetron Injection, USP is recommended even when the incidence of postoperative nausea and/or vomiting is low. For patients who do not receive prophylactic Ondansetron Injection, USP and experience nausea and/or vomiting postoperatively, Ondansetron Injection, USP may be given to prevent further episodes. Ondansetron Injection, USP is approved for patients aged 1 month and older.

DOSAGE AND ADMINISTRATION SECTION Prevention of nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy ( 2.1 ): Dilution of Ondansetron Injection in 50 mL of 5% Dextrose Injection or 0.9% Sodium Chloride is required before administration to adult and pediatric patients. Adults and pediatric patients 6 months of age and older: The recommended dosage is 0.15 mg/kg per dose for 3 doses (maximum of 16 mg per dose), infused intravenously over 15 minutes. Administer the first dose 30 minutes before the start of chemotherapy and subsequent doses 4 and 8 hours after the first dose. Prevention of Postoperative Nausea and/or Vomiting ( 2.2 ): Dilution of Ondansetron Injection is not required before administration to adult and pediatric patients. See full prescribing information for the recommended dosage and administration instructions for adult and pediatric patients 1 month of age and older. Patients with severe hepatic impairment ( 2.3 ): Do not exceed a total daily dose of 8 mg. 2.1 Prevention of Nausea and Vomiting Associated with Initial and Repeat Courses of Emetogenic Chemotherapy Important Preparation Instructions Dilution of Ondansetron Injection in 50 mL of 5% Dextrose Injection or 0.9% Sodium Chloride Injection is required before administration to adult and pediatric patients for the prevention of nausea and vomiting associated with emetogenic chemotherapy. For pediatric patients between 6 months and 1 year of age and/or 10 kg or less: Depending on the fluid needs of the patient, Ondansetron Injection may be diluted in 10 to 50 mL of 5% Dextrose Injection or 0.9% Sodium Chloride Injection. Dilution of Ondansetron Injection in 50 mL of 5% Dextrose Injection or 0.9% Sodium Chloride Injection is required before administration to adult and pediatric patients for the prevention of nausea and vomiting associated with emetogenic chemotherapy. For pediatric patients between 6 months and 1 year of age and/or 10 kg or less: Depending on the fluid needs of the patient, Ondansetron Injection may be diluted in 10 to 50 mL of 5% Dextrose Injection or 0.9% Sodium Chloride Injection. Occasionally, ondansetron precipitates at the stopper/vial interface in vials stored upright. Potency and safety are not affected. If a precipitate is observed, resolubilize by shaking the vial vigorously.Occasionally, ondansetron precipitates at the stopper/vial interface in vials stored upright. Potency and safety are not affected. If a precipitate is observed, resolubilize by shaking the vial vigorously. Do not mix Ondansetron Injection with solutions for which physical and chemical compatibility has not been established. In particular, this applies to alkaline solutions as a precipitate may form.Do not mix Ondansetron Injection with solutions for which physical and chemical compatibility has not been established. In particular, this applies to alkaline solutions as a precipitate may form. Inspect the diluted Ondansetron Injection solution for particulate matter and discoloration before administration; discard if present.Inspect the diluted Ondansetron Injection solution for particulate matter and discoloration before administration; discard if present. Storage : After dilution, do not use beyond 24 hours. Although Ondansetron Injection is chemically and physically stable when diluted as recommended, sterile precautions should be observed because diluents generally do not contain preservative. Storage : After dilution, do not use beyond 24 hours. Although Ondansetron Injection is chemically and physically stable when diluted as recommended, sterile precautions should be observed because diluents generally do not contain preservative. Compatibility : Ondansetron Injection is compatible and stable at room temperature under normal lighting conditions for 48 hours after dilution with the following intravenous fluids: 0.9% Sodium Chloride Injection, 5% Dextrose Injection, 5% Dextrose and 0.9% Sodium Chloride Injection, 5% Dextrose and 0.45% Sodium Chloride Injection, and 3% Sodium Chloride Injection. Compatibility : Ondansetron Injection is compatible and stable at room temperature under normal lighting conditions for 48 hours after dilution with the following intravenous fluids: 0.9% Sodium Chloride Injection, 5% Dextrose Injection, 5% Dextrose and 0.9% Sodium Chloride Injection, 5% Dextrose and 0.45% Sodium Chloride Injection, and 3% Sodium Chloride Injection. Dosage and Administration The recommended dosage for adult and pediatric patients 6 months of age and older for prevention of nausea and vomiting associated with emetogenic chemotherapy is 0.15-mg/kg per dose for 3 doses (maximum of 16 mg per dose). Caution : Dilution of Ondansetron Injection is required in adult and pediatric patients prior to administration. Infuse intravenously over 15 minutes beginning 30 minutes before the start of emetogenic chemotherapy and then repeat 4 and 8 hours after the first dose. 2.2 Prevention of Postoperative Nausea and Vomiting.1 SPL UNCLASSIFIED SECTION Dosage and Administration The recommended dose and administration instructions for adult and pediatric patients 1 month of age and older for prevention of postoperative nausea and vomiting are shown in Table 1. Table 1. Recommended Dose and Administration of Ondansetron Injection for Prevention of Postoperative Nausea and Vomiting Population Recommended Single Dose Administration Instructions Timing of Administration Adults and pediatric patients older than 12 years of age 4 mg Few patients above 80 kg have been studied. May be administered intravenously or intramuscularly: Intravenously: infuse undiluted syringe contents (4 mg) over at least 30 seconds and preferably longer (over 2 to 5 minutes). Intramuscularly: inject undiluted syringe contents (4 mg) Administer immediately before induction of anesthesia, or postoperatively if the patient did not receive prophylactic antiemetics and experiences nausea and/or vomiting occurring within 2 hours after surgery Administration of a second intravenous dose of 4 mg ondansetron postoperatively in adult patients who received a 4 mg prophylactic dose does not provide additional control of nausea and vomiting [ see Clinical Studies (14.3)] , For pediatric patients (1 month to 12 years) prevention of nausea and vomiting was only studied in patients who had not received prophylactic ondansetron. Pediatric patients 1 month to 12 years and more than 40 kg 4 mg Infuse intravenously over at least 30 seconds preferably longer (over 2 to 5 minutes). Pediatric patients 1 month to 12 years and 40 kg or less 0.1 mg/kg Infuse intravenously over at least 30 seconds and preferably longer (over 2 to 5 minutes). Important Preparation Instructions Dilution of Ondansetron Injection, USP is not required before administration to adult and pediatric patients.Dilution of Ondansetron Injection, USP is not required before administration to adult and pediatric patients. Inspect Ondansetron Injection visually for particulate matter and discoloration before administration; discard if present.Inspect Ondansetron Injection visually for particulate matter and discoloration before administration; discard if present. 2.3 Dosage Adjustment for Patients with Hepatic Impairment In patients with severe hepatic impairment (Child-Pugh score of 10 or greater), a single maximal daily dose of 8 mg infused over 15 minutes beginning 30 minutes before the start of the emetogenic chemotherapy is recommended. There is no experience beyond first-day administration of ondansetron in these patients [ see Use in Specific Populations (8.6) ].

WARNINGS AND PRECAUTIONS • Hypersensitivity Reactions, Including Anaphylaxis and Bronchospasm : Discontinue ondansetron if suspected. Monitor and treat promptly per standard of care until signs and symptoms resolve. ( 5.1 ) • QT Interval Prolongation and Torsade de Pointes : Avoid ondansetron in patients with congenital long QT syndrome; monitor with electrocardiograms (ECGs) if concomitant electrolyte abnormalities, cardiac failure or arrhythmias, or use of other QT prolonging drugs. ( 5.2 ) • Serotonin Syndrome : Reported with 5-HT 3 receptor antagonists alone but particularly with concomitant use of serotonergic drugs. If such symptoms occur, discontinue ondansetron and initiate supportive treatment. If concomitant use of ondansetron with other serotonergic drugs is clinically warranted, patients should be made aware of a potential increased risk for serotonin syndrome. ( 5.3 ) • Myocardial Ischemia : Monitor or advise patients for signs and symptoms of myocardial ischemia after oral administration. ( 5.4 ) • Masking of Progressive Ileus and/or Gastric Distension Following Abdominal Surgery or Chemotherapy-Induced Nausea and Vomiting : Monitor for decreased bowel activity, particularly in patients with risk factors for gastrointestinal obstruction. ( 5.5 ) • Phenylketonuria: Patients should be informed that ondansetron orally disintegrating tablets contain phenylalanine (a component of aspartame). Each 4 mg orally disintegrating tablet contains 1.68 mg phenylalanine and 8 mg orally disintegrating tablet contains 3.37 mg phenylalanine. ( 5.6 ) 5.1 Hypersensitivity Reactions Hypersensitivity reactions, including anaphylaxis and bronchospasm, have been reported in patients who have exhibited hypersensitivity to other selective 5-HT 3 receptor antagonists. If hypersensitivity reactions occur, discontinue use of ondansetron; treat promptly per standard of care and monitor until signs and symptoms resolve [see Contraindications (4) ] . 5.2 QT Prolongation Electrocardiogram (ECG) changes, including QT interval prolongation have been seen in patients receiving ondansetron. In addition, postmarketing cases of Torsade de Pointes have been reported in patients using ondansetron. Avoid ondansetron in patients with congenital long QT syndrome. ECG monitoring is recommended in patients with electrolyte abnormalities (e.g., hypokalemia or hypomagnesemia), congestive heart failure, bradyarrhythmias, or patients taking other medicinal products that lead to QT prolongation [see Clinical Pharmacology (12.2) ] . 5.3 Serotonin Syndrome The development of serotonin syndrome has been reported with 5-HT 3 receptor antagonists alone. Most reports have been associated with concomitant use of serotonergic drugs (e.g., selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), monoamine oxidase inhibitors, mirtazapine, fentanyl, lithium, tramadol, and intravenous methylene blue). Some of the reported cases were fatal. Serotonin syndrome occurring with overdose of ondansetron alone has also been reported. The majority of reports of serotonin syndrome related to 5-HT 3 receptor antagonist use occurred in a post-anesthesia care unit or an infusion center. Symptoms associated with serotonin syndrome may include the following combination of signs and symptoms: mental status changes (e.g., agitation, hallucinations, delirium, and coma), autonomic instability (e.g., tachycardia, labile blood pressure, dizziness, diaphoresis, flushing, hyperthermia), neuromuscular symptoms (e.g., tremor, rigidity, myoclonus, hyperreflexia, incoordination), seizures, with or without gastrointestinal symptoms (e.g., nausea, vomiting, diarrhea). Patients should be monitored for the emergence of serotonin syndrome, especially with concomitant use of ondansetron and other serotonergic drugs. If symptoms of serotonin syndrome occur, discontinue ondansetron and initiate supportive treatment. Patients should be informed of the increased risk of serotonin syndrome, especially if ondansetron is used concomitantly with other serotonergic drugs [see Drug Interactions (7.1) , Overdosage (10) ] . 5.4 Myocardial Ischemia Myocardial ischemia has been reported in patients treated with ondansetron. In some cases, predominantly during intravenous administration, the symptoms appeared immediately after administration but resolved with prompt treatment. Coronary artery spasm appears to be the most common underlying cause. Therefore, monitor or advise patients for signs or symptoms of myocardial ischemia after oral administration of ondansetron [see Adverse Reactions (6.2) ]. 5.5 Masking of Progressive Ileus and Gastric Distension The use of ondansetron in patients following abdominal surgery or in patients with chemotherapy-induced nausea and vomiting may mask a progressive ileus and/or gastric distension. Monitor for decreased bowel activity, particularly in patients with risk factors for gastrointestinal obstruction. Ondansetron is not a drug that stimulates gastric or intestinal peristalsis. It should not be used instead of nasogastric suction. 5.6 Phenylketonuria Phenylketonuric patients should be informed that ondansetron orally disintegrating tablets contain phenylalanine (a component of aspartame). Each 4 mg orally disintegrating tablet contains 1.68 mg phenylalanine and 8 mg orally disintegrating tablet contains 3.37 mg phenylalanine.

CONTRAINDICATIONS Ondansetron Injection, USP is contraindicated for patients known to have hypersensitivity (e.g., anaphylaxis) to this product or any of its components. Anaphylactic reactions have been reported in patients taking ondansetron. [ See Adverse Reactions (6.2) ]. The concomitant use of apomorphine with ondansetron is contraindicated based on reports of profound hypotension and loss of consciousness when apomorphine was administered with ondansetron. Patients known to have hypersensitivity (e.g., anaphylaxis) to this product or any of its components. ( 4 ) Concomitant use of apomorphine. ( 4 , 7.2 )

DRUG INTERACTIONS 7.1 Drugs Affecting Cytochrome P-450 Enzymes Ondansetron does not appear to induce or inhibit the cytochrome P-450 drug-metabolizing enzyme system of the liver. Because ondansetron is metabolized by hepatic cytochrome P-450 drug-metabolizing enzymes (CYP3A4, CYP2D6, CYP1A2), inducers or inhibitors of these enzymes may change the clearance and, hence, the half-life of ondansetron [see Clinical Pharmacology (12.3) ] . On the basis of limited available data, no dosage adjustment is recommended for patients on these drugs. 7.2 Apomorphine Based on reports of profound hypotension and loss of consciousness when apomorphine was administered with ondansetron, the concomitant use of apomorphine with ondansetron is contraindicated [see Contraindications (4) ]. 7.3 Phenytoin, Carbamazepine, and Rifampin In patients treated with potent inducers of CYP3A4 (i.e., phenytoin, carbamazepine, and rifampin), the clearance of ondansetron was significantly increased and ondansetron blood concentrations were decreased. However, on the basis of available data, no dosage adjustment for ondansetron is recommended for patients on these drugs [see Clinical Pharmacology (12.3) ] . 7.4 Tramadol Although there are no data on pharmacokinetic drug interactions between ondansetron and tramadol, data from two small trials indicate that concomitant use of ondansetron may result in reduced analgesic activity of tramadol. Patients on concomitant ondansetron self administered tramadol more frequently in these trials, leading to an increased cumulative dose in patient-controlled administration (PCA) of tramadol. 7.5 Serotonergic Drugs Serotonin syndrome (including altered mental status, autonomic instability, and neuromuscular symptoms) has been described following the concomitant use of 5-HT 3 receptor antagonists and other serotonergic drugs, including selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs) [see Warnings and Precautions (5.3) ] . 7.6 Chemotherapy In humans, carmustine, etoposide, and cisplatin do not affect the pharmacokinetics of ondansetron. In a crossover trial in 76 pediatric patients, intravenous ondansetron did not increase blood levels of high-dose methotrexate. 7.7 Temazepam The coadministration of ondansetron had no effect on the pharmacokinetics and pharmacodynamics of temazepam. 7.8 Alfentanil and Atracurium Ondansetron does not alter the respiratory depressant effects produced by alfentanil or the degree of neuromuscular blockade produced by atracurium. Interactions with general or local anesthetics have not been studied. 7.5 Serotonergic Drugs Serotonin syndrome (including altered mental status, autonomic instability, and neuromuscular symptoms) has been described following the concomitant use of 5-HT 3 receptor antagonists and other serotonergic drugs, including selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs) [see Warnings and Precautions (5.3) ] .

ADVERSE REACTIONS The following clinically significant adverse reactions are described elsewhere in the labeling: • Hypersensitivity Reactions [see Warnings and Precautions (5.1) ] • QT Prolongation [see Warnings and Precautions (5.2) ] • Serotonin Syndrome [see Warnings and Precautions (5.3) ] • Myocardial Ischemia [see Warnings and Precautions, (5.4) ] • Masking of Progressive Ileus and Gastric Distention [see Warnings and Precautions (5.5) ] Chemotherapy-Induced Nausea and Vomiting: • The most common adverse reactions (≥ 7%) in adults are diarrhea, headache, and fever. ( 6.1 ) Postoperative Nausea and/or Vomiting: • The most common adverse reaction (≥ 10%) which occurs at a higher frequency compared with placebo in adults is headache. ( 6.1 ) • The most common adverse reaction (≥ 2 %) which occurs at a higher frequency compared with placebo in pediatric patients aged 1 to 24 months is diarrhea. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Hikma Pharmaceuticals USA Inc. at 1-877-845-0689 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. The following adverse reactions have been reported in clinical trials of adult patients treated with ondansetron, the active ingredient of intravenous Ondansetron Injection across a range of dosages. A causal relationship to therapy with Ondansetron Injection (ondansetron) was unclear in many cases. Chemotherapy-Induced Nausea and Vomiting Table 2. Adverse Reactions Reported in >5% of Adult Patients Who Received Ondansetron at a Dosage of Three 0.15-mg/kg Doses Adverse Reaction Number of Adult Patients With Reaction Ondansetron Injection 0.15 mg/kg x 3 (n = 419) Metoclopramide (n = 156) Placebo (n = 34) Diarrhea 16% 44% 18% Headache 17% 7% 15% Fever 8% 5% 3% Cardiovascular: Rare cases of angina (chest pain), electrocardiographic alterations, hypotension, and tachycardia have been reported. Gastrointestinal: Constipation has been reported in 11% of chemotherapy patients receiving multiday ondansetron. Hepatic: In comparative trials in cisplatin chemotherapy patients with normal baseline values of aspartate transaminase (AST) and alanine transaminase (ALT), these enzymes have been reported to exceed twice the upper limit of normal in approximately 5% of patients. The increases were transient and did not appear to be related to dose or duration of therapy. On repeat exposure, similar transient elevations in transaminase values occurred in some courses, but symptomatic hepatic disease did not occur. Integumentary: Rash has occurred in approximately 1% of patients receiving ondansetron. Neurological: There have been rare reports consistent with, but not diagnostic of, extrapyramidal reactions in patients receiving Ondansetron Injection, and rare cases of grand mal seizure. Other: Rare cases of hypokalemia have been reported. Postoperative Nausea and/or Vomiting The adverse reactions in Table 3 have been reported in ≥2% of adults receiving ondansetron at a dosage of 4 mg intravenous over 2 to 5 minutes in clinical trials. Table 3. Adverse Reactions Reported in ≥ 2% (and with Greater Frequency than the Placebo Group) of Adult Patients Receiving Ondansetron at a Dosage of 4 mg Intravenous Over 2 to 5 Minutes Adverse Reaction a,b Ondansetron Injection 4 mg Intravenous (n = 547) Placebo (n = 547) Headache 92 (17%) 77 (14%) Drowsiness/Sedation 44 (8%) 37 (7%) Injection-site reaction 21 (4%) 18 (3%) Fever 10 (2%) 6 (1%) Cold sensation 9 (2%) 8 (1%) Pruritus 9 (2%) 3 (<1%) Paresthesia 9 (2%) 2 (<1%) a Adverse reactions: Rates of these reactions were not significantly different in the ondansetron and placebo groups. b Patients were receiving multiple concomitant perioperative and postoperative medications. Pediatric Use: Rates of adverse reactions were similar in both the ondansetron and placebo groups in pediatric patients receiving ondansetron (a single 0.1-mg/kg dose for pediatric patients weighing 40 kg or less, or 4 mg for pediatric patients weighing more than 40 kg) administered intravenously over at least 30 seconds. Diarrhea was seen more frequently in patients taking Ondansetron Injection (2%) compared with placebo (<1%) in the 1-month to 24-month age-group. These patients were receiving multiple concomitant perioperative and postoperative medications. 6.2 Postmarketing Experience The following adverse reactions have been identified during postapproval use of ondansetron. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. The reactions have been chosen for inclusion due to a combination of their seriousness, frequency of reporting, or potential causal connection to ondansetron. Cardiovascular Arrhythmias (including ventricular and supraventricular tachycardia, premature ventricular contractions, and atrial fibrillation), bradycardia, electrocardiographic alterations (including second-degree heart block, QT/QTc interval prolongation, and ST segment depression), palpitations, and syncope. Rarely and predominantly with intravenous ondansetron, transient ECG changes, including QT/QTc interval prolongation have been reported [see Warnings and Precautions (5.2) ] . Myocardial ischemia was reported predominately with intravenous administration [see Warnings and Precautions (5.4) ] . General Flushing : Rare cases of hypersensitivity reactions, sometimes severe (e.g., anaphylactic reactions, angioedema, bronchospasm, cardiopulmonary arrest, hypotension, laryngeal edema, laryngospasm, shock, shortness of breath, stridor) have also been reported. A positive lymphocyte transformation test to ondansetron has been reported, which suggests immunologic sensitivity to ondansetron. Hepatobiliary Liver enzyme abnormalities have been reported. Liver failure and death have been reported in patients with cancer receiving concurrent medications, including potentially hepatotoxic cytotoxic chemotherapy and antibiotics. Local Reactions Pain, redness, and burning at site of injection. Lower Respiratory Hiccups. Neurological Oculogyric crisis, appearing alone, as well as with other dystonic reactions . Transient dizziness during or shortly after intravenous infusion. Skin Urticaria, Stevens-Johnson syndrome, and toxic epidermal necrolysis. Eye Disorders Cases of transient blindness, predominantly during intravenous administration, have been reported. These cases of transient blindness were reported to resolve within a few minutes up to 48 hours. Transient blurred vision, in some cases associated with abnormalities of accommodation, has also been reported. 6.2 Postmarketing Experience The following adverse reactions have been identified during postapproval use of ondansetron. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. The reactions have been chosen for inclusion due to a combination of their seriousness, frequency of reporting, or potential causal connection to ondansetron. Cardiovascular Arrhythmias (including ventricular and supraventricular tachycardia, premature ventricular contractions, and atrial fibrillation), bradycardia, electrocardiographic alterations (including second-degree heart block, QT/QTc interval prolongation, and ST segment depression), palpitations, and syncope. Rarely and predominantly with intravenous ondansetron, transient ECG changes, including QT/QTc interval prolongation have been reported [see Warnings and Precautions (5.2) ] . Myocardial ischemia was reported predominately with intravenous administratio

CLINICAL PHARMACOLOGY Pharmacodynamics Ondansetron is a selective 5-HT 3 receptor antagonist. While its mechanism of action has not been fully characterized, ondansetron is not a dopamine-receptor antagonist. Serotonin receptors of the 5-HT 3 type are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema. It is not certain whether ondansetron’s antiemetic action is mediated centrally, peripherally, or in both sites. However, cytotoxic chemotherapy appears to be associated with release of serotonin from the enterochromaffin cells of the small intestine. In humans, urinary 5-HIAA (5-hydroxyindoleacetic acid) excretion increases after cisplatin administration in parallel with the onset of emesis. The released serotonin may stimulate the vagal afferents through the 5-HT 3 receptors and initiate the vomiting reflex. In animals, the emetic response to cisplatin can be prevented by pretreatment with an inhibitor of serotonin synthesis, bilateral abdominal vagotomy and greater splanchnic nerve section, or pretreatment with a serotonin 5-HT 3 receptor antagonist. In normal volunteers, single intravenous doses of 0.15 mg/kg of ondansetron had no effect on esophageal motility, gastric motility, lower esophageal sphincter pressure, or small intestinal transit time. Multiday administration of ondansetron has been shown to slow colonic transit in normal volunteers. Ondansetron has no effect on plasma prolactin concentrations. Ondansetron does not alter the respiratory depressant effects produced by alfentanil or the degree of neuromuscular blockade produced by atracurium. Interactions with general or local anesthetics have not been studied. Pharmacokinetics Ondansetron is well absorbed from the gastrointestinal tract and undergoes some first-pass metabolism. Mean bioavailability in healthy subjects, following administration of a single 8 mg tablet, is approximately 56%. Ondansetron systemic exposure does not increase proportionately to dose. AUC from a 16 mg tablet was 24% greater than predicted from an 8 mg tablet dose. This may reflect some reduction of first-pass metabolism at higher oral doses. Bioavailability is also slightly enhanced by the presence of food but unaffected by antacids. Ondansetron is extensively metabolized in humans, with approximately 5% of a radiolabeled dose recovered as the parent compound from the urine. The primary metabolic pathway is hydroxylation on the indole ring followed by subsequent glucuronide or sulfate conjugation. Although some nonconjugated metabolites have pharmacologic activity, these are not found in plasma at concentrations likely to significantly contribute to the biological activity of ondansetron. In vitro metabolism studies have shown that ondansetron is a substrate for human hepatic cytochrome P-450 enzymes, including CYP1A2, CYP2D6, and CYP3A4. In terms of overall ondansetron turnover, CYP3A4 played the predominant role. Because of the multiplicity of metabolic enzymes capable of metabolizing ondansetron, it is likely that inhibition or loss of one enzyme (e.g., CYP2D6 genetic deficiency) will be compensated by others and may result in little change in overall rates of ondansetron elimination. Ondansetron elimination may be affected by cytochrome P-450 inducers. In a pharmacokinetic study of 16 epileptic patients maintained chronically on CYP3A4 inducers, carbamazepine, or phenytoin, reduction in AUC, C max , and T ½ of ondansetron was observed. 1 This resulted in a significant increase in clearance. However, on the basis of available data, no dosage adjustment for ondansetron is recommended (see PRECAUTIONS: Drug Interactions ). In humans, carmustine, etoposide, and cisplatin do not affect the pharmacokinetics of ondansetron. Gender differences were shown in the disposition of ondansetron given as a single dose. The extent and rate of ondansetron's absorption is greater in women than men. Slower clearance in women, a smaller apparent volume of distribution (adjusted for weight), and higher absolute bioavailability resulted in higher plasma ondansetron levels. These higher plasma levels may in part be explained by differences in body weight between men and women. It is not known whether these gender-related differences were clinically important. More detailed pharmacokinetic information is contained in Tables 1 and 2 taken from 2 studies. Table 1. Pharmacokinetics in Normal Volunteers: Single 8 mg Ondansetron Tablet Dose Age- group (years) Mean Weight (kg) n Peak Plasma Concentration (ng/mL) Time of Peak Plasma Concentration (h) Mean Elimination Half-life (h) Systemic Plasma Clearance L/h/kg Absolute Bioavailability 18-40 M F 69 62.7 6 5 26.2 42.7 2 1.7 3.1 3.5 0.403 0.354 0.483 0.663 61-74 M F 77.5 60.2 6 6 24.1 52.4 2.1 1.9 4.1 4.9 0.384 0.255 0.585 0.643 ≥75 M F 78 67.6 5 6 37 46.1 2.2 2.1 4.5 6.2 0.277 0.249 0.619 0.747 Table 2. Pharmacokinetics in Normal Volunteers: Single 24 mg Ondansetron Tablet Dose Age-group (years) Mean Weight (kg) n Peak Plasma Concentration (ng/mL) Time of Peak Plasma Concentration (h) Mean Elimination Half-life (h) 18-43 M F 84.1 71.8 8 8 125.8 194.4 1.9 1.6 4.7 5.8 A reduction in clearance and increase in elimination half-life are seen in patients over 75 years of age. In clinical trials with cancer patients, safety and efficacy were similar in patients over 65 years of age and those under 65 years of age; there was an insufficient number of patients over 75 years of age to permit conclusions in that age-group. No dosage adjustment is recommended in the elderly. In patients with mild-to-moderate hepatic impairment, clearance is reduced 2-fold and mean half-life is increased to 11.6 hours compared to 5.7 hours in normals. In patients with severe hepatic impairment (Child-Pugh 2 score of 10 or greater), clearance is reduced 2-fold to 3-fold and apparent volume of distribution is increased with a resultant increase in half-life to 20 hours. In patients with severe hepatic impairment, a total daily dose of 8 mg should not be exceeded. Due to the very small contribution (5%) of renal clearance to the overall clearance, renal impairment was not expected to significantly influence the total clearance of ondansetron. However, ondansetron oral mean plasma clearance was reduced by about 50% in patients with severe renal impairment (creatinine clearance <30 mL/min). This reduction in clearance is variable and was not consistent with an increase in half-life. No reduction in dose or dosing frequency in these patients is warranted. Plasma protein binding of ondansetron as measured in vitro was 70% to 76% over the concentration range of 10 to 500 ng/mL. Circulating drug also distributes into erythrocytes. Four and 8 mg doses of either ondansetron oral solution or ondansetron orally disintegrating tablets are bioequivalent to corresponding doses of ondansetron tablets and may be used interchangeably. One 24 mg ondansetron tablet is bioequivalent to and interchangeable with three 8 mg ondansetron tablets. Clinical Trials Chemotherapy-Induced Nausea and Vomiting Highly Emetogenic Chemotherapy In 2 randomized, double-blind, monotherapy trials, a single 24 mg ondansetron tablet was superior to a relevant historical placebo control in the prevention of nausea and vomiting associated with highly emetogenic cancer chemotherapy, including cisplatin ≥50 mg/m 2 . Steroid administration was excluded from these clinical trials. More than 90% of patients receiving a cisplatin dose ≥50 mg/m 2 in the historical placebo comparator experienced vomiting in the absence of antiemetic therapy. The first trial compared oral doses of ondansetron 24 mg once a day, 8 mg twice a day, and 32 mg once a day in 357 adult cancer patients receiving chemotherapy regimens containing cisplatin ≥50 mg/m 2 . A total of 66% of patients in the ondansetron 24 mg once-a-day group, 55% in the ondansetron 8 mg twice-a-day group, and 55% in the ondansetron 32 mg once-a-day