Age and gender effects on ondansetron pharmacokinetics: evaluation of healthy aged volunteers

Oral ondansetron pharmacokinetics: the effect of chemotherapy

The effect of a typical 5-day chemotherapy treatment with cisplatin (20-40 mg/m2 per day) and 5-fluorouracil (5-FU, 1 gm/m2 per day) on the pharmacokinetics of ondansetron was investigated. Twenty cancer patients received 8 mg of ondansetron in three periods, including an oral tablet on day 1, an intravenous infusion on day 4, and an oral tablet on day 5. Absolute bioavailability after the oral dosing on day 1 was 87.5 +/- 31.3%, and on day 5 was 85.2 +/- 22.1% (P > .05). Mean values of AUC, Cmax, Tmax, and half life on days 1 and 5 were 399 +/- 275 and 381 +/- 222 ng.hour/mL, 53.3 +/- 26.8 and 43.6 +/- 21.7 ng/mL, 1.9 +/- 1.4 and 2 +/- 1.4 hours, and 5.21 +/- 1.78 and 6.19 +/- 1.99 hours, respectively. These values were not significantly different (P > .05). In summary, this study showed that cisplatin and 5-FU did not significantly alter the pharmacokinetics of oral ondansetron in cancer patients during the 5 days of chemotherapy. Oral bioavailability of ondansetron appeared to be greater in cancer patients than in healthy subjects.

Ondansetron absorption in adults: effect of dosage form, food, and antacids

Ondansetron is a competitive serotonin 5-HT3 receptor blocker that has proved useful in the prevention of emesis due to cisplatin and other cancer chemotherapeutic agents. In a randomized, open-label, crossover study in 24 healthy male subjects, the relative bioavailability of a single 8-mg tablet was compared with that of an 8-mg solution using the two one-sided t-tests. The tablet and solution formulations were bioequivalent, as confirmed by similarities in mean Cmax (26.3 vs 27.7 ng/mL), Tmax (1.79 vs 1.70 h), and AUC (166.0 vs 167.3 ng.h/mL) values. In another randomized, open-label, crossover study in 12 healthy male subjects, the bioavailability of an 8-mg ondansetron tablet administered 5 min after a standard meal was slightly but significantly greater than in fasted subjects, as indicated by comparative mean AUC values [201.4 ng.h/mL (fed) vs 172.5 ng.h/mL (fasted)]. Coadministration of a magnesium hydroxide/aluminum hydroxide antacid did not affect the bioavailability of the ondansetron tablet.

The pharmacokinetics of ondansetron after intravenous injection in healthy volunteers phenotyped as poor or extensive metabolisers of debrisoquine

The pharmacokinetics of the 5-HT3 receptor antagonist ondansetron following an 8 mg i.v. dose were investigated in 12 subjects previously phenotyped with debrisoquine. Six subjects were poor metabolisers (debrisoquine metabolic ratios 29-131) and six were extensive metabolisers (debrisoquine metabolic ratios 0.45-3.4). There was no significant difference in AUC, Cmax, CL or t1/2 between the poor and extensive metabolisers. It is concluded that ondansetron clearance is not mediated exclusively by cytochrome P-450 2D6.

Comparison of the pharmacokinetics of an ondansetron solution (8 mg) when administered intravenously, orally, to the colon, and to the rectum

Ondansetron, an antagonist of the serotonin type 3 (5-HT3) receptor, is indicated for the treatment of chemotherapy-induced emesis. This study compares the pharmacokinetics, especially the bioavailability, of an ondansetron 8-mg solution when administered intravenously, orally, to the colon via nasogastric intubation, and to the rectum using a retention enema. Six healthy, male volunteers received ondansetron infused into the colon during the first treatment period. These subjects then received the remaining three treatments in random order, with a minimum 1-week washout period between treatments. Serial plasma samples were obtained for up to 24 hr after dosing in each treatment period. Absolute bioavailability after the oral dosing, colonic infusion, and rectal administration averaged 71 +/- 14, 74 +/- 26, and 58 +/- 18%, respectively. These values were not significantly different (P > 0.05). Values of Tmax and Cmax were also not significantly different among the nonparenteral routes. Mean absorption half-lives were 0.66, 1.1, and 0.75 hr after the oral, colonic, and rectal administrations, respectively. These results indicate that ondansetron is well absorbed in the intestinal segments studied including the upper small intestine, the colon, and the rectum and that sustained-release and suppository formulations of ondansetron are feasible.

Ondansetron. An update of its therapeutic use in chemotherapy-induced and postoperative nausea and vomiting

Ondansetron is a selective 5-HT3 receptor antagonist which has previously been reported in the Journal to be a promising new agent for use as prophylaxis against nausea and vomiting caused by chemotherapy and radiotherapy. Since the publication of this original review, further studies have been published that show ondansetron to be an effective antiemetic agent in patients receiving chemotherapy and radiotherapy. Several studies have shown ondansetron to be a more effective antiemetic agent than high-dose metoclopramide in patients with emesis induced by high- and low-dose cisplatin treatment, and noncisplatin chemotherapy-induced emesis. The drug as mono-therapy does not appear to offer any advantage over alternative therapies against delayed high-dose cisplatin-induced nausea and vomiting; however, extremely limited data suggest that ondansetron plus dexamethasone may be useful in this indication. Trials have shown combination therapy with ondansetron and dexamethasone to be significantly more effective than both ondansetron monotherapy and a standard antiemetic regimen comprising metoclopramide, dexamethasone and diphenhydramine against acute high-dose cisplatin-induced emesis. Results from a number of small scale trials suggest that ondansetron may be an effective treatment for chemotherapy-induced emesis refractory to conventional antiemetic therapy. Ondansetron also appears to be more effective against refractory emesis induced by noncisplatin chemotherapy than that induced by cisplatin chemotherapy. Several trials have shown ondansetron to be more effective than placebo as prophylaxis against postoperative nausea and vomiting; a further trial has shown single-dose ondansetron to be significantly more effective than single-dose droperidol or metoclopramide in this indication. In addition, several trials have shown ondansetron to be more effective than placebo as treatment for nausea and vomiting that has commenced postoperatively. The overall incidence of adverse events in ondansetron recipients during chemotherapy-induced emesis studies was 36%. Headache and constipation are the most common adverse events during ondansetron therapy. Thus, recent data affirms the efficacy of ondansetron in the treatment of acute chemotherapy-induced nausea and vomiting and shows it to be especially efficacious when combined with dexamethasone. It appears that the drug will also have a substantial role in the prophylaxis and treatment of postoperative nausea and vomiting.

The pharmacokinetics of intravenous ondansetron in patients with hepatic impairment

The pharmacokinetics of the 5-HT3 receptor antagonist ondansetron were investigated following a single 8 mg intravenous dose given over 5 min in 19 patients with varying degrees of hepatic impairment and in six young healthy subjects. In comparison with the healthy controls, the patients with severe hepatic impairment had a lower mean plasma clearance (96 ml min-1 vs 478 ml min-1) and increased AUC (1383 ng ml-1 h vs 279 ng ml-1 h) and t1/2 (21 h vs 3.6 h). These differences were all statistically significant (P < 0.001). The corresponding values for patients with mild or moderate hepatic impairment fell between these extremes. Vss was greater in all patient groups than the control group, but the magnitude of the change was smaller than for the other parameters and did not reflect the increasing severity of hepatic impairment. There were no significant changes in Cmax. There were no drug-related adverse events in the patients studied. It is recommended that the dosing frequency of ondansetron be limited to once daily in patients with severe hepatic impairment.