Mechanism of Action

Palonosetron is a 5-HT₃ receptor antagonist with a strong binding affinity for this receptor and little or no affinity for other receptors.

Cancer chemotherapy may be associated with a high incidence of nausea and vomiting, particularly when certain agents, such as cisplatin, are used. 5-HT₃ receptors are located on the nerve terminals of the vagus in the periphery and centrally in the chemoreceptor trigger zone of the area postrema. It is thought that chemotherapeutic agents produce nausea and vomiting by releasing serotonin from the enterochromaffin cells of the small intestine and that the released serotonin then activates 5-HT₃ receptors located on vagal afferents to initiate the vomiting reflex.

Pharmacodynamics

The effect of palonosetron on blood pressure, heart rate, and ECG parameters including QTc were comparable to ondansetron and dolasetron in clinical trials. In non-clinical studies palonosetron possesses the ability to block ion channels involved in ventricular de- and re-polarization and to prolong action potential duration. In clinical trials, the dose-response relationship to the QTc interval has not been fully evaluated.

Pharmacokinetics

After intravenous dosing of palonosetron in healthy subjects and cancer patients, an initial decline in plasma concentrations is followed by a slow elimination from the body. Mean maximum plasma concentration (Cmax) and area under the concentration-time curve (AUC_0-∞ ) are generally dose-proportional over the dose range of 0.3-90 mcg/kg in healthy subjects and in cancer patients. Following single IV dose of palonosetron at 3 mcg/kg (or 0.21 mg/70 kg) to six cancer patients, mean (±SD) maximum plasma concentration was estimated to be 5.6 ± 5.5 ng/mL and mean AUC was 35.8 ± 20.9 ng•hr/mL. Following IV administration of palonosetron 0.25 mg once every other day for 3 doses in 11 cancer patients, the mean increase in plasma palonosetron concentration from Day 1 to Day 5 was 42±34%. Following IV administration of palonosetron 0.25 mg once daily for 3 days in 12 healthy subjects, the mean (±SD) increase in plasma palonosetron concentration from Day 1 to Day 3 was 110±45%.

Distribution

Palonosetron has a volume of distribution of approximately 8.3 ± 2.5 L/kg. Approximately 62% of palonosetron is bound to plasma proteins.

Metabolism

Palonosetron is eliminated by multiple routes with approximately 50% metabolized to form two primary metabolites: N-oxide-palonosetron and 6-S-hydroxy-palonosetron. These metabolites each have less than 1% of the 5-HT₃ receptor antagonist activity of palonosetron. In vitro metabolism studies have suggested that CYP2D6 and to a lesser extent, CYP3A4 and CYP1A2 are involved in the metabolism of palonosetron. However, clinical pharmacokinetic parameters are not significantly different between poor and extensive metabolizers of CYP2D6 substrates.

Elimination

After a single intravenous dose of 10 mcg/kg [¹⁴C]-palonosetron, approximately 80% of the dose was recovered within 144 hours in the urine with palonosetron representing approximately 40% of the administered dose. In healthy subjects, the total body clearance of palonosetron was 160 ± 35 mL/h/kg and renal clearance was 66.5± 18.2 mL/h/kg. Mean terminal elimination half-life was approximately 40 hours.

Clinical studies

Efficacy of single-dose palonosetron injection in preventing acute and delayed nausea and vomiting induced by both moderately and highly emetogenic chemotherapy was studied in three Phase 3 trials and one Phase 2 trial. In these double-blind studies, complete response rates (no emetic episodes and no rescue medication) and other efficacy parameters were assessed through at least 120 hours after administration of chemotherapy. The safety and efficacy of palonosetron in repeated courses of chemotherapy was also assessed.

Moderately Emetogenic Chemotherapy

Two Phase 3, double-blind trials involving 1132 patients compared single-dose IV ALOXI (palonosetron hydrochloride) with either single-dose IV ondansetron (study 1) or dolasetron (study 2) given 30 minutes prior to moderately emetogenic chemotherapy including carboplatin, cisplatin ≤50 mg/m², cyclophosphamide <1500 mg/m², doxorubicin >25 mg/m², epirubicin, irinotecan, and methotrexate >250 mg/m². Concomitant corticosteroids were not administered prophylactically in study 1 and were used by 4-6% of patients in study 2. The majority of patients in these studies were women (77%), White (65%) and naïve to previous chemotherapy (54%). The mean age was 55 years.

Highly Emetogenic Chemotherapy

A Phase 2, double-blind, dose-ranging study evaluated the efficacy of single-dose IV palonosetron from 0.3 to 90 mcg/kg (equivalent to < 0.1 mg to 6 mg fixed dose) in 161 chemotherapy-naïve adult cancer patients receiving highly-emetogenic chemotherapy (either cisplatin 70 mg/m² or cyclophosphamide > 1100 mg/m²). Concomitant corticosteroids were not administered prophylactically. Analysis of data from this trial indicates that 0.25 mg is the lowest effective dose in preventing acute nausea and vomiting induced by highly emetogenic chemotherapy.

A Phase 3, double-blind trial involving 667 patients compared single-dose IV ALOXI (palonosetron hydrochloride) with single-dose IV ondansetron (study 3) given 30 minutes prior to highly emetogenic chemotherapy including cisplatin 60 mg/m², cyclophosphamide > 1500 mg/m², and dacarbazine. Corticosteroids were co-administered prophylactically before chemotherapy in 67% of patients. Of the 667 patients, 51% were women, 60% White, and 59% naïve to previous chemotherapy. The mean age was 52 years.

Efficacy Results

The antiemetic activity of ALOXI (palonosetron hydrochloride) was evaluated during the acute phase (0-24 hours) [Table 2], delayed phase (24-120 hours) [Table 3], and overall phase (0-120 hours) [Table 4] post-chemotherapy in Phase 3 trials.

Table 2: Prevention of Acute Nausea and Vomiting (0-24 hours): Complete Response Rates

Chemotherapy	Study	Treatment Group	N a	% with Complete Response	p-value b	97.5% Confidence Interval ALOXI (palonosetron hydrochloride) minus Comparator c
Moderately Emetogenic	1	ALOXI 0.25 mg	189	81	0.009
		Ondansetron 32 mg IV	185	69
	2	ALOXI 0.25 mg	189	63	NS
		Dolasetron 100 mg IV	191	53
Highly Emetogenic	3	ALOXI 0.25 mg	223	59	NS
		Ondansetron 32 mg IV	221	57
a Intent-to-treat cohort b 2-sided Fisher's exact test. Significance level at α=0.025. c These studies were designed to show non-inferiority. A lower bound greater than -15% demonstrates non-inferiority between ALOXI (palonosetron hydrochloride) and comparator.

These studies show that ALOXI (palonosetron hydrochloride) was effective in the prevention of acute nausea and vomiting associated with initial and repeat courses of moderately and highly emetogenic cancer chemotherapy. In study 3, efficacy was greater when prophylactic corticosteroids were administered concomitantly. Clinical superiority over other 5-HT3 receptor antagonists has not been adequately demonstrated in the acute phase.

Table 3: Prevention of Delayed Nausea and Vomiting (24-120 hours): Complete Response Rates

Chemotherapy	Study	Treatment Group	N a	% with Complete Response	p-value b	97.5% Confidence Interval ALOXI (palonosetron hydrochloride) minus Comparator c
Moderately Emetogenic	1	ALOXI 0.25 mg	189	74	<0.001
		Ondansetron 32 mg IV	185	55
	2	ALOXI 0.25 mg	189	54	0.004
		Dolasetron 100 mg IV	191	39
a Intent-to-treat cohort b 2-sided Fisher's exact test. Significance level at α=0.025. c These studies were designed to show non-inferiority. A lower bound greater than -15% demonstrates non-inferiority between ALOXI (palonosetron hydrochloride) and comparator.

These studies show that ALOXI (palonosetron hydrochloride) was effective in the prevention of delayed nausea and vomiting associated with initial and repeat courses of moderately emetogenic chemotherapy.

Table 4: Prevention of Overall Nausea and Vomiting (0-120 hours): Complete Response Rates

Chemotherapy	Study	Treatment Group	N a	% with Complete Response	p-value b	97.5% Confidence Interval ALOXI (palonosetron hydrochloride) minus Comparator c
Moderately Emetogenic	1	ALOXI 0.25 mg	189	69	<0.001
		Ondansetron32 mg IV	185	50
	2	ALOXI 0.25 mg	189	46	0.021
		Dolasetron 100 mg IV	191	34
a Intent-to-treat cohort b 2-sided Fisher's exact test. Significance level at α=0.025. c These studies were designed to show non-inferiority. A lower bound greater than -15% demonstrates non-inferiority between ALOXI (palonosetron hydrochloride) and comparator.

These studies show that ALOXI (palonosetron hydrochloride) was effective in the prevention of nausea and vomiting throughout the 120 hours (5 days) following initial and repeat courses of moderately emetogenic cancer chemotherapy.

Last reviewed on RxList: 9/27/2007
This monograph has been modified to include the generic and brand name in many instances.