Pharmacokinetics

In healthy volunteers and adult cancer patients undergoing chemotherapy, administration of Granisetron HCl Tablets produced mean pharmacokinetic data shown in Table 1.

Table 1 Pharmacokinetic Parameters (Median [range]). Following Granisetron HCl Tablets

Absorption

When Granisetron hydrochloride tablets were administered with food, AUC was decreased by 5% and Cmax increased by 30% in non-fasted healthy volunteers who received a single dose of 10 mg.

Distribution

Plasma protein binding is approximately 65% and granisetron distributes freely between plasma and red blood cells.

Metabolism

Granisetron metabolism involves N-demethylation and aromatic ring oxidation followed by conjugation. In vitro liver microsomal studies show that granisetron's major route of metabolism is inhibited by ketoconazole, suggestive of metabolism mediated by the cytochrome P-450 3A subfamily. Animal studies suggest that some of the metabolites may also have 5-HT3 receptor antagonist activity.

Elimination

Clearance is predominantly by hepatic metabolism. In normal volunteers, approximately 11% of the orally administered dose is eliminated unchanged in the urine in 48 hours. The remainder of the dose is excreted as metabolites, 48% in the urine and 38% in the feces.

Subpopulation

Gender
The effects of gender on the pharmacokinetics of Granisetron HCl Tablets have not been studied. However, after intravenous infusion of Granisetron HCl, no difference in mean AUC was found between males and females, although males had a higher Cmax generally.

In elderly and pediatric patients and in patients with renal failure or hepatic impairment, the pharmacokinetics of granisetron was determined following administration of intravenous granisetron hydrochloride.
 Elderly

The ranges of the pharmacokinetic parameters in elderly volunteers (mean age 71 years), given a single 40 mcg/kg intravenous dose of granisetron hydrochloride injection, were generally similar to those in younger healthy volunteers; mean values were lower for clearance and longer for half-life in the elderly.

  Renal Failure Patients

Total clearance of granisetron was not affected in patients with severe renal failure who received a single 40 mcg/kg intravenous dose of granisetron hydrochloride Injection.

 

Hepatically Impaired Patients: A pharmacokinetic study with intravenous granisetron hydrochloride in patients with hepatic impairment due to neoplastic liver involvement showed that total clearance was approximately halved compared to patients without hepatic impairment. Given the wide variability in pharmacokinetic parameters noted in patients and the good tolerance of doses well above the recommended dose, dosage adjustment in patients with possible hepatic functional impairment is not necessary.

 

Pediatric Patients: A pharmacokinetic study in pediatric cancer patients (2 to 16 years of age), given a single 40 mcg/kg intravenous dose of granisetron hydrochloride Injection, showed that volume of distribution and total clearance increased with age. No relationship with age was observed for peak plasma concentration or terminal phase plasma half-life. When volume of distribution and total clearance are adjusted for body weight, the pharmacokinetics of granisetron are similar in pediatric and adult cancer patients.

Chemotherapy-Induced Nausea and vomiting

Granisetron HCl Tablets prevent nausea and vomiting associated with initial and repeat courses of emetogenic cancer therapy, as shown by 24-hour efficacy data from studies using both moderately- and highly-emetogenic chemotherapy.

Moderately Emetogenic Chemotherapy
 
The first trial compared Granisetron HCl tablets doses of 0.25 mg to 2 mg bid, in 930 cancer patients receiving, principally, cyclophosphamide, carboplatin, and cisplatin (20 mg/m2 to 50 mg/m2). Efficacy was based on complete response (ie, no vomiting, no moderate or severe nausea, no rescue medication), no vomiting, and no nausea. Table 2 summarizes the results of this study. 

 
Results from a second double-blind, randomized trial evaluating Granisetron HCl Tablets 2 mg qd and Granisetron HCl Tablets 1 mg bid were compared to prochlorperazine 10 mg bid derived from a historical control. At 24 hours, there was no statistically significant difference in efficacy between the two Granisetron HCl Tablet regimens. Both regimens were statistically superior to the prochlorperazine control regimen (see Table 3).
 

 

Results from a Granisetron HCl Tablets 2 mg qd alone treatment arm in a third double-blind, randomized trial, were compared to prochlorperazine (PCPZ), 10 mg bid, derived from a historical control. The 24-hour results for Granisetron HCl Tablets 2 mg qd were statistically superior to PCPZ for all efficacy parameters: complete response (58%), no vomiting (79%), no nausea (51%), total control (49%). The PCPZ rates are shown in Table 3. 

Cisplatin -Based Chemotherapy

The first double-blind trial compared Granisetron HCl Tablets 1 mg bid, relative to placebo (historical control), in 119 cancer patients receiving high-dose cisplatin (mean dose 80 mg/m2). At 24 hours, Granisetron HCl Tablets 1 mg bid was significantly (P<0.001) superior to placebo (historical control) in all efficacy parameters: complete response (52%), no vomiting (56%) and no nausea (45%). The placebo rates were 7%, 14%, and 7%, respectively, for the three efficacy parameters.

 

Results from a Granisetron HCl Tablets 2 mg qd alone treatment arm in a second double-blind, randomized trial, were compared to both Granisetron HCl Tablets 1 mg bid and placebo historical controls. The 24-hour results for Granisetron HCl Tablets 2 mg qd were: complete response (44%), no vomiting (58%), no nausea (46%), total control (40%). The efficacy of Granisetron HCl Tablets 2 mg qd was comparable to Granisetron HCl Tablets 1 mg bid and statistically superior to placebo. The placebo rates were 7%, 14%, 7%, and 7%, respectively, for the four parameters.

No controlled study comparing granisetron injection with the oral formulation to prevent chemotherapy-induced nausea and vomiting has been performed.

Radiation-Induced Nausea and Vomiting

Total Body Irradiation
 In a double-blind randomized study, 18 patients receiving granisetron hydrochloride tablets, 2 mg daily, experienced significantly greater antiemetic protection compared to patients in a historical negative control group who received conventional (non-5-HT3 antagonist) antiemetics. Total body irradiation consisted of 11 fractions of 120 cGy administered over 4 days, with three fractions on each of the first 3 days, and two fractions on the fourth day. Granisetron HCl Tablets were given one hour before the first radiation fraction of each day.
 
Twenty-two percent (22%) of patients treated with Granisetron HCl Tablets did not experience vomiting or receive rescue antiemetics over the entire 4-day dosing period, compared to 0% of patients in the historical negative control group (P<0.01).
 
In addition, patients who received Granisetron HCl Tablets also experienced significantly fewer emetic episodes during the first day of radiation and over the 4-day treatment period, compared to patients in the historical negative control group. The median time to the first emetic episode was 36 hours for patients who received granisetron hydrochloride tablets. 

Fractionated Abdominal Radiation

The efficacy of Granisetron HCl Tablets, 2 mg daily, was evaluated in a double-blind, placebo-controlled randomized trial of 260 patients. Granisetron HCl Tablets were given 1 hour before radiation, composed of up to 20 daily fractions of 180 to 300 cGy each. The exceptions were patients with seminoma or those receiving whole abdomen irradiation who initially received 150 cGy per fraction. Radiation was administered to the upper abdomen with a field size of at least 100 cm2.

The proportion of patients without emesis and those without nausea for Granisetron HCl Tablets, compared to placebo, was statistically significant (P<0.0001) at 24 hours after radiation, irrespective of the radiation dose. Granisetron HCl was superior to placebo in patients receiving up to 10 daily fractions of radiation, but was not superior to placebo in patients receiving 20 fractions.

Patients treated with Granisetron HCl Tablets (n=134) had a significantly longer time to the first episode of vomiting (35 days vs. 9 days, P<0.001) relative to those patients who received placebo (n=126), and a significantly longer time to the first episode of nausea (11 days vs. 1 day, P<0.001). Granisetron HCl provided significantly greater protection from nausea and vomiting than placebo.

Drug Interactions

Granisetron does not induce or inhibit the cytochrome P-450 drug-metabolizing enzyme system in vitro. There have been no definitive drug-drug interaction studies to examine pharmacokinetic or pharmacodynamic interaction with other drugs; however, in humans, Granisetron hydrochloride Injection has been safely administered with drugs representing benzodiazepines, neuroleptics, and anti-ulcer medications commonly prescribed with antiemetic treatments. Granisetron hydrochloride Injection also does not appear to interact with emetogenic cancer chemotherapies. Because granisetron is metabolized by hepatic cytochrome P-450 drug-metabolizing enzymes, inducers or inhibitors of these enzymes may change the clearance and, hence, the half-life of granisetron. No specific interaction studies have been conducted in anesthetized patients. In addition, the activity of the cytochrome P-450 subfamily 3A4 (involved in the metabolism of some of the main narcotic analgesic agents) is not modified by granisetron hydrochloride in vitro.
 
In in vitro human microsomal studies, ketoconazole inhibited ring oxidation of Granisetron HCl. However, the clinical significance of in vivo pharmacokinetic interactions with ketoconazole is not known. In a human pharmacokinetic study, hepatic enzyme induction with phenobarbital resulted in a 25% increase in total plasma clearance of intravenous Granisetron HCl. The clinical significance of this change is not known.

Carcinogenesis, Mutagenesis, Impairment Of Fertility

In a 24-month carcinogenicity study, rats were treated orally with granisetron 1, 5 or 50 mg/kg/day (6, 30 or 300 mg/m2/day). The 50mg/kg/day dose was reduced to 25 mg/kg/day (150 mg/m2/day) during week 59 due to toxicity. For a 50 kg person of average height (1.46 m2 body surface area), these doses represent 4, 20, and 101 times the recommended clinical dose (1.48 mg/m2, oral) on a body surface area basis. There was a statistically significant increase in the incidence of hepatocellular carcinomas and adenomas in males treated with 5 mg/kg/day (30 mg/m2/day, 20 times the recommended human dose based on body surface area) and above, and in females treated with 25 mg/kg/day (150 mg/m2/day, 101 times the recommended human dose based on body surface area). No increase in liver tumors was observed at a dose of 1 mg/kg/day (6 mg/m2/day, 4 times the recommended human dose based on body surface area) in males and 5 mg/kg/day (30 mg/m2/day, 20 times the recommended human dose based on body surface area) in females. In a 12-month oral toxicity study, treatment with granisetron 100 mg/kg/day (600 mg/m2/day, 405 times the recommended human dose based on body surface area) produced hepatocellular adenomas in male and female rats while no such tumors were found in the control rats. A 24-month mouse carcinogenicity study of granisetron did not show a statistically significant increase in tumor incidence, but the study was not conclusive.

Because of the tumor findings in rat studies, granisetron hydrochloride should be prescribed only at the dose and for the indication recommended (see INDICATIONS AND USAGE, and DOSAGE AND ADMINISTRATION). 

Granisetron was not mutagenic in in vitro Ames test and mouse lymphoma cell forward mutation assay, and in vivo mouse micronucleus test and in vitro and ex vivo rat hepatocyte UDS assays. It, however, produced a significant increase in UDS in HeLa cells in vitro and a significant increased incidence of cells with polyploidy in an in vitro human lymphocyte chromosomal aberration test. 

Granisetron at oral doses up to 100 mg/kg/day (600 mg/m2/day, 405 times the recommended human dose based on body surface area) was found to have no effect on fertility and reproductive performance of male and female rats.

Pregnancy

Teratogenic Effects
 
Pregnancy Category B.
 
Reproduction studies have been performed in pregnant rats at oral doses up to 125 mg/kg/day (750 mg/m2/day, 507 times the recommended human dose based on body surface area) and pregnant rabbits at oral doses up to 32 mg/kg/day (378 mg/m2/day, 255 times the recommended human dose based on body surface area) and have revealed no evidence of impaired fertility or harm to the fetus due to granisetron. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

Nursing Mothers

It is not known whether granisetron is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Granisetron HCl is administered to a nursing woman.

Pediatric Use

Safety and effectiveness in pediatric patients have not been established.

Geriatric Use

During clinical trials, 325 patients 65 years of age or older received Granisetron HCl Tablets; 298 were 65 to 74 years of age, and 27 were 75 years of age or older. Efficacy and safety were maintained with increasing age.

Chemotherapy-Induced Nausea and Vomiting

Over 3700 patients have received Granisetron HCl Tablets in clinical trials with emetogenic cancer therapies consisting primarily of cyclophosphamide or cisplatin regimens.           

In patients receiving GranisetronHCl Tablets 1 mg bid for 1, 7 or 14 days, or 2 mg qd for 1 day, adverse experiences reported in more than 5% of the patients with comparator and placebo incidences are listed in Table 4.

Other adverse events reported in clinical trials were:

Table 4 Principal Adverse Events in Clinical Trials

Gastrointestinal:In single-day dosing studies in which adverse events were collected for 7 days, nausea (20%) and vomiting (12%) were recorded as adverse events after the 24-hour efficacy assessment period.

Hepatic:In comparative trials, elevation of AST and ALT (>2 times the upper limit of normal) following the administration of granisetron hydrochloride tablets occurred in 5% and 6% of patients, respectively. These frequencies were not significantly different from those seen with comparators (AST: 2%; ALT: 9%).

Cardiovascular:Hypertension (1%); hypotension, angina pectoris, atrial fibrillation, and syncope have been observed rarely.

Central Nervous System:Dizziness (5%), insomnia (5%), anxiety (2%), somnolence (1%). One case compatible with, but not diagnostic of, extrapyramidal symptoms have been reported in a patient treated with Granisetron HCl Tablets.

Hypersensitivity:Rare cases of hypersensitivity reactions, sometimes severe (eg, anaphylaxis, shortness of breath, hypotension, urticaria) have been reported.

Other:Fever (5%). Events often associated with chemotherapy also have been reported: leukopenia(9%), decreased appetite (6%), anemia (4%), alopecia (3%), thrombocytopenia (2%).

Over 5000 patients have received injectable granisetron hydrochloride in clinical trials.

Table 5gives the comparative frequencies of the five commonly reported adverse events (≥3%) in patients receiving granisetron hydrochloride Injection, 40 mcg/kg, in single-day chemotherapy trials. These patients received chemotherapy, primarily cisplatin, and intravenous fluids during the 24-hour period following granisetron hydrochloride Injection administration.

 
In the absence of a placebo group, there is uncertainty as to how many of these events should be attributed to granisetron hydrochloride, except for headache, which was clearly more frequent than in comparison groups.

Radiation-Induced Nausea and Vomiting

In controlled clinical trials, the adverse events reported by patients receiving Granisetron HCl Tablets and concurrent radiation were similar to those reported by patients receiving Granisetron HCl Tablets prior to chemotherapy. The most frequently reported adverse events were diarrhea, asthenia, and constipation. Headache, however, was less prevalent in this patient population.