Relistor

In a study of subjects with varying degrees of renal impairment receiving RELISTOR injection subcutaneously, there was a significant increase in the exposure to methylnaltrexone in subjects with moderate and severe renal impairment (creatinine clearance less than 60 mL/minute as estimated by Cockcroft-Gault) compared to healthy subjects

Therefore, a dosage reduction of RELISTOR tablets and RELISTOR injection is recommended in patients with moderate and severe renal impairment

Between the oral dosage range of 150 mg to 450 mg for RELISTOR tablets and the subcutaneous dosage range of 0.15 mg/kg to 0.50 mg/kg for RELISTOR injection, the mean C_maxand area under the plasma concentration-time curve (AUC) of methylnaltrexone increased in a dose-proportional manner. There was no significant accumulation of methylnaltrexone following once-daily oral dosing of 450 mg RELISTOR tablets or subcutaneous dosing of 12 mg RELISTOR injection for seven consecutive days in healthy subjects.

Following administration of a single 450 mg dose of RELISTOR tablets in OIC patients or healthy subjects, peak concentrations (C_max) of methylnaltrexone were observed at approximately 1.5 hours. The absolute bioavailability of oral methylnaltrexone bromide has not been determined. The C_maxand AUC in healthy subjects were 48.1 ng/mL and 382 ng·hr/mL, respectively, following a single 450 mg dose of RELISTOR tablets. Exposure in the OIC patient population was approximately 27% lower than in healthy subjects.

Administration of a single 450 mg dose of RELISTOR tablets to healthy subjects with a high-fat breakfast (containing approximately 800 to 1000 total calories, with 60%, 25% and 15% of calories derived from fat, carbohydrate and protein, respectively) resulted in a decrease in the C_maxof methylnaltrexone by 60%, the AUC by 43% and delayed the T_maxby 2 hours

Following administration of RELISTOR injection subcutaneously, methylnaltrexone achieved peak concentrations (C_max) at approximately 0.5 hours (see

The steady-state volume of distribution (Vss) of methylnaltrexone is approximately 1.1 L/kg. The fraction of methylnaltrexone bound to human plasma proteins is 11% to 15%, as determined by equilibrium dialysis.

Following oral administration of a single 450 mg dose of RELISTOR tablets, concentrations of methylnaltrexone declined in multiphasic manner with a terminal half-life (t_1/2) of approximately 15 hours.

In an intravenous mass balance study, approximately 44% of the administered radioactivity was recovered in the urine over 24 hours with 5 distinct metabolites. None of the detected metabolites was in amounts over 6% of administered radioactivity. Conversion to methyl-6-naltrexol isomers (5% of total) and methylnaltrexone sulfate (1% of total) appear to be the primary pathways of metabolism. N-demethylation of methylnaltrexone to produce naltrexone is not significant.

Systemic exposure of methylnaltrexone metabolites after oral administration of a single 450 mg dose of RELISTOR tablets are greater than the systemic exposure of methylnaltrexone metabolites after subcutaneous administration of a single 12 mg dose of RELISTOR injection. Subcutaneous administration is not subject to first-pass hepatic metabolism prior to appearance in the systemic circulation. After 12 mg subcutaneous once daily dosing the mean AUC_0-24ratio of metabolites to methylnaltrexone at steady-state was 30%, 19%, and 9% for methylnaltrexone sulfate, methyl-6α-naltrexol, and methyl-6β-naltrexol, respectively. After 450 mg oral once daily dosing, the ratio of the mean AUC_0-24of metabolites to methylnaltrexone at steady-state was 79%, 38%, and 21% for methylnaltrexone sulfate, methyl-6α-naltrexol, and methyl-6β-naltrexol, respectively. Methylnaltrexone sulfate is a weak mu-opioid receptor antagonist; methyl-6α-naltrexol, and methyl-6β-naltrexol are active mu-opioid receptor antagonists.

Methylnaltrexone is conjugated by sulfotransferase SULT1E1 and SULT2A1 isoforms to methylnaltrexone sulfate. Conversion to methyl-6-naltrexol isomers is mediated by aldo-keto reductase 1C enzymes.

In an intravenous mass balance study, approximately half of the dose was excreted in the urine (54%), and 17% of administered dose was excreted in the feces up to 168 hours postdose; however, radiolabeled recovery in this study was only 71% after 7 days. Methylnaltrexone is excreted primarily as the unchanged drug in the urine and feces. Active renal secretion of methylnaltrexone is suggested by renal clearance of methylnaltrexone that is approximately 4- to 5-fold higher than creatinine clearance.

No mass balance clinical studies were conducted with oral administration of methylnaltrexone bromide. However, following once daily dosing of 450 mg RELISTOR tablets for 1 week, the percentage of dose recovered in the urine as the parent methylnaltrexone was low (approximately 1% on both Day 1 and Day 7).

A study was conducted to characterize the pharmacokinetics of methylnaltrexone after a single dose of 24 mg methylnaltrexone bromide via intravenous infusion over 20 min in healthy adults between 18 and 45 years of age and in healthy adults aged 65 years and older. In elderly subjects (mean age 72 years old), mean clearance was about 20% lower (56 L/h versus 70 L/h) and AUC_∞was 26% higher than in subjects between 18 and 45 years of age (mean age 30 years old)

Administration of a single subcutaneous dose of 0.3 mg/kg of RELISTOR injection in subjects with varying degrees of renal impairment (8 subjects each cohort) resulted in a 1.3-, 1.7- and 1.9-fold higher AUC_0-∞of methylnaltrexone, respectively, compared to 8 subjects with normal renal function [

Administration of a single 450 mg dose of RELISTOR tablets in subjects with mild, moderate, and severe hepatic impairment (6 subjects each of Child-Pugh Class A, B, and C) resulted in a 1.7-, 4.8- and 3.8-fold higher C_maxof methylnaltrexone, respectively, compared to 6 subjects with normal liver function. The AUC_0-∞, was comparable between healthy subjects and subjects with mild hepatic impairment, but increased approximately 2.1-fold in subjects with moderate and severe hepatic impairment

Administration of a single dose of 0.3 mg/kg of RELISTOR injection subcutaneously in 8 subjects with mild hepatic impairment (Child-Pugh Class A) and 8 subjects with moderate hepatic impairment (Child-Pugh Class B) did not result in any meaningful change in the AUC or C_maxwhen compared to 8 healthy subjects with normal hepatic function. The effect of severe (Child-Pugh Class C) hepatic impairment on the pharmacokinetics of RELISTOR injection has not been studied

Based on the

A clinical drug interaction study in healthy adult subjects evaluated the effects of cimetidine, a drug that inhibits the active renal secretion of organic cations, on the pharmacokinetics of methylnaltrexone (24 mg administered as an intravenous infusion over 20 minutes). A single dose of methylnaltrexone bromide was administered before cimetidine dosing and with the last dose of cimetidine (400 mg every 8 hours for 6 days). Mean C_maxand AUC of methylnaltrexone increased by 10% with concomitant cimetidine administration. The renal clearance of methylnaltrexone decreased about 40%. This change is not considered to be clinically meaningful.

The recommended dosage of RELISTOR in patients with moderate and severe renal impairment (i.e., creatinine clearance less than 60 mL/minute as estimated by Cockcroft-Gault)

• RELISTOR tablets: 150 mg once daily in the morning.
• RELISTOR injection: 6 mg administered subcutaneously once daily

RELISTOR injection: The recommended dosage regimen is one dose every other day, as needed is shown in

*Calculate the injection volume for these patients by multiplying the patient weight in kilograms by 0.00375 and then rounding up the volume to the nearest 0.1 mL.

Between the oral dosage range of 150 mg to 450 mg for RELISTOR tablets and the subcutaneous dosage range of 0.15 mg/kg to 0.50 mg/kg for RELISTOR injection, the mean C_maxand area under the plasma concentration-time curve (AUC) of methylnaltrexone increased in a dose-proportional manner. There was no significant accumulation of methylnaltrexone following once-daily oral dosing of 450 mg RELISTOR tablets or subcutaneous dosing of 12 mg RELISTOR injection for seven consecutive days in healthy subjects.

Following administration of a single 450 mg dose of RELISTOR tablets in OIC patients or healthy subjects, peak concentrations (C_max) of methylnaltrexone were observed at approximately 1.5 hours. The absolute bioavailability of oral methylnaltrexone bromide has not been determined. The C_maxand AUC in healthy subjects were 48.1 ng/mL and 382 ng·hr/mL, respectively, following a single 450 mg dose of RELISTOR tablets. Exposure in the OIC patient population was approximately 27% lower than in healthy subjects.

Administration of a single 450 mg dose of RELISTOR tablets to healthy subjects with a high-fat breakfast (containing approximately 800 to 1000 total calories, with 60%, 25% and 15% of calories derived from fat, carbohydrate and protein, respectively) resulted in a decrease in the C_maxof methylnaltrexone by 60%, the AUC by 43% and delayed the T_maxby 2 hours

Following administration of RELISTOR injection subcutaneously, methylnaltrexone achieved peak concentrations (C_max) at approximately 0.5 hours (see

The steady-state volume of distribution (Vss) of methylnaltrexone is approximately 1.1 L/kg. The fraction of methylnaltrexone bound to human plasma proteins is 11% to 15%, as determined by equilibrium dialysis.

Following oral administration of a single 450 mg dose of RELISTOR tablets, concentrations of methylnaltrexone declined in multiphasic manner with a terminal half-life (t_1/2) of approximately 15 hours.

In an intravenous mass balance study, approximately 44% of the administered radioactivity was recovered in the urine over 24 hours with 5 distinct metabolites. None of the detected metabolites was in amounts over 6% of administered radioactivity. Conversion to methyl-6-naltrexol isomers (5% of total) and methylnaltrexone sulfate (1% of total) appear to be the primary pathways of metabolism. N-demethylation of methylnaltrexone to produce naltrexone is not significant.

Systemic exposure of methylnaltrexone metabolites after oral administration of a single 450 mg dose of RELISTOR tablets are greater than the systemic exposure of methylnaltrexone metabolites after subcutaneous administration of a single 12 mg dose of RELISTOR injection. Subcutaneous administration is not subject to first-pass hepatic metabolism prior to appearance in the systemic circulation. After 12 mg subcutaneous once daily dosing the mean AUC_0-24ratio of metabolites to methylnaltrexone at steady-state was 30%, 19%, and 9% for methylnaltrexone sulfate, methyl-6α-naltrexol, and methyl-6β-naltrexol, respectively. After 450 mg oral once daily dosing, the ratio of the mean AUC_0-24of metabolites to methylnaltrexone at steady-state was 79%, 38%, and 21% for methylnaltrexone sulfate, methyl-6α-naltrexol, and methyl-6β-naltrexol, respectively. Methylnaltrexone sulfate is a weak mu-opioid receptor antagonist; methyl-6α-naltrexol, and methyl-6β-naltrexol are active mu-opioid receptor antagonists.

Methylnaltrexone is conjugated by sulfotransferase SULT1E1 and SULT2A1 isoforms to methylnaltrexone sulfate. Conversion to methyl-6-naltrexol isomers is mediated by aldo-keto reductase 1C enzymes.

In an intravenous mass balance study, approximately half of the dose was excreted in the urine (54%), and 17% of administered dose was excreted in the feces up to 168 hours postdose; however, radiolabeled recovery in this study was only 71% after 7 days. Methylnaltrexone is excreted primarily as the unchanged drug in the urine and feces. Active renal secretion of methylnaltrexone is suggested by renal clearance of methylnaltrexone that is approximately 4- to 5-fold higher than creatinine clearance.

No mass balance clinical studies were conducted with oral administration of methylnaltrexone bromide. However, following once daily dosing of 450 mg RELISTOR tablets for 1 week, the percentage of dose recovered in the urine as the parent methylnaltrexone was low (approximately 1% on both Day 1 and Day 7).

A study was conducted to characterize the pharmacokinetics of methylnaltrexone after a single dose of 24 mg methylnaltrexone bromide via intravenous infusion over 20 min in healthy adults between 18 and 45 years of age and in healthy adults aged 65 years and older. In elderly subjects (mean age 72 years old), mean clearance was about 20% lower (56 L/h versus 70 L/h) and AUC_∞was 26% higher than in subjects between 18 and 45 years of age (mean age 30 years old)

Administration of a single subcutaneous dose of 0.3 mg/kg of RELISTOR injection in subjects with varying degrees of renal impairment (8 subjects each cohort) resulted in a 1.3-, 1.7- and 1.9-fold higher AUC_0-∞of methylnaltrexone, respectively, compared to 8 subjects with normal renal function [

Administration of a single 450 mg dose of RELISTOR tablets in subjects with mild, moderate, and severe hepatic impairment (6 subjects each of Child-Pugh Class A, B, and C) resulted in a 1.7-, 4.8- and 3.8-fold higher C_maxof methylnaltrexone, respectively, compared to 6 subjects with normal liver function. The AUC_0-∞, was comparable between healthy subjects and subjects with mild hepatic impairment, but increased approximately 2.1-fold in subjects with moderate and severe hepatic impairment

Administration of a single dose of 0.3 mg/kg of RELISTOR injection subcutaneously in 8 subjects with mild hepatic impairment (Child-Pugh Class A) and 8 subjects with moderate hepatic impairment (Child-Pugh Class B) did not result in any meaningful change in the AUC or C_maxwhen compared to 8 healthy subjects with normal hepatic function. The effect of severe (Child-Pugh Class C) hepatic impairment on the pharmacokinetics of RELISTOR injection has not been studied

Based on the

A clinical drug interaction study in healthy adult subjects evaluated the effects of cimetidine, a drug that inhibits the active renal secretion of organic cations, on the pharmacokinetics of methylnaltrexone (24 mg administered as an intravenous infusion over 20 minutes). A single dose of methylnaltrexone bromide was administered before cimetidine dosing and with the last dose of cimetidine (400 mg every 8 hours for 6 days). Mean C_maxand AUC of methylnaltrexone increased by 10% with concomitant cimetidine administration. The renal clearance of methylnaltrexone decreased about 40%. This change is not considered to be clinically meaningful.

Between the oral dosage range of 150 mg to 450 mg for RELISTOR tablets and the subcutaneous dosage range of 0.15 mg/kg to 0.50 mg/kg for RELISTOR injection, the mean C_maxand area under the plasma concentration-time curve (AUC) of methylnaltrexone increased in a dose-proportional manner. There was no significant accumulation of methylnaltrexone following once-daily oral dosing of 450 mg RELISTOR tablets or subcutaneous dosing of 12 mg RELISTOR injection for seven consecutive days in healthy subjects.

Following administration of a single 450 mg dose of RELISTOR tablets in OIC patients or healthy subjects, peak concentrations (C_max) of methylnaltrexone were observed at approximately 1.5 hours. The absolute bioavailability of oral methylnaltrexone bromide has not been determined. The C_maxand AUC in healthy subjects were 48.1 ng/mL and 382 ng·hr/mL, respectively, following a single 450 mg dose of RELISTOR tablets. Exposure in the OIC patient population was approximately 27% lower than in healthy subjects.

Administration of a single 450 mg dose of RELISTOR tablets to healthy subjects with a high-fat breakfast (containing approximately 800 to 1000 total calories, with 60%, 25% and 15% of calories derived from fat, carbohydrate and protein, respectively) resulted in a decrease in the C_maxof methylnaltrexone by 60%, the AUC by 43% and delayed the T_maxby 2 hours

Following administration of RELISTOR injection subcutaneously, methylnaltrexone achieved peak concentrations (C_max) at approximately 0.5 hours (see

The steady-state volume of distribution (Vss) of methylnaltrexone is approximately 1.1 L/kg. The fraction of methylnaltrexone bound to human plasma proteins is 11% to 15%, as determined by equilibrium dialysis.

Following oral administration of a single 450 mg dose of RELISTOR tablets, concentrations of methylnaltrexone declined in multiphasic manner with a terminal half-life (t_1/2) of approximately 15 hours.

In an intravenous mass balance study, approximately 44% of the administered radioactivity was recovered in the urine over 24 hours with 5 distinct metabolites. None of the detected metabolites was in amounts over 6% of administered radioactivity. Conversion to methyl-6-naltrexol isomers (5% of total) and methylnaltrexone sulfate (1% of total) appear to be the primary pathways of metabolism. N-demethylation of methylnaltrexone to produce naltrexone is not significant.

Systemic exposure of methylnaltrexone metabolites after oral administration of a single 450 mg dose of RELISTOR tablets are greater than the systemic exposure of methylnaltrexone metabolites after subcutaneous administration of a single 12 mg dose of RELISTOR injection. Subcutaneous administration is not subject to first-pass hepatic metabolism prior to appearance in the systemic circulation. After 12 mg subcutaneous once daily dosing the mean AUC_0-24ratio of metabolites to methylnaltrexone at steady-state was 30%, 19%, and 9% for methylnaltrexone sulfate, methyl-6α-naltrexol, and methyl-6β-naltrexol, respectively. After 450 mg oral once daily dosing, the ratio of the mean AUC_0-24of metabolites to methylnaltrexone at steady-state was 79%, 38%, and 21% for methylnaltrexone sulfate, methyl-6α-naltrexol, and methyl-6β-naltrexol, respectively. Methylnaltrexone sulfate is a weak mu-opioid receptor antagonist; methyl-6α-naltrexol, and methyl-6β-naltrexol are active mu-opioid receptor antagonists.

Methylnaltrexone is conjugated by sulfotransferase SULT1E1 and SULT2A1 isoforms to methylnaltrexone sulfate. Conversion to methyl-6-naltrexol isomers is mediated by aldo-keto reductase 1C enzymes.

In an intravenous mass balance study, approximately half of the dose was excreted in the urine (54%), and 17% of administered dose was excreted in the feces up to 168 hours postdose; however, radiolabeled recovery in this study was only 71% after 7 days. Methylnaltrexone is excreted primarily as the unchanged drug in the urine and feces. Active renal secretion of methylnaltrexone is suggested by renal clearance of methylnaltrexone that is approximately 4- to 5-fold higher than creatinine clearance.

No mass balance clinical studies were conducted with oral administration of methylnaltrexone bromide. However, following once daily dosing of 450 mg RELISTOR tablets for 1 week, the percentage of dose recovered in the urine as the parent methylnaltrexone was low (approximately 1% on both Day 1 and Day 7).

A study was conducted to characterize the pharmacokinetics of methylnaltrexone after a single dose of 24 mg methylnaltrexone bromide via intravenous infusion over 20 min in healthy adults between 18 and 45 years of age and in healthy adults aged 65 years and older. In elderly subjects (mean age 72 years old), mean clearance was about 20% lower (56 L/h versus 70 L/h) and AUC_∞was 26% higher than in subjects between 18 and 45 years of age (mean age 30 years old)

Administration of a single subcutaneous dose of 0.3 mg/kg of RELISTOR injection in subjects with varying degrees of renal impairment (8 subjects each cohort) resulted in a 1.3-, 1.7- and 1.9-fold higher AUC_0-∞of methylnaltrexone, respectively, compared to 8 subjects with normal renal function [

Administration of a single 450 mg dose of RELISTOR tablets in subjects with mild, moderate, and severe hepatic impairment (6 subjects each of Child-Pugh Class A, B, and C) resulted in a 1.7-, 4.8- and 3.8-fold higher C_maxof methylnaltrexone, respectively, compared to 6 subjects with normal liver function. The AUC_0-∞, was comparable between healthy subjects and subjects with mild hepatic impairment, but increased approximately 2.1-fold in subjects with moderate and severe hepatic impairment

Administration of a single dose of 0.3 mg/kg of RELISTOR injection subcutaneously in 8 subjects with mild hepatic impairment (Child-Pugh Class A) and 8 subjects with moderate hepatic impairment (Child-Pugh Class B) did not result in any meaningful change in the AUC or C_maxwhen compared to 8 healthy subjects with normal hepatic function. The effect of severe (Child-Pugh Class C) hepatic impairment on the pharmacokinetics of RELISTOR injection has not been studied

Based on the

A clinical drug interaction study in healthy adult subjects evaluated the effects of cimetidine, a drug that inhibits the active renal secretion of organic cations, on the pharmacokinetics of methylnaltrexone (24 mg administered as an intravenous infusion over 20 minutes). A single dose of methylnaltrexone bromide was administered before cimetidine dosing and with the last dose of cimetidine (400 mg every 8 hours for 6 days). Mean C_maxand AUC of methylnaltrexone increased by 10% with concomitant cimetidine administration. The renal clearance of methylnaltrexone decreased about 40%. This change is not considered to be clinically meaningful.

• RELISTOR tablets: The recommended dosage in adult patients with moderate or severe hepatic impairment (Child-Pugh Class B or C) is 150 mg, once daily in the morning [
  see Use in Specific Populations ].
• RELISTOR injection: If considering dose adjustment for patients with severe hepatic impairment, follow the recommendations in
  Table 3
  [see Use in Specific Populations ].

* Calculate the injection volume for these patients by multiplying the patient weight in kilograms by 0.00375 and then rounding up the volume to the nearest 0.1 mL.