DEXMEDETOMIDINE HYDROCHLORIDE (Page 4 of 7)

8.6 Hepatic Impairment

Since dexmedetomidine hydrochloride in 0.9% sodium chloride injection clearance decreases with increasing severity of hepatic impairment, dose reduction should be considered in patients with impaired hepatic function [see Dosage and Administration (2.2) and Clinical Pharmacology (12.3)].

9 DRUG ABUSE AND DEPENDENCE

9.1 Controlled Substance

Dexmedetomidine hydrochloride in 0.9% sodium chloride injection (dexmedetomidine hydrochloride) is not a controlled substance.

9.3 Dependence

The dependence potential of dexmedetomidine hydrochloride in 0.9% sodium chloride injection has not been studied in humans. However, since studies in rodents and primates have demonstrated that dexmedetomidine hydrochloride in 0.9% sodium chloride injection exhibits pharmacologic actions similar to those of clonidine, it is possible that dexmedetomidine hydrochloride in 0.9% sodium chloride injection may produce a clonidine-like withdrawal syndrome upon abrupt discontinuation [see Warnings and Precautions (5.5)].

10 OVERDOSAGE

The tolerability of dexmedetomidine hydrochloride in 0.9% sodium chloride injection was studied in one study in which healthy adult subjects were administered doses at and above the recommended dose of 0.2 to 0.7 mcg/kg/hr. The maximum blood concentration achieved in this study was approximately 13 times the upper boundary of the therapeutic range. The most notable effects observed in two subjects who achieved the highest doses were first degree atrioventricular block and second degree heart block. No hemodynamic compromise was noted with the atrioventricular block and the heart block resolved spontaneously within one minute.
Five adult patients received an overdose of dexmedetomidine hydrochloride in 0.9% sodium chloride injection in the intensive care unit sedation studies. Two of these patients had no symptoms reported; one patient received a 2 mcg/kg loading dose over 10 minutes (twice the recommended loading dose) and one patient received a maintenance infusion of 0.8 mcg/kg/hr. Two other patients who received a 2 mcg/kg loading dose over 10 minutes, experienced bradycardia and/or hypotension. One patient who received a loading bolus dose of undiluted dexmedetomidine hydrochloride in 0.9% sodium chloride injection (19.4 mcg/kg), had cardiac arrest from which he was successfully resuscitated.

11 DESCRIPTION

Dexmedetomidine hydrochloride in 0.9% Sodium Chloride Injection is a sterile, nonpyrogenic ready to use solution suitable for intravenous infusion. Dexmedetomidine hydrochloride is the S-enantiomer of medetomidine and is chemically described as (+)-4-(S)-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole monohydrochloride. Dexmedetomidine hydrochloride has a molecular weight of 236.7 and the empirical formula is C13 H16 N2 • HCl and the structural formula is:

dexmed-structure
(click image for full-size original)

Dexmedetomidine hydrochloride is a white or almost white powder that is freely soluble in water and has a pKa of 7.1. Its partition coefficient in-octanol: water at pH 7.4 is 2.89. Dexmedetomidine hydrochloride in 0.9% Sodium Chloride Injection is supplied as a clear, colorless, isotonic solution with a pH of 4.5 to 8.0. Each mL contains 4.72 mcg of dexmedetomidine hydrochloride equivalent to 4 mcg (0.004 mg) of dexmedetomidine, 1 mg of L-Methionine and 9 mg sodium chloride in water and is ready to be used. The solution is preservative-free.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Dexmedetomidine hydrochloride in 0.9% sodium chloride injection is a relatively selective alpha2 -adrenergic agonist with sedative properties. Alpha2 selectivity is observed in animals following slow intravenous infusion of low and medium doses (10-300 mcg/kg). Both alpha1 and alpha2 activity is observed following slow intravenous infusion of high doses (≥1000 mcg/kg) or with rapid intravenous administration.

12.2 Pharmacodynamics

In a study in healthy volunteers (N = 10), respiratory rate and oxygen saturation remained within normal limits and there was no evidence of respiratory depression when dexmedetomidine hydrochloride in 0.9% sodium chloride injection was administered by intravenous infusion at doses within the recommended dose range (0.2–0.7 mcg/kg/hr).

12.3 Pharmacokinetics

Following intravenous administration, dexmedetomidine exhibits the following pharmacokinetic parameters: a rapid distribution phase with a distribution half-life (t1/2 ) of approximately 6 minutes; a terminal elimination half-life (t1/2 ) of approximately 2 hours; and steady-state volume of distribution (Vss ) of approximately 118 liters. Clearance is estimated to be approximately 39 L/h. The mean body weight associated with this clearance estimate was 72 kg.

Dexmedetomidine exhibits linear pharmacokinetics in the dosage range of 0.2 to 0.7 mcg/kg/hr when administered by intravenous infusion for up to 24 hours. Table 8 shows the main pharmacokinetic parameters when dexmedetomidine hydrochloride in 0.9% sodium chloride injection was infused (after appropriate loading doses) at maintenance infusion rates of 0.17 mcg/kg/hr (target plasma concentration of 0.3 ng/mL) for 12 and 24 hours, 0.33 mcg/kg/hr (target plasma concentration of 0.6 ng/mL) for 24 hours, and 0.70 mcg/kg/hr (target plasma concentration of 1.25 ng/mL) for 24 hours.

Table 8: Mean ± SD Pharmacokinetic Parameters

Parameter Loading Infusion (min)/Total Infusion Duration (hrs)
10 min/12 hrs 10 min/24 hrs 10 min/24 hrs 35 min/24 hrs
Dexmedetomidine Target Plasma Concentration (ng/mL) and Dose (mcg/kg/hr)
0.3/0.17 0.3/0.17 0.6/0.33 1.25/0.70
t1/2 *, hour 1.78 ± 0.30 2.22 ± 0.59 2.23 ± 0.21 2.50 ± 0.61
CL, liter/hour 46.3 ± 8.3 43.1 ± 6.5 35.3 ± 6.8 36.5 ± 7.5
Vss , liter 88.7 ± 22.9 102.4 ± 20.3 93.6 ± 17.0 99.6 ± 17.8
Avg Css # , ng/mL 0.27 ± 0.05 0.27 ± 0.05 0.67 ± 0.10 1.37 ± 0.20

* Presented as harmonic mean and pseudo standard deviation.

# Mean Css = Average steady-state concentration of dexmedetomidine. The mean Css was calculated based on post-dose sampling from 2.5 to 9 hours samples for 12 hour infusion and post-dose sampling from 2.5 to 18 hours for 24 hour infusions.

The loading doses for each of the above indicated groups were 0.5, 0.5, 1 and 2.2 mcg/kg, respectively.

Dexmedetomidine pharmacokinetic parameters after dexmedetomidine hydrochloride in 0.9% sodium chloride injection maintenance doses of 0.2 to 1.4 mcg/kg/hr for >24 hours were similar to the PK parameters after dexmedetomidine hydrochloride in 0.9% sodium chloride injection maintenance dosing for < 24 hours in other studies. The values for clearance (CL), volume of distribution (V), and t1/2 were 39.4 L/hr, 152 L, and 2.67 hours, respectively.

Distribution

The steady-state volume of distribution (Vss ) of dexmedetomidine was approximately 118 liters. Dexmedetomidine protein binding was assessed in the plasma of normal healthy male and female subjects. The average protein binding was 94% and was constant across the different plasma concentrations tested. Protein binding was similar in males and females. The fraction of dexmedetomidine hydrochloride in 0.9% sodium chloride injection that was bound to plasma proteins was significantly decreased in subjects with hepatic impairment compared to healthy subjects.

The potential for protein binding displacement of dexmedetomidine by fentanyl, ketorolac, theophylline, digoxin and lidocaine was explored in vitro , and negligible changes in the plasma protein binding of dexmedetomidine hydrochloride in 0.9% sodium chloride injection were observed. The potential for protein binding displacement of phenytoin, warfarin, ibuprofen, propranolol, theophylline and digoxin by dexmedetomidine hydrochloride in 0.9% sodium chloride injection was explored in vitro and none of these compounds appeared to be significantly displaced by dexmedetomidine hydrochloride in 0.9% sodium chloride injection.

Metabolism

Dexmedetomidine undergoes almost complete biotransformation with very little unchanged dexmedetomidine excreted in urine and feces. Biotransformation involves both direct glucuronidation as well as cytochrome P450 mediated metabolism. The major metabolic pathways of dexmedetomidine are: direct N-glucuronidation to inactive metabolites; aliphatic hydroxylation (mediated primarily by CYP2A6 with a minor role of CYP1A2, CYP2E1, CYP2D6 and CYP2C19) of dexmedetomidine to generate 3­ hydroxy-dexmedetomidine, the glucuronide of 3-hydroxy-dexmedetomidine, and 3-carboxy­ dexmedetomidine; and N-methylation of dexmedetomidine to generate 3-hydroxy N-methyl­ dexmedetomidine, 3-carboxy N-methyl-dexmedetomidine, and dexmedetomidine-N-methyl O­ glucuronide.

Elimination

The terminal elimination half-life (t1/2 ) of dexmedetomidine is approximately 2 hours and clearance is estimated to be approximately 39 L/h. A mass balance study demonstrated that after nine days an average of 95% of the radioactivity, following intravenous administration of radiolabeled dexmedetomidine, was recovered in the urine and 4% in the feces. No unchanged dexmedetomidine was detected in the urine.

Approximately 85% of the radioactivity recovered in the urine was excreted within 24 hours after the infusion. Fractionation of the radioactivity excreted in urine demonstrated that products of N-glucuronidation accounted for approximately 34% of the cumulative urinary excretion. In addition, aliphatic hydroxylation of parent drug to form 3-hydroxy-dexmedetomidine, the glucuronide of 3-hydroxy-dexmedetomidine, and 3-carboxylic acid-dexmedetomidine together represented approximately 14% of the dose in urine. N-methylation of dexmedetomidine to form 3-hydroxy N-methyl dexmedetomidine, 3-carboxy N-methyl dexmedetomidine, and N-methyl O-glucuronide dexmedetomidine accounted for approximately 18% of the dose in urine. The N-Methyl metabolite itself was a minor circulating component and was undetected in urine. Approximately 28% of the urinary metabolites have not been identified.

Gender

There was no observed difference in dexmedetomidine hydrochloride in 0.9% sodium chloride injection pharmacokinetics due to gender.

Geriatrics

The pharmacokinetic profile of dexmedetomidine hydrochloride in 0.9% sodium chloride injection was not altered by age. There were no differences in the pharmacokinetics of dexmedetomidine hydrochloride in 0.9% sodium chloride injection in young (18–40 years), middle age (41–65 years), and elderly (>65 years) subjects.

Hepatic Impairment

In subjects with varying degrees of hepatic impairment (Child-Pugh Class A, B, or C), clearance values for dexmedetomidine hydrochloride in 0.9% sodium chloride injection were lower than in healthy subjects. The mean clearance values for patients with mild, moderate, and severe hepatic impairment were 74%, 64% and 53% of those observed in the normal healthy subjects, respectively. Mean clearances for free drug were 59%, 51% and 32% of those observed in the normal healthy subjects, respectively.

Although dexmedetomidine hydrochloride in 0.9% sodium chloride injection is dosed to effect, it may be necessary to consider dose reduction in subjects with hepatic impairment [see Dosage and Administration (2.2), Warnings and Precautions (5.7) ].

Renal Impairment

Dexmedetomidine pharmacokinetics (Cmax , Tmax , AUC, t1/2 , CL, and Vss ) were not significantly different in patients with severe renal impairment (creatinine clearance: <30 mL/min) compared to healthy subjects.

Drug Interactions

In vitro studies: In vitro studies in human liver microsomes demonstrated no evidence of cytochrome P450 mediated drug interactions that are likely to be of clinical relevance.

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