Revex

REVEX- nalmefene hydrochloride injection, solution
Baxter Healthcare Corporation

DESCRIPTION

REVEX (nalmefene hydrochloride injection), an opioid antagonist, is a 6-methylene analogue of naltrexone. The chemical structure is shown below:

Image from Drug Label Content

Molecular Formula: C 21 H25 NO3 •HCl

Molecular Weight: 375.9, CAS # 58895-64-0

Chemical Name: 17-(Cyclopropylmethyl)-4,5α-epoxy-6-methylenemorphinan-3,14-diol, hydrochloride salt.

Nalmefene hydrochloride is a white to off-white crystalline powder which is freely soluble in water up to 130 mg/mL and slightly soluble in chloroform up to 0.13 mg/mL, with a pK a of 7.6.

REVEX is available as a sterile solution for intravenous, intramuscular, and subcutaneous administration in two concentrations, containing 100 µg or 1.0 mg of nalmefene free base per mL. The 100 µg/mL concentration contains 110.8 µg of nalmefene hydrochloride and the 1.0 mg/mL concentration contains 1.108 mg of nalmefene hydrochloride per mL. Both concentrations contain 9.0 mg of sodium chloride per mL and the pH is adjusted to 3.9 with hydrochloric acid.

Concentrations and dosages of REVEX are expressed as the free base equivalent of nalmefene.

CLINICAL PHARMACOLOGY

Pharmacodynamics

REVEX prevents or reverses the effects of opioids, including respiratory depression, sedation, and hypotension. Pharmacodynamic studies have shown that REVEX has a longer duration of action than naloxone at fully reversing doses. REVEX has no opioid agonist activity.

REVEX is not known to produce respiratory depression, psychotomimetic effects, or pupillary constriction. No pharmacological activity was observed when REVEX was administered in the absence of opioid agonists.

REVEX has not been shown to produce tolerance, physical dependence, or abuse potential.

REVEX can produce acute withdrawal symptoms in individuals who are opioid dependent.

Pharmacokinetics

Nalmefene exhibited dose proportional pharmacokinetics following intravenous administration of 0.5 mg to 2.0 mg. Pharmacokinetic parameters for nalmefene after a 1 mg intravenous administration in adult male volunteers are listed in Table 1.

Table 1: Mean (CV%) Nalmefene Pharmacokinetic Parameters
In Adult Males Following a 1 mg Intravenous Dose
Parameter Young, N=18 Elderly, N=11
Age 19-32 62-80
Cp at 5 min. (ng/mL) 3.7 (29) 5.8 (38)
Vdss (L/kg) 8.6 (19) 8.6 (29)
Vc (L/kg) 3.9 (29) 2.8 (41)
AUC0 -inf (ng-hr/mL) 16.6 (27) 17.3 (14)
Terminal T½ (hr) 10.8 (48) 9.4 (49)
Clplasma (L/hr/kg) 0.8 (23) 0.8 (18)

Absorption

Nalmefene was completely bioavailable following intramuscular or subcutaneous administration in 12 male volunteers relative to intravenous nalmefene. The relative bioavailabilities of intramuscular and subcutaneous routes of administration were 101.5%± 8.1% (Mean ± SD) and 99.7%± 6.9%, respectively. Nalmefene will be administered primarily as an intravenous bolus, however, nalmefene can be given intra-muscularly (IM) or subcutaneously (SC) if venous access cannot be established. While the time to maximum plasma nalmefene concentration was 2.3 ± 1.1 hours following intramuscular and 1.5 ± 1.2 hours following subcutaneous administrations, therapeutic plasma concentrations are likely to be reached within 5-15 minutes after a 1 mg dose in an emergency. Because of the variability in the speed of absorption for IM& SC dosing, and the inability to titrate to effect, great care should be taken if repeated doses must be given by these routes.

Distribution

Following a 1 mg parenteral dose, nalmefene was rapidly distributed. In a study of brain receptor occupancy, a 1 mg dose of nalmefene blocked over 80% of brain opioid receptors within 5 minutes after administration. The apparent volumes of distribution centrally (Vc ) and at steady-state (Vdss ) are 3.9 ± 1.1 L/kg and 8.6 ± 1.7 L/kg, respectively. Ultrafiltration studies of nalmefene have demonstrated that 45% (CV 4.1%) is bound to plasma proteins over a concentration range of 0.1 to 2µg/mL. An in vitro determination of the distribution of nalmefene in human blood demonstrated that nalmefene distributed 67% (CV 8.7%) into red blood cells and 39% (CV 6.4%) into plasma. The whole blood to plasma ratio was 1.3 (CV 6.6%) over the nominal concentration range in whole blood from 0.376 to 30 ng/mL.

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