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Evzio

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Evzio

CLINICAL PHARMACOLOGY

Mechanism Of Action

Naloxone hydrochloride is an opioid antagonist that antagonizes opioid effects by competing for the same receptor sites.

Naloxone hydrochloride reverses the effects of opioids, including respiratory depression, sedation, and hypotension. Also, it can reverse the psychotomimetic and dysphoric effects of agonist-antagonists such as pentazocine.

Pharmacodynamics

When naloxone hydrochloride is administered intravenously, the onset of action is generally apparent within two minutes. The time to onset of action is shorter for intravenous compared to subcutaneous or intramuscular routes of administration.

The duration of action is dependent upon the dose and route of administration of naloxone hydrochloride.

Pharmacokinetics

In one pharmacokinetic study in 30 healthy subjects, a single 0.4 mg subcutaneous or intramuscular naloxone injection administered using EVZIO provides equivalent naloxone AUC and 15% greater naloxone Cmax in comparison to a single 0.4 mg subcutaneous or intramuscular naloxone injection administered using a standard syringe.

Following a single EVZIO injection, the median Tmax of naloxone was reached at 15 minutes (range 5 minutes to 1.2 hours), with a mean (± SD) Cmax value of 1.24 (± 0.64) ng/mL. The mean (± SD) plasma half-life of naloxone in healthy adults was 1.28 (± 0.48) hours. In the same study, following administration of a single dose of 0.4 mg naloxone injection using a standard syringe, the median Tmax was 20 minutes (range 5 minutes to 2.03 hours) and the mean (± SD) Cmax value was 1.07 (± 0.48) ng/mL. The mean (± SD) plasma half-life was 1.36 (± 0.32) hours.

Distribution

Following parenteral administration, naloxone is distributed in the body and readily crosses the placenta. Plasma protein binding occurs but is relatively weak. Plasma albumin is the major binding constituent but significant binding of naloxone also occurs to plasma constituents other than albumin. It is not known whether naloxone is excreted into human milk.

Metabolism

Naloxone hydrochloride is metabolized in the liver, primarily by glucuronide conjugation with naloxone-3-glucoronide as the major metabolite.

Elimination

After an oral or intravenous dose, about 25-40% of naloxone is excreted as metabolites in urine within 6 hours, about 50% in 24 hours, and 60-70% in 72 hours. Following a single EVZIO injection, the mean (± SD) plasma half-life of naloxone in healthy adults was 1.28 (± 0.48) hours. In a neonatal study of naloxone injection, the mean (± SD) plasma half-life was observed to be 3.1 (± 0.5) hours.

Last reviewed on RxList: 4/14/2014
This monograph has been modified to include the generic and brand name in many instances.

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