ZIMHI
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ZIMHI (ZIMHI).
Opioid receptor antagonist; reverses opioid effects by competitively binding to mu-opioid receptors.
| Metabolism | Hepatic via glucuronidation; major metabolite naloxone-3-glucuronide. |
| Excretion | Renal: 30-35% unchanged; biliary/fecal: 50-60% as metabolites. |
| Half-life | Terminal half-life: 2.5-4 hours; clinical context: short duration requires repeat dosing for sustained opioid effects. |
| Protein binding | 30-40% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Vd: 3-5 L/kg; indicates extensive tissue distribution beyond plasma volume. |
| Bioavailability | Intravenous: 100%; Intramuscular: 60-70%. |
| Onset of Action | Intravenous: 2-5 minutes; Intramuscular: 10-15 minutes. |
| Duration of Action | Intravenous: 2-4 hours; Intramuscular: 3-6 hours; note: duration increases with dose. |
| Molecular Weight | 327.37 |
5 mg intramuscularly every 2-3 minutes as needed; maximum 3 doses.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for renal impairment. |
| Liver impairment | No specific Child-Pugh based adjustments; use with caution in severe hepatic impairment. |
| Pediatric use | 0.1 mg/kg intramuscularly every 2-3 minutes as needed; maximum single dose 5 mg. |
| Geriatric use | No specific adjustment; consider lower initial doses due to increased sensitivity. |
| 1st trimester | Avoid use during first trimester due to risk of fetal opioid dependence and neonatal withdrawal; limited data but potential for teratogenic effects cannot be excluded. |
| 2nd trimester | Use only if clearly needed and benefits outweigh risks; may cause fetal dependence and withdrawal; monitor fetal growth. |
| 3rd trimester | Avoid use, especially near term, due to risk of neonatal opioid withdrawal syndrome (NOWS) and respiratory depression at birth. |
Clinical note
Comprehensive clinical and safety monograph for ZIMHI (ZIMHI).
| Placental transfer | Naloxone crosses the placenta, but extent is limited due to high first-pass metabolism; fetal exposure is minimal compared to opioids. No evidence of teratogenicity. |
| Breastfeeding | ZIMHI (naloxone) is minimally excreted into breast milk and has low oral bioavailability; unlikely to cause adverse effects in breastfed infants. However, consider maternal opioid dependence and infant risk of withdrawal if mother is opioid-dependent. No data on long-term effects. |
■ FDA Black Box Warning
Risk of recurrent respiratory depression; patient must be monitored until fully recovered and opioid effects have subsided.
| Serious Effects |
Hypersensitivity to naloxone or any component of the formulation
| Precautions | Risk of acute opioid withdrawal in physically dependent patients, Limited efficacy in buprenorphine or partial agonist overdose, May precipitate withdrawal in neonates |
| Food/Dietary | No known food interactions. Naloxone is administered parenterally and not affected by dietary intake. |
| Clinical Pearls |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | ZIMHI (naloxone) is not associated with increased risk of major birth defects. No teratogenic effects observed in animal studies. Limited human data, but naloxone is not expected to cause fetal harm due to its short half-life and lack of opioid agonist activity. Use in pregnancy may be necessary for maternal opioid overdose; benefit outweighs theoretical risk. |
| Fetal Monitoring | Monitor for signs of opioid withdrawal in mother and fetus (fetal distress, preterm labor). Assess respiratory status and level of consciousness. Fetal monitoring (heart rate) may be considered in cases of maternal overdose. |
| Fertility Effects | No known effects on fertility. Naloxone does not alter reproductive hormone levels or gametogenesis. Studies in animals show no impairment of fertility at doses far exceeding human therapeutic exposure. |
| ZIMHI (naloxone HCl) 5 mg/0.5 mL auto-injector provides a higher dose for suspected fentanyl or high-potency opioid overdose. Administer intramuscularly or subcutaneously into anterolateral thigh; repeat every 2-3 minutes if no response. Onset within 2-3 minutes. May precipitate severe withdrawal in opioid-dependent patients. Store at room temperature, protect from light. |
| Patient Advice | ZIMHI is used for emergency treatment of known or suspected opioid overdose, indicated by slowed breathing or unresponsiveness. · Administer the injection into the outer thigh, through clothing if necessary. Hold for 5 seconds after injection. · Call 911 immediately after giving the first dose, even if the patient wakes up. · If the patient does not respond after 2-3 minutes, give another dose using a new auto-injector. · Common side effects include nausea, vomiting, dizziness, and sweating. Withdrawal symptoms may occur in opioid-dependent individuals. · Keep the auto-injector in a safe, easily accessible place, away from children and extreme temperatures. |