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Naloxone pharmacokinetics in the newborn
British Journal of Clinical Pharmacology
|June 1, 1980
Summary
Neonatal naloxone HCl pharmacokinetics were studied after intravenous and intramuscular administration. Intramuscular naloxone showed prolonged plasma levels, suggesting a longer duration of action in neonates.
Area of Science:
- Pharmacology
- Neonatal Medicine
- Pharmacokinetics
Background:
- Neonatal Abstinence Syndrome (NAS) is a significant concern.
- Naloxone is a crucial opioid antagonist used in neonatal care.
- Understanding naloxone's pharmacokinetic profile in neonates is essential for effective treatment.
Purpose of the Study:
- To determine plasma naloxone levels in neonates following intravenous (IV) and intramuscular (IM) administration.
- To compare the pharmacokinetic profiles of different naloxone doses and routes.
- To investigate the duration of action of naloxone in the neonatal population.
Main Methods:
- Radioimmunoassay (RIA) was used to measure plasma naloxone concentrations.
- Three groups of neonates received different naloxone HCl doses: 35 mcg IV (n=6), 70 mcg IV (n=6), and 200 mcg IM (n=17).
- Plasma samples were collected over 6-36 hours post-administration.
Main Results:
- Intravenous naloxone (35 and 70 mcg) reached peak levels of 4-15 ng/ml and 9-20 ng/ml respectively within 5-40 minutes, with a mean plasma half-life of 3.1 ± 0.5 hours.
- Intramuscular naloxone (200 mcg) achieved peak levels of 7-35 ng/ml between 0.5-2 hours.
- Plasma levels after IM administration remained elevated for longer, with levels at 24-36 hours comparable to levels 4 hours after IV administration.
Conclusions:
- Intravenous naloxone provides rapid but shorter-acting opioid antagonism in neonates.
- Intramuscular naloxone demonstrates a biphasic elimination with prolonged therapeutic levels.
- The prolonged plasma concentrations after IM naloxone suggest a potentially longer duration of action, which may be clinically advantageous for managing neonatal opioid withdrawal.