Melatonin half life
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Melatonin Half-Life: A Comprehensive Overview
Introduction to Melatonin Half-Life
Melatonin, a hormone primarily secreted by the pineal gland, plays a crucial role in regulating circadian rhythms and sleep-wake cycles. Understanding its half-life is essential for optimizing its therapeutic use in various clinical settings, including sleep disorders and neuroprotection.
Melatonin Half-Life in Different Species
Melatonin Half-Life in Rats
Research on melatonin half-life in rats has shown variability depending on the method of measurement. In one study, the half-life of melatonin in rat plasma was found to be 23 minutes when measured using tritiated melatonin and 17 minutes using radioimmunoassay (RIA) .
Melatonin Half-Life in Humans
General Population
In humans, the half-life of melatonin varies significantly based on the formulation and dosage. For instance, after oral administration of melatonin in gelatin capsules, the elimination half-life ranged from 0.54 to 0.67 hours . Another study reported a half-life of approximately 0.45 to 1 hour, with extensive inactivation occurring in the liver .
Older Adults
In older adults, the pharmacokinetics of melatonin can differ due to altered metabolism. A study comparing low-dose (0.4 mg) and high-dose (4.0 mg) melatonin in older adults found elimination half-lives of 1.8 hours and 2.1 hours, respectively .
Melatonin Half-Life in Preterm and Term Newborns
Preterm Newborns
Preterm infants exhibit a significantly longer half-life of melatonin compared to adults. Studies have shown that the half-life in preterm newborns ranges from 7.98 to 10.94 hours . Another study reported a median half-life of 15.82 hours in preterm infants receiving melatonin at 0.1 µg·kg⁻¹·h⁻¹ for 2 hours . This extended half-life suggests a different pharmacokinetic profile in preterm infants, necessitating careful consideration of dosing regimens.
Term Newborns
The half-life of melatonin in term newborns is also prolonged compared to adults, with one study indicating a half-life of approximately 15 hours . This prolonged half-life in neonates highlights the need for tailored dosing strategies to achieve therapeutic efficacy without causing adverse effects.
Factors Influencing Melatonin Half-Life
Formulation and Dosage
The formulation of melatonin significantly impacts its half-life. Immediate-release formulations tend to have shorter half-lives, while controlled-release formulations can extend the duration of elevated plasma melatonin levels. For example, a slow-release preparation maintained high plasma concentrations for 5-7 hours .
Nutritional Status
Nutritional status can also affect the pharmacokinetics of melatonin. The timing of peak plasma concentrations and the half-life of melatonin can vary depending on whether the individual is fasting or fed .
Conclusion
The half-life of melatonin varies widely across different species, age groups, and formulations. In rats, the half-life ranges from 17 to 23 minutes, while in humans, it can range from 0.45 to 2.1 hours in adults and up to 15 hours in preterm and term newborns. These variations underscore the importance of considering individual patient characteristics and specific clinical contexts when administering melatonin. Understanding these differences is crucial for optimizing therapeutic outcomes and minimizing potential side effects.
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