From the Guidelines
The half-life of phenobarbital in infants is approximately 20-133 hours, in children it is around 37-73 hours, and in neonates it can range from 45-500 hours. This significant variation in half-life is crucial to consider in clinical practice, as it affects the timing of brain death examinations and the interpretation of neurologic tests [ 1 ]. The half-life of phenobarbital is influenced by various factors, including age, liver function, and renal function, which can impact the drug's metabolism and elimination [ 1 ].
Key Considerations
- The half-life of phenobarbital is longer in neonates compared to infants and children, which may require adjustments in dosing and timing of brain death examinations [ 1 ].
- The elimination half-life of phenobarbital does not guarantee therapeutic drug levels, and drug levels should be obtained to ensure that levels are in a low to mid therapeutic range prior to neurologic examination [ 1 ].
- Physicians should be aware of the total amounts of administered medication that can affect drug metabolism and levels, and consider the potential for drug interactions due to the prolonged half-life of phenobarbital [ 1 ].
Clinical Implications
- The prolonged half-life of phenobarbital requires careful consideration in clinical practice, particularly in the context of brain death examinations and the interpretation of neurologic tests [ 1 ].
- The significant variation in half-life among different age groups highlights the importance of individualized dosing and monitoring in pediatric patients [ 1 ].
From the FDA Drug Label
In adults, the plasma half-life of phenobarbital is 53 to 118 hours (mean 79 hours) and in children/newborns, the plasma half-life is 60 to 180 hours (mean 110 hours). The half-life of phenobarbital is 53 to 118 hours (mean 79 hours) in adults and 60 to 180 hours (mean 110 hours) in children/newborns 2.
From the Research
Half Life of Phenobarbital
- The half-life of phenobarbital is approximately 5.8 days after an intravenous dose and 5.1 days after an oral dose, as reported in a study published in the Journal of Clinical Pharmacology 3.
- The elimination half-life of phenobarbital can vary depending on the individual and the dosage form, but 5-6 days is a commonly cited range.
- Other studies have not specifically reported on the half-life of phenobarbital, but have discussed its pharmacokinetics and efficacy in treating epilepsy 4, 5, 6, 7.
Factors Affecting Half Life
- The half-life of phenobarbital can be influenced by factors such as liver function, kidney function, and drug interactions.
- However, the exact impact of these factors on the half-life of phenobarbital is not well understood and requires further study.
Clinical Significance
- Understanding the half-life of phenobarbital is important for determining the optimal dosage and frequency of administration in patients with epilepsy.
- The half-life of phenobarbital can also impact the risk of adverse effects, such as sedation and cognitive impairment, which are commonly associated with this medication 7.