From the Guidelines
I strongly advise against giving the missed 8:00 PM dose of phenobarbital 97.2 mg at midnight. The pharmacokinetics of phenobarbital, as outlined in the study by the extrip workgroup 1, indicate that it has a long elimination half-life of 80-120 hours, which means it stays in the system for an extended period. Given that the next scheduled dose is approaching, taking the missed dose at midnight could lead to an accumulation of the drug in the system, potentially increasing the risk of adverse effects such as excessive sedation or even overdose.
Key Considerations
- The long half-life of phenobarbital reduces the need for taking a missed dose close to the next scheduled time 1.
- The risk of overdose and adverse effects is higher when taking barbiturates, especially when combined with other central nervous system depressants 1.
- It is crucial to consult with a healthcare provider before making any adjustments to the medication schedule, as they can provide personalized guidance based on the individual's medical condition and treatment plan.
Recommendations
- If a dose of phenobarbital is missed, it is generally recommended to skip that dose and resume the regular dosing schedule rather than taking it late.
- Patients should contact their healthcare provider for specific guidance on handling missed doses, as individual circumstances may vary.
- Healthcare providers should be aware of the potential risks associated with barbiturate use, including the risk of overdose and adverse effects, and provide appropriate monitoring and guidance to patients.
From the Research
Phenobarbital Dosing
- The question of whether to give phenobarbital 97.2 mg at 12 midnight if the 8:00pm dose is missed can be informed by studies on the pharmacokinetics and replacement dosing of phenobarbital 2.
- According to a study on the effect of nonadherence on phenobarbital concentrations, the impact of missed phenobarbital doses on its concentrations depends on the daily dose, and replacement with a respective regular dose or one and a half regular dose may be appropriate for one or two missed doses scenarios 2.
- However, the study does not provide specific guidance on the timing of replacement doses, and the decision to give a missed dose at 12 midnight should be based on clinical judgment and consideration of the patient's individual circumstances.
Clinical Considerations
- Phenobarbital is a medication with a long history of use in the treatment of seizures and status epilepticus, and its efficacy and safety have been established in various studies 3, 4.
- The medication has a strong antiseizure effect with remarkably little sedation, and it exerts its clinical effects through the increase of GABA-ergic inhibition and decrease of glutamatergic excitation 3.
- However, phenobarbital can have adverse effects, such as hypotension, arrhythmias, and hypopnea, and its use should be carefully monitored and managed 3.
Replacement Dosing
- A study on the replacement dosing of phenobarbital suggests that weight does not influence the proper replacement dosing scheme, and the same replacement scheme may be appropriate for patients receiving phenobarbital monotherapy or in combination with other medications 2.
- However, the study emphasizes the importance of clinical judgment and consideration of the patient's individual circumstances in determining the replacement dosing scheme 2.
- In the absence of specific guidance on the timing of replacement doses, clinicians should exercise caution and consider the potential risks and benefits of giving a missed dose at 12 midnight, taking into account the patient's medical history, current condition, and other relevant factors 2, 5, 6.