Should I switch from oral (po) phenobarbital to intravenous (IV) administration if a patient is unable to take it orally?

From the Guidelines

You should switch from oral phenobarbital to intravenous administration if a patient is unable to take it orally, as this ensures continuous therapeutic coverage and maintains stable serum drug levels. When converting from oral to IV phenobarbital, it's crucial to use the same daily dose as the oral regimen since phenobarbital has nearly 100% bioavailability 1. For instance, if the patient was taking 60 mg orally twice daily, administer 60 mg IV twice daily.

Key Considerations for Administration:

• IV phenobarbital should be diluted and administered slowly, typically at a rate not exceeding 1 mg/kg per min, to avoid adverse effects such as hypotension and arrhythmias, especially with rapid infusion 1.
• Monitor vital signs closely during administration, including heart rate and oxygen saturation, as there is an increased incidence of apnea when combined with other sedative agents 1.
• Be prepared to provide respiratory support if necessary. The IV route provides reliable drug delivery when the oral route is compromised due to unconsciousness, inability to swallow, gastrointestinal absorption issues, or NPO status before procedures.

Clinical Context:

• Once the patient regains the ability to take oral medications, you can switch back to the oral form at the same daily dose, ensuring therapeutic continuity and maintaining stable serum drug levels, which is particularly important for preventing breakthrough seizures in patients taking phenobarbital for epilepsy.
• It's also important to note that neonates have an increased risk of toxicity because of decreased protein binding, and thus, phenobarbital is preferred in this population 1.

From the FDA Drug Label

Parenteral routes should be used only when oral administration is impossible or impractical Intravenous Administration Intravenous injection is restricted to conditions in which other routes are not feasible, either because the patient is unconscious (as in cerebral hemorrhage, eclampsia or status epilepticus), or because the patient resists (as in delirium) or because prompt action is imperative

If a patient is unable to take phenobarbital orally, it is acceptable to switch to intravenous (IV) administration. However, this should only be done when oral administration is impossible or impractical. The decision to switch to IV administration should be made on a case-by-case basis, considering the patient's individual needs and circumstances. It is essential to follow the recommended guidelines for IV administration, including slow injection and careful monitoring of the patient's vital signs 2.

From the Research

Administration of Phenobarbital

When a patient is unable to take phenobarbital orally (po), switching to intravenous (IV) administration may be considered. The following points highlight the key aspects of IV phenobarbital administration:

• Efficacy and Safety: A study published in 1992 3 demonstrated that IV phenobarbital-sodium is highly effective and safe in the treatment of status epilepticus, with mild and transient side-effects.
• Dosage and Administration: The same study 3 used an initial dose of 9 to 12 mg/kg of body weight, increased to 36 mg/kg when seizures were stopped, with a rate of infusion of 100 mg/min.
• Comparison of Routes: A study from 1989 4 compared intraosseous and IV routes of anticonvulsant administration in a porcine model, finding that IV administration resulted in statistically significantly higher anticonvulsant levels.
• Therapeutic Levels: The 1989 study 4 also found that phenobarbital levels were therapeutic by the intraosseous route, while phenytoin levels were below the therapeutic range after the ten-minute interval.
• Emergency Management: A 1989 overview 5 of emergency management of seizures mentioned the use of IV phenytoin and lorazepam, as well as intermittent oral or rectal administration of diazepam, but did not specifically address the switch from po to IV phenobarbital.
• Side-Effects and Hypersensitivity: A 2019 case report 6 highlighted the risk of antiepileptic hypersensitivity syndrome (AHS) to phenobarbital, which can be potentially life-threatening.
• IV Phenobarbital for Alcohol Withdrawal: A 1987 study 7 used IV phenobarbital to treat alcohol withdrawal syndrome, demonstrating its safety and efficacy in this context.

Key Considerations

When considering switching from po to IV phenobarbital, the following points should be taken into account:

• The patient's inability to take the medication orally
• The potential benefits and risks of IV administration, including efficacy, safety, and side-effects
• The dosage and administration guidelines, as well as the monitoring of therapeutic levels and potential side-effects.