Central nervous system depression, coma, and respiratory arrest may result, especially with rapid bolus or excessive doses.
Hypotension may result from rapid intravenous administration. This can be prevented by limiting the rate of administration to less than 50 mg/min (children: 1 mg/kg/min). Hypotension may be due to the drug itself or to the diluent propylene glycol.
Parenteral solutions are highly alkaline, and precautions need to be taken to avoid extravasation. Intra-arterial infusions may cause vasospasms and gangrene. Subcutaneous administration may cause necrosis and is not recommended.
Use in pregnancy. FDA Category D (possible fetal risk). Phenobarbital readily crosses the placenta, and chronic use may cause hemorrhagic disease of the newborn (owing to vitamin K deficiency) or neonatal dependency and withdrawal syndrome. However, these potential effects do not preclude its acute, short-term use in a seriously symptomatic patient (See Introduction in Section III).