Central nervous system depression, coma, and respiratory arrest may occur, especially with rapid bolus or excessive doses.
Hypotension may result, especially with rapid intravenous infusion (>50 mg/min). This may be caused by the drug itself or the propylene glycol diluent.
Laryngospasm and bronchospasm have been reported after rapid intravenous injection, although the mechanism is unknown.
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). Pentobarbital 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 Phenytoin and Fosphenytoin).