Pentobarbital Sodium Interactions

Doxycycline: Phenobarbital has been shown to shorten the half-life of doxycycline for as long as 2 weeks after barbiturate therapy is discontinued. If phenobarbital and doxycycline are administered concurrently, the clinical response to doxycycline should be monitored closely.

Source: FDA drug label - pentobarbital sodium

Estradiol, estrone, progesterone and other steroidal hormones: Pretreatment with or concurrent administration of phenobarbital may decrease the effect of estradiol by increasing its metabolism.

Source: FDA drug label - pentobarbital sodium