Nursing care
Barbiturates: respiratory depression, enzyme induction and withdrawal safety
Written and reviewed by Emily Thompson, BSN, RN, CCRN · 4 min read · Updated October 2026
Short answer
Barbiturates such as phenobarbital depress the central nervous system and, as levels rise, breathing. Nursing priorities are checking sedation and respiratory status, avoiding alcohol, opioids and other depressants, remembering that enzyme induction weakens warfarin, corticosteroids and hormonal contraceptives, and teaching that stopping suddenly after regular use can cause withdrawal seizures and delirium.
How barbiturates work and why they differ from benzodiazepines
Barbiturates enhance the inhibitory effect of GABA in the brain. The label describes a continuum: as the level rises, the effect moves from mild sedation to hypnosis, anaesthesia and deep coma, and overdose can be fatal. Phenobarbital is the barbiturate a nurse is most likely to meet, mainly as a long-acting anticonvulsant.
For exam purposes, the key contrast with benzodiazepines is safety margin. Barbiturates cause more profound respiratory depression in overdose, have no specific reversal agent, and induce liver enzymes that change how many other drugs are handled. Tolerance to the sleep-inducing effect also develops within weeks of regular use, which is one reason they are rarely chosen for insomnia now.
Adverse effects: sedation, breathing and paradoxical excitement
The effects that matter most are drowsiness, slowed or shallow breathing, apnoea, low blood pressure and, in overdose, nystagmus, ataxia, hypothermia and depressed reflexes. Older or debilitated adults may react with marked excitement, depression or confusion, and some children repeatedly become excited rather than sedated. Both patterns raise falls and safety concerns.
Contraindications listed in the label include porphyria, marked liver impairment and respiratory disease in which breathlessness or obstruction is evident. The label also advises caution, if the drug is used at all, in people who are depressed, have suicidal tendencies or have a history of drug misuse, so mood and access to stored tablets are part of the assessment.
What to monitor and when to hold or report
Before each dose, assess level of consciousness, respiratory rate and depth, oxygen saturation and blood pressure, and compare with the last set of findings. Hold the dose and contact the prescriber if the patient is difficult to rouse, breathing is slow or shallow, blood pressure has dropped, or new confusion has appeared. Serum drug levels are checked when the prescriber orders them.
When phenobarbital is given intravenously, for example during prolonged seizures, have suction, oxygen and airway equipment ready, because too-rapid injection can cause severe respiratory depression, apnoea and laryngospasm. The solution is highly alkaline, so check the line carefully to avoid extravasation or intra-arterial injection. In overdose, care is supportive: protect the airway, support ventilation and perfusion, and monitor vital signs, blood gases and electrolytes.
Interactions that matter: additive sedation and enzyme induction
Alcohol, opioids, benzodiazepines, sedating antihistamines and other central nervous system depressants add to barbiturate sedation and breathing suppression. Ask about all of them, including over-the-counter sleep aids, and report combined use rather than giving the next dose automatically.
Barbiturates induce hepatic microsomal enzymes, which speeds the breakdown of other drugs. Warfarin becomes less effective, so prothrombin time and INR need closer review when phenobarbital is started or stopped. Corticosteroid doses may need adjusting, and oestrogen-containing contraceptives can fail, so the label suggests an alternative contraceptive method.
Withdrawal teaching and a worked exam-style example
Stopping a barbiturate suddenly after prolonged use can cause withdrawal with anxiety, tremor, insomnia, delirium and convulsions, and the label warns it can be fatal. Teach the patient not to stop or skip doses on their own, to keep a supply on hand, and to ask the prescriber about a gradual reduction plan if the drug is to be discontinued.
Consider a hypothetical patient on long-term phenobarbital for epilepsy who is made nil by mouth before surgery and says they will just skip their tablets for a day. Options include recording the dose as held until the patient eats, contacting the prescriber about the dose and route, giving a double dose after surgery, or reassuring the patient that one missed day is harmless. Contacting the prescriber is best, because an unplanned gap risks withdrawal and breakthrough seizures. Doubling later risks oversedation, and the other two choices ignore the withdrawal risk.
Sources and further reading
DailyMed: Phenobarbital tablets prescribing information. CNS depression continuum, respiratory depression, contraindications, older adult and paradoxical reactions, enzyme induction with warfarin, corticosteroids and contraceptives, withdrawal and supportive overdose care.
DailyMed: Phenobarbital sodium injection prescribing information. Use in status epilepticus, respiratory depression and apnoea with too-rapid IV injection, alkaline solution with extravasation and intra-arterial injection risk, and withdrawal after abrupt cessation.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our neurological practice questions are the closest set to what this page covers.
Common questions
Can phenobarbital be stopped once seizures are controlled?
Not suddenly. Abrupt cessation after regular use can trigger withdrawal delirium and seizures, so any reduction is planned and supervised by the prescriber, usually gradually.
Why does phenobarbital make warfarin less effective?
Phenobarbital induces liver enzymes that break down warfarin faster, lowering its anticoagulant effect. INR is reviewed more closely when phenobarbital is added or withdrawn, and the warfarin dose may need adjusting.
Is there a reversal agent for barbiturate overdose?
There is no specific antidote. Treatment is supportive: protect the airway, support breathing and circulation, and monitor vital signs, blood gases and electrolytes while the drug is cleared.