Barbiturates have various onsets of action, durations, half-lives, and toxic levels, depending on the lipid solubility and rate of metabolic inactivation. The onset of action for oral administration ranges from 20 to 60 minutes, and intravenous administration can range from almost immediate to 5 minutes. High lipid-solubility in some (amobarbital, pentobarbital, and thiopental) allow them to be well absorbed and rapidly redistributed. Most are rapidly metabolized to inactive compounds before they are excreted in the urine. However, phenobarbital is only partially converted and can be found unchanged in the urine. Phenobarbital is a long-acting, polar drug that is slowly absorbed and slowly redistributed, contributing to its longer duration of action. Barbiturates easily cross the placenta and are excreted into breast milk.

Barbiturates are also hepatic enzyme inducers which means that they will induce the metabolism of other medications, including other barbiturates. Pentobarbital and phenobarbital have increased the clearance rate and reduced the plasma concentrations of some beta blockers. Abrupt cessation of these barbiturates while taking a beta blocker could increase the effect of the beta blocker or cause frank toxicity.

Patient history should focus on determining the exact type and amount of medication taken and whether there has been co-ingestion of other substances. Symptoms of barbiturate toxicity vary from case to case, but commonly include difficulty thinking, decreased level of consciousness, bradycardia or rapid and weak pulse, poor coordination, vertigo, nausea, muscle weakness, thirst, oliguria, decreased temperature, and dilated or contracted pupils. Fatal cases are marked by coma, hypotension (low blood pressure), and respiratory depression (decreased efforts to breathe) evidenced by cyanosis and hypotension. Pulmonary edema is another complication associated with barbiturate toxicity and contributing to respiratory depression and death.  It is also important to determine if the individual has taken other substances that may have additive effects, such as ethanol (alcohol), benzodiazepines, and opiates.  

Chronic abusers can develop severe withdrawal symptoms within 8 to 15 hours of cessation.  Symptoms include restlessness, tremors, hyperthermia, sweating, insomnia, anxiety, seizures, circulatory failure, and potentially death.

Physical examination should include serial mental status, vital signs, and neurologic examinations conducted at regular intervals. Barbiturates also have been associated with thrombocytopenia and pulmonary eosinophilia (with febarbamate).

As with most drug and medication-related toxicities, evaluation often includes a qualitative assessment of the amount of drug taken with a plasma or urine screening test. Plasma barbiturate concentration and ingested dose have been implicated as the most important correlates of toxicity. Immunoassays (EIA) can provide a cost-effective and sensitive method to detect barbiturates and other substances that may be in the body. Another method often used is gas chromatography/mass spectrometry (GC/MS) which can further identify and confirm the presence of a particular barbiturate.

Treatment of barbiturate toxicity remains supportive as there is no specific antidote for overdose. The first step in treatment, as with any overdose, is assessing the patient’s airway, breathing, and circulation. With significant sedation and respiratory depression, intubation and mechanical ventilation may become necessary. Early treatment with activated charcoal may be useful and can be given via nasogastric tube. Patients will likely need to be admitted or observed. During recovery, the patient should receive counseling about the dangers of barbiturate misuse. Long-term barbiturate use can cause tolerance and physical dependence. Therefore, withdrawal symptoms can occur with abrupt discontinuation. [6][1]

Other options for managing barbiturate toxicity include forced alkaline diuresis and hemodialysis for severe cases. Bemegride (Megimide) is a central nervous system stimulant that increases respiration and can be used as a treatment for depressant toxicity. It is, however, an emetic which raises the concern of emesis and aspiration.

Management of long-term use involves restoring central nervous system (CNS) inhibitory tone. Abrupt cessation can lead to severe symptoms of withdrawal; therefore, discontinuance of barbiturates should be a gradual taper using medications that demonstrate cross-tolerance, with the first line being benzodiazepines.

The differential diagnosis should include intoxication by other substances with sedative effects, such as benzodiazepines, anticonvulsants (carbamazepine), alcohols (ethanol, ethylene glycol, methanol), opioids, carbon monoxide, sleep aids, and gamma-Hydroxybutyric acid (GHB – a known date rape drug). Natural disease that can result in disorientation may be in the differential, including hypoglycemia and myxedema coma. In the right setting, hypothermia should be ruled out. 

Individuals suffering from barbiturate overdose typically do well if they receive prompt medical treatment and are otherwise healthy. Patient outcome depends on the amount of barbiturate taken, the specific barbiturate used, other drugs that were ingested or injected, promptness of medical care, and comorbidities. Individuals with other significant health conditions, such as heart and pulmonary disease, may have a more complicated clinical course. For example, an individual with coronary artery atherosclerosis and/or cardiomegaly (an enlarged heart) will be already prone to suffering a myocardial infarction. Respiratory depression or hypotension from a depressant drug (like a barbiturate) will further decrease the amount of oxygen reaching the heart. An individual with a chronic obstructive pulmonary disease (COPD) or another pulmonary disease will have an increased risk for complications since respiratory drive is compromised with barbiturate toxicity.

Complications include hypotension, coma, and respiratory depression.  It is important to maintain the respiratory and cardiovascular status, as failure to do so can result in hypoxic brain injury and death. Rarely, phenobarbital has been associated with Steven-Johnson syndrome, a medical emergency that results in blisters (especially mucous membranes), fever, and widespread pain.

Long-term abuse has been associated with depression, loss of appetite, achiness, and rarely liver damage. As previously discussed, withdrawal symptoms can be severe, and the patient should be monitored carefully and treated accordingly. 

Barbiturate toxicity is not very common today because this class of drugs is less frequently prescribed. However, it is important for all healthcare workers to understand the toxicity of the drug and how to manage it. Despite the lack of an antidote, survival with supportive therapy is excellent. Mortality rates associated with barbiturate toxicity is less than 2%. However, the management of the patient is usually in the ICU with very close monitoring. The key to preventing morbidity and mortality from barbiturate overdose is patient education. The parents should be asked to store the drug in a locked cabinet away from the easy reach of children. Any patient who intentionally takes an overdose of barbiturate should be referred to a mental health counselor prior to discharge.  Patients with drug addiction should be referred to a drug rehabilitation center. [7][8]