LabMed

Overdose of Barbiturate

At a Glance

Barbiturate overdose is less frequent than overdoses with other abused drugs due to the decreasing therapeutic and recreational use of barbiturates. However, in general, short acting barbiturates, such as pentobarbital and secobarbital, which are more lipid soluble than long acting barbiturates, such as phenobarbital, cause more serious toxicity. Characteristics of barbiturate overdose include central nervous system (CNS) depression, hypotension, constricted pupils reacting to light, and depression of cardiovascular system. Moderate barbiturate intoxication may look like alcohol poisoning.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

A urine drug screen for barbiturates should be ordered in any patient presenting with a clinical history or symptoms suggestive of barbiturate overdose. Urine drug screens provide rapid turnaround time and are available in most laboratories. A positive-screening result in a patient with clinical symptoms is suggestive of barbiturate overdose. If clinical suspicion for barbiturate overdose is high, patients should be treated immediately, regardless of the testing results.

Although most barbiturate immunoassays are calibrated for detecting secobarbital, other widely abused barbiturates, such as pentobarbital, amobarbital, and phenobarbital, have adequate cross-reactivity and will trigger a positive result using the 200 ng/mL cutoff if present.

Serum or plasma testing for phenobarbital is available in many laboratories and can be ordered to assist with the diagnosis of barbiturate overdose.

If available, confirmatory techniques, such as gas chromatography-mass spectrometry (GC/MS), can be utilized to confirm the presence of a specific barbiturate and provide quantitative results.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Urine drug screens have limitations, including the generation of false-positive and false-negative results. False-negative results may be seen if the screening assay utilized has low cross-reactivity for the ingested barbiturate. False-positive results with barbiturate immunoassays are uncommon. Barbiturate immunoassays are not affected by over-the-counter drugs (OTC) or herbal supplements. However, if a patient is prescribed phenobarbital for a clinical condition, such as seizures, it will cause analytical true positive immunoassay result and confirmation. Barbiturate drug screens can be positive for several days to weeks after barbiturate ingestion, depending on the half-life of the barbiturate. For this reason, a positive result may not indicate acute ingestion.

What Lab Results Are Absolutely Confirmatory?

Confirmatory techniques, such as GC/MS, can be utilized to confirm the presence of a specific barbiturate and provide quantitative results.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Usually short acting barbiturates stay in urine 2-3 days after abuse, whereas a long-acting barbiturate can be detected for up to a week. If a person stops abusing barbiturates, a random urine test can be ordered after the wash out period to ensure the patient is drug free.

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