From the Guidelines
Barbiturates can be detected in urine drug screens for up to 2-3 weeks after the last dose, depending on the specific type used, with long-acting agents like phenobarbital having the longest detection window. The detection time of barbiturates in urine drug screens varies based on their pharmacokinetic properties, which are classified into long-acting and short-acting agents 1.
Factors Influencing Detection Time
- The individual's metabolism, with hepatic metabolism being the main route of endogenous clearance of all barbiturates 1
- Kidney function, as long-acting barbiturates are excreted as active drugs by the kidneys more readily 1
- Urine pH, with urinary alkalinization potentially enhancing the removal of long-acting agents 1
- Hydration status, which can affect the concentration of the drug in the urine
- Frequency of use, with chronic users potentially having longer detection periods due to accumulation of the drug in fatty tissues
- Dosage, which can impact the duration of action and elimination half-life of the barbiturate
Detection Windows for Different Types of Barbiturates
- Short-acting barbiturates like pentobarbital: 1-4 days after use
- Intermediate-acting barbiturates like butalbital: 3-7 days after use
- Long-acting barbiturates like phenobarbital: up to 2-3 weeks after the last dose The standard urine immunoassay tests used in most clinical settings can detect barbiturates at concentrations of 200-300 ng/mL, though confirmation testing using more specific methods like gas chromatography-mass spectrometry may be required to identify the specific barbiturate and rule out false positives 1.
From the FDA Drug Label
Approximately 25 to 50 percent of a dose of phenobarbital is eliminated unchanged in the urine, whereas the amount of other barbiturates excreted unchanged in the urine is negligible. The plasma half-life of phenobarbital is 53 to 118 hours (mean 79 hours) and in children/newborns, the plasma half-life is 60 to 180 hours (mean 110 hours). The plasma half-life for secobarbital sodium in adults ranges between 15 to 40 hours, with a mean of 28 hours.
The duration that barbiturates can be detected in a urine drug screen varies depending on the specific barbiturate and individual factors.
- Phenobarbital: can be detected in urine for up to 7-14 days due to its long plasma half-life of 53-118 hours 2.
- Secobarbital: can be detected in urine for up to 2-4 days due to its shorter plasma half-life of 15-40 hours 3 and 3. Key factors that influence detection time include:
- Dose and frequency of use
- Individual metabolism and excretion rates
- Urine pH and flow rate
- Sensitivity of the drug test used
From the Research
Detection Time of Barbiturates in Urine
- The detection time of barbiturates in urine can vary depending on several factors, including the dose and sensitivity of the method used, preparation and route of administration, duration of use, and interindividual variation in metabolic and renal clearance 4.
- In general, the detection time is longest in hair, followed by urine, sweat, oral fluid, and blood 4.
- For a single dose of barbiturates, the detection time in urine is typically 1.5 to 4 days 4.
- In chronic users, barbiturates can be detected in urine for approximately 1 week after last use, and in extreme cases even longer 4.
- A specific study on the detection of flunitrazepam, a type of barbiturate, found that it can be detected in urine for up to 4 weeks after a single dose 4.
Analysis of Barbiturates in Urine
- Gas chromatography-mass spectrometry (GC-MS) is a commonly used method for the analysis of barbiturates in urine, serum, and plasma 5.
- The analysis of barbiturates is useful for both clinical and forensic purposes 5.
- The method described in the study involves extracting barbiturates from urine using an acidic phosphate buffer and methylene chloride, and then injecting the extract into a gas chromatogram mass spectrometer 5.