Enantiomeric Identification of Pregabalin by GC‐MS via Methylation and S‐TPC Chiral Derivatization

Pregabalin is a Schedule V controlled substance which is defined as the (S) enantiomer of 3‐(aminomethyl)‐5‐methylhexanoic acid. It is used legitimately to treat neuropathy in patients with diabetes as well as for epilepsy and fibromyalgia. Pregabalin is an amino acid and an amphoteric compound, which makes it difficult to analyze using the conventional GC‐MS instrumentation found in most forensic drug analysis laboratories. Problems associated with the traditional GC‐MS analysis of pregabalin include selective solubility, ring closure to the corresponding lactam in the GC injection port and/or the MS transfer line and difficulty with chiral derivatization due to the presence of a carboxylic acid moiety. Here, we show that these challenges can be overcome by methylating (capping) the carboxylic acid portion of the pregabalin molecule and converting to the corresponding methyl ester. Once the methyl ester is synthesized, chiral derivatization at the amine can be achieved to identify the controlled (S) enantiomer of pregabalin via GC‐MS.     

Determining the Toxicological Significance of Pregabalin in Fatalities

Pregabalin has become more widely prescribed and abused in recent years but is still not always included in laboratory analysis. An LC‐MS‐MS method has been developed and applied to measure pregabalin in 93 postmortem cases, including drug‐related deaths, alternative causes of death, and fatalities where pregabalin was likely to have contributed to death. Other drugs or alcohol was detected, and the most common drug types (in decreasing frequency) were antidepressants, opioids, benzodiazepines, opiates, alcohol, antipsychotics, cocaine, cardiac drugs, amphetamines, cannabis, anticonvulsants, and antihistamines. New psychoactive substances (methoxphenidine and synthetic cannabinoids) were only found in two cases. The results provide further data to assist in evaluating the significance of postmortem pregabalin concentrations and a toxicologically significant concentration of 25 mg/L is proposed. Pregabalin, especially with concomitant use of other CNS depressant drugs, presents a significant toxicological risk and existing laboratory protocols should be reviewed for their suitability to detect pregabalin.