Rapid and accurate verification of drug identity, purity and quality by 1H-NMR using similarity calculations and differential NMR

Abstract

The illegal trade in counterfeit and fake drugs is a worldwide multi-billion dollar industry, not only generating enormous economic losses, but health problems for the general population, through direct toxicity, treatment failure and the increased generation of antibiotic resistance. Techniques for high-throughput testing of suspect medicines are needed to face the challenges of the problem. In this study we show that with nuclear magnetic resonance spectroscopy (NMR) drug compliance can be verified in a few minutes, providing data on drug identity, purity and quality without the necessity to develop a specific methodology and using a direct extraction with deuterated solvent. The evaluation of the data is facilitated by similarity calculations and differential NMR spectroscopy. The viability and limitations of this method were assessed, with the application on five different drugs, namely sertraline hydrochloride, alprazolam, vitamin D₃, enalapril maleate and paracetamol, in which the individual dosage quantity of the active ingredient ranged from 750 mg down to 0.25 mg. The appropriate sample weight, solvent and internal standard were determined for each drug and quantification was carried out by choosing the most adequate NMR signals for each compound and the internal standard. With the method the accuracy of the quantification is somewhat sacrificed for increased speed in the analysis, but the measurements offer excellent precision and offer the possibility of external calibration. Spectral similarity calculations and differential NMR spectroscopy were used to compare different generic brands and detect eventual undeclared constituents and contaminants. In one brand of alprazolam tablets the undeclared constituent tristearin was found, while in paracetamol tablets the contaminant para-aminophenol was found at a level above the allowed by the legislation. The applicability and limitations of the method are discussed.

Keywords: (1)H NMR; Counterfeit; Differential NMR; Drugs; Quality verification; Similarity.