Comparison of Authentic and Suspect Pharmaceuticals - Pharmaceutical Technology

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Comparison of Authentic and Suspect Pharmaceuticals
The authors applied near-infrared (NIR) spectrophotometry to assess whether eight drug products were authentic or counterfeit.


Pharmaceutical Technology
Volume 33, Issue 8, pp. 46-52


Table II: Near-infrared spectra comparisons of test product to reference product using ρm and δa.
Table II lists NIR spectra comparison results in terms of the ρm and δacriteria. Essentially, ρm is a ratio-based method, but δa is based on the absolute difference between two spectra (10, 11). Each method compares profiles at the same wavelength and can include all or selected wavelengths. If the profiles are identical, ρm = 0. Dissimilar profiles result in ρm that approaches infinity. This approach results in a ratio to assess spectra similarity, in which the larger value of either R t /T t or Tt/R t is considered at each wavelength. By virtue of being a ratio approach, ρm normalizes the differences between the profiles against the size of the profiles (i.e., it results in a value that quantifies the relative difference between the two profiles). δa also considers the relative size of the profiles. The authors used critical limits of ρm > 0.15 and δa > 15 to denote products that were not similar to their references because these limits represent a difference of more than 15% from the reference.


Figure 7. Near-infrared spectra of Norvasc 10 mg test and reference products and authentic generic amlodipine besylate 10 mg.
Spectra were compared over the 400–2500-nm range and over the 800–2500-nm range. Because 400–800 nm is the visible range and color differences (e.g., between dyes) are frequently and easily imparted to products designed for different countries, the narrower 800–2500-nm range was used to minimize colorant differences.


Figure 8. Near-infrared spectra of Viagra 50 mg test and reference products.
The results of ρm and δa generally followed the results of simple visual inspection of the tablets (see Table II). Most test spectra were similar to the reference spectra (i.e., ρm < 0.15 and δa < 15), and most products appeared to be authentic. Hence, the authors concluded that test Cialis 20 mg, test Lamisil 250 mg, test Levitra 20 mg, test Norvasc 5 mg, test Viagra 50 mg, and test Viagra 100 mg were authentic. TLC results from the terbinafine hydrochloride products and API indicated that test Lamisil 250 mg contained the labeled drug. TLC results from sildenafil citrate products and API indicated that test Viagra products contained the labeled drug.


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