In the present study, we demonstrated that organoleptic properties, solubility, pH, and density of CS and GlcN samples, two raw materials obtained from two different Brazilian pharmaceutical companies, are in accordance with the standards required by ANVISA, responsible for pharmaceutical product regulation in Brazil . Despite this, the pH and density values of both samples were different between the suppliers and opened the possibility that parameters required by the ANVISA cannot be sufficient to assess the appropriate quality control of raw materials. Indeed, FT-IR analyses indicated that there is non-homogeneity in the CS and GlcN samples tested, indicating that both manufacturers distribute the drugs in different concentrations which could compromise the quality and therapeutic efficiency of the pharmaceutical formulation used for osteoarthritis treatment. These formulations are prepared in pharmacies authorized by the Health Surveillance secretariats, which can be either state or municipal, according to ANVISA Directors’ Collegiate Resolution (RDC) 67/2007 , updated by RDC 44/2009  and RDC 41/2012 , which define the Good Manufacturing Practices (GMP) for compounded medicines for human use in pharmacies.
Quality control encompasses a group of measurements intended to ensure the production of numerous medicines and other products that meet the standards of identity, activity, content, purity, effectiveness, and safety . The specifications and quality tests for pharmaceutical raw materials and formulations are described in detail in pharmacopeia monographs, including average weight, weight uniformity, hardness, disintegration time, dissolution, and dose uniformity [25, 34]. All raw materials are submitted to organoleptic evaluations, solubility, pH, melting point, and density, according to the Brazilian pharmacopeial specifications . In the present study, the organoleptic properties and solubility of CS and GlcN samples obtained from pharmacy analyses and the supplier’s specifications are in accordance with the standards required by ANVISA [18, 21, 24, 25, 29, 30].
CS and GlcN are available as pharmaceutical-grade products, and the latter have great variations in preparation, composition, purity, and effects [1, 12, 35]. Some products contain a negligible amount of CS; among samples with reasonable amounts, in vitro testing showed widely varying effects [11, 36, 37]. This could be related to contaminants, which depend on the origin, production, and purification process [11, 38]. In our study, the comparative analyses of the physicochemical parameters of CS and GlcN between pharmacy tests and technical specifications provided by two Brazilian suppliers showed that the pH and density values are statistically different, although they agree with the standards required by ANVISA [18, 21, 24, 25, 29, 30]. In addition, while the values are under the standards required by ANVISA, ICC analyses for pH and density values demonstrated a low correlation between the data obtained from the pharmacy and the specification report provided by the manufacturer.
The CS density presents excellent concordance; however, the GlcN density showed low reproducibility for the two suppliers in the Bland-Altman analyses. The agreement values for different suppliers in terms of pH and density for S1 remained along and near the mean differences for CS, which are important values for the agreement parameter. For the GlcN samples, the agreement values sometimes either underestimated or overestimated values relative to pharmacy estimates. However, it is understood that more tests would be required to approve or disapprove the raw material, as there was no satisfactory agreement with the methods used, considering the range between the limits of agreement. It is worth mentioning that the values found in the tests are in the range required for each raw material according to Martindale and Parfitt  and the GMP of RDCs [26, 32, 33].
It is important to say that the margin between the minimum and maximum values of the physicochemical parameters required by ANVISA  is very large, which may compromise the quality of the product, change the concentration of the active ingredient in these formulations, and, consequently, reduce the therapeutic efficacy of pharmaceutical compounding. In fact, in our study, FT-IR analyses indicated non-homogeneity in the CS and GlcN samples between S1 and S2, showing that both manufacturers distribute the drugs in different concentrations, although both declare the same concentration in the product technical specifications.
The purity of raw materials was evaluated by FT-IR, which identified only functional groups attached to molecules of CS and GlcN, according to the literature [39,40,41,42]. Analyses of peak areas of different bands of CS samples showed that region spectra above 2000 cm− 1 were dominated by the OH stretching vibration . The band at 1350 cm− 1 was due to the sulfate. The band at 1250 cm− 1 has been assigned to S=O corresponding to the band assignment by Cabassi et al. . The peak at 850 cm− 1 was due to the C–O–S vibration according to Honda et al. . The spectrum of GlcN is similar to that of glucose, as they share very similar structures  and it was possible to identify the N–H band above the 3000 cm− 1, amine group between 1500 and 1700 cm− 1, S=O band around 1230 cm− 1, and C–O band between 1200 and 1000 cm− 1.
Although the raw materials meet the current legislation regarding the physicochemical parameters in Brazil, the vibrational analysis of bands from CS and GlcN revealed that the samples have different intensities in the absorption peaks. In CS, the N–H, amine group, on each ring structure and C–O bands were different between suppliers. Similarly, the peak areas of OH, sulfate, S=O, and C–O–S bands of GlcN samples were also different. The decrease in radiant energy detected when a beam of radiation passes through a material medium is proportional to the beam power and quantity of a radiation-absorbing substance found in its path through the medium, according to Beer’s law . Therefore, a correlation can be made between the intensity of the peaks and the concentration of the substance by calculating the area of the peak. Thus, our data indicated non-homogeneity in the concentration of the CS and GlcN samples from the same supplier as well as between S1 and S2, suggesting that both are distributing the pharmaceutical form in different concentrations, although both declare the same concentration in the product technical specifications. Additionally, these differences in the concentration of drugs could explain the large variation of the physicochemical data obtained between the pharmacy and the technical specifications of suppliers.
The implantation of RDC 67/2007  was considered a great advance in Brazil, though we believe that the strategies adopted for the assessment of drug quality should be more accurate because, as shown in our study, attending to physicochemical standards is not sufficient to guarantee the quality and reproducibility of the production of pharmaceutical compounding and can negatively impact the quality of these products.