Comparison of the Properties of Brand-Name and Generic Nadifloxacin Creams

Summary. Background and Objective. In external preparations, types and ratios of additives are not necessarily the same for brand-name drugs and generic drugs. Thus, the physicochemical properties of preparations may differ despite the fact that they contain the same ingredients or additives. This study examined differences in brand-name and generic versions of nadifloxacin (NFX) creams


Introduction
The rationalization of health care expenditures is a high priority for the governments of many countries in the industrialized world.Generic drugs contain the same active ingredients as their brandname counterparts, but they have different additives such as preservatives and coloring agents (1).Generic formulations are made by the same manufacturer as the brand-name drug, but their quality is often questioned by physicians and pharmacists since the excipients used may differ.Generics registered with the European Medicines Agency (EMA) should include the same amount of the active ingredients but can have different excipients.Excipients that are given exceptions include preservatives, pH adjusters, antioxidants, thickening agents, buffers, and substances to adjust tonicity.Although generic formulations are always less expensive than the corresponding brand-name drugs, they are not always as safe or effective.In addition, generic drugs are considered to be of the same quality as the original drugs, but many feel that information about those generics is inadequate (2).Among physicians, there are perceptions that generic drugs will immediately be discontinued and concerns about consistent supply.Such factors might explain why generic drugs have gained little attraction in Japan despite accounting for half of the drug market in the United States and the United Kingdom (3,4).As stated earlier, although generic formulations are always less expensive than the corresponding brand-name drugs, they are not always as safe or effective.When a generic drug is registered with the EMA, the clinical effi cacy and safety of that generic is considered essentially similar to the innovator or brand-name drug, and the same holds true for local-acting drugs.That said, topical agents in the form of ointments and creams are used to treat a local infl ammation or rash, so reports have indicated that differences in additives and differences in additive content can lead to differences in penetration of and absorption by the skin, in turn affecting the therapeutic effectiveness of the ointment or cream (5)(6)(7).Penetration of the skin by the antiviral acyclovir (ACV) is reported to differ with preparations that contain different amounts of polyethylene glycol.All marketed ACV creams are not bioequivalent to the clinically proven innovator (8).Substantial differences in bio-availability are believed to bring into question the therapeutic equivalence of these formulations.
Nadifl oxacin (NFX) is a tricyclic fl uoroquinolone antibiotic with a benzoquinolizine skeleton and is the active ingredient in the world's fi rst quinolone topical preparation, Acuatim ® (9).Since it contains fl uorine (F), NFX is a synthetic bactericidal fl uoroquinolone with a broad-spectrum antibacterial activity against aerobic gram-positive and gramnegative bacteria and anaerobic bacteria including Propionibacterium acnes and Staphylococcus epidermidis; NFX is also clinically useful in treating acne vulgaris (10,11).NFX has been found to have a broad antibacterial spectrum.Formulations are available in 3 forms -creams, lotions, and ointments -for use in accordance with the patient's condition.NFX creams that have recently come into use include both brandname and generic versions.However, differences in the types or amounts of additives in a cream that is used locally would presumably affect the physicochemical properties of preparation, such as its emulsifi cation and viscosity.To test this hypothesis, the physicochemical properties of a brand-name NFX cream were compared with those of two leading generic NFX creams.This study sought to observe the characteristics of preparations, determine their viscosity, and assay those preparations as a quality test.In addition, this study examined the molecular state of those preparations resulting from differences in additives they contained.

Materials and Methods
Reagents.The NFX creams used were those available commercially and were designated NFX-A (Acuatim ® ), NFX-B (NADIFLO ® ), and NFX-C (NADIROXISAN ® ).NFX crystals were purchased from Sigma-Aldrich.Acetonitrile, chloroform, sodium hydroxide, and acetic acid were of special commercial grade and were purchased from Wako Pure Chemical Industries.
Preparation of Humidity-Controlled Samples.NFX-A, NFX-B, and NFX-C were stored in a thermostated bath at 40°C for 7 days in a desiccator (relative humidity, 82%) in the presence of KClsaturated aqueous solution.
Microscopy.Polarization microscopy was done using an OLYMPUS model BX51 microscope.In addition, a polarizing plate with a wavelength of 488 nm was used.
Determination of Viscosity.Viscosity was measured at 20°C using a type-E rotational viscometer (model TVE-20H) from Toki Sangyo.One milliliter of each cream was poured into a sample cup, and viscosity was measured at 1 rpm using a 1°34´×R24 cone rotor; measuring time was 900 s, and viscosity was read after 180 s of rotation.Creams were incubated in a water bath at 20°C before measurements.
X-Ray Powder Diffraction.X-ray powder diffraction was measured at room temperature with a Rigaku Minifl ex Diffractometer using CuKα radiation.Diffraction was done at 30 kV, 15 mA with a scanning speed of 4°/min and measurement range of 2θ=5°-35°.
Assay.One gram of each cream was weighed accurately and placed in a stoppered centrifuge tube.Twenty milliliters of chloroform/0.01mol/L sodium hydroxide (1:1) was added, and the solution was shaken and then centrifuged (4000 rpm for 30 min).The clear portion of the top layer was fi ltered with a 0.45-μm fi lter, and the fi ltrate served as the sample solution.A calibration curve was prepared using NFX that had separately been dried for 24 h at 105°C.NFX was assayed with a high-performance liquid chromatograph (HPLC, LC-20ADvp, Shimadzu).NFX assay conditions were a column of Inertsil ODS-3 (4.6×250 mm, φ5 μm), column temperature of 35°C, mobile phase of water/acetonitrile/acetic acid=130/70/1, and detection wavelength of 280 nm; conditions were tailored for NFX to produce a peak at 15 min.

Results
In the current study, viscosity was determined using a rotational viscometer so that individual creams could be compared (Fig. 1).NFX-A, NFX-B, and NFX-C had a viscosity of 24.6 Pa • s, 14.5 Pa • s, and 17.9 Pa • s, respectively, so results in order of viscos- ity were NFX-A>C>B.A spread meter was used to compare the fl uidity of the creams, and the results of this comparison are shown in Fig. 1 and Table 1.After 360 s, NFX-B had a spread diameter of 41.5 mm, NFX-C had a spread diameter of 39.9 mm, and NFX-A had a spread diameter of 35.3 mm.Flattening was greatest for NFX-B, followed by NFX-C and then NFX-A.As an indicator of hardness, the yield value was 498.4 dynes/cm 2 for NFX-A, 222.9 dynes/cm 2 for NFX-B, and 270.6 dynes/cm 2 for NFX-C.Thus, light microscopy was used to examine the emulsifi -Comparison of the Properties of Brand-Name and Generic Nadifl oxacin Creams cation of the preparations.The results of polarization microscopy of NFX-A, NFX-B, NFX-C, and NFX crystals are shown in Fig. 2. Results revealed that NFX-A and NFX-B were evenly and uniformly dispersed in general.In contrast, NFX-C was found to have clefts and precipitation of needle-shaped crystals.These fi ndings confi rmed that NFX-A and NFX-B were uniformly emulsifi ed, but crystals and voids were found in NFX-C, indicating that NFX-C was not uniformly emulsifi ed.Since crystals were found in NFX-C, NFX-C was irradiated with light at a wavelength of 488 nm and observed.Its needleshaped crystals were found to fl uoresce.When NFX crystals were irradiated with light at a wavelength of 488 nm, they had similar fl uorescence (Fig. 3).
X-ray powder diffraction patterns of NFX-A, NFX-B, NFX-C, and NFX crystals were obtained in order to study the crystals observed in polarization microscopy (Fig. 4).NFX crystals were found to have a characteristic peak at 2θ=20.3°.NFX-A, NFX-B, and NFX-C were found to have peaks at approximately 2θ=21.0°.However, an interesting fi nding is that NFX-C was found to have an x-ray diffraction peak at 2θ=20.4°, unlike the peaks of NFX-A and NFX-B.
Near-infrared absorption spectroscopy was per- formed to examine the molecular state of the creams (Fig. 5).Results revealed that the spectra of NFX-A, NFX-B, and NFX-C lacked the characteristic peak of NFX crystals.Since the preparations had a low NFX content (1%), NFX peaks may have overlapped because of excipients in the preparations.With fatty bases, spectra resulting from olefi n groups have been observed in the regions between 4200 and 4400 cm -1 as well as 5600 and 5800 cm -1 (12).As shown in Fig. 6, NFX-A and NFX-C had roughly the same content based on the second derivative of the near-infrared absorption spectra, but NFX-B was found to have slightly fewer fats and oils than did the other 2 creams.Spectra presumably due to differences in water content resulting from hydroxyl groups have been observed in the region between 5100 and 5400 cm -1 (13).Based on differences in absorption spectra, water content was highest in NFX-B, followed by NFX-C and then NFX-A; NFX-B in particular had a higher water content than the other 2 creams.Thus, the second derivative of near-infrared absorption spectra of excipients is shown in Fig. 7. Results indicated that spectra of individual excipients were similar regardless of the region; NFX-C was found to have a spectrum simi- lar to that of isopropyl myristate in the region between 5900 and 6100 cm -1 .An assay using HPLC was performed to study the NFX content in creams, and the results of this assay are shown in Table 2.
Results revealed that NFX-A, NFX-B, and NFX-C had an NFX content of 90% or more.

Discussion
Pharmaceutical creams have rheologic properties that are crucial to the physical performance of the product when used by the consumer.Most creams are intended to be thick when standing to prevent them from fl owing away from the intended area of use.Differences in additives contained in preparations may affect the fl attening and adherence of  creams.Results of comparing the viscosity and fl attening of NFX creams in this study indicated that individual preparations had different physicochemical properties.Because of viscosimetry, high viscosity at a near zero shear rate characterizes this behavior; determining the yield stress value quantifi es this desired property.Creams are also engineered to be easy to apply when rubbed.Differences in viscosity as were noted here are thought to occur due to differences in the type and amount of additives contained in the preparations.In addition, NFX-C was more likely to have a slightly higher viscosity at about 500 s and 700 s.Typically, when a cream is uniformly emulsifi ed, its viscosity is found to decrease with time.However, determining the viscosity of NFX-C was hampered, so NFX-C is surmised to have a different level of emulsifi cation than that found in NFX-A and NFX-B.From a result of the fl atting measurement, NFX-C spread unevenly and not in a concentric fashion.If the preparation were adequately emulsifi ed, viscosity and fl attening would be measured consistently.However, determination of viscosity revealed that viscosity temporarily increased approximately 500 s and 700 s for NFX-C, and differences in fl attening and the yield values of preparations were noted.Such fi ndings may indicate that differences in additives affected the physical properties of the preparations.When NFX crystals were irradiated with light at a wavelength of 488 nm, they had similar fl uorescence, so the NFX-C crystals are surmised to be NFX crystals (Fig. 3).As shown in Fig. 4, the fact that similar powder x-ray diffraction peaks appeared for the 3 preparations may be due to excipients contained in the preparations.The NFX-C was found to produce powder x-ray diffraction peaks at 2θ=20.4°.This peak coincides with the peak due to NFX crystals, so results suggested that the NFX-C crystals observed with polarization microscopy are NFX crystals.In terms of the typical changes in viscosity over time, if a certain amount of force is applied and a yield value of the substance is exceeded, then its structure will be disrupted.Its viscosity will decrease and the substance will fl atten out.Under conditions where a substance structure is disrupted, its viscosity will seldom increase again.However, NFX-C was found to have a temporary increase in viscosity at 500 s and 700 s.This was potentially caused by the prepa-ration not being uniformly dispersed since the NFX crystals in NFX-C precipitated.In light of these fi ndings, NFX crystal precipitation and emulsifi cation are surmised to have contributed to differences in the emulsifi cation and viscosity of the creams.Based on these fi ndings of the near-infrared absorption spectroscopy, the small amount of fats and oils and high water content in NFX-B may have been factors that affected the viscosity and fl attening of the preparation.In other words, differences in the viscosity and fl attening of the creams may refl ect differences in the content and quality of fats and oils in additives and differences in water content.The spectrum for NFX-C was found to have its peak in a different location than the peaks of spectra for NFX-A and NFX-B in the regions between 4400 and 4500 cm -1 as well as 5800 and 6100 cm -1 .This may indicate differences in spectra that arose because of differences in excipients in the preparations.As shown in Fig. 7, neither NFX-A nor NFX-B contained isopropyl myristate as an excipient, so this additive is thought somehow to affect the emulsifi cation of the cream.The properties of individual creams differ, so presumably this would affect an assay of NFX and its stability.Precipitation of NFX crystals in NFX-C was confi rmed by microscopy.Since an assay using HPLC was performed by dissolving creams in a solvent and quantitatively measuring NFX, results were converted into the NFX content.Disparities in absorbance by and feel on the skin are thought to occur when creams are actually used clinically despite an assay indicating an NFX content of 90% or more.Clearly, differences among NFX-A, NFX-B, and NFX-C arose because of compounding ratios and manufacturing processes despite the preparations being formulated with the same additives.These differences are expected to affect the emulsifi cation of creams.Thus, differences in the emulsifi cation technique used in the cream may affect the preparation, but differences in emulsifi cation, viscosity, and additives may be refl ected in differences in how the preparation feels on the skin in clinical settings.In other words, differences in fl attening lead to different amounts applied by patients in clinical settings and different feel on the skin, and these variations may affect the therapeutic effectiveness of the preparation.Near-infrared absorption spectroscopy, a nondestructive method of analysis, is a useful method of identifying differences in preparations (14).As the current study indicated, differences may affect skin penetration since preparations are used on areas with a thin layer of skin, like the face, to treat conditions like acne.In a study using corticosteroids, Stoughton reported that preparations with different additives resulted in different levels of bioavailability despite the preparations having the same active ingredients and the