Stress Degradation Studies of Tebipenem and a Validated Stability-Indicating LC Method

Identification of related impurities in an oral pharmaceutical formulation of tebipenem pivoxil using ultra-high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry

RATIONALE

Tebipenem pivoxil (TBPM-PI) has been developed as the first oral carbapenem drug in the world to treat otolaryngological and respiratory infections in pediatric patients. Due to its structural properties and external factors, some related impurities, which may cause side effects in patients, might be formed during the synthesis and storage of TBPM-PI. It was vital to rapidly separate and identify the related impurities to guarantee the safe use of TBPM-PI.

METHODS

A method using ultra-high-performance liquid chromatography (UHPLC) coupled with quadrupole time-of-flight tandem mass spectrometry (QTOF-MS/MS) was developed to separate and detect TBPM-PI and related impurities in an oral pharmaceutical formulation. LC/MS and MS/MS spectra of these compounds in the formulation were acquired to confirm their elemental compositions and propose their structures based on LC/MS data and fragmentation pathways of available reference substances.

RESULTS

LC/MS parameters and MS/MS fragmentation pathways of reference substances of TBPM-PI and related impurities were summarized in detail. Based on this, a total of 23 related impurities were found and characterized in the oral pharmaceutical formulation. Eight of these were verified by comparison with reference substances and the structures of the other 15 were proposed for the first time. In addition, four of these compounds were produced by the reaction of excipients and pre-existing related impurities.

CONCLUSIONS

A UHPLC/QTOF-MS method was established and used for the separation and identification of 23 related impurities in a TBPM-PI oral pharmaceutical formulation. Moreover, it was proved that new related impurities could be produced by the reaction of excipients in the pharmaceutical formulation and related impurities in the corresponding active pharmaceutical ingredient (API).

Tebipenem pivoxyl. Derivative spectroscopy study of stability of the first oral carbapenem

A simple and selective derivative spectrophotometric method was developed for the quantitative determination of tebipenem and its pivoxyl ester in the presence of degradation products formed during degradation in aqueous solutions (hydrolysis, oxidation, phosphate buffer pH ∼6.0) and in the solid state (photolysis, thermolysis in dry air and at an increased relative air humidity). The method was based on zero-crossing first-derivative spectrophotometry (λ=341 nm for tebipenem pivoxyl and λ=320 nm for tebipenem), which eliminated the overlapping caused by various degradation products. The selectivity of the method for determination of tebipenem pivoxyl and tepipenem during stability studies was an effect of lack of substituents containing π-bond system chromophores in degradation products. It was also confirmed by comparison of the experimental spectra sample with the theoretical UV spectra and their first derivatives which were obtained by using the density functional theory with the B3LYP hybrid functional and 6-31G(d,p) basis set. The method were linear in the concentration range 16.70-220.0 μg mL(-1) for tebipenem (λ=320 nm; r=0.9989) and 10.70-160.0 μg mL(-1) for tebipenem pivoxyl (λ=341 nm, r=0.9990). The limits of detection and quantitation were 4.72 and 15.60 μg mL(-1) for tebipenem and 2.54 and 8.40 μg mL(-1) for tebipenem pivoxyl, respectively. The method had a good intra-day precision (RSD from 0.12% to 0.62%) and inter-day precision (RSD from 0.22% to 2.13%). The recovery of tebipenem and tebipenem pivoxyl ranged from 99.61% to 99.86% and from 99.38% to 99.87%, respectively. First-derivative spectrophotometry was used for a routine analysis of tebipenem and its ester as well as to monitor the conversion of tebipenem pivoxyl to tebipenem and to predict their degradation pathways.

An Approach to Transfer Methods from HPLC to UHPLC Techniques in Some Carbapenems

Stability-indicating LC methods were developed and validated for the quantitative determination of doripenem, meropenem and tebipenem in the presence of their degradation products formed during forced degradation studies. Isocratic HPLC and UHPLC separations were performed with a core–shell Kinetex 1.7, 2.6 and 5 µm, all C18, 100A, 100 × 2.1 mm columns and the mobile phase composed of acetonitrile and 12 mmol L⁻¹ ammonium acetate in different ratios. The flow rates of the mobile phase were: 0.5 mL min⁻¹ for 1.7 µm column, and 1.0 mL min⁻¹ for 2.6 and 5 µm ones. Detection wavelength was 298 nm and temperature was set at 30 °C. All analysed drugs were exposed to stress conditions which caused their hydrolysis and thermal degradation. The methods were validated by evaluation of linearity, accuracy, precision, selectivity and robustness. Proposed methods were successfully applied for the determination of investigated antibiotics during kinetic studies in aqueous solutions and in the solid state. The advantages of chromatographic procedures which are based on the use of C18 stationary phases with different particle sizes in the analysis of selected carbapenems were discussed.

Natural product and natural product derived drugs in clinical trials

The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.