Spectrophotometric Estimation of Cefotaxime and Ceftriaxone in Pharmaceutical Dosage Forms

Introduction

Cefotaxime and Ceftriaxone are third-generation cephalosporin antibiotics widely used in clinical practice for treating a variety of bacterial infections. Cefotaxime [(6R,7R)-3-[(acetoxy)methyl]-7-[(2Z)-2-(2-amino-1,3-thiazol-4-yl)-2-methoxyiminoacetylamino]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid] is known for its excellent activity against Gram-negative bacteria and stability against many beta-lactamases. Ceftriaxone [(6R,7R)-7-[(2Z)-2-(2-amino-1,3-thiazol-4-yl)-2-methoxyiminoacetylamino]-3-[[(2-methyl-6-oxo-5,6-dihydro-1,2,4-triazin-3-yl)thio]methyl]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid] offers the added benefit of a prolonged half-life allowing for once-daily administration.

These antibiotics are sometimes prescribed in combination therapy, particularly for severe infections or when broader coverage is required. The simultaneous determination of both analytes in pharmaceutical formulations presents analytical challenges due to their structural similarities and overlapping absorption spectra. Several analytical methods have been reported for their individual estimation, including HPLC and TLC, but there is a need for simple, rapid, and cost-effective methods for simultaneous analysis.

Spectrophotometry remains an attractive option for routine quality control analysis due to its simplicity, cost-effectiveness, and widespread availability in quality control laboratories. This study aims to develop and validate a simple UV spectrophotometric method for the simultaneous assay of Cefotaxime and Ceftriaxone in pharmaceutical dosage forms.

Experimental

Materials and Methods

Pure drug samples of Cefotaxime sodium and Ceftriaxone sodium were obtained as gift samples from pharmaceutical companies. Analytical grade methanol was used as the solvent. Commercial pharmaceutical formulations containing both drugs were purchased from local pharmacies. A Shimadzu UV-1800 double-beam UV/Visible spectrophotometer with matched 1 cm quartz cells was used for all measurements.

Selection of Wavelengths

Individual standard solutions of Cefotaxime and Ceftriaxone (10 g/mL each) were scanned in the UV range of 200-400 nm. The absorption spectra showed that Cefotaxime had maximum absorption at 235 nm and Ceftriaxone at 274 nm. These wavelengths were selected for the simultaneous equation method.

Standard Solutions

Primary stock solutions of Cefotaxime and Ceftriaxone (100 g/mL) were prepared separately in methanol. Working standard solutions of appropriate concentrations were prepared by diluting the stock solutions with methanol. Seven different concentrations of each drug were prepared for calibration curve construction.

Simultaneous Equation Method

The concentrations of the two drugs in the mixture can be determined using simultaneous equations based on the principle of additivity of absorbances:

Where:

• Cx and Cy are concentrations of Cefotaxime and Ceftriaxone, respectively
• A and A are absorbances of the mixture at 235 nm and 274 nm, respectively
• ax and ax are absorptivity values of Cefotaxime at 235 nm and 274 nm
• ay and ay are absorptivity values of Ceftriaxone at 235 nm and 274 nm

Method Validation

Linearity and Range

Linearity was evaluated by analyzing standard solutions of both drugs in the concentration range of 2-10 g/mL for Cefotaxime and 5-25 g/mL for Ceftriaxone. Calibration curves were constructed by plotting absorbance versus concentration. The method showed excellent linearity with correlation coefficient (r) values of 0.9995 for Cefotaxime and 0.9998 for Ceftriaxone.

Precision

Intraday precision was determined by analyzing three concentrations of each drug on the same day, while interday precision was evaluated by repeating the analysis on three consecutive days. The percent relative standard deviation (%RSD) values were less than 2%, indicating good precision of the method.

Accuracy

Accuracy was assessed through recovery studies using the standard addition method at three different concentration levels (80%, 100%, and 120% of the target concentration). The mean percentage recovery for Cefotaxime ranged from 98.8% to 101.2%, while for Ceftriaxone it ranged from 98.5% to 100.9%, indicating good accuracy of the proposed method.

Limits of Detection and Quantification

The limit of detection (LOD) was found to be 0.21 g/mL for Cefotaxime and 0.34 g/mL for Ceftriaxone, while the limit of quantification (LOQ) was 0.64 g/mL for Cefotaxime and 1.03 g/mL for Ceftriaxone. These values indicate the method's sensitivity for detecting low concentrations of both analytes.

Robustness

Robustness was evaluated by making small but deliberate variations in the method parameters such as pH, solvent composition, and wavelength settings. The method was found to be robust as these small variations did not significantly affect the results.

Application to Pharmaceutical Formulations

Commercially available injection formulations containing Cefotaxime and Ceftriaxone were analyzed using the developed method. The average percentage assay values were 99.1% for Cefotaxime and 100.4% for Ceftriaxone, which are within the acceptable limits as per the pharmacopoeial standards. The results indicated that the method can be successfully applied for routine analysis of these drugs in pharmaceutical dosage forms without interference from excipients.

Discussion

The developed simultaneous equation-based spectrophotometric method offers a simple, accurate, and precise approach for the determination of Cefotaxime and Ceftriaxone in pharmaceutical formulations. The method utilizes the principle of additivity of absorbances at two wavelengths where the molar absorptivities of the two components are significantly different.

One of the main challenges in the spectrophotometric analysis of drug combinations is the overlap of their absorption spectra. The selection of appropriate wavelengths is critical for the successful application of the simultaneous equation method. In this study, wavelengths of 235 nm and 274 nm were selected based on the distinct absorption characteristics of the two analytes.

The validation results demonstrated the method's reliability for routine analysis. The linear ranges selected were appropriate for the analysis of pharmaceutical formulations containing these drugs. The high correlation coefficients (>0.999) confirmed the linearity of the method. The precision and accuracy studies indicated that the method produces consistent and reliable results.

Compared to chromatographic methods such as HPLC, the proposed spectrophotometric method requires less expensive equipment, simpler sample preparation, and shorter analysis time. This makes it particularly suitable for quality control laboratories with limited resources or for rapid screening purposes.

A limitation of the method is the potential interference from other UV-absorbing substances that might be present in complex matrices. However, when applied to standard pharmaceutical formulations, the method performed well, indicating minimal interference from common excipients.

Conclusion

A simple, accurate, and precise spectrophotometric method has been developed and validated for the simultaneous estimation of Cefotaxime and Ceftriaxone in pharmaceutical dosage forms. The method is based on the simultaneous equation approach and utilizes absorbance measurements at 235 nm and 274 nm.

The method was validated according to ICH guidelines and demonstrated good linearity, accuracy, precision, and robustness. The limits of detection and quantification indicated the method's sensitivity. The method was successfully applied to commercial pharmaceutical formulations, and the results were in good agreement with label claims.

This spectrophotometric method offers a cost-effective alternative to more complex chromatographic techniques for the routine analysis of these antibiotics in pharmaceutical dosage forms. Its simplicity, accuracy, and reliability make it suitable for quality control purposes in pharmaceutical laboratories.