Solid phase extraction and high performance liquid chromatographic determination of doxophylline in plasma

A Sensitive Microscale HPLC-UV Method for the Determination of Doxofylline and its Metabolites in Plasma: An Adapted Method for Therapeutic Drug Monitoring in Children

Background:

Doxofylline (DXE) is a novel methylxanthine derivative used in the treatment of asthma and Chronic Obstructive Pulmonary Diseases (COPD). Therapeutic Drug Monitoring (TDM) has been proposed in adults, while the adapted analytical method and TDM data are still missing in children.

Methods:

A highly sensitive and stability indicating High-Performance Liquid Chromatography (HPLC) method of DXE with caffeine as the internal standard, was developed and validated by separating its metabolites, β-Hydroxyethyltheophylline (HPE) and Theophylline (TPE). HPLC separation is achieved on C18 column connected to an ultraviolet detector (276 nm), using acetonitrile and ultra-pure water in a gradient mode of elution at a flow rate of 0.9 mL/min at 25°C. A liquid-liquid extraction method using ethyl acetate was developed with a small sample volume of plasma of 50 μL. Trough concentration was monitored in children receiving DXE therapy.

Results:

The method was linear over the concentration ranges from 0.4-20 µg/mL for DXE, HPE and TPE, respectively, in plasma. The limits of quantification were 0.4 µg/mL. Intra- and interday coefficients of variation did not exceed 6.5%, and the accuracy ranged from 94.9% to 112.5%. A total of 39 children (mean age of 1.8 years, range: 0.3-5.7 years) were included. The pediatric patients had detectable DXE concentrations with a mean value of 1.78 µg/mL (range from 0.49 to 6.36 µg/mL), and HPE measurable concentrations with a mean value of 0.52 µg/mL (range from 0.40 to 0.82 µg/mL), while the TPE could not be measured in any patient.

Conclusion:

A sensitive, reliable, and adapted HPLC method has been developed for the simultaneous analysis of DXE and its metabolites in children. The DXE and its metabolites trough concentrations showed large inter-individual variability.

Stability-Indicating RP-HPLC Method for the Simultaneous Estimation of Doxofylline and Terbutalinesulphate in Pharmaceutical Formulations

An isocratic, stability-indicating, reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed for the quantitative determination of doxofylline and terbutaline sulphate, used for the treatment of respiratory problems. The chromatographic separation was achieved on a Zorbax-SB Phenyl 250 × 4.6mm × 5 μm column with the mobile phase consisting of a mixture of 25 mM ammonium acetate (pH 5.0) : acetonitrile (85:15 %v/v) at a flow rate of 1.0 ml/min. The eluate was monitored at 274 nm using a PDA detector. Forced degradation studies were performed on the bulk sample of doxofylline and terbutaline sulphate using acid (0.1N HCl), base (0.1N NaOH), oxidation (10% hydrogen peroxide), photolytic, and thermal degradation conditions. Good resolution was observed between the degradants and analytes. Degradation products resulting from the stress studies did not interfere with the detection of doxofylline and terbutaline sulphate, thus the assay is stability-indicating. The method has the requisite accuracy, selectivity, sensitivity, and precision for the simultaneous estimation of doxofylline and terbutaline sulphate in bulk and pharmaceutical dosage forms. The limit of quantitation and limit of detection were found to be 1.16 μg/ml and 0.38 μg/ml for doxofylline, 2.08 μg/ml and 0.62 μg/ml for terbutaline sulphate, respectively.

Spectrophotometric and reversed-phase high-performance liquid chromatographic method for the determination of doxophylline in pharmaceutical formulations

Two methods are described for determination of Doxophylline in a solid dosage form. The first method was based on ultraviolet (UV)-spectrophotometric determination of the drug. It involves absorbance measurement at 274 nm (λ(max) of Doxophylline) in 0.1 N hydrochloric acid. The calibration curve was linear, with the correlation coefficient between 0.99 and 1.0 over a concentration range of 0.20-30 mg/ml for the drug. The second method was based on high-performance liquid chromatography (HPLC) separation of the drug in reverse-phase mode using the Hypersil ODS C(18) column (250 × 4.6 mm, 5 mm). The mobile phase constituted of buffer acetonitrile (80:20) and pH adjusted to 3.0, with dilute orthophosphoric acid delivered at a flow rate 1.0 ml/min. Detection was performed at 210 nm. Separation was completed within 7 min. The calibration curve was linear, with the correlation coefficient between 0.99 and 1.0 over a concentration range of 0.165-30 mg/ml for the drug. The relative standard deviation was found to be <2.0% for the UV-spectrophotometry and HPLC methods. Both these methods have been successively applied to the solid dosage pharmaceutical formulation, and were fully validated according to ICH guidelines.