Determination of amoxicillin and cotrimoxazole concentrations in sputum of patients with cystic fibrosis

In the management of cystic fibrosis, treatments against Staphylococcus aureus and Haemophilus influenzae such as amoxicillin or cotrimoxazole have to be prescribed and the antibiotherapy's efficacy may be linked to the concentration that reaches the infected site. As cystic fibrosis patients present disturbed pharmacokinetics parameters, drug monitoring would be relevant to assess the lung distribution of antibiotics and to optimize dosing regimens. In this context, the aim of the study was to develop and validate HPLC-based methods for the determination of both antibiotics in bronchial sputum from cystic fibrosis patients, in order to assess the distribution of the drugs into the lungs. Plasma proteins were precipitated by acetonitrile and amoxicillin concentrations in sputum were determined by HPLC coupled with tandem-mass spectrometry. Following liquid extraction with ethyl acetate, cotrimoxazole was quantified by HPLC using ultraviolet detection. Both methods were rapid, specific, accurate and reproducible. The method was applied to patient samples. In three treated patients, concentrations of amoxicillin in sputum were similar and below the lower limit of quantification (0.1 mu g/g) and in six patients, sputum concentrations up to 11.1 and 6.4 mu g/g were measured for sulfamethoxazole and trimethoprim, respectively.

Automated summary

This study aimed to develop and validate HPLC-based methods for determining the concentrations of amoxicillin and cotrimoxazole in bronchial sputum from cystic fibrosis patients in order to assess drug distribution in the lungs. The methods were found to be accurate, specific, rapid, and reproducible. Results showed lower concentrations of amoxicillin and higher concentrations of sulfamethoxazole and trimethoprim in sputum from treated patients.