Development and Validation of an HPLC-UV Assay to Quantify Plasma Levels of Sulfametrol: A Preferential Antibiotic in Children.

BACKGROUND: Sulfonamides in combination with trimethoprim are frequently used antibiotics. They work synergistic. In infections with Pneumocystis jiroveci or Stenotrophomonas maltophilia, higher dosages are indicated than in other infections. Therapeutic drug monitoring (TDM) is warranted to assure the efficacy while limiting toxicity. Although trimethoprim in combination with sulfamethoxazole is the most common combination with established TDM target concentrations, the intravenous formulation is not suited for children because of its additives ethanol and propylene glycol to increase solubility. An alternative can be sulfametrol in combination with trimethoprim. When sulfametrol was introduced in the hospital, there was a need for a TDM method for sulfametrol.

METHODS: A High Pressure Liquid Chromatography-Ultraviolet (HPLC-UV) detection method for sulfametrol determination in plasma was developed and validated according to the International Conference on Harmonization guidelines. Linearity, limit of detection, lower limit of quantification, recovery, process efficiency, selectivity, within-run precision, between-run precision, and sample stability were tested.

RESULTS: All tested parameters met the required criteria. For linearity, r was 0.9948, lower limit of quantification was 10 mg/L, and limit of detection was 6 mg/L. Recovery was 100.4% and process efficiency 94.4%. Selectivity was met with no interfering peaks at the retention time of 4.2 minutes. Between-run precision and within-run precision were evaluated by replicating quality control levels, resulting in a within-run relative average standard deviation of 0.8% and a between-run relative standard deviation of 2.3%. Recovery of the samples after storing 8 days was 101.9% and recovery of already tested vials was 98.8% after 48 hours.

CONCLUSIONS: In conclusion, an HPLC-UV method for sulfametrol determination in human plasma was developed and validated. The method is fast, accurate, reproducible, and has a short analysis time. It is now being used in routine TDM in our clinic.