Exploring antibiotic consumption between urban and sub-urban catchments using both parent drugs and related metabolites in wastewater-based epidemiology

Consumption of antibiotics leads to the dissemination of antimicrobial resistance worldwide. Better knowledge of temporal and spatial consumption of antibiotics helps public health authorities to control their usage and combat antimicrobial resistance. However, measuring antibiotic consumption with population surveys, sales data, and production statistics remains challenging due to the complexity of prescription preference, patient compliance, and direct disposal of unused drugs. With the approach of wastewater-based epidemiology (WBE), this study aims to evaluate the consumption of eight commonly-used antibiotics between developed urban and developing sub-urban catchments in China and to characterise the ratios of parent drugs to metabolites in studying the consumption. Seven parent antibiotics were detected in all the wastewater samples (n = 56), whereas some metabolites were detected sporadically. The ratios of parent chemicals to metabolites varied among locations and were often higher than the ratios in pharmacokinetic studies. Estimated consumption of antibiotics ranged from 3.2 ± 2.0 mg/day/1000 inhabitants for trimethoprim to 28,400 ± 7800 mg/day/1000 inhabitants for roxithromycin in the studied catchments. Higher consumption of sulfapyridine, sulfadiazine and roxithromycin was observed in urban than suburban catchments, while consumption of sulfamethoxazole, norfloxacin, and trimethoprim was higher in suburban than in urban catchments. Using the literature data, we found more than 95% reduction of antibiotic use in an urban catchment. Our study revealed the geographical pattern in antibiotic use across different urban and suburban catchments via WBE, and the potential of monitoring parent-to-metabolite ratios for WBE in estimating antibiotic use. These results provide a basis for health authorities to plan different drug-specific control policies between urban and suburban catchments, and for future WBE studies to be aware of other sources, such as animal husbandry and disposals of unused drugs, that can influence the estimated consumption.