Wastewater-based epidemiology to assess pharmaceutical consumption. Spanish perspective

Wastewater-based epidemiology (WBE) is a well-established approach that can provide objective and real-time data on the consumption of substances such as pharmaceuticals. However, most of the studies reported so far compares consumption data obtained using WBE with those derived from prescription data from public health systems, which is often incomplete and might represent a source of uncertainty. This study aims to compare the measured pharmaceutical consumption back calculated with the WBE approach with consumption derived from dispensed pharmaceuticals in two regions of Spain, managed by two different Health Systems. To do so, a group of 17 pharmaceuticals, including the most representative ones of every therapeutic family, were monitored in influent wastewater (IWW) samples collected over a week campaign in spring 2022 at four different wastewater treatment plants (WWTPs) in Spain: two WWTPs in Madrid city (center of Spain) and two WWTPs in Catalonia (Northeast of Spain). Population-normalized daily loads (PNDL) revealed that the patterns of pharmaceutical occurrence in the different WWTPs are very similar, being acetaminophen, 4-acetamidoantipyrine and valsartan the pharmaceuticals with the highest PNDL values: 17162 ± 1457 mg day^-1 1000 inh^-1 for acetaminophen, 2365 ± 696 and 2429 ± 263 mg day^-1 1000 inh^-1 for 4-acetamidoantipyrine, 2006 ± 541 and 2041 ± 352 mg day^-1 1000 inh^-1 for valsartan. Pharmaceutical PNLDs were then transformed into measured pharmaceutical consumption (MC) and compared with dispensed consumption (DC) data obtained from the pharmacies in the catchment area where the WWTPs are located. A ratio MC/DC within 0.8 to 1.2 was obtained for 11 out of the 17 studied pharmaceuticals. Highlighting a match in all the cardiovascular system pharmaceuticals, with the exception of losartan (1.29-1.39 ratio) and valsartan (1.35-1.43) in all WWTPs. In summary, the degree of correlation between MC/DC is higher than those previously reported comparing with the prescribed pharmaceutical consumption.