The photoreactions of trimethoprim in solution

Photolytic degradation of sulfamethoxazole and trimethoprim using UV-A, UV-C and vacuum-UV (VUV)

The photolytic degradation of the non-degradable pharmaceuticals sulfamethoxazole (SMX) and trimethoprim (TMP) in an aqueous solution was investigated using three kinds of low-pressure mercury lamp UV-A (352 nm), UV-C (254 nm), and vacuum-UV (VUV, 185 nm and 254 nm). The degradation rates were highly dependent on the target compounds as well as the UV sources. No degradation of the target compounds was observed using UV-A treatment, because there was no overlap between the UV-A emission spectrum and absorption spectrum of the target compounds. On the other hand, UVC and VUV revealed higher reactivity. The results also indicated that SMX had a greater potential to react photochemically than TMP. Among the UV sources, VUV was the most effective process for the degradation of target compounds. Furthermore, the addition of oxidants such as hydrogen peroxide (H2O2) and sodium persulfate (Na2S2O8) to the reaction system improved the overall degradation rate significantly.The experimental results for the VUV-irradiated samples with the addition of methanol as a hydroxyl radical scavenger revealed that hydroxyl radicals contribute significantly to the elimination of the target compound. Overall, the degradation rate of the target compounds was in the order: VUV = UV-C > UV-A for sulfamethoxazole and VUV/H2O2 > VUV/ Na2S2O8 > VUV >UV-C >UV-A for trimethoprim.

Trimethoprim: kinetic and mechanistic considerations in photochemical environmental fate and AOP treatment

Trimethoprim (TMP), a bacteriostatic antibiotic, has recently been detected in wastewater and surface waters. In this study the sunlight mediated photochemical fate, and treatment using advanced oxidation and reduction (free radical) processes, have been investigated with respect to their effect on TMP. Photochemical fate, in the presence of humic acid, and advanced oxidation treatment both involve the hydroxyl radical (OH) as one of the reactive species of interest. Another reactive oxygen species, singlet oxygen (1O2), may also be important in the photochemical fate of TMP. The bimolecular reaction rate constants of TMP with 1O2 and OH were evaluated to be (3.2±0.2)×10(6) M(-1) s(-1) and 8.66×10(9) M(-1) s(-1), respectively. The reaction kinetics for the sub-structural moieties of TMP, 1,2,3-trimethoxybenzene (TMBz) and 2,4-diaminoprimidine (DAP), was evaluated to facilitate an understanding of the loss mechanisms. For TMBz and DAP the reaction rate constants with 1O2 were <1.0×10(4) and (3.0±0.1)×10(6) M(-1) s(-1), while with OH they were 8.12×10(9) and 1.64×10(9) M(-1) s(-1), respectively. The data suggests that the 1O2 attacks the DAP and the OH radical attacks the TMBz moiety. However, for TMP, 1O2 and OH reactions accounted for only ∼19% and ∼6%, of its total photodegradation, respectively. Therefore, the reaction of TMP with excited state natural organic matter is postulated as a significant degradation pathway for the loss of TMP in sunlit waters containing natural organic matter. There was no effect of pH on the direct or indirect photolysis of TMP. To complete the study for reductive treatment processes, the solvated electron reaction rates for the destruction of TMP, TMBz and DAP were also evaluated. The absolute bimolecular reaction rates obtained were, (13.6±0.01)×10(9), (6.36±0.11)×10(7) and (10.1±0.01)×10(9) M(-1) s(-1), respectively.

Oxidation of antibiotics during water treatment with potassium permanganate: reaction pathways and deactivation

Recent work demonstrates that three widely administered antibiotics (ciprofloxacin, lincomycin, and trimethoprim) are oxidized by potassium permanganate [KMnO(4), Mn(VII)] under conditions relevant to water treatment operations. However, tests show that little to no mineralization occurs during reactions with Mn(VII), so studies were undertaken to characterize the reaction products and pathways and to assess the effects of Mn(VII)-mediated transformations on the antibacterial activity of solutions. Several oxidation products were identified for each antibiotic by liquid chromatography-tandem mass spectrometry (LC-MS/MS). For ciprofloxacin, 12 products were identified, consistent with oxidation of the tertiary aromatic and secondary aliphatic amine groups on the piperazine ring and the cyclopropyl group. For lincomycin, seven products were identified that indicate structural changes to the pyrrolidine ring and thioether group. For trimethoprim, seven products were identified, consistent with Mn(VII) reaction at C═C double bonds on the pyrimidine ring and the bridging methylene group. Oxidation pathways are proposed based on the identified products. Bacterial growth inhibition bioassays (E. coli DH5α) show that the mixture of products resulting from Mn(VII) reactions with the antibiotics collectively retain negligible antibacterial potency in comparison to the parent antibiotics. These results suggest that permanganate can be an effective reagent for eliminating the pharmaceutical activity of selected micropollutants during drinking water treatment.

Direct and indirect photolysis of sulfamethoxazole and trimethoprim in wastewater treatment plant effluent

The photolysis of two antibacterial compounds, sulfamethoxazole and trimethoprim, was studied in wastewater effluent. The rate of loss of sulfamethoxazole was enhanced in wastewater effluent due to indirect photolysis reactions, specifically reactions with hydroxyl radicals and triplet excited state effluent organic matter. Photolysis in the presence of natural organic matter, however, did not lead to enhanced degradation of sulfamethoxazole. Trimethoprim was also found to be susceptible to indirect photolysis in wastewater effluents, with hydroxyl radical and triplet excited effluent organic matter being the responsible species. Deoxygenation of solutions led to more rapid direct photolysis of sulfamethoxazole and trimethoprim, indicating that direct photolysis proceeds through a triplet excited state, which was verified by demonstrating that trimethoprim is a singlet oxygen sensitizer. In the wastewater effluents tested, photolysis could be apportioned into direct photolysis (48% for sulfamethoxazole, 18% for trimethoprim), reaction with hydroxyl radicals (36% and 62%, respectively) and reaction with triplet excited effluent organic matter (16% and 20%, respectively). These results indicate that allowing photolysis in wastewater stabilization ponds or wastewater treatment wetlands may lead to enhanced pharmaceutical removal prior to discharge and that effluent organic matter has different photoreactivity than natural organic matter.

Comparison between liquid chromatography-UV detection and liquid chromatography-mass spectrometry for the characterization of impurities and/or degradants present in trimethoprim tablets

The characterization of impurities and/or degradants present in pharmaceutical compounds is an important part of the drug development process. Although LC-UV is commonly employed for impurities and degradant compound determination, LC-MS techniques are proposed in this work to be a viable modem alternative for the characterization of these compounds. LC-UV and LC-MS were compared for the detection of impurities present in different brands of trimethoprim tablets by using an in-line LC-UV-MS system with atmospheric pressure chemical ionization source (APCI) coupled with a reversed-phase gradient HPLC system. It was shown that, although chemical noise was higher when using full-scan LC-MS compared to LC-UV, low level impurities were better detected by mass spectrometry (MS) when modern software algorithms are employed. These included the "Contour" chromatogram algorithm and/or the "component detection algorithm" (CODA). In addition, MS allowed for the simultaneous determination of the molecular masses and some structural information of the impurities and/or degradants. The results also showed a large difference in the purity of trimethoprim among different manufacturers. LC-MS and tandem MS techniques were employed to acquire fragmentation patterns for trimethoprim and its degradants to gain insight into their structures.