| The rational combination of antimicrobials is known to offer several advantages,including enhanced efficacy,reduced bacterial resistance,and diminished toxic side effects.Florfenicol（FFL）is commonly administered as an antibacterial agent to treat respiratory and intestinal bacterial diseases in livestock and poultry.On the other hand,Sulfamonomethoxine Sodium（SMM-Na）is used to address bacterial infections of the intestinal tract,urinary tract,and soft skin tissues as well as inhibiting Coccidia and Toxoplasma gondii.The combination of these two drugs is frequently prescribed in veterinary practice not just to broaden the antimicrobial spectrum but also to treat mixed infections caused by bacteria and protozoa.However,there is a lack of comprehensive research reporting the effects of this drug combination on in vitro and ex vivo antimicrobial activity,as well as in vivo pharmacokinetic characteristics.In order to established a scientific basis for the use of FFL and SMM-Na in combination,this study aims to comprehensively evaluate their interaction effect on drug absorption,in vitro and ex vivo antibacterial activity,and effect on pharmacokinetic parameters.1.The current study employed the checkboard assay and the temporal inhibition curve to investigate the in vitro antibacterial effect of the combination of florfenicol（FFL）and sulfamonomethoxine sodium（SMM-Na）.The results showed that the combination of the two showed additive effects against E.coli E21-25 and E21-86（FICI=0.75）;synergistic effects against Staphylococcus aureus ATCC25923（FICI=0.375）;synergistic（FICI=0.375）and additive（FICI=0.75）effects against Klebsiella pneumoniae F21-72 and F21-55respectively.Moreover,the combination of the drugs showed an overall synergistic or additive effect on all tested bacteria.The results of the inhibition curves of the combination of S.aureus and Klebsiella pneumoniae,which showed synergistic effects,showed that the combination of 1/2MIC was significantly more effective against ATCC25923 and F21-72than 1/2MIC alone,and that the combination of the two drugs significantly improved the in vitro antibacterial efficacy.A mouse lung infection model was established by tracheal bacteriophage drip method to evaluate the in vivo therapeutic effect of FFL and SMM-Na on Staphylococcus aureus ATCC25923 infection.The results showed that the oral administration of FFL and SMM-Na to the infection model halved the dosing in the combination treatment group compared with the monotherapy group,but the bacterial load in the combination group was reduced by 3log10CFU/m L compared with the model group and by 2log10CFU/m L compared with the SMM-Na monotherapy group,and the combination of the two drugs significantly improved the efficacy of in vivo infection with ATCC25923.2.The objective was to examine the impact of combining florfenicol and sulfamonomethoxine sodium on drug absorption in the intestinal tract through the establishment of an in vivo circulating intestinal perfusion model.The study focused primarily on the small intestine,with simultaneous determination of FFL and SMM-Na in rat intestinal perfusate and examination of the physicochemical stability of the combination of FFL and SMM-Na by HPLC.Our findings indicate that the contents of FFL and SMM-Na remained stable at room temperature for 7 hours.Furthermore,the combination resulted in significantly higher Kavalues of 0.2429±0.0079μg/h·cm2and0.4601±0.0191μg/h·cm2in the small intestine,as well as Peffvalues of 0.5551±0.0172cm/h and 1.1638±0.0140cm/h,which were highly significant（P<0.01）in comparison to the single-use group.Consequently,we observed that the absorption of the combined drugs in the intestinal tract of rats was significantly enhanced compared to that of single-use.This outcome is advantageous to the antibacterial activity of both drugs when administered in vivo.3.To examine the effects of the combination of florfenicol and sulfamonomethoxine sodium on pharmacokinetic characteristics.Eighteen SD rats were randomly divided into three groups:FFL alone（50 mg/kg·bw）,SMM-Na alone（166.7 mg/kg·bw）and the combination group（50 mg/kg·bw+166.7 mg/kg·bw）.The plasma contents of FFL and SMM-Na were determined by HPLC and pharmacokinetic parameters were calculated by DAS2.0 software.The results showed that the in vivo processes in the FFL alone group,SMM-Na alone group and the combination group were in accordance with the primary absorption two-compartment model.Pharmacokinetic parameters for the non-compartment model showed that the peak concentration(Cmax),area under under concentration-time curve（AUC）and time to peak(Tmax)for FFL and SMM-Na alone were 23.79±0.69 and454.66±21.67mg/L,102.88±2.96 and 5708.05±136.33 mg·h/L,1.67±0.47 and 0.54±0.09h.The AUC（117.26±3.63 mg·h/L）and Cmax（32.19±3.24 mg/L）of FFL were significantly increased（P<0.01）and Tmax（0.83±0.12h）was significantly shortened（P<0.01）compared to FFL alone after the combination,which showed that the combination accelerated and promoted the absorption of FFL.The AUC of SMM-Na（6464.44±134.39 mg·h/L）was highly significantly increased（P<0.01）,Tmax（5.67±0.75h）was highly significantly prolonged（P<0.01）,MRT（17.96±0.80h）was highly significantly prolonged（P<0.01）,and Cmax（279.89±30.30 mg/L）were highly significantly reduced（P<0.01）,which indicated the combination promoted absorption and delayed elimination,and the combined SMM-Na had a distinct slow release profile.In conclusion,the combination of florfenicol and sulfamonomethoxine sodium enhances the antibacterial activity in vitro and in vivo,effectively promotes intestinal absorption and increases oral bioavailability,which is an important reference for overcoming the increasing FFL and SMM-Na resistance in veterinary clinics,and provides technical support for the combination of the two in veterinary clinics to reduce the use of veterinary antibiotics. |
