Pharmacokinetics Study Of Sulfamethoxazole Under Hypoxia Environment At High Altitude

High altitude environment have hypoxia, low pressure, cold, strong radiation and other basic characteristics, which hypoxia is a major factor affecting the activities of human life. After the body reached the plateau region from the plain, the special natural conditions of plateau make the body produce a series of pathological, physiological and biochemical changes, and even anatomical histological changes. There is a certain relationship between body's compensatory and decompensated adjustment reaction to external environment and the changes of absorption, distribution, metabolism and excretion of drugs. Sulfamethoxazole is an antibacterial sulfonamide which is primarily used to treat a variety of bacterial infections such as acute and chronic urinary tract infections, meningitis, respiratory infections. Sulfamethoxazole is widely used as prophylactic treatment for respiratory infection associated with high altitude. Although the pharmacokinetic parameters for sulfamethoxazole in plasma have been reported previously in the absence of exposure to high altitude and under normal conditions, its pharmacokinetic study at high altitude has not been reported.In order to understand pharmacokinetics characteristics of sulfamethoxazole in the special environment of high altitude hypoxia, this paper regard healthy volunteers living at the plain as control group, and study pharmacokinetics characteristics of sulfamethoxazole in healthy volunteers after acute and chronic exposure to high altitude, and native Han and Tibetan volunteers living at high altitude, and research the related mechanism from physiological indicators, the binding rate of protein and erythrocyte with sulfamethoxazole and the activity of N-acetyl-transferaseⅡ. The study will provide valuable references and new ideas to study drug's metabolism in special environment of high altitude hypoxia, and give the guidance to clinical reasonable medication, avoiding adverse reactions and personalized medicine in plateau areas.1. Pharmacokinetics sduty of sulfamethoxazole in healthy male volunteers living at plain, after acute and chronic exposure to high altitude, and native Han and Tibetan volunteers living at high altitudeA sensitive, accurate and simple RP-HPLC method was developed and validated for simultaneous determination of sulfamethoxazole and its metabolite N4-acetylsulfamethoxazole in biological samples. plasma were treated by perchloric acid and separated by HPLC on a C18 reversed-phase column (250 mm×4.6 mm,5μm) using mobile phase of acetonitrile-water-acetic acid-triethylamine (250 mm×4.6 mm,5μm) at a flow rate of 1 ml/min. Calibration curves, which were linear over the range 1 to 160μg/ml for sulfamethoxazole and 0.5 to 20μg/mL for it's metabolite N4-acetylsulfamethoxazole, were analyzed contemporaneously with each batch of samples. The lower limit of quantification was 1μg/mL for sulfamethoxazole and 0.5μg/mL for N4-acetylsulfamethoxazole. The intra-and inter-day precision in terms of RSD for sulfamethoxazole were both under 8.4%, and the intra-and inter-day precision in terms of RSD for N4-acetylsulfamethoxazole were both under 9.6%. The accuracy of sulfamethoxazole and N4-acetylsulfamethoxazole ranged from 99.3% to 105.1% and 92.5% to 106.8%, respectively. The recovery of sulfamethoxazole and N4-acetylsulfamethoxazole ranged from 82.5% to 90.8% and 90.8% to 97.7%, respectively. The method was sensitive, accurate and simple for the simultaneous determination of sulfamethoxazole and it's metabolite N4-acetylsulfamethoxazole in human plasma, it has been used successfully to study pharmacokinetics of sulfamethoxazole and it's metabolite in healthy subjects.The pharmacokinetics of sulfamethoxazole were investigated in healthy male volunteers under hypoxia environment at high altitude by the RP-HPLC method. Healthy male volunteers were divided plain control group (P), acute exposure to high altitude group (HA), chronic exposure to high altitude group (HC), native Han group (HNH), and native Tibetan group (HNT). The following pharmacokinetics parameters of sulfamethoxazole were recorded in plain, acute exposure, chronic exposure, native Han and native Tibetan groups after administration of 1200 mg sulfamethoxazole, respectively:ke,0.076,0.067,0.063,0.064, and 0.067 hours-1; tmax,1.4,1.7,1.6,2.0, and 1.8 hour; Cmax,94.42,91.70,98.72,89.33, and 87.43μg/ml; t1/2,9.30,10.37, 11.15,10.99, and 10.44 hours; Vd,13.27,12.35,14.65,12.81, and 13.28 L/kg; CL, 1.01,0.83,0.92,0.81, and 0.89 L/kg/h; AUC0-48,1202.5,1416.3,1298.5,1434.7, and 1302.8μg-h/ml; AUC0-∞,1240.7,1479.3,1368.8,1511.5, and 1363.9μg-h/ml; MRT, 12.06,13.15,13.00,13.65, and 13.35 hours. The following pharmacokinetics parameters of metabolite N4-acetylsulfamethoxazole were recorded in plain, acute exposure, chronic exposure, native Han and native Tibetan groups after administration of 1200 mg sulfamethoxazole, respectively:tmax,5.7,6.1,5.2,7.1, and 8.4 hour; Cmax, 10.48,10.79,12.13,10.98, and 10.55μg/ml; t1/2,12.43,14.17,13.68,13.32, and 14.04 hours; Vd,34.49,34.21,31.45,31.05, and 33.63 L/kg; CL,1.99,1.69,1.63, 1.64, and 1.67 L/kg/h; AUC0-48,240.9,270.7,290.0,294.4, and 274.9μg-h/ml; AUC0-∞,263.6,303.8,322.1,328.1, and 307.6μg-h/ml; MRT,15.40,16.89,16.82, 17.69, and 17.43 hours.This study found significant changes in the pharmacokinetics of sulfamethoxazole under the special environment of high altitude hypoxia. The ke was 11.8%,17.1%, 15.8% and 11.8% lower in the acute exposure, chronic exposure, native Han and native Tibetan groups, respectively, compared with the plain group. The t1/2 was 11.5%,19.9%,18.2% and 12.3% higher in the acute exposure, chronic exposure, native Han and native Tibetan groups, respectively, than in the plain group. The MRT was 9.0%,7.8%,13.2% and 10.7% higher in the acute exposure, chronic exposure, native Han and native Tibetan groups, respectively, than in the plain group. The CL was 17.8%,19.8% and 11.9% lower in the acute exposure, native Han and native Tibetan groups, respectively, compared with the plain group. The tmax was 42.8% higher in the native Han group compared with the plain group. The AUC0-48 was 17.8% and 19.3% higher in the acute exposure and native Han groups, respectively, compared with the plain group.There are some differences among pharmacokinetics parameters of sulfamethoxazole obtained from the acute exposure, chronic exposure, native Han and native Tibetan groups in the special environment of high altitude hypoxia. The t1/2 and Vd were significantly higher in the chronic exposure group than in the acute exposure group. The Vd, CL and Cmax were significantly lower and AUC was significantly higher in the native Han group than in the chronic exposure group. The Cmax was significantly lower in the Tibetan Han group than in the chronic exposure group. The AUC0-∞was significantly lower in the native Tibetan group than in the native Han group.This study also found significant changes in the pharmacokinetics of metabolite N4-acetylsulfamethoxazole under the special environment of high altitude hypoxia. The MRT was significantly higher and the CL was significantly lower compared with the plain group.2. Comparison of main physiological indexes in healthy male volunteers living at plain, after acute and chronic exposure to high altitude, and native Han and Tibetan volunteers living at high altitudeIn this study, main physiological indexes such as HCT, RBC, HGB, TPR, ALB, Dbil, GPT, GOT, BUN and GLU were determined in healthy male volunteers living at plain, after acute and chronic exposure to high altitude, and native Han and Tibetan volunteers living at high altitude. The HCT, HGB and GLU were significantly higher in the acute exposure, chronic exposure, native Han and native Tibetan groups, respectively, compared with the plain group. The RBC and Dbil were significantly higher in the chronic exposure group than in the plain group. The TPR was significantly higher in the acute exposure, native Han and native Tibetan groups, respectively, compared with the plain group. The GPT, GOT and BUN obtained from 5 groups were within the normal range.3. Comparison of the binding rate of plasma protein and RBC with sulfamethoxazole in healthy male volunteers living at plain, after acute and chronic exposure to high altitude, and native Han and Tibetan volunteers living at high altitudeThe ultrafiltration method was used and the binding rate with HPLC was determined. The binding rate of plasma protein with sulfamethoxazole in vivo was 65.24%,77.50%,71.33%,67.33% and 70.47% in the plain, acute exposure, chronic exposure, native Han and native Tibetan groups, respectively. The binding rate of plasma protein with sulfamethoxazole was 18.8%,9.3% and 8.0% higher in acute exposure, chronic exposure and native Tibetan groups, respectively, compared with the plain group. The binding rate of plasma protein with sulfamethoxazole was no significant difference between the native Han and plain groups.The binding rate of RBC with sulfamethoxazole was 6.04%,6.90%,9.24%,7.39% and 8.29% in the plain, acute exposure, chronic exposure, native Han and native Tibetan groups, respectively. The binding rate of RBC with sulfamethoxazole was 53.0%,22.4% and 37.3% higher in chronic exposure, native Han and native Tibetan groups, respectively, compared with the plain group. The binding rate of RBC with sulfamethoxazole was no significant difference between the acute exposure and plain groups. The free sulfamethoxazole concentration decreased and the bound sulfamethoxazole concentration increased with the binding rate of plasma protein and RBC with sulfamethoxazole increasing in the special environment of high altitude hypoxia, so the elimination of sulfamethoxazole reduced. 4. The effect of high altitude hypoxia on the activity of N-acetyltransferaseⅡin ratsCoffein was used as the probe drugs in this study. Three major metabolites of caffeine including 5-acetylamino-6-formylamino-3-methyl-uracil (AFMU),1-meth-ylxanthine (1X) and 1-methyluric acid (1U) were determined by HPLC method in the urine of rats living at low altitude,1,3, and 7 days after acute exposure to high altitude, and after chronic exposure to high altitude. The rate of AFMU/(AFMU+1U +1X) was calculated and then evaluated the activity of N-acetyltransferaseⅡ. The rate of AFMU/(AFMU+1U+1X) was 0.31,0.26,0.19,0.23 and 0.24 in rats living at low altitude,1,3, and 7 days after acute exposure to high altitude, and after chronic exposure to high altitude, respectively. The rate of AFMU/(AFMU+1U+1X) was 38.75% lower in rats 3 days after acute exposure to high altitude than in rats living at low altitude. Although the rate of AFMU/(AFMU+1U+1X) was lower in rats 1, and 7 days after acute exposure to high altitude, and after chronic exposure to high altitude, respectively, there was no significant difference compared with the low altitude group.This study found that high altitude hypoxia made the activity of N-acetyltransferaseⅡdecreased, and indicated there is a certain relationship between the slow metabolism of sulfamethoxazole and the decreased activity of N-acetyltransferaseⅡin the special environment of high altitude hypoxia.