Effect of urine pH and flow on renal clearance of methotrexate

Summary Hydration and urinary alkalinization are used with high doses of methotrexate (MTX) to prevent precipitation of the drug in the renal tubules and consequential nephrotoxicity. The quantitative effect of these measures on the renal clearance of MTX was studied in 8 patients with normal renal function, and in 3 patients with reduced renal function. Multiple regression analysis indicated an influence of both factors on the ratio of the renal clearances of MTX and creatinine. In the eleven patients there was a linear correlation between this ratio and urine pH (p<0.001); the ratio increased from 0.88 at pH 5.5 to 2.62 at pH 8.4. The pH effect on this ratio was similar in the patients with normal and reduced kidney function. An increase in urine flow did not significantly increase the ratio between renal clearance of MTX and creatinine. The effect of urinary alkalinization on renal MTX clearance could be clinically exploited in patients with delayed elimination of MTX. The probable modifying effect of alkalinization of urine on the intentionally high plasma concentration after high dose MTX infusions should be further evaluated, particularly in patients with normal renal function.     

Urinary pH and urine flow independent renal clearance of methotrexate in dogs

The effects of urine flow and pH on methotrexate renal clearance were studied in seven conditioned male Beagle-Mongrel dogs. Steady-state plasma methotrexate and inulin concentrations were achieved by i.v. infusions preceded by i.v. bolus doses. Plasma and urine concentrations of methotrexate were quantitated by a sensitive high-performance liquid chromatographic assay, while those of inulin were measured by a colorimetric method. Since plasma protein binding of methotrexate was pH and concentration independent, methotrexate/inulin renal clearance without correcting for plasma binding was used for most of the data analyses. The results showed that the renal clearance ratios at the plasma methotrexate levels (approximately 0.1, 1.0, 20.0 and 100 micrograms/ml) studied remained relatively constant when urine pH (differences of up to about 2.5 units) and flow rate (differences of up to approximately 30 times) were changed. This indicated that renal reabsorption of methotrexate in these dogs was negligible. However, concentration-dependent renal clearance was observed. The mean renal clearances were 3.84, 3.94, 2.73, and 2.72 ml/min/kg at plasma concentrations of about 0.1, 1.0, 20.0, and 100.0 micrograms/ml, respectively, when urine was alkalized by sodium bicarbonate. The corresponding clearances were 4.02, 4.28, 2.62,and 2.65 ml/min/kg when urine was acidified by ammonium chloride. These showed the existence of saturable tubular secretion of methotrexate. No 7-hydroxy-methotrexate, a metabolite found in other species, was detected in the urine and plasma of the dogs.     

Nonlinear renal elimination kinetics of methotrexate due to saturation of renal tubular reabsorption

Summary The plasma concentration and urinary excretion of methotrexate were followed in twelve psoriatic patients after intravenous and oral doses of methotrexate ranging from 7.5 to 30 mg. In six of the patients, a nonlinear relation was found between the fractional amount of methotrexate excreted in the urine and the corresponding area under the plasma concentration-time curve. The methotrexate clearance was found to be increased during the initial high plasma concentration, probably due to saturation of the tubular reabsorption of methotrexate. Considerable interindividual variation was found in the apparent saturation point of the active reabsorption, but up to 500–800 ng/ml first order kinetics still applied. At plasma concentrations below saturation, the renal clearance of methotrexate ranged from 52–102 ml/min (mean±SD, 83±19.4 ml/min).     

肌酐清除率对大剂量甲氨蝶呤化疗中血药浓度的影响

目的：研究肌酐清除率对于大剂量甲氨蝶呤（HDMTX）化疗中甲氨蝶呤（MTX）血药浓度的影响。方法：收集2006年2月至2008年5月住院期间使用HDMTX化疗方案化疗的44名急性淋巴细胞白血病或非霍奇金淋巴瘤患儿共106次化疗资料,使用SPSS12．0版本回顾性地分析了肌酐清除率和24、42h的血药浓度的相关性。结果：肌酐清除率和24h血药浓度有显著相关性（P〈0．05）。肌酐清除率和42h血药浓度无相关性（P〉0．05）。结论：肌酐清除率对于24hMTX血药浓度有影响,对于预计24hMIX血药浓度有一定参考价值。     

Variability in the renal clearance of cephalexin in experimental renal failure

This study forms a part of an investigation into the extent to which the type of renal damage influences the renal clearance of drugs. We have already demonstrated an effect of different types of experimental renal failure (ERF) on the renal clearance of two cations: cimetidine, a drug that is filtered and secreted by the nephron, and lithium, which is filtered and reabsorbed by more than one segment of the nephron. In this report the renal clearance of cephalexin (CL _CEX )is investigated, a drug that has a different mode of renal elimination, since it is filtered, secreted, and reabsorbed by the proximal tubules. The aim was to extend our earlier studies to an organic onion, and to provide an opportunity to evaluate the feasibility of using the renal clearance of N-1-methylnicotinamide (NMN) to predict the renal clearance of anionic drugs in renal failure. Different models of sitespecific ERF have been developed in the rat; proximal tubular necrosis (induced by cisplatin), papillary necrosis (induced by 2-bromoethylamine), andglomerulonephritis (induced by sodium aurothiomalate or by antiglomerular basement membrane antibodies). Glomerular function (GFR)was assessed by the clearance of inulin (CL _NULIN ),and tubular function was assessed by the clearance of endogenous NMN (CL _NLM .Our results show that even if the models of ERF used were not absolutely site-specific, glomerular function and tubular function did not decrease to the same extent in the different ERF. Therefore, glomerulo-tubular imbalance existed, which is incompatible with the intact nephron hypothesis, i.e., the site of the damage along the nephron and not only the degree of renal dysfunction, is a potential source of variability in the clearance of certain drugs. The renal clearance ofcephalexin was estimated more accurately by CL_NMN than GFR (r= 0.90). We conclude that the clearance of the endogenous cation NMN can be used to predict the renal clearance of drugs that are not only filtered by the glomeruli but also secreted and/or reabsorbed by the proximal tubules, and in the limited examples investigated appears to apply to both anionic and cationic compounds. In this respect the GFRalone was not an adequate parameter for the prediction of the renal clearance of such drugs.     

Prediction of the renal clearance of cimetidine using endogenousN-1-methylnicotinamide

We investigated the influence of the type rather than the degree of renal insufficiency on the renal clearance of drugs. Different models of site specific experimental renal failure (ERF) have been developed in the rat; proximal tubular necrosis, induced by cisplatin; papillary necrosis, induced by 2-bromoethylamine, and glomerulonephritis, induced by sodium aurothiomalate or by antiglomerular basement membrane antibody. Several parameters of kidney function were assessed: the clearance of inulin, PAH, and endogenous N-1-methylnicotinamide (NMN). Plasma BUN and creatinine concentrations, and the presence of proteinuria and glucosuria were also measured. Our results showed a nonparallel decrease in glomerular filtration rate (GFR)and tubular secretion as measured by the secretory clearance of endogenous NMN or by the secretory clearance of p-aminohippuric acid (PAH), that is incompatible with the intact nephron hypothesis. As a result, the renal clearance of cimetidine, a drug eliminated mainly by renal secretion, correlated better with the renal clearance of endogenous NMN than with the GFR.We conclude that (i) our models of ERF demonstrated the existence of glomerulo-tubular imbalance that is contrary to expectations based on the intact nephron hypothesis; (iii) the type of the renal disease has a direct influence on the renal clearance of cimetidine; (in) the clearance of endogenous NMN may be a valuable noninvasive test for assessing renal tubular secretion which could be useful in predicting the clearance of drugs eliminated predominantly by tubular secretion.     

Relationship between total body clearance of caffeine and urine flow rate in elderly men

The total body clearance (CL), renal clearance (CLR), and nonrenal clearance (CLNR) of caffeine from plasma were determined following the intravenous administration of caffeine (4 mg kg-1) to ten healthy men (aged 66-86 years) on three separate occasions. Positive correlations were observed between CL and urine flow rate (UFR), between CLR and UFR, and between CLNR and UFR (r = 0.8947, p = 0.0002; r = 0.8832, p = 0.0003; and r = 0.8920, p = 0.0002, respectively). Previous studies have established similar relationships between CLR and UFR for caffeine and its initial dimethylxanthine metabolites; theophylline, theobromine, and paraxanthine. A relationship between CL and UFR has not been reported previously.     

High haemodialysis clearance of ornidazole in the presence of a negligible renal clearance

Summary The pharmacokinetics of ornidazole was studied in 6 patients treated by haemodialysis and in 8 subjects with a creatinine clearance between 4 and 99 ml/min × 1.73 m². Blood and urine collections were performed for 72 h after i.v. and oral administration of 1.0 g ornidazole.Total body clearance, half-life, volume of distribution and systemic availability were independent of renal function and did not differ from previously reported values in normal volunteers. The haemodialysis clearance of ornidazole was >100% higher than the total body clearance. The renal clearance of ornidazole accounted for less than 7% of the total body clearance. The percentage of the dose of ornidazole recovered in urine as parent compound or as the biologically active metabolites [-(chloromethyl)-2 hydroxymethyl-5 nitroimidazole-1 ethanol and 3-(2 methyl-5 nitroimidazole-1-yl)1,2 propanediol] decreased linearly with decreasing renal function.Although the sum of those three compounds recovered in urine accounted for less than 10% of the total dose of ornidazole administered, they yielded therapeutic concentrations (>4 µg/ml) in urine over 24 h after dosing.Due to the peculiar pharmacokinetic behaviour of ornidazole, i.e. high haemodialysis clearance in the absence of significant renal clearance, no dosage adjustment is necessary while renal function declines, but an increased dose is mandatory while patients are on dialysis.     

Differential effects of the degree of renal damage on p-aminohippuric acid and inulin clearances in rats

Kidney disease is generally thought to affect all segments of a nephron equally. Bricker and co-workers first proposed this as the Intact Nephron hypothesis in 1971, and evidence to date has usually supported this hypothesis. However, most supporting studies have involved severe renal failure, which may not be suitable to differentiate effects on functional sites or to test the hypothesis. The work included here examines the effects of limited renal failure on two separate functions of the nephron: glomerular filtration, as measured by inulin clearance and proximal tubular organic anion secretory function, as measured by p-aminohippuric acid (PAH) clearance. Renal failure was induced in rats by intravenous administration of uranyl nitrate, a nephrotoxin. Doses used were 0.3, 1.0, and 3.0 mg/kg rat body weight. Five days later, rats were given an intravenous infusion of PAH and inulin. Renal clearance of each compound was calculated. Results obtained in these experiments show that, at the lowest uranyl nitrate dose, PAH clearance was significantly decreased but inulin clearance was not. The ratio of CL_PAH/CL_IN was decreased from 2.55 in control rats to 1.21 in rats given the low dose of nephrotoxin. At higher uranyl nitrate doses, both clearance rates were significantly decreased and the ratio of CL_PAH/CL_IN remained close to 1.0. These results indicate that the active transport functions of the nephron can be differentiated from passive transport functions. Caution should be exercised in extrapolating renal disease changes in active renal secretion to changes in passive renal elimination and the reverse.This work was supported in part by NIH grants GM 26691 and GM 36633. C.A.G. was supported in part by a fellowship from the American Foundation for Pharmaceutical Education.     

高效液相色谱法测定氨甲喋呤的血药浓度

目的:建立高效液相色谱法测定血清中氨甲喋呤浓度的方法.方法:以乙腈-水(30:70)为流动相,检测波长294 nm,以咖啡因为内标.结果:在0.05～25 mg·L-1范围内呈良好线性关系,r=0.999 9.日内及日间RSD分别为3.94%,3.63%,平均回收率为99.38%,血清中最低检测浓度为0.025 mg·L-1.结论:本方法具有快速、准确、操作简便等优点.     

高效液相色谱法测定人体血浆中甲氨蝶呤浓度方法的改进

目的:建立高效液相色谱法测定人体血浆中甲氨蝶呤浓度的方法。方法:血浆样品经处理后,色谱分离采用Zorbax-ODSC18(250mm×4.6mm,5μm)色谱柱,检测波长为302nm,流动相为0.01mol.L-1磷酸盐(用磷酸溶液调pH6.7)-甲醇(80∶20),流速为1.0mL.min-1,柱温为35℃。结果:甲氨蝶呤血药质量浓度在0.2～50mg.L-1(r=0.9997)范围内线性关系良好,最低检测质量浓度为5μg.L-1,提取回收率为96.5%～98.7%,方法回收率为98.2%～101.2%,日内、日间RSD分别为3.62%和4.57%。结论:该方法简单、快速、准确适用于临床甲氨蝶呤浓度监测及药动学研究。     

The role of the liver in the clearance ofl-dopa from plasma

The role of the liver in the plasma clearance of l-dopa in the rat was examined. Some published studies which ascribe an important role to the liver in l-dopa clearance are discussed and critically evaluated. Contrary evidence suggesting that the liver is not a significant site of l-dopa clearance in vivo ispresented. The plasma concentration of l-dopa during intravenous infusion of the drug was not significantly reduced after a single passage through the liver. All of the data discussed are consistent with the conclusion that the liver plays a minor role in l-dopa clearance in vivo.It is suggested that the small intestine is the major site of metabolism of orally administered l-dopa.     

Steady state serum concentrations and renal clearance of digoxin in neonates,infants and children

Summary Steady state serum concentrations of digoxin were determined repeatedly in 34 infants with congenital heart disease. Simultaneous measurements of renal clearances of digoxin, creatinine and urea were obtained in 29 of the subjects. Serum digoxin concentrations were markedly higher in children under the age of 3 months than in those over this age, despite equal weight — adjusted 24 h doses. This finding was explained by a very rapid increase in renal digoxin clearance in the first 3 months — 32±7 ml/min/1.73m² at 1 week to 65.6±30 at 3 months. The subsequent increase in digoxin clearance was much slower, e.g. to 87.7±43 ml/min/1.73m² at 12 months. Renal clearance of digoxin was equally well correlated with creatinine clearance (r=0.87) as with urea clearance (r=0.83), but it exceeded that of creatinine in all age groups. The findings indicate that both glomerular and tubular function is involved in the renal elimination of digoxin in young children, and that development of renal elimination of the drug parallels that of the maturation of renal function in the early months of life. The neonate and infant with congestive heart failure display impaired ability to eliminate digoxin. The impairment lessens rapidly with the development of renal function over the first 3 months of life. Diminished doses of digoxin should be advocated in this age group if therapeutic serum concentrations of the drug are to be maintained and toxicity avoided.     

HPLC法测定体液中氨溴索浓度及其药代动力学参数

建立了 HPLC测定人血浆及尿中盐酸氨溴索含量的方法 :Hypersill C18柱 (4.6mm× 2 50 mm,5μm) ,乙腈 -甲醇 - 0 .0 1 mol/L磷酸盐缓冲液 -四氢呋喃 (35∶ 35∶ 2 7.5∶ 2 .5,V/V)为流动相 ,流速 1 .5ml/min,检测波长 2 4 2 nm。结果表明 :最低检测浓度为 5ng/ml,血药浓度在 1 0～ 32 0 ng/ml范围内线性良好 ,尿药浓度在 0 .2 5～ 8.0μg/ml范围内线性良好 ,氨溴索生物半衰期为 (4.2 1± 0 .93) h。     

HPLC-UV法测定人血浆及尿液中比阿培南的浓度

目的建立HPLC-UV法测定人血浆及尿液中比阿培南的浓度。方法血浆样品经超滤离心法提取后,采用XB-C18柱分离,流动相:乙腈-0.1 mol.L-1醋酸铵缓冲液(pH 4.6)=3∶97(v/v),流速:1.0 mL.min-1,检测波长:300 nm,柱温:40℃,进样量:30μL;尿样处理方法同血样,但以甲醇代替乙腈,进样量20μL。结果比阿培南与血浆、尿液中内源性物质分离度好,血药、尿药浓度分别在0.1~50、0.5~300 mg.L-1与峰面积线性关系良好,定量下限分别为0.1、0.5 mg.L-1,绝对回收率分别在90.9%~97.3%、99.1%~102.5%,相对回收率分别为102.1%~110.1%、100.3%~104.4%,日内精密度(RSD)分别<3.4%、2.1%,日间精密度(RSD)分别<5.7%、2.8%。均满足生物样本测定要求。结论所建立方法高效、灵敏、简捷快速、专属性好、重现性高,可用于比阿培南药动学研究。     

肾移植受者术后咪唑立宾血药浓度监测及肌酐清除率对其影响

目的：建立肾移植受者术后咪唑立宾浓度的高效液相色谱串联质谱（HPLC-MS/MS）分析方法,测定咪唑立宾浓度并探讨肌酐清除率对咪唑立宾血药浓度的影响。方法：HPLC色谱柱XDB-C₁₈（150 mm×4.6 mm,5 μm）;流动相0.1%甲酸水溶液（A）-乙腈（B）,梯度洗脱：0~2 min 70% A,2~4 min 40% A,4~7 min 70% A;流速0.6 mL·min^-1;电喷雾离子源ESI负离子模式。肾移植受者术后口服咪唑立宾（100 mg bid）,在初次服药后第10日与第15日分别于服药前半小时和服药后3 h测定血药浓度,观察肌酐清除率对药物浓度的影响。结果：目标化合物咪唑立宾与内标BA-TPQ的离子质荷比（m/z）分别为258.2→126.1和278→91.1。二者分离完全,保留时间分别为2.14 min和2.74 min,提取回收率稳定,日内、日间精密度RSD低于15%,血浆样品在低温环境中稳定。肾移植受者血药浓度监测表明,咪唑立宾浓度与肌酐清除率高度相关,随肌酐清除率降低而升高,不良反应可能与峰浓度高有关。结论：肾移植术后监测咪唑立宾血药浓度,根据肌酐清除率调整给药剂量,有助于降低排异反应,减少不良反应的发生。     

高效液相色谱法测定血浆和尿中头孢唑肟浓度

本文建立了高效液相色谱法测定人血浆和尿中头孢唑肟浓度。血样经高氯酸沉淀蛋白后,直接进样测定;尿样稀释后直接进样测定。固定相为C_(18),5μm颗粒,流动相为乙腈:水:磷酸:二乙胺—1:9:0.013:0.017(v/v)。检测波长为UV254nm(血浆)和290nm(尿),采用内标法定量。方法的线性范围分别为1～160μg/ml(血浆)和10～1600μg/ml(尿),检测限为2ng,平均回收率分别为99.0±1.0%(血浆)和100.3±0.6%(尿)。日内及日间CV%均小于5%。     

Influence of renal failure on the hepatic clearance of bufuralol in man

The beta-blocking agent bufuralol is subject to first-pass metabolism and is eliminated from the body almost entirely by biotransformation. Its major metabolite in plasma (1-hydroxy-bufuralol) is biologically active and may contribute to the pharmacological effect of the drug. The effect of renal failure on the behavior of the parent compound and three of its metabolites was studied by comparing their kinetics in normal volunteers and in patients with severe renal insufficiency. Bufuralol was given orally to all subjects (20 mg); some of the healthy volunteers also received the drug intravenously (5 mg). Renal failure was found to be associated with a marked increase of the areas under the plasma concentration-time curves of the parent compound, whereas its halflife of elimination was not markedly influenced. The behavior of 1-hydroxy-bufuralol was consistent with a decreased renal clearance. The behavior of bufuralol in patients with renal failure was analyzed using the clearance approach. From this analysis it appears that the presystemic biotransformation of bufuralol is decreased in renal failure and that changes in systemic clearance are compensated in our patients by modifications of the volume of distribution, resulting in little net change in the halflife of elimination.     

HPLC-MS/MS测定人体血浆和尿液中罗通定的浓度

目的 建立一种简便、灵敏的测定人体血浆和尿液中罗通定浓度的高效液相色谱串联质谱( HPLC-MS/MS)方法.方法 血浆、尿液样品分别采用乙腈沉淀处理后,进样分析.采用Agilent-ECLIPSE-C18柱(2.1mm×150 mm,5μm),以乙腈-0.2％甲酸溶液=85∶15为流动相,采用正离子,多反应监测方式测定样品浓度.检测离子为m/z356.3→192.3(罗通定)和m/z 285.0→193.0(地西泮,内标).结果 罗通定血浆及尿样均在2.5～1000 ng· mL-1与峰面积线性关系良好(r=0.999 4);最低定量浓度均为2.5 ng·mL-1.日内与日间RSD均＜10％,血浆样品回收率在91.4％～109.2％,尿样回收率在88.63％～115.8％.结论 本方法简便快速、灵敏准确,适用于罗通定在人体内的药物动力学研究.