On-chip ion pair-based dispersive liquid-liquid extraction for quantitative determination of histamine H2 receptor antagonist drugs in human urine.

In the present work, an ion-pair based dispersive liquid-liquid microextraction was performed on a centrifugal chip for the first time. The entire DLLME procedure, including flow direction, desperation, and sedimentation of the extracting phase, can be fulfilled automatically on a solitary chip. The chip was made of Poly(methyl methacrylate) (PMMA) and was of two units for two parallel extractions, each consisting of three chambers (for the sample solution, extracting solvents, and sedimentation). As the chip rotated, fluids flowed within the chip, and the dispersion, mixing, extraction, and sedimentation of the final phase were performed on the chip by simply adjusting the spin speed. Determination of two histamine H2 receptor antagonist drugs, cimetidine and ranitidine, as the model analytes from the urine samples was done using the developed on-chip ion-pair based DLLME method followed by an HPLC-UV. The effective parameters on the extraction efficiency of the model analytes were investigated and optimized using the one variable at a time method. Under optimized conditions, the calibration curve was linear in the range of 15-2000 µg L-1 with a coefficient of determination (R2) more than 0.9987. The relative standard deviations (RSD %) for extraction and determination of the analytes were less than 3.7% based on five replicated measurements. LODs less than 10.0 µg L-1 and preconcentration factors higher than 39-fold were obtained for both of the model analytes. The proposed chip enjoys the advantages of both the DLLME method and miniaturization on a centrifugal chip.

Colorimetric sensor for cimetidine detection in human urine based on d-xylose protected gold nanoparticles.

Herein, a simple, novel, and rapid colorimetric sensor for cimetidine (Cim) detection based on d-xylose protected gold nanoparticles (d-x@AuNPs) has been developed for the first time. The d-x@AuNPs were characterized by UV-vis, TEM and FT-IR techniques. Cimetidine causes the aggregation of d-x@AuNPs due to the formation of a strong covalent Au-N bond and electrostatic binding. As the cimetidine concentration increased, the color of the solutions gradually changed from wine-red to blue, and the large absorption band shifted from 533 to 680 nm upon d-x@AuNP aggregation. The effects of different experimental parameters were investigated. A comparative study on the detection of Cim using citrated capped AuNPs and d-x@AuNPs was presented. Under optimum conditions, the UV-vis spectra showed that the absorption ratio (A680/A533) increased linearly with the concentration of cimetidine in the range of 7 × 10-8 to 3 × 10-6 M with a correlation coefficient of 0.9956 and a limit of detection of 1 × 10-8 M without needing any complicated instruments. The selectivity of the d-x@AuNP detection system for cimetidine was excellent when compared with other ions and analytes. Due to their rapid and visible color changes, and their remarkable selectivity, the d-x@AuNPs synthesized in this study were suitable and could be applied to the detection of cimetidine in human urine.

Altered pharmacokinetics of cimetidine caused by down-regulation of renal rat organic cation transporter 2 (rOCT2) after liver ischemia-reperfusion injury.

The renal tubular secretion of cationic drugs is dominated by basolateral organic cation transporter 2 (rOCT2/SLC22A2) and luminal multidrug and toxin extrusion 1 (rMATE1/SLC47A1). Little is known about the variation in the expression of these renal transporters after liver ischemia-reperfusion (I/R) injury. Here, we examined the pharmacokinetics of a cationic drug, cimetidine, and renal rOCT2 and rMATE1 levels as well as their regulation after liver I/R. Rats were subjected to 60 min of liver ischemia followed by 12 h of reperfusion. The antioxidant Trolox was administered intravenously 5 min before reperfusion. The systemic and tubular secretory clearances of cimetidine (78% and 55%) as well as renal rOCT2 and rMATE1 levels (67% and 61%) in I/R rats were decreased compared with those in sham-operated rats, respectively. However, the renal tissue-to-plasma concentration ratio but not the renal tissue-to-urine clearance ratio of cimetidine was decreased after liver I/R. Moreover, Trolox prevented the decreases in renal rOCT2 levels and systemic clearance of cimetidine after liver I/R. These results demonstrate that liver I/R decreases the tubular secretion of cimetidine, mainly because of the decreased rOCT2 level in the kidney, and that oxidative stress should be responsible in part for decreased renal rOCT2 after liver I/R injury.

Determination of ranitidine, nizatidine, and cimetidine by a sensitive fluorescent probe.

A validated, simple, and sensitive fluorescence quenching method for the determination of ranitidine, nizatidine, and cimetidine in tablets and biological fluids is presented. This is the first single fluorescence method reported for the analysis of all three H(2) antagonists. The competitive reaction between the investigated drug and the palmatine probe for the occupancy of the cucurbit[7]uril (CB[7]) cavity was studied using spectrofluorometry. CB[7] was found to react with the probe to form a stable complex. The fluorescence intensity of the complex was also enhanced greatly. However, the addition of the drug dramatically quenched the fluorescence intensity of the complex. Accordingly, a new fluorescence quenching method for the determination of the studied drugs was established. The different experimental parameters affecting the fluorescence quenching intensity were studied carefully. At optimum reaction conditions, the rectilinear calibration graphs between the fluorescence quenching values (ΔF) and the medicament concentration were obtained in the concentration range of 0.04-1.9 µg mL(-1) for the investigated drugs. The limits of detection ranged from 0.013 to 0.030 µg mL(-1) at 495 nm using an excitation wavelength of 343 nm. The proposed method can be used for the determination of the three H(2) antagonists in raw materials, dosage forms and biological fluids.

Simple and universal HPLC-UV method to determine cimetidine, ranitidine, famotidine and nizatidine in urine: application to the analysis of ranitidine and its metabolites in human volunteers.

A validated, simple and universal HPLC-UV method for the determination of cimetidine, famotidine, nizatidine and ranitidine in human urine is presented. This is the first single HPLC method reported for the analysis of all four H(2) antagonists in human biological samples. This method was also utilized for the analysis of ranitidine and its metabolites in human urine. All calibration curves showed good linear regression (r(2)>0.9960) within test ranges. The method showed good precision and accuracy with overall intra- and inter-day variations of 0.2-13.6% and 0.2-12.1%, respectively. Separation of ranitidine and its metabolites using this assay provided significantly improved resolution, precision and accuracy compared to previously reported methods. The assay was successfully applied to a human volunteer study using ranitidine as the model compound.

Creatinine for evaluation of glomerular filtration rate in children.

This report is to provide primary care physicians with a convenient method for identifying children with impaired kidney function. This is important because of the prevalence of chronic kidney disease in adults and because intervention may delay disease progression. The glomerular filtration rate (GFR) measured using cimetidine clearance and calculated using height and serum creatinine concentration were compared during 222 clearance studies in 32 pediatric patients over 8 years. A child 1 year or older with a calculated GFR<60 mL/min/1.73 m2 has a significantly reduced GFR and should be referred to a pediatric nephrologist for further evaluation.

Timed-urine collections for renal clearance studies.

The purpose of this study was to describe the reproducibility of timed-urine collections for renal clearance studies and the effect variations in urine collection has on measurement of glomerular filtration rate (GFR). Data from 222 cimetidine clearance studies (GFR-Cim) were obtained from 32 pediatric renal patients over a period of 8 years. There were three to 18 studies per child aged 4.8 years to 21 years at the time of a study. The urinary creatinine excretion rate is measured during supervised urine collection periods. The creatinine excretion rates in each child were compared to obtain data on the reproducibility of the urine collections. The coefficient of variation (CV) of the creatinine excretion rate is approximately 10% in both children and adults. The variation in GFR to be expected during repeated renal clearance studies in subjects with stable GFR, using voided urine collections, was similar in children and adults, with a CV of 12% to 14%.

Renal interaction between itraconazole and cimetidine.

Renal drug interactions can result from competitive inhibition between drugs that undergo extensive renal tubular secretion by transporters such as P-glycoprotein (P-gp). The purpose of this study was to evaluate the effect of itraconazole, a known P-gp inhibitor, on the renal tubular secretion of cimetidine in healthy volunteers who received intravenous cimetidine alone and following 3 days of oral itraconazole (400 mg/day) administration. Glomerular filtration rate (GFR) was measured continuously during each study visit using iothalamate clearance. Iothalamate, cimetidine, and itraconazole concentrations in plasma and urine were determined using high-performance liquid chromatography/ultraviolet (HPLC/UV) methods. Renal tubular secretion (CL(sec)) of cimetidine was calculated as the difference between renal clearance (CL(r)) and GFR (CL(ioth)) on days 1 and 5. Cimetidine pharmacokinetic estimates were obtained for total clearance (CL(T)), volume of distribution (Vd), elimination rate constant (K(el)), area under the plasma concentration-time curve (AUC(0-240 min)), and average plasma concentration (Cp(ave)) before and after itraconazole administration. Plasma itraconazole concentrations following oral dosing ranged from 0.41 to 0.92 microg/mL. The cimetidine AUC(0-240 min) increased by 25% (p < 0.01) following itraconazole administration. The GFR and Vd remained unchanged, but significant reductions in CL(T) (655 vs. 486 mL/min, p < 0.001) and CL(sec) (410 vs. 311 mL/min, p = 0.001) were observed. The increased systemic exposure of cimetidine during coadministration with itraconazole was likely due to inhibition of P-gp-mediated renal tubular secretion. Further evaluation of renal P-gp-modulating drugs such as itraconazole that may alter the renal excretion of coadministered drugs is warranted.

Validation of a simplified method for determination of cimetidine in human plasma and urine by liquid chromatography with ultraviolet detection.

A HPLC method was developed for determination of cimetidine in human plasma and urine. Plasma samples were alkalinized followed by liquid extraction with water-saturated ethyl acetate then evaporated under nitrogen. The extracts were reconstituted in mobile phase and injected onto a C(18) reversed-phase column; UV detection was set at 228 nm. Urine samples were diluted with an internal standard/mobile phase mixture (1:9) prior to injection. The lower limit of quantification in plasma and urine were 100 ng/ml and 10 microg/ml, respectively; intra- and inter-day coefficients of variation were

Spectrophotometric determination of cimetidine in pharmaceuticals and urine using batch and flow-injection methods.

Two sensitive and fast spectrophotometric methods using batch and flow-injection procedures for the determination of cimetidine (CMT) are proposed. The methods are based on the formation of a green complex between this drug and Cu(II) in acetic/acetate medium of pH 5.9. The calibration graphs resulting from measuring the absorbance at 330 nm are linear over the ranges 2.5 x 10(-6)-1.0 x 10(-3) and 5 x 10(-6)-2.0 x 10(-3) M with detection limits of 9.5 x 10(-7) and 2.1 x 10(-6) for batch and flow-injection methods, respectively. The methods are applied to the routine analysis of CMT in pharmaceuticals and human urine.

Down-regulation of rat organic cation transporter rOCT2 by 5/6 nephrectomy.

BACKGROUND: In rat kidneys, the organic ion transporters rOCT1, rOCT2, rOAT1 and rOAT3 are considered to mediate the basolateral uptake of various ionic compounds. However, their changes in chronic renal failure (CRF) are poorly understood. The present study examined the renal handling of organic ions and the expression of these transporters under CRF. METHODS: 5/6 Nephrectomized rats were used as the animal model of CRF. Renal handlings of cimetidine and paraaminohippuric acid (PAH) were examined by in vivo experiments. rOAT1, rOAT3, rOCT1 and rOCT2 expressions were determined by Western blotting. RESULTS: The tubular secretion rates of both PAH and cimetidine were markedly decreased in CRF rats. Although the distribution rates of PAH into the kidney cortex and medulla, and of cimetidine into the kidney cortex were maintained, the distribution rate of cimetidine into the kidney medulla was significantly decreased in CRF rats. The expression level of the rOCT2 protein was markedly depressed in CRF rats, but those of rOCT1, rOAT1 and rOAT3 were maintained. In addition, the plasma concentration of testosterone, a regulator of rOCT2 expression, was significantly reduced by CRF. Both the renal clearance of cimetidine and rOCT2 expression were recovered by the exogenous administration of testosterone in CRF rats. CONCLUSIONS: The levels of urinary excretion of cationic drugs, especially substrates for rOCT2, were reduced under CRF partly due to the reduced expression of rOCT2, and the lowered plasma level of testosterone was suggested to be responsible for the depressed rOCT2 expression in CRF.

Pharmacokinetics of intravenous and intragastric cimetidine in horses. I. Effects of intravenous cimetidine on pharmacokinetics of intravenous phenylbutazone.

Cimetidine was administered intravenously and by the intragastric route to six mares at a dose of 4.0 mg/kg of body weight (bw). Specific and sensitive high performance liquid chromatographic methods for the determination of cimetidine in horse plasma and urine and cimetidine sulfoxide in urine are described. Plasma cimetidine concentration vs. time data were analysed by non-linear least squares regression analysis to determine pharmacokinetic parameter estimates. The median (range) plasma clearance (Cl) was 8.20 (4.96-10.2) mL/min.kg of body weight, that of the steady-state volume of distribution (Vdss) was 0.771 (0.521-1.15) L/kg bw, and that of the terminal elimination half-life (t1/2 beta) was 92.4 (70.6-125) minutes. The median (range) renal clearance of cimetidine was 4.08 (2.19-6.23) mL/min.kg bw or 55.4 (36.3-81.8)% of the corresponding plasma clearance. Cimetidine sulfoxide was excreted in urine and its urinary excretion through 8 h accounted for 12.0 (9.8-16.6)% of the plasma clearance of cimetidine. The median (range) extent of intragastric bioavailability was 14.4 (6.82-21.8)% and the maximum plasma concentration after intragastric administration was 0.31 (0.24-0.50) microgram/mL. Intravenous cimetidine had no effect on the disposition of intravenous phenylbutazone or its metabolites except that the maximum plasma concentration of gamma-hydroxyphenylbutazone was less after cimetidine treatment.

Lack of pharmacokinetic interaction between butorphanol nasal spray and cimetidine.

The potential for a pharmacokinetic interaction between butorphanol nasal spray and cimetidine, under steady state conditions, was evaluated in 16 healthy male volunteers. Subjects received either a 1 mg butorphanol nasal spray every 6 h or a 300 mg cimetidine tablet every 6 h on days 1 4, the combination of two compounds every 6 h on days 5-8 and the original treatment as described in the first segment (days 1-4) on days 9-12. Serial blood and urine samples were collected on days 4, 8 and 12, and additional blood samples were taken immediately, prior to the morning dose on days 3, 7 and 11. Based on the analysis of the Cmin samples, the plasma concentrations of cimetidine and butorphanol achieved steady state by the third day of dosing. No statistically significant differences were found in the plasma concentrations of butorphanol or cimetidine (except for t1/2 and MRT) between any of the treatment phases. Butorphanol nasal spray and cimetidine can be co-administered without any adjustment of dosage for either drug.

Renal tubular transport of cimetidine in the isolated perfused kidney of the rat.

The renal handling of cimetidine (pKa = 6.8) was studied in the isolated perfused rat kidney (IPK). Concentrations in the therapeutic range (< 10 micrograms/ml) had little adverse effects on the functional parameters of the IPK, and even a concentration of 250 micrograms/ml still had only minor effects. When initial perfusate concentrations were low (< 2.5 micrograms/ml), the ratio of renal clearance over filtered amount (CLR/GF) was approximately 3, indicating net tubular secretion. CLR/GF decreased at increasing perfusate concentrations, and above 25 micrograms/ml, there was progressive net reabsorption (CLR/GF < 1). CLR/GF was highly dependent on variations in urine flow and pH, which is indicative of substantial tubular reabsorption by nonionic diffusion. A kinetic model was used to describe the renal handling of cimetidine. This model incorporates the variables influencing the clearance of cimetidine, like urine flow, glomerular filtration rate, and urine pH. Cimetidine was subject to active tubular secretion following Michaelis-Menten kinetics and passive tubular reabsorption of the unionized fraction. The constant for reabsorption was 197 +/- 40 microliters/min, the Michaelis-Menten constant for tubular secretion was 0.2 +/- 0.1 microgram/ml, and the maximum transport capacity was 1.3 +/- 0.3 microgram/min. Cimetidine did not accumulate in IPK, with kidney to perfusate ratios of approximately 2. In conclusion, the renal handling of cimetidine in the IPK is concentration-dependent and is determined by glomerular filtration, active tubular secretion, and a substantial flow- and pH-dependent passive reabsorption.

Chemical, enzymatic, and human enantioselective S-oxygenation of cimetidine.

The S-oxygenation of cimetidine was investigated using achiral chemical and chiral chemical and enzymatic S-oxygenation procedures. The products of the reactions were thoroughly characterized by spectral, chiroptical, chromatographic, and stereochemical correlation methods. S-Oxygenation by the Kagan method or in the presence of pig liver microsomes or pig liver flavin-containing monooxygenase (FMO) (form I) all gave essentially identical enantioselectivity: the average enantiomeric excess was -13.4% and the stereopreference was for formation of (+)-cimetidine S-oxide in a ratio of (+)56.7%:(-)43.3%. The profile of immunoreactivity and the effect of metabolism inhibitors on cimetidine S-oxide formation in the presence of pig liver microsomes were consistent with a role of FMO (form I) in enantioselective (+)-cimetidine S-oxide formation. Administration of cimetidine to seven healthy male volunteers provided pharmacokinetic parameters for cimetidine and cimetidine S-oxide that were typical of those for previously reported studies. The urinary cimetidine S-oxide was isolated and the stereopreference was for formation of (-)-cimetidine S-oxide in a ratio of (+)25.5%:(-)74.5%. In good agreement with the enantiomeric enrichment values observed for the adult human urinary metabolite, the relative configuration of cimetidine S-oxide formed in adult human liver microsomes was (+)-15.8%:(-)-84.2%. Because the enantioselectivity and profile of immunoreactivity and the effect of metabolism inhibitors on cimetidine S-oxygenation in adult human liver microsomes are consistent with a role of FMO (form II) in cimetidine S-oxide formation and because the enantioselectivity of cimetidine S-oxide observed in adult humans is similar, we conclude that in vivo, cimetidine is S-oxygenated principally by FMO (form II).

The effect of probenecid on the renal elimination of cimetidine.

It is generally assumed that the systems involved in the transport of organic cations and organic anions in the renal proximal tubule are substrate selective (i.e., organic anions do not inhibit organic cation transport and vice versa). However, recent data obtained in vitro have suggested that the organic anion probenecid inhibits the renal transport of the organic cation cimetidine. We addressed the question of whether this interaction is biologically relevant in human beings. The study involved a two-treatment, randomized crossover design. Six healthy male subjects were given an intravenous infusion of 300 mg cimetidine alone as one treatment and, as the other treatment, received multiple oral doses of probenecid before receiving the cimetidine infusion. The renal clearance of cimetidine and inulin was determined in each period. There were no significant differences between treatments in cimetidine plasma concentrations, apparent volume of distribution, systemic clearance, half-life, amount of drug excreted unchanged in the urine, or nonrenal clearance. Probenecid significantly decreased the renal clearance of cimetidine by decreasing both the filtration clearance and the net secretory clearance. These effects were most evident in the first 1/2 to 1 hour after cimetidine administration, when probenecid levels in plasma and renal tissue would have been the highest. Because there was no effect of probenecid on cimetidine plasma concentrations, this interaction is not clinically relevant to the therapeutic use of these two compounds. However, the study demonstrates that renal interactions between organic cations and organic anions can occur in human beings. The mechanism of this interaction and the implications to other drug combinations are being explored.

Renal tubular secretion of amiloride and its inhibition by cimetidine in humans and in an animal model.

The histamine H2 antagonist cimetidine has been shown to reduce the renal tubular secretion of other organic cations through competition for the specific transport system with organic cations in the renal proximal tubule. The potential interaction between cimetidine and the potassium-sparing diuretic amiloride was investigated in humans and in the isolated perfused rat kidney. A chronic dosing study was conducted in eight healthy subjects who received, in random order, amiloride (5 mg daily), cimetidine (400 mg twice daily), both drugs together, and a control phase in which no drug was present. Cimetidine reduced the renal clearance of amiloride by a mean of 17%, from 358 +/- 134 to 299 +/- 118 ml/min (p less than 0.05), and the urinary excretion of amiloride from 65 +/- 11 to 53 +/- 13% of the dose (p less than 0.05). Amiloride reduced the excretion of cimetidine from 43 +/- 7 to 32 +/- 9% of the dose (p less than 0.05) and the area under the plasma concentration-time curve for cimetidine by a mean of 14% (p less than 0.05) but had no effect on the renal clearance of cimetidine. In the perfused rat kidney, cimetidine reduced the amiloride unbound renal clearance to glomerular filtration rate ratio from 5-7:1 to 1-2:1 (p less than 0.05). These studies demonstrate that cimetidine inhibits the renal tubular secretion of amiloride in humans and in rats to a similar extent. In addition, in humans the gastrointestinal absorption of both amiloride and cimetidine appear to be reduced by each other, by an as yet unknown mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal transport of drugs: an overview of methodology with application to cimetidine.

The development of new methods to study transport processes in renal epithelia has greatly enhanced our knowledge of the mechanisms involved in the transport of a number of endogenous compounds. More recently, these methods have been applied to study mechanisms of specific drug transport. This article is intended to provide an overview of the various methods used to study renal elimination of compounds. References to more detailed reviews of the individual methods are provided. Studies of the renal transport of cimetidine, a histamine H2-receptor antagonist, are presented to illustrate the application of these methods to the study of specific drugs. Methods such as clearance techniques and the Sperber chicken preparation used to study renal elimination of compounds in whole animals are briefly described. Techniques to identify the site of renal transport including stop flow, isolated perfused tubules, and micropuncture methods are discussed and references to more technical reviews are cited. The more recently developed methods of isolated membrane vesicles for studying transport across the individual polar membranes of the proximal tubule are discussed along with the relevant studies of the use of these membranes in elucidating the mechanisms involved in the renal transport of cimetidine. Finally, the use of cultured renal epithelial cell lines in studying renal transport is described. Knowledge of drug transport mechanisms in the kidney is important both in drug targeting to the kidney and in understanding the pharmacokinetics of renally eliminated drugs. As exemplified by the studies with cimetidine, only by combining the data from experiments using diverse methodology can the mechanisms involved in the renal excretion of compounds be delineated.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of dietary protein-calorie restriction on the renal elimination of cimetidine.

The renal elimination of the weak-base cimetidine was studied in five healthy male subjects during normal and restricted (low-protein, low-calorie) diets in a randomized crossover fashion. An intravenous dose of cimetidine, 7 mg/kg, was administered on day 7 of the normal (100 gm/70 kg protein/day) and the restricted (19 gm/70 kg protein/day) diets. The renal clearance of cimetidine was unchanged by the dietary restriction; however, the fractional excretion of cimetidine increased from 3.06 to 3.94 (P less than 0.05), indicating an apparent increase in net tubular secretion of cimetidine during the restricted diet. We conclude that cimetidine dosage adjustments are apparently not necessary for patients with acutely restricted nutrient intake, although other weakly acidic and basic drugs may require dosage changes.