A microfabricated potentiometric sensor for metoclopramide determination utilizing a graphene nanocomposite transducer layer.

In the recent drug analysis arena, optimizing a green, eco-friendly, and cost-effective technique is the main target. In order to cope with green analytical chemistry principles and the trending development of miniaturized portable and handheld devices, an innovative microfabricated ion-selective electrode for the analysis of metoclopramide (MTP) was developed. The fabricated electrode adopted a two-step optimization process. The first step of optimization depended on screening different ionophores in order to enhance the sensor selectivity. Calix-4-arene showed the maximal selectivity towards MTP. The second step was utilizing a graphene nanocomposite as an ion-to-electron transducer layer between the calix-4-arene polymeric membrane and the microfabricated copper solid-contact ion-selective electrode. The graphene nanocomposite layer added more stability to electrode potential drift and short response times (10 s), probably due to the hydrophobic behavior of the graphene nanocomposite, which precludes the formation of a water layer at the Cu electrode/polymeric membrane interface. The proposed MTP sensor has been characterized according to IUPAC recommendations and the linear dynamic range estimated to be 1 × 10-6 to 1 × 10-2 M with LOD of 3 × 10-7 M. The proposed sensor has been successfully employed in the selective determination of MTP in bulk powder, pharmaceutical formulation, and biological fluid. No statistical significant difference was observed upon comparing the results with those of the official method. The Eco-score of the method was assessed using the Eco-Scale tool and was compared with that of the official method. Graphical abstract.

Validation and application of high performance liquid chromatographic method for the estimation of metoclopramide hydrochloride in plasma.

The objective of this study was validation of a reverse phase HPLC method for the estimation of metoclopramide HCl in plasma already validated for determination of metoclopramide HCl in tablets dosage form. A reverse chromatographic method was used for estimation of metoclopramide HCl with the mobile phase of acetonitrile, 20mM potassium dihydrogen phosphate buffer solution (pH 3.0 adjusted with orthophosphoric acid) in the ratio of 40: 60. The column used was Waters C18 3.9×300mm µBondapak (RP). The flow rate of the mobile phase was 2ml/ minute. The detector was set at the wavelength of 275nm. This method validated in plasma and was found to be linear, with correlation coefficient (R2), value of 0.9988, in the range of 48 ng/ml-0.25ng/ml. The method modified was accurate, precise, sensitive and showed good stability results. The % RSD of the retention time and peak area of metoclopramide HCl was 0.19% and 1.44% respectively. All the parameters such as specificity, linearity, range, accuracy, precision, system suitability, solution stability, detection and quantification limits were evaluated to validate this method and were found within the acceptance limits. The method can be effectively used for estimation of metoclopramide HCl in plasma.

Successful Prediction of Human Steady-State Unbound Brain-to-Plasma Concentration Ratio of P-gp Substrates Using the Proteomics-Informed Relative Expression Factor Approach.

In order to optimize central nervous system (CNS) drug development, accurate prediction of the drug's human steady-state unbound brain interstitial fluid-to-plasma concentration ratio (Kp,uu,brain ) is critical, especially for drugs that are effluxed by the multiple drug resistance transporters (e.g., P-glycoprotein, P-gp). Due to lack of good in vitro human blood-brain barrier models, we and others have advocated the use of a proteomics-informed relative expressive factor (REF) approach to predict Kp,uu,brain . Therefore, we tested the success of this approach in humans, with a focus on P-gp substrates, using brain positron emission tomography imaging data for verification. To do so, the efflux ratio (ER) of verapamil, N-desmethyl loperamide, and metoclopramide was determined in human P-gp-transfected MDCKII cells using the Transwell assay. Then, using the ER estimate, Kp,uu,brain of the drug was predicted using REF (ER approach). Alternatively, in vitro passive and P-gp-mediated intrinsic clearances (CLs) of these drugs, estimated using a five-compartmental model, were extrapolated to in vivo using REF (active CL) and brain microvascular endothelial cells protein content (passive CL). The ER approach successfully predicted Kp,uu,brain of all three drugs within twofold of observed data and within 95% confidence interval of the observed data for verapamil and N-desmethyl loperamide. Using the in vitro-to-in vivo extrapolated clearance approach, Kp,uu,brain was reasonably well predicted but not the brain unbound interstitial fluid drug concentration-time profile. Therefore, we propose that the ER approach be used to predict Kp,uu,brain of CNS candidate drugs to enhance their success in development.

Sensitive and selective liquid chromatography-tandem mass spectrometry method for the determination of metoclopramide in human plasma: application to a bioequivalence study.

A simple, sensitive and rapid method has been developed and validated for determination of the metoclopramide (MCP) in 100 microL human plasma. The analytical procedure involves a liquid-liquid extraction method using tramadol as an internal standard (IS). Chromatographic separation was carried out on a HyPURITY ADVANCE column using a mobile phase consisting of acetonitrile and 10 mm ammonium acetate buffer in the ratio of 80:20 (v/v) at a flow rate of 0.3 mL/min. The total run time of analysis was 2.5 min and elution of MCP and IS occurred at 0.9 and 1.3 min, respectively. A linear response function was established for the range of concentrations 0.53-42.07 ng/mL (r > 0.99). The intra- and inter-day precision values for MCP met the acceptance as per FDA guidelines. MCP was stable in a battery of stability studies viz., bench-top, auto-sampler and freeze-thaw cycles. The developed assay method was successfully applied to an oral bioequivalence study in humans.

The effects of oral administration of Cola nitida on the pharmacokinetic profile of metoclopramide in rabbits.

BACKGROUND: Cola nitida is commonly chewed in many West African cultures to ease hunger pangs and sometimes for their stimulant and euphoriant qualities. Metoclopramide is a known substrate for P-gp, SULT2A1 and CYP2D6 and studies have revealed that caffeine- a major component of Cola nitida can induce P-glycoprotein (P-gp), SULT2A1 and SULT1A1, hence a possible drug interaction may occur on co-administration. The aim of this study was to investigate the pharmacokinetic interactions of Cola nitida and metoclopramide in rabbits. METHODS: The study was performed in two stages using five healthy male rabbits with a 1-week washout period between treatments. Stage one involved oral administration of metoclopramide (0.5 mg/kg) alone while in the second stage, metoclopramide (0.5 mg/kg) was administered concurrently with Cola nitida (0.7 mg/kg). Blood samples were collected after each stage at predetermined intervals and analyzed for plasma metoclopramide concentration using HPLC. RESULTS: Compared with control, the metoclopramide/Cola nitida co-administration produced a decrease in plasma concentration of metoclopramide at all the time intervals except at the 7th hour. The following pharmacokinetic parameters were also decreased: area under the curve (51%), peak plasma concentration (39%), half-life (51%); while an increase in elimination rate constant (113%) and clearance rate (98%) were noted indicating rapid elimination of the drug. A minimal decrease in absorption rate (10%) was also observed. CONCLUSIONS: The results of this study reveal a possible herb-drug interaction between Cola nitida and metoclopramide.

Influence of Rifampicin Pre-treatment on the In vivo Pharmacokinetics of Metoclopramide in Pakistani Healthy Volunteers Following Concurrent Oral Administration.

BACKGROUND: Metoclopramide is metabolized by various cytochrome P450 (CYP) enzymes such as CYP3A4, CYP1A2, CYP2D6, CYP2C9, and CYP2C19. Rifampicin is a non-selective inducer of P-glycoprotein (P-gp) and CYP enzymes such as CYP3A4 and others. OBJECTIVE: This study was aimed at the evaluation of rifampicin's enzyme induction effect on the pharmacokinetic parameters of orally administered metoclopramide. METHOD: This randomized, single-blind, two-phase cross-over pharmacokinetic study separated by a 4-week washout period was conducted at a single center in Pakistan. It involved twelve Pakistani healthy male volunteers (nonsmokers) divided into two groups. In the reference phase, each volunteer received a single oral dose of 20 mg metoclopramide (Maxolon 10 mg, GlaxoSmithKline, Pakistan), while in the rifampicin-treated phase, each volunteer received 600 mg rifampicin once daily for 6 days through oral route. On day 6, metoclopramide (20 mg) was administered 2 hours after the last pretreatment dose of rifampicin. The serial blood samples were collected on predetermined time points (0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 14, and 18 h) and analyzed using a validated HPLC method for the determination of pharmacokinetic parameters, i.e. Cmax, Tmax, and AUC0-∞ of metoclopramide. The whole study was monitored by an unblinded clinician for the purpose of volunteer's health safety. RESULTS: All the volunteers participated in the study until the end. Twelve healthy Pakistani males having mean age 26.0 (range 20.6-34.1) years and body mass index 25.1 (range 16.2-31.5) kg/m2 were included in this study after taking written informed consent. Rifampicin significantly (P<0.05) decreased the mean Cmax, AUC0-∞ and T1/2 of metoclopramide by 35%, 68%, and 44%, respectively. The laboratory tests did not reveal any significant change in the biochemical, physical, hematological, or urinalytical values before and after metoclopramide treatment. None of the volunteers complained of any discomfort during the study. CONCLUSION: Rifampicin noticeably decreased the concentration of plasma metoclopramide. These results give in vivo confirmation of the CYP3A4 involvement in the metoclopramide metabolism, in addition to CYP2D6. Therefore, metoclopramide pharmacokinetics may be clinically affected by rifampicin and other potent enzyme inducers.

Impact of P-Glycoprotein Function on the Brain Kinetics of the Weak Substrate 11C-Metoclopramide Assessed with PET Imaging in Humans.

PET with avid substrates of P-glycoprotein (ABCB1) provided evidence of the role of this efflux transporter in effectively restricting the brain penetration of its substrates across the human blood-brain barrier (BBB). This may not reflect the situation for weak ABCB1 substrates including several antidepressants, antiepileptic drugs, and neuroleptics, which exert central nervous system effects despite being transported by ABCB1. We performed PET with the weak ABCB1 substrate 11C-metoclopramide in humans to elucidate the impact of ABCB1 function on its brain kinetics. Methods: Ten healthy male subjects underwent 2 consecutive 11C-metoclopramide PET scans without and with ABCB1 inhibition using cyclosporine A (CsA). Pharmacokinetic modeling was performed to estimate the total volume of distribution (VT) and the influx (K1) and efflux (k2) rate constants between plasma and selected brain regions. Furthermore, 11C-metoclopramide washout from the brain was estimated by determining the elimination slope (kE,brain) of the brain time-activity curves. Results: In baseline scans, 11C-metoclopramide showed appreciable brain distribution (VT = 2.11 ± 0.33 mL/cm3). During CsA infusion, whole-brain gray matter VT and K1 were increased by 29% ± 17% and 9% ± 12%, respectively. K2 was decreased by 15% ± 5%, consistent with a decrease in kE,brain (-32% ± 18%). The impact of CsA on outcome parameters was significant and similar across brain regions except for the pituitary gland, which is not protected by the BBB. Conclusion: Our results show for the first time that ABCB1 does not solely account for the "barrier" property of the BBB but also acts as a detoxifying system to limit the overall brain exposure to its substrates at the human blood-brain interface.

Second derivative synchronous fluorescence spectroscopy for the simultaneous determination of metoclopramide and pyridoxine in syrup and human plasma.

A rapid, simple, and highly sensitive second derivative synchronous fluorometric method has been developed for the simultaneous determination of metoclopramide (MT) and pyridoxine (PY) in a binary mixture. The method is based on measurement of the native fluorescence of these drugs at delta lambda = 80 nm in methanol. The different experimental parameters affecting the native fluorescence of the drugs were carefully studied and optimized. The fluorescence-concentration plots were rectilinear over the ranges of 0.02-0.4 and 0.1-2 microg/mL for MT and PY, respectively. The limits of detection were 0.003 and 0.007 microg/mL and the limits of quantification were 0.008 and 0.02 microg/mL for MT and PY, respectively. The proposed method was successfully applied to the determination of MT and PY in synthetic mixtures and in commercial syrup. The results were in good agreement with those obtained with a reported method. The high sensitivity attained by the proposed method allowed the determination of MT in spiked and real human plasma samples. The mean percent recoveries of MT from spiked and real human plasma (n = 3) were 93.72 +/- 3.15 and 89.72 +/- 2.19 respectively.

P-Glycoprotein (ABCB1) Inhibits the Influx and Increases the Efflux of 11C-Metoclopramide Across the Blood-Brain Barrier: A PET Study on Nonhuman Primates.

PET imaging using radiolabeled avid substrates of the ATP-binding cassette (ABC) transporter P-glycoprotein (ABCB1) has convincingly revealed the role of this major efflux transporter in limiting the influx of its substrates from blood into the brain across the blood-brain barrier (BBB). Many drugs, such as metoclopramide, are weak ABCB1 substrates and distribute into the brain even when ABCB1 is fully functional. In this study, we used kinetic modeling and validated simplified methods to highlight and quantify the impact of ABCB1 on the BBB influx and efflux of 11C-metoclopramide, as a model of a weak ABCB1 substrate, in nonhuman primates. Methods: The regional brain kinetics of a tracer dose of 11C-metoclopramide (298 ± 44 MBq) were assessed in baboons using PET without (n = 4) or with (n = 4) intravenous coinfusion of the ABCB1 inhibitor tariquidar (4 mg/kg/h). Metabolite-corrected arterial input functions were generated to estimate the regional volume of distribution (VT), as well as the influx (K1) and efflux (k2) rate constants, using a 1-tissue-compartment model. Modeling outcome parameters were correlated with image-derived parameters, that is, areas under the regional time-activity curves (AUCs) from 0 to 30 min and from 30 to 60 min (SUV⋅min) and the elimination slope (kE; min-1) from 30 to 60 min. Results: Tariquidar significantly increased the brain distribution of 11C-metoclopramide (VT = 4.3 ± 0.5 mL/cm3 and 8.7 ± 0.5 mL/cm3 for baseline and ABCB1 inhibition conditions, respectively, P < 0.001), with a 1.28-fold increase in K1 (P < 0.05) and a 1.64-fold decrease in k2 (P < 0.001). The effect of tariquidar was homogeneous across different brain regions. The parameters most sensitive to ABCB1 inhibition were VT (2.02-fold increase) and AUC from 30 to 60 min (2.02-fold increase). VT correlated significantly (P < 0.0001) with AUC from 30 to 60 min (r2 = 0.95), with AUC from 0 to 30 min (r2 = 0.87), and with kE (r2 = 0.62). Conclusion:11C-metoclopramide PET imaging revealed the relative importance of both the influx hindrance and the efflux enhancement components of ABCB1 in a relevant model of the human BBB. The overall impact of ABCB1 on drug delivery to the brain can be noninvasively estimated from image-derived outcome parameters without the need for an arterial input function.

Nasal absorption of metoclopramide from different Carbopol 981 based formulations: In vitro, ex vivo and in vivo evaluation.

There is a need for nasal drug delivery of metoclopramide HCI (MTC) in specific patient populations where the use of commercially available intravenous and oral dosage forms may be inconvenient and/or unfeasible. In this perspective, nasal dosage forms (solution, gel and lyophilized powder) of MTC were prepared by using a mucoadhesive polymer Carbopol 981 (CRB 981). The drug release studies of formulations were performed by using a modified horizontal diffusion chamber with cellulose membrane and excised cattle nasal mucosa as diffusion barriers. After the ex vivo experiments, the morphological appearances of the nasal mucosa were analyzed with the light microscopic studies. In vivo experiments were carried on sheep model. The release of MTC from solution and powder formulations was found higher than gel formulation (p < 0.05) and no severe damage was found on the integrity of nasal mucosa after ex vivo experiments. The penetration enhancing effect of dimethyl-beta-cyclodextrin (DM-beta-CD) used in powder formulations was observed in ex vivo and in vivo experiments. In contrast to in vitro and ex vivo experiments the nasal bioavailability of gel formulation was found higher than those of the solution and powder (p < 0.05) and might represent a promising novel tool for the systemic delivery of MTC.

Rapid-onset intranasal delivery of metoclopramide hydrochloride Part II: Safety of various absorption enhancers and pharmacokinetic evaluation.

In the present study, several nasal absorption enhancers, used in metoclopramide hydrochloride (MCP HCl) nasal solutions, have been screened for their possible damaging effect in the in vitro human erythrocytes lysis experiment. Moreover, the in vivo leaching of biological markers from the rat nasal epithelium was used as a quantitative assessment for possible nasal mucosal irritation whereby the extent of release of total protein and lactate dehydrogenase (LDH) in the nasal lavage fluid was determined. Results showed that insignificant hemolysis from normal saline (P<0.05) occurred with the enhancer protamine sulphate while poly-l-arginine and sodium cholate demonstrated very low (<15%) hemolysis and caused insignificant protein and LDH release from the rat nasal mucosa. Conversely, sodium deoxycholate and chitosan polymers (either of low or high molecular weight) showed high (>60%) hemolysis in vitro and the release of the biological markers in vivo was significantly higher (P<0.05) than the control solution (no enhancer). A significant correlation (P<0.05) existed between the enhancement effect of MCP HCl nasal absorption and the amounts of protein (r=0.85) and LDH (r=0.88). Furthermore, the pharmacokinetics of MCP HCl was determined after intravenous (IV), per-oral and intranasal administration of 10mg drug dose in rabbits. The application of a nasal spray (NS) solution containing 0.5% sodium cholate resulted in a significant improvement (P<0.05) in both the rate and extent of absorption of MCP HCl where the T(max) achieved was 23.3min as compared to 50min in case of the oral solution while the area under the serum concentration-time curve (AUC(0-infinity)) were 506.1, 434.9 and 278.7microg/mlmin for IV, NS and oral solutions, respectively. These values corresponded to absolute bioavailabilities of 87.21 and 55.61% for the NS and oral solutions, respectively. It could thus be concluded that NS of MCP HCl represents a viable approach to achieving rapid and high systemic drug absorption during the emergency treatment of severe emesis.

An accelerated background subtraction algorithm for processing high-resolution MS data and its application to metabolite identification.

BACKGROUND: Metabolite identification without radiolabeled compound is often challenging because of interference of matrix-related components. RESULTS: A novel and an effective background subtraction algorithm (A-BgS) has been developed to process high-resolution mass spectral data that can selectively remove matrix-related components. The use of a graphics processing unit with a multicore central processing unit enhanced processing speed several 1000-fold compared with a single central processing unit. A-BgS algorithm effectively removes background peaks from the mass spectra of biological matrices as demonstrated by the identification of metabolites of delavirdine and metoclopramide. CONCLUSION: The A-BgS algorithm is fast, user friendly and provides reliable removal of matrix-related ions from biological samples, and thus can be very helpful in detection and identification of in vivo and in vitro metabolites.

Clinical pharmacokinetics of high-dose metoclopramide in cancer patients receiving cisplatin therapy.

Using a sensitive and specific high-pressure liquid chromatographic (HPLC) assay, we measured serum levels of metoclopramide in 18 cancer patients receiving high-dose intravenous (IV) therapy to prevent cisplatin-induced emesis. Ten patients were treated with one or more courses with metoclopramide alone (1.0 to 3.0 mg/kg) in an open-label study, and eight patients were treated with a fixed 2.0 mg/kg dose of metoclopramide with or without adjunct dexamethasone (20 mg) using a randomized, crossover design. The pharmacokinetics of metoclopramide were determined, and the relationship between serum levels and clinical response was evaluated. The pharmacokinetic parameters of high-dose metoclopramide were found to be similar to those reported for standard promotility doses, and no dose dependency was demonstrated over the range of doses studied. No clear correlation between serum metoclopramide levels and prevention of cisplatin-induced emesis was observed. The addition of dexamethasone resulted in clinical improvement in two of eight patients, but had no effect on serum metoclopramide levels or kinetic parameters. Results in this study population do not show metoclopramide levels to be related to antiemetic effect following IV cisplatin therapy.

Validated method for determination of bromopride in human plasma by liquid chromatography--electrospray tandem mass spectrometry: application to the bioequivalence study.

A simple, sensitive and specific liquid chromatography-tandem mass spectrometry method for the quantification of bromopride I in human plasma is presented. Sample preparation consisted of the addition of procainamide II as the internal standard, liquid-liquid extraction in alkaline conditions using hexane-ethyl acetate (1 : 1, v/v) as the extracting solvent, followed by centrifugation, evaporation of the solvent and sample reconstitution in acetonitrile. Both I and II (internal standard, IS) were analyzed using a C18 column and the mobile-phase acetonitrile-water (formic acid 0.1%). The eluted compounds were monitored using electrospray tandem mass spectrometry. The analyses were carried out by multiple reaction monitoring (MRM) using the parent-to-daughter combinations of m/z 344.20 > 271.00 and m/z 236.30 > 163.10. The areas of peaks from analyte and IS were used for quantification of I. The achieved limit of quantification was 1.0 ng/ml and the assay exhibited a linear dynamic range of 1-100.0 ng/ml and gave a correlation coefficient (r) of 0.995 or better. Validation results on linearity, specificity, accuracy, precision and stability, as well as application to the analysis of samples taken up to 24 h after oral administration of 10 mg of I in healthy volunteers demonstrated the applicability to bioequivalence studies.

Metoclopramide suppositories in the treatment of diabetic gastroparesis.

Gastroparesis diabeticorum is a common complication that develops in patients with diabetes mellitus. Although the pathogenesis remains unclear, the clinical symptoms of nausea, vomiting, and gastric dilatation frequently respond to metoclopramide hydrochloride, an agent that stimulates gastric emptying in addition to acting centrally as an antiemetic. Occasionally, patients are encountered whose severe gastroparesis is unresponsive to oral metoclopramide and who require intravenous therapy or drainage procedures (eg, pyloroplasty or gastrojejunostomy). Rectal administration of metoclopramide successfully controlled the clinical symptoms of gastroparesis diabeticorum in an outpatient after failure of oral dosing, thus avoiding the need for intravenous therapy. Gastric emptying studies and serum metoclopramide levels following a 25-mg rectal dose of metoclopramide hydrochloride verified the efficacy of therapy.

Pharmacokinetics of metoclopramide in calves with renal dysfunction.

To clarify the effect of renal dysfunction on pharmacokinetics of the prokinetic agent metoclopramide (MCP), we administered intravenously 0.4 mg/kg MCP to healthy calves and calves subjected to right kidney vessel ligation (ligation) without or with a subsequent left nephrectomy (ligation plus removal). Plasma MCP concentration, glomerular filtration rate (GFR) and plasma prolactin level were measured by liquid chromatography-tandem mass spectrometry, simplified equation using iodixanol and enzyme-linked immunosorbent assay, respectively. Only in calves with ligation plus removal, plasma MCP concentrations were increased significantly 6, 8 and 12 hr after injection, showing that a negative correlation was observed between the plasma MCP concentrations and GFR value. A tendency to increase in plasma PRL concentration was noted also in these calves. In conclusions, plasma MCP concentrations depend on the GFR mode in calves, and its critical GFR value was estimated.

Increased dopaminergic activity inhibits basal and metoclopramide-stimulated prolactin and thyrotropin secretion.

The influence of physiological to pharmacological doses of dopamine (DA) on basal and metoclopramide (MTC)-stimulated PRL and TSH secretion was studied in 11 regularly menstruating women between days 3 and 8 of the cycle. In groups of 6, the women received 5-h infusions of either 5% glucose or DA in a solution of 5% glucose at a rate of 12-16 ml/h, adjusted according to weight. Infusion rates of DA were 0.04 microgram/kg . min (low), 0.4 microgram/kg . min (medium), and 4.0 micrograms/kg . min (high). After 3 h of infusion, 10 mg MTC were given iv. Blood samples were collected every 15 min from 1 h before to 2 h after the infusion, for a total of 8 h, for measurements of PRL and TSH. The mean serum PRL concentrations declined significantly (P less than 0.05) during DA infusions to nadir values of 62 +/- 5% (+/- SEM; low), 43 +/- 3% (medium), and 43 +/- 6% (high) of the basal levels, whereas basal TSH levels declined significantly, to 64 +/- 5% of basal levels (P less than 0.05), during both the medium and high dose DA infusions. On paired comparisons, the hormone responses to MTC were lower (P less than 0.05) during the infusion of high dose DA (PRL, 2286 +/- 495% vs. 891 +/- 328%; TSH, 100 +/- 43% vs. 60 +/- 15%), but were not changed when MTC was given during the low and medium doses of DA. A rebound phenomenon was found for PRL (P less than 0.05) after the medium and high doses of DA and for TSH (P less than 0.05) after the high dose. These results indicate that doses of DA considered physiological inhibit PRL and TSH secretion and larger doses inhibit their responses to the DA antagonist MTC.

Metoclopramide kinetics at high-dose infusion rates for prevention of cisplatin-induced emesis.

Eleven male subjects aged 24 to 58 yr received cisplatin, 90 to 120 mg/m2 iv, in combination with other cytostatic drugs such as doxorubicin HCl and bleomycin. To prevent emesis, two high-dose metoclopramide regimens were started 2 hr before cytostatic therapy. Regimen A (n = 7) consisted of a loading dose infusion of 1 mg/kg/hr over 2 hr, followed by a maintenance infusion of 0.5 mg/kg/hr over 24 hr (total dose was 14 mg/kg in each cytostatic cycle). Regimen B (n = 6) consisted of half the metoclopramide dose. The following kinetics were derived from the metoclopramide steady-state plasma levels and the t1/2 of the elimination phase 26 to 38 hr after dosing (median value and range are listed): Steady-state plasma concentration in group A and group B was 750 (480 to 1520) and 360 (300 to 480) ng/ml plasma. Drug clearance in group A and group B was 0.67 (0.3 to 1.0) and 0.70 (0.5 to 0.8) l/hr/kg. Volumes of drug distribution in group A and group B were 4.4 (1.9 to 6.5) and 4.3 (3.2 to 5.9) l/kg. Values for the t1/2 in the elimination phase in group A and group B were 4.7 (3.0 to 5.4) and 4.3 (3.7 to 5.1) hr. It appears that metoclopramide kinetics at high doses were dose linear, i.e., without evidence of cumulation. There were few side effects; vomiting was effectively suppressed by both regimens.

Metoclopramide kinetics in patients with impaired renal function and clearance by hemodialysis.

Metoclopramide kinetics were examined in 24 adult patients with diminished renal function and in eight healthy subjects with normal renal function. Creatinine clearance correlated with metoclopramide plasma clearance, renal clearance, nonrenal clearance, and elimination t1/2. Regardless of renal function, renal clearance accounted for less than or equal to 21% of total plasma clearance. Nonrenal clearance was reduced in patients and accounted for most of the reduction in plasma clearance. The comparatively small plasma clearances in patients imply that maintenance doses should be reduced accordingly to avoid drug cumulation. Metoclopramide clearance by hemodialysis was also assessed in four patients. Metoclopramide losses from hemodialysis were relatively small compared to estimates of total body metoclopramide stores. Compensatory dosage increases are probably unnecessary for most patients. These data also suggest that hemodialysis is not likely to be effective in metoclopramide overdose.

Metoclopramide decreases renal plasma flow.

Intravenous dopamine has been shown to increase renal plasma flow in man. The role of endogenous dopamine in the maintenance of renal plasma flow has not been described. We speculated that if endogenous dopamine activity is important in the maintenance of renal plasma flow, then high doses of a potent dopamine blocking drug such as metoclopramide would decrease renal flow. To test this hypothesis, we measured renal plasma flow using a single-injection technique with 131I-labeled orthoiodohippurate. Measurements were made before and after the administration of high doses of metoclopramide (1 to 2.5 mg/kg) to 20 patients receiving metoclopramide as an antiemetic before chemotherapy. Seven control subjects underwent sequential measurements of renal plasma flow without intervening metoclopramide dosing. Mean (+/- SD) renal plasma flow did not change in the control population (from 441 +/- 198 to 437 +/- 117 ml/min), but declined significantly in the patients who received metoclopramide (443 +/- 115 ml/min before metoclopramide and 387 +/- 137 ml/min after metoclopramide; P less than 0.001). In 25% of our study population the decline in renal plasma flow was greater than 20% below baseline levels. The magnitude of the effect did not appear to correlate with the pretreatment creatinine clearance, age, or sex of the patients. We conclude that high doses of metoclopramide decrease renal plasma flow in man. These data suggest a role for dopamine in the maintenance of renal plasma flow in patients receiving intravenous hydration. Changes of the magnitude we observed may well be of clinical importance. These findings therefore also suggest the possibility of metoclopramide potentiation of cisplatin nephrotoxicity.