Pharmacokinetic and concentration-effect studies with intravenous metoclopramide

Photodegradation, toxicity and density functional theory study of pharmaceutical metoclopramide and its photoproducts

Pharmaceuticals as ubiquitous organic pollutants in the aquatic environment represent substances whose knowledge of environmental fate is still limited. One such compound is metoclopramide, whose direct and indirect photolysis and toxicological assessment have been studied for the first time in this study. Experiments were performed under solar radiation, showing metoclopramide as a compound that can easily degrade in different water matrices. The effect of pH-values showed the faster degradation at pH = 7, while the highly alkaline conditions at pH = 11 slowed photolysis. The highest value of quantum yield of metoclopramide photodegradation (ϕ = 43.55·10^-4) was obtained at pH = 7. Various organic and inorganic substances (NO₃^-, Fe(III), HA, Cl^-, Br^-, HCO₃^-, SO₄^2-), commonly present in natural water, inhibited the degradation by absorbing light. In all experiments, kinetics followed pseudo-first-order reaction with r² greater than 0.98. The structures of the photolytic degradation products were tentatively identified, and degradation photoproducts were proposed. The hydroxylation of the aromatic ring and the amino group's dealkylation were two major photoproduct formation mechanisms. Calculated thermochemical quantities are in agreement with the experimentally observed stability of different photoproducts. Reactive sites in metoclopramide were studied with conceptual density functional theory and regions most susceptible to ^•OH attack were characterized. Metoclopramide and its degradation products were neither genotoxic for bacteria Salmonella typhimurium in the SOS/umuC assay nor acutely toxic for bacteria Vibrio fischeri.

Metoclopramide as intermittent and continuous infusions in critically ill patients: a pilot randomized clinical trial

AIM

Metoclopramide is commonly used as a prokinetic agent in critically ill patients with enteral feeding intolerance. In this study, noninferiority of metoclopramide as intermittent versus continuous infusion was examined in critically ill patients with enteral feeding intolerance.

METHODS

Forty critically ill adults patients were assigned to receive metoclopramide as either intermittent (10 mg every 6 h) or continuous (2 mg/h) infusion. Frequency of feeding intolerance and adverse effects of metoclopramide were assessed during 7 days of study.

RESULTS

Number of patients with feeding intolerance during different times of the course was not different between the groups. Although not statistically significant, diarrhea and cardiac rhythm were more common in continuous than intermittent infusion group.

CONCLUSION

Continuous and intermittent infusions of metoclopramide showed equivalent effectiveness in critically ill patients.

Connectome and molecular pharmacological differences in the dopaminergic system in restless legs syndrome (RLS): plastic changes and neuroadaptations that may contribute to augmentation

Restless legs syndrome (RLS) is primarily treated with levodopa and dopaminergics that target the inhibitory dopamine receptor subtypes D3 and D2. The initial success of this therapy led to the idea of a hypodopaminergic state as the mechanism underlying RLS. However, multiple lines of evidence suggest that this simplified concept of a reduced dopamine function as the basis of RLS is incomplete. Moreover, long-term medication with the D2/D3 agonists leads to a reversal of the initial benefits of dopamine agonists and augmentation, which is a worsening of symptoms under therapy. The recent findings on the state of the dopamine system in RLS that support the notion that a dysfunction in the dopamine system may in fact induce a hyperdopaminergic state are summarized. On the basis of these data, the concept of a dynamic nature of the dopamine effects in a circadian context is presented. The possible interactions of cell adhesion molecules expressed by the dopaminergic systems and their possible effects on RLS and augmentation are discussed. Genome-wide association studies (GWAS) indicate a significantly increased risk for RLS in populations with genomic variants of the cell adhesion molecule receptor type protein tyrosine phosphatase D (PTPRD), and PTPRD is abundantly expressed by dopamine neurons. PTPRD may play a role in the reconfiguration of neural circuits, including shaping the interplay of G protein-coupled receptor (GPCR) homomers and heteromers that mediate dopaminergic modulation. Recent animal model data support the concept that interactions between functionally distinct dopamine receptor subtypes can reshape behavioral outcomes and change with normal aging. Additionally, long-term activation of one dopamine receptor subtype can increase the receptor expression of a different receptor subtype with opposite modulatory actions. Such dopamine receptor interactions at both spinal and supraspinal levels appear to play important roles in RLS. In addition, these interactions can extend to the adenosine A₁ and A_2A receptors, which are also prominently expressed in the striatum. Interactions between adenosine and dopamine receptors and dopaminergic cell adhesion molecules, including PTPRD, may provide new pharmacological targets for treating RLS. In summary, new treatment options for RLS that include recovery from augmentation will have to consider dynamic changes in the dopamine system that occur during the circadian cycle, plastic changes that can develop as a function of treatment or with aging, changes in the connectome based on alterations in cell adhesion molecules, and receptor interactions that may extend beyond the dopamine system itself.

Commonly used gastrointestinal drugs

This chapter reviews the spectrum and mechanisms of neurologic adverse effects of commonly used gastrointestinal drugs including antiemetics, promotility drugs, laxatives, antimotility drugs, and drugs for acid-related disorders. The commonly used gastrointestinal drugs as a group are considered safe and are widely used. A range of neurologic complications are reported following use of various gastrointestinal drugs. Acute neurotoxicities, including transient akathisias, oculogyric crisis, delirium, seizures, and strokes, can develop after use of certain gastrointestinal medications, while disabling and pervasive tardive syndromes are described following long-term and often unsupervised use of phenothiazines, metoclopramide, and other drugs. In rare instances, some of the antiemetics can precipitate life-threatening extrapyramidal reactions, neuroleptic malignant syndrome, or serotonin syndrome. In contrast, concerns about the cardiovascular toxicity of drugs such as cisapride and tegaserod have been grave enough to lead to their withdrawal from many world markets. Awareness and recognition of the neurotoxicity of gastrointestinal drugs is essential to help weigh the benefit of their use against possible adverse effects, even if uncommon. Furthermore, as far as possible, drugs such as metoclopramide and others that can lead to tardive dyskinesias should be used for as short time as possible, with close clinical monitoring and patient education.

A trial of midazolam vs diphenhydramine in prophylaxis of metoclopramide-induced akathisia

STUDY OBJECTIVE

The study aimed to evaluate the effects of midazolam and diphenhydramine for the prevention of metoclopramide-induced akathisia.

METHODS

This randomized, double-blind, and controlled trial aimed to investigate coadministered midazolam vs diphenhydramine in the prophylaxis of metoclopramide-induced akathisia. Patients 18 to 65 years of age who presented to the emergency department with primary or secondary complaints of nausea and/or moderate to severe vascular-type headache were eligible for this study. Patients were randomized to one of the fallowing 3 groups: (1) metoclopramide 10 mg + midazolam 1.5 mg; (2) metoclopramide 10 mg + diphenhydramine 20 mg; (3) metoclopramide 10 mg + placebo. Metoclopramide was administered as a 2-minute bolus infusion. Midazolam, diphenhydramine, and normal saline solution were administered as a 15-minute slow infusion. The whole procedure was observed; and akathisia and sedation scores and vital changes were recorded.

RESULTS

There were significant differences among groups with respect to akathisia (P = .016) and sedation (P < .001). The midazolam group showed the lowest mean akathisia score but the highest mean sedation score. Akathisia scores of the diphenhydramine group were not different from placebo. There were significant differences among groups in terms of changes in mean vital findings such as respiration rates, pulse rates, and systolic blood pressures (P < .05). There were no significant difference among groups in terms of changes in mean diastolic blood pressures (P = .09).

CONCLUSION

Coadministered midazolam reduced the incidence of akathisia induced by metoclopramide compared to placebo but increased the rate of sedation. No difference was detected from diphenhydramine. Routine coadministered 20 mg diphenhydramine did not prevent metoclopramide-induced akathisia.

Rate of metoclopramide infusion affects the severity and incidence of akathisia

OBJECTIVE

To investigate the effect of the rate of metoclopramide infusion on akathisia incidence, severity, onset of symptoms, and duration in patients with headache, and/or nausea/vomiting in the emergency department (ED) setting.

METHODS

Prospective, double blind, randomised clinical study comparing two rates of intravenous infusion of metoclopramide over a period of six months at a tertiary university hospital ED.

RESULTS

A total of 300 patients presented to the ED met the inclusion criteria: 151 (50.3%) with nausea/vomiting, 108 (36%) with headache, and 41 (13.7%) with headache and nausea/vomiting. Of these, 154 patients (51.3%) were given 10 mg metoclopramide as a slow intravenous infusion over 15 minutes plus placebo (SIG group) and 146 patients were given 10 mg metoclopramide intravenous bolus infusion over two minutes plus placebo (BIG group). Nine of the 154 patients in the SIG group (5.8%) had akathisia compared with 36/146 patients (24.7%) in the BIG group (p < 0.001, OR 5.273, 95% CI 2.43 to 11.403). Severe akathisia were observed in 13/45 (28.8%). The incidence of severe akathisia was significantly higher in the BIG group (30.5%; 11/36) than in the SIG group (22.2%; 2/9), p = 0.009. Metoclopramide successfully relieved the presenting symptom(s) of 137/146 (90.8%) and 139/154 (90.2%) patients in the BIG and SIG groups, respectively.

CONCLUSIONS

This study suggests that slowing the rate of infusion of metoclopramide is an effective strategy for reducing the incidence of akathisia in patients with headache, and/or nausea/vomiting in ED.

Relative efficacy of some prokinetic drugs in morphine-induced gastrointestinal transit delay in mice

AIM: To study the relative efficacy of cisapride, metoclopramide, domperidone, erythromycin and mosapride on gastric emptying (GE) and small intestinal transit (SIT) in morphine treated mice.

METHODS: Phenol red marker meal was employed to estimate GE and SIT in Swiss albino mice of either sex. The groups included were control, morphine 1 mg/kg (s.c. 15 min before test meal) alone or with (45 min before test meal p.o.) cisapride 10 mg/kg, metoclopramide 20 mg/kg, domperidone 20 mg/kg, erythromycin 6 mg/kg and mosapride 20 mg/kg.

RESULTS: Cisapride, metoclopramide and mosapride were effective in enhancing gastric emptying significantly (P < 0.001) whereas other prokinetic agents failed to do so in normal mice. Metoclopramide completely reversed morphine induced delay in gastric emptying followed by mosapride. Metoclopramide alone was effective when given to normal mice in increasing the SIT. Cisapride, though it did not show any significant effect on SIT in normal mice, was able to reverse morphine induced delay in SIT significantly (P < 0.001) followed by metoclopramide and mosapride.

CONCLUSION: Metoclopramide and cisapride are most effective in reversing morphine-induced delay in gastric emptying and small intestinal transit in mice respectively.

Quantitative determination of domperidone in rat plasma by high-performance liquid chromatography with fluorescence detection

A sensitive and selective analytical method for the determination of domperidone in rat plasma is described. The procedure involves liquid-liquid extraction followed by reversed-phase high-performance chromatographic analysis with fluorometric detection at 282 nm for excitation and 328 nm for emission. The detection limit was 1 ng ml(-1) using 1 ml of plasma. This assay procedure should be useful for the pharmacokinetic study of domperidone in small animals such as rats.

Subhypnotic doses of propofol do not possess antidopaminergic properties

In order to investigate the possible interactions of propofol with the dopaminergic system, a prospective, randomized, double-blind, placebo-controlled study was performed on the profile of prolactin secretion, since prolactin blood levels are known to increase when dopaminergic receptors are blocked. Ten fasting female patients scheduled to receive cancer chemotherapy were allocated to receive either propofol at a rate of 1 mg.kg-1.h-1 or Intralipid 0.1 ml.kg-1.h-1. The study included two consecutive chemotherapy cycles; each patient received in a random order propofol or Intralipid. The infusions were started 4 h prior to induction of chemotherapy; prolactin blood levels were determined at time 0, 30, 60, 120, and 240 min (end of the study period). The basal prolactin blood levels were 14.2 +/- 4.3 vs 12.8 +/- 2.7 and 10.7 +/- 1.7 vs 14.0 +/- 3.6 ng/mL at the end of the study for propofol and Intralipid, respectively. These results suggest that the antiemetic properties of propofol are not mediated via interactions with the dopaminergic system.

Postoperative nausea and vomiting. 2: Management and treatment

The management and nursing care of patients experiencing postoperative nausea and vomiting (PONV) are discussed, together with the various types of pharmacological and complementary approaches to treatment. These treatments are examined in relation to the causes of PONV and a scientific approach to the use of antiemetics which links causation and treatment is suggested. It is argued that by adopting this approach PONV could be minimized, drug bills reduced, patient choice encouraged and postoperative recovery enhanced.

Pharmacological attempts to improve the bioavailability of oral etoposide

Etoposide demonstrates incomplete and variable bioavailability after oral dosing, which may be due to its concentration and pH-dependent stability in artificial gastric and intestinal fluids. The use of agents that may influence etoposide stability and, thereby, bioavailability, was investigated in a number of clinical studies. Drugs that influence the rate of gastric emptying, while modulating the time of drug absorption, did not significantly alter the etoposide area under the concentration-time curve (AUC) or bioavailability. Specifically, metoclopramide had little effect on the etoposide absorption profile and did not significantly alter the AUC (AUC with etoposide alone, 68.4 +/- 20.3 micrograms ml-1 h, versus 74.3 +/- 25.9 micrograms ml-1 h with metoclopramide), suggesting that in most patients the drug is already emptied rapidly from the stomach. In contrast, propantheline produced a dramatic effect on etoposide absorption, delaying the time of maximal concentration tmax from 1.1 to 3.5 h (P < 0.01), but again without a significant improvement in drug AUC or bioavailability across the 24-h study period (AUC with etoposide alone 78.3 +/- 19.1 micrograms ml-1 h, versus 88.1 +/- 23.6 micrograms ml-1 h with propantheline). The effect of these drugs on the absorption of oral paracetamol, a drug included in the study as a marker of gastric emptying, was exactly the same as that found for etoposide, with no change in AUC being observed after metoclopramide or propantheline administration but a significant delay in tmax being seen on co-administration with etoposide and propantheline. The co-administration of ethanol or bile salts (agents that significantly improved the stability of etoposide in artificial intestinal fluid) with oral etoposide similarly had no effect on improving the etoposide AUC or reducing the variability in AUC, suggesting that drug stability in vivo was not affected by these agents. In the third study the co-administration of cimetidine had no effect on the pharmacokinetics of oral or i.v. etoposide, despite the previous observation that etoposide stability was markedly improved at pH 3-5 as compared with pH 1 in artificial gastric fluid. This series of studies, designed to investigate factors that improved etoposide stability in laboratory studies, failed to demonstrate any potentially useful improvement in AUC or bioavailability in the clinical setting.

Determination of metoclopramide and two of its metabolites using a sensitive and selective gas chromatographic-mass spectrometric assay

A modified gas chromatographic-mass spectrometric (GC-MS) assay has been developed to quantitate metoclopramide (MCP) and two of its metabolites [monodeethylated-MCP (mdMCP), dideethylated-MCP (ddMCP)] in the plasma, bile and urine of sheep. The heptafluorobutyryl derivatives of the compounds were formed and quantitated using electron-impact ionization in the selected-ion monitoring mode (MCP, m/z 86, 380; mdMCP, m/z 380 and ddMCP, m/z 380). No interference was observed from endogenous compounds following the extraction of various biological fluids obtained from non-pregnant sheep. Sample preparation has been simplified and the method is more selective and sensitive (2 fold) than our previous assay using electron-capture detection. The limit of quantitation for MCP, mdMCP and ddMCP was 1 ng/ml in plasma, urine and bile, requiring 0.5 ml of sample. This represents 2.5 pg of the analytes at the detector. The standard curves were linear over a working range of 1-40 ng/ml. Absolute recoveries in plasma ranged from 76.5-94.7%, 79.2-96.8%, 80.3-102.2% for MCP, mdMCP and ddMCP, respectively. In urine, recoveries ranged from 56.5-87.8%, 61.5-87.5%, 62.6-90.2% for MCP, mdMCP and ddMCP, respectively. Recoveries in bile ranged from 83.5-100.9%, 78.5-90.5%, 66.9-79.2% for MCP, mdMCP and ddMCP, respectively. Overall intra-day precision ranged from 2.9% for MCP in plasma to 12.6% for mdMCP in bile. Overall inter-day precision ranged from 5.9% for MCP in urine to 14.9% for ddMCP in bile. Bias was the greatest at the 1 ng/ml concentration in all biological fluids ranging from a low of 2.4% for mdMCP in plasma to a high of 11.9% for ddMCP in urine. Applicability of the assay for pharmacokinetic studies of MCP, mdMCP and ddMCP in the plasma and urine of a non-pregnant ewe is demonstrated.

Pharmacokinetics of metoclopramide in goats

The pharmacokinetics of a parenteral formulation of metoclopramide (monochloride monohydrate) were determined following single intravenous (i.v.) and intramuscular (i.m.) 0.5-mg/kg doses to two groups of 4 goats in a crossover design. Mean serum concentrations of metoclopramide following i.v. administration of 0.5 mg/kg declined rapidly from a peak of 277.5 ng/ml at 3 min post-dosing to 25 ng/ml at 90 min. Serum concentrations were not detectable by 120 min after drug administration. The curve of serum concentrations vs. time was characteristic of a two-compartment open model. Mean parameters from analysis of the individual i.v. data gave a biological half-life of 0.62 h and a volume of distribution of the central compartment of 1.34 l/kg. Serum concentrations of metoclopramide following i.m. administration of 0.5 mg/kg rose rapidly to a peak of 160.9 ng/ml at 15 min post-dosing and then declined in parallel with the elimination phase of the i.v. study. These data were best described by a two-compartment open model with first-order absorption. The mean biological half-life was 1.04 h. There were no adverse reactions associated with metoclopramide at the 0.5-mg/kg dose administered by either route.

Clinical pharmacokinetics of drugs used in the treatment of gastrointestinal diseases (Part II)

Part I of this article, which appeared in the previous issue of the Journal, covered the following agents: histamine H2-receptor antagonists (cimetidine, ranitidine, famotidine, nizatidine); muscarinic-M1-receptor antagonists (pirenzepine); proton pump inhibitors (omeprazole); site-protective agents (colloidal bismuth subcitrate, sucralfate); antacids and prostaglandin analogues; antiemetics and prokinetics (metoclopramide, domperidone, cisapride); and antispasmodics. In Part II, we consider the anti-inflammatory salicylates, nonspecific antidiarrhoeal agents, laxatives and cathartics.

Effect of metoclopramide, bethanechol, and loperamide on gastric residence time, gastric emptying, and mouth-to-cecum transit time

The effects of metoclopramide, bethanechol, and loperamide on the gastric residence time (GRT), gastric emptying (GE), and mouth-to-cecum transit time (MCTT) of a solution were investigated in three separate studies of five healthy male volunteers each. Metoclopramide in doses of 5, 10, and 15 mg prolonged GRT by 33, 88, and 162%, respectively, almost reaching statistical significance (p 0.058). A relationship was observed between GRT prolongation, and metoclopramide area under the plasma-time curve (p 0.01) and metoclopramide observed time to maximum concentration (p 0.01). Metoclopramide had an inconsistent effect on MCTT. Bethanechol 50 mg prolonged GRT by 64% (p 0.031) and had no effect on MCTT. Loperamide at doses of 2 and 8 mg prolonged GRT by 18 and 115% (p 0.043) and MCTT by 30 and 130% (p 0.0001), respectively. None of these motility-altering agents affected GE.

A single dose pharmacokinetic study of Gastrobid Continus and Maxolon in the perioperative period

1. A single dose pharmacokinetic comparison of Gastrobid Continus and Maxolon was carried out perioperatively in two groups of 12 gynaecological patients; each group comprised six patients for major surgery and six patients for minor surgery. 2. The areas under the plasma drug concentration-time curves were similar after both preparations. 3. In the minor surgery group after Gastrobid Continus the plasma drug concentration-time curve was wider at half Cmax (P less than 0.01), Cmax was reduced (P less than 0.05) and delayed (median (range) 4 (3-6) vs 2.5 (2-4) h) compared with Maxolon, and the log of the metoclopramide concentration did not have a linear relationship with time from 2-9 h. 4. A flattening of the plasma drug concentration-time curve was the only difference between the two preparations in the major surgery groups. 5. The plasma drug concentration-time curve was wider (P less than 0.05) at at half Cmax in the minor compared with the major surgery groups receiving Gastrobid Continus. 6. Pharmacokinetic parameters were similar for Maxolon in both surgical groups. 7. Sustained release pharmacokinetic characteristics were most pronounced in the minor surgery group which did not receive opiate medication but in which there were more moderately anxious patients prior to induction and in whom anxiety may have delayed gastric emptying.

A radioimmunoassay for metoclopramide

A radioimmunoassay for the anti-emetic drug, metoclopramide, in the pmol range was developed. The immunogen was prepared by photolytic coupling of metoclopramide to bovine serum albumin. A crosslinking reagent, N-hydroxy-succinimidyl-4-azidobenzoate, was first reacted with serum albumin through nucleophilic substitution. Ultraviolet irradiation (lambda greater than 300 nm) of the photoactive serum albumin conjugate in the presence of metoclopramide resulted in covalent attachment of the drug to the protein. An 125I-labelled metoclopramide derivative was prepared by diazotisation of the aromatic amine group and substitution of the resultant diazo group with 125I-. Binding data of the antibody with radioiodinated metoclopramide gave a linear Scatchard plot indicative of a homogeneous antibody population. A dissociation constant of 3 X 10(-11) mol/l was calculated for the antigen-antibody interaction. The antibodies showed negligible cross-reactivity with lignocaine which is structurally closely related to metoclopramide.

Determination of metoclopramide and its glucuronide and sulphate conjugates in human biological fluids (plasma, urine and bile) by ion-pair high-performance liquid chromatography

Metoclopramide was determined in human biological fluids (plasma, urine and bile) by reversed-phase ion-pair high-performance liquid chromatography using a newly introduced cyanopropyl column. The method is precise, selective and sensitive: the mean recoveries of metoclopramide from plasma, urine and bile were 74.4, 99.1 and 85.9%, respectively; the mean within- and between-run coefficients of variation were, respectively, 0.8 and 8.5% for plasma and 2.0 and 8.2% for urine at the drug concentration of 100 ng/ml, and 2.3 and 11.2% for bile at the concentration of 20 ng/ml; the lower detection limit was 2 ng/ml for 1 ml of each biological fluid. Enzymic hydrolysis of a urine or bile specimen was used in the identification of metoclopramide, as well as its glucuronide and sulphate conjugates, from the human samples. A preliminary study on metoclopramide determinations from plasma and urine samples of a healthy subject and from bile samples of a patient demonstrated the clinical applicability of the method for therapeutic monitoring and pharmacokinetic studies.

Bioavailability and disposition of metoclopramide after single- and multiple-dose administration in diabetic patients with gastroparesis

The disposition of metoclopramide after acute and chronic administration was determined in four diabetic patients with gastroparesis who had a creatinine clearance of 70.8 +/- 10.7 mL/min (mean +/- SD). Single, 10-mg oral and intravenous doses were administered on days 1 and 2, respectively, followed by 10 mg orally every six hours for three weeks. A second, 10-mg intravenous bolus dose was administered on the last morning of chronic therapy. Metoclopramide concentrations were determined by high performance liquid chromatography. The elimination half-life, steady-state volume of distribution, and total body clearance after the initial intravenous dose were 3.9 +/- 1.2 hr, 2.7 +/- 0.3 L/kg, and 0.57 +/- 0.14 L/hr/kg, respectively. The initial bioavailability was 67.7 +/- 12.6%. After three weeks of chronic therapy, no significant differences in total body clearance (0.72 +/- 0.42 L/hr/kg) or bioavailability (77.5 +/- 16.8%) were observed. Thus the pharmacokinetics and bioavailability of metoclopramide were not altered during chronic therapy in these diabetic patients.

Pharmacokinetics of high-dose i.v. alizapride in prevention of cisplatin-induced emesis

Alizapride is a new antidopaminergic-related benzamide with specific antiemetic properties. Pharmacokinetics at a high repetitive dose (16 mg/kg) shows a biexponential plasma decay with T1/2 alpha of 8.33 +/- 2.47 min and T1/2 beta 2.8 +/- 0.7 hr. Large Vdss and high total body clearance are apparent. We demonstrate an increase in drug exposure during the first 6 hr after CDDP infusion by shortening the interval between injections. We conclude that the rate of infusion of alizapride could be important in the efficacy of the drug.

Vomiting after ophthalmic surgery. Effects of intra-operative antiemetics and postoperative oral fluid restriction

The usefulness of intra-operative antiemetics and postoperative oral fluid restriction in the prevention of vomiting following anaesthesia for ophthalmic surgery, was studied in 200 patients. They were allocated into four groups of 50 and given either saline (as control), droperidol, metoclopramide or prochlorperazine. Oral intake was restricted postoperatively in half of the patients of each group. Anaesthesia comprised morphine and atropine premedication and a halothane, nitrous oxide and oxygen spontaneous breathing technique. No significant beneficial effects resulted from intra-operative antiemetics; vomiting incidences of 26% after saline and droperidol, 28% after metoclopramide and 14% after prochlorperazine were observed. Younger patients and females vomited most frequently. Restriction of oral fluids did not decrease the incidence of vomiting but demonstrated that approximately half of those patients who vomit do so with their first postoperative oral intake. Vomiting was observed more frequently after non intra-ocular surgery than after intra-ocular surgery (37% cf. 16%, p less than 0.01) and postoperative analgesics were required by more non intra-ocular patients than by intra-ocular patients (25% cf. 5%, p less than 0.001). Squint patients vomited most frequently (48%) and most frequently required postoperative analgesia (35%).

Preliminary studies of the pharmacokinetics and pharmacodynamics of prochlorperazine in healthy volunteers

The pharmacokinetics and pharmacodynamics of prochlorperazine were studied in healthy volunteers using a recently developed h.p.l.c. assay. Eight subjects received 12.5 mg and 6.25 mg i.v. doses of prochlorperazine, a 25 mg oral dose and placebo in random order. Plasma half-life (t1/2) of prochlorperazine was 6.8 +/- 0.7 h and 6.9 +/- 0.8 h for the 12.5 mg and 6.25 mg i.v. doses respectively. Apparent volume of distribution and plasma clearance were high and the kinetics did not appear to be dose-related. Absorption of oral prochlorperazine appeared to be slow and bioavailability was very low. A metabolite, possibly prochlorperazine sulphoxide, was noted after oral dosing. Mild sedation was common after i.v. prochlorperazine, but cardiovascular effects were minimal. The main adverse effect was akathisia which was reported by five out of eight subjects after the higher i.v. dose. These results provide preliminary information on the pharmacokinetics of i.v. prochlorperazine which were previously unknown.

Pharmacokinetics of high-dose metoclopramide in cancer patients

The introduction of new cytotoxic drug regimens has been associated with an increase in the incidence and severity of adverse effects. This in turn has highlighted the need for more effective adjuvant therapy. The use of metoclopramide for the prophylaxis of nausea and vomiting, in high intravenous doses (50 to 1000 mg), has become established since 1981. As a lipid-soluble drug, metoclopramide has a large volume of distribution. The reported mean values after high doses range between 2.8 and 4.6 L/kg. The mean values for total body clearance and terminal half-life range from 0.31 to 0.69 L/kg/h and from 4.5 to 8.8 hours, respectively. The values of these pharmacokinetic parameters are essentially similar to those obtained after conventional doses (less than 50mg). Pharmacokinetic parameters appear unaffected by age, although no high-dose study has been conducted in children. Bodyweight is apparently correlated with clearance. An influence of renal function indices on terminal half-life and clearance has been shown, which is rather surprising since renal clearance accounts for only 20% of the total clearance. No thorough investigations exist which examine the influence of hepatic disease, cancer type and cytotoxic drug regimen on the disposition of metoclopramide. A relationship between dose (or concentration) and therapeutic or adverse effects of metoclopramide is outlined. The therapeutic benefit of high doses (up to 14 mg/kg) may be dependent on age, and on the combination of cytotoxic drugs. The advantages of high doses of metoclopramide are most apparent when the drug is used as protection against the adverse effects of high doses of cisplatin (greater than 60 mg/m2). Despite considerable pharmacokinetic variability, intravenous administration of high doses of metoclopramide is relatively safe due to its large therapeutic index.

A comparison of the gastric and central nervous system effects of two substituted benzamides in normal volunteers

Eight healthy male volunteers participated in a single-blind, random allocation, crossover, comparison of intravenous metoclopramide (10 mg), the peripherally acting, gastrointestinal stimulant BRL 20627 (10 mg) and saline. The central nervous system effects were assessed by quantitative electroencephalography (EEG) and by visual analogue scales. Gastric motility and emptying were assessed by epigastric impedance. Metoclopramide increased the EEG amplitude by 10.4% (a statistically significant, P less than 0.05, effect) and increased frequencies above 22 Hz, whereas both BRL 20627 and placebo had only minor effect on the EEG frequencies and slightly decreased the EEG amplitude. Ratings on visual analogue scales showed that metoclopramide caused statistically significant (P less than 0.01 difference from placebo) restlessness and slight but significantly less (P less than 0.05 difference from placebo) feeling of happiness. Epigastic impedance changes indicated that both metoclopramide and BRL 20627 increased gastric contractile activity, but the rate of gastric emptying was not significantly altered by either drug although it tended to be shortened following metoclopramide but not BRL 20627 treatment. It is concluded that since the published animal data show that BRL 20627 has only weak dopamine antagonistic properties this study further implicates dopamine receptor blockade in the akathisia but not in the gastric effect of metoclopramide.

The action of cisapride on gastric emptying and the pharmacodynamics and pharmacokinetics of oral diazepam

The effects of the benzamide cisapride (C) (8 mg) i.v. have been compared to placebo (P) in a double blind randomised study. The effects on gastric emptying, the absorption and effects of oral diazepam, and BP and pulse were observed. Cisapride increased the rate of gastric emptying of 500 ml liquid containing diazepam 10 mg (t 1/2 C: 7.4 min, P: 14.9 min). The initial rate of absorption of diazepam contained in the drink was increased by C (AUC 0-1 h C: 328 micrograms h l-1, P: 253 micrograms h l-1, but there was no change in overall bioavailability. This change in diazepam kinetics was associated with a significantly greater impairment in reaction time in the first 45 min after drinking but not in self rated sedation. Cisapride produced a significant tachycardia (e.g. after 10 min C: 82 beats/min, P: 69 beats/min) which probably reflects a peripheral vasodilator action. Cisapride may therefore alter the pharmacokinetics and dynamics of concurrently administered drugs.

The pharmacokinetics of high dose metoclopramide in patients with neoplastic disease

High dose metoclopramide infusions (10 mg/kg) were administered to nineteen patients with bronchial carcinoma who were receiving intravenous cyclophosphamide as single agent chemotherapy. Considerable interindividual variability in metoclopramide disposition was observed. Mean clearance was 0.33 +/- 0.13 (s.d.) l h-1 kg-1, mean volume of distribution at steady state was 3.8 +/- 1.2 (s.d.) l/kg and mean elimination half-life was 8.3 +/- 4.4 (s.d.) h. These results were significantly different from mean values previously reported for young healthy volunteers given conventional doses (0.70 l h-1 kg-1, 2.2 l/kg and 2.6 h respectively). Significant correlations were found between serum urea, serum creatinine and metoclopramide clearance. The metoclopramide regimens were well tolerated and, with the exception of two patients, were completely effective in the prevention of nausea and vomiting. To achieve and maintain target serum metoclopramide concentrations of 1 microgram/ml, we now administer a loading infusion of 3.61 mg/kg over 30 min followed by a maintenance infusion of 0.36 mg kg-1 h-1 for 10 h. Cyclophosphamide is normally administered concurrently with the second infusion. For patients with evidence of mild renal impairment, the maintenance infusion rate of metoclopramide hydrochloride should be adjusted according to the predicted individual clearance value; CL (l h-1 kg-1) = 0.57 - [0.036 X urea (mmol/l)].

Evaluation of a high pressure liquid chromatographic technique for metoclopramide analysis

High-dose metoclopramide has found an established place in the prophylaxis of nausea and vomiting which may be induced by cancer chemotherapy. A simple reliable high pressure liquid chromatographic technique for the measurement of this drug in serum has been developed and evaluated. The methodology will find application in the study of metoclopramide pharmacokinetics and in the monitoring of high-dose metoclopramide therapy in individual patients with neoplastic disease.

Effect of ethanol and pH on the adsorption of drugs to activated charcoal: studies in vitro and in man

The effect of ethanol on the adsorption of aspirin, quinidine and amitriptyline to activated charcoal was studied in vitro at pH 1.2 and 7.0. The adsorption of these drugs was greatly dependent on the charcoal-drug ratio and on the pH. Ethanol (10%) significantly (P less than 0.001) increased the percentage of their unadsorbed fraction at both pHs in vitro. In six healthy volunteers activated charcoal (50 g), ingested 5 min. after aspirin (1000 mg) and quinidine sulfate (200 mg), reduced their bioavailability by about 70% (aspirin) and 99% (quinidine). A significant desorption of aspirin but not that of quinidine from charcoal was obvious on the second and third days and seemed to be related to the effect of pH. The absorption of ethanol was not significantly prevented by charcoal. The concomitant ingestion of alcohol (50 g) with drugs antagonized only slightly the ability of charcoal to reduce the absorption of aspirin and quinidine.

The determination of metoclopramide in plasma by reversed-phase ion-pair high-performance liquid chromatography

Methodology based on reversed-phase ion-pair high-performance liquid chromatography is described for the determination of metoclopramide in plasma. The chromatography was optimized in terms of the peak shape for the drug and its resolution from endogenous plasma components by investigating the effects of quaternary ammonium (competing) ions and alkylsulphate (pairing) ions in an acidic mobile phase containing acetonitrile (20%) and 20 mM acetic acid. Optimum chromatographic conditions were obtained with an ODS-Hypersil column and a mobile phase containing 20% acetonitrile, 20 mM acetic acid, 0.6 mM sodium octylsulphate and 0.5 mM tetrabutylammonium chloride. A simplified method of sample preparation is described in which only 1 ml of plasma is required. The limit of detection (at 310 nm) was 7 ng/ml and no interference from endogenous plasma components or from any drugs commonly used in the treatment of cancer was observed. Consequently the methodology should be applicable to pharmacokinetic studies on metoclopramide, when used clinically to control the gastro-intestinal side-effects of chemotherapy.

Clinical pharmacokinetics of metoclopramide

Metoclopramide is rapidly and well absorbed from the gastrointestinal tract, and in man undergoes variable first-pass metabolism (oral bioavailability 32 to 100%). In man, N-4 sulphate conjugation is an important pathway of metabolism and after oral administration the ratio of free to conjugated metoclopramide in urine correlates with the plasma AUC. The elimination half-life of metoclopramide is dose-dependent after both intravenous and oral administration of single doses between 5 and 20mg. Metabolic profiles in animal species studied are very different from man. The clearance of metoclopramide is reduced in patients with renal failure to approximately 50% of normals and the terminal half-life is prolonged; this is despite the fact that renal clearance of free drug accounts for only 20% of the administered dose in normals. Preliminary studies after 'high dose' metoclopramide demonstrate accumulation to high plasma concentrations with linear kinetics, suggesting that current high dose regimens are unnecessarily cumbersome.

Metoclopramide. An updated review of its pharmacological properties and clinical use

Since previously reviewed in the Journal (Vol. 12, No. 2), metoclopramide has been confirmed as an effective drug in treating and preventing various types of vomiting and as a useful agent in oesophageal reflux disease, gastroparesis, dyspepsia, and in a variety of functional gastrointestinal disorders. Of considerable importance is the recent evidence of its efficacy when administered intravenously in high dosages in preventing severe vomiting associated with cisplatin. Good results have been achieved in patients not previously treated with cisplatin, but further studies are needed to determine its level of efficacy in patients who have experienced severe vomiting during earlier courses of cytotoxic therapy. Side effects consisting of mild sedation, diarrhoea and reversible extrapyramidal reactions have occurred, but are tolerated by many patients.

Dystonic reactions and the pharmacokinetics of metoclopramide in children

The pharmacokinetics of metoclopramide have been studied in nine children receiving the drug as prophylaxis for cytotoxic induced vomiting. Plasma concentrations of metoclopramide have also been studied in three children with dystonic reactions to the drug. The pharmacokinetics in children were similar to those reported in healthy adults. There was no difference in the plasma concentration of metoclopramide of children with dystonia when compared to those without this adverse effect. Kinetic differences in childhood do not explain the occurrence of dystonia, which in the individual appears to be related to factors other than plasma drug concentrations.

Metoclopramide in tardive dyskinesia

The effect of single intravenous doses of metoclopramide (10 mg, 20 mg and 40 mg) have been compared with placebo (saline) in a double blind randomised study in 10 patients with tardive dyskinesia following long term neuroleptic therapy. Tardive dyskinesia rating scores were decreased significantly (P<0.01) 6 hours after administration of metoclopramide 20 mg and 40 mg when compared with placebo. Reduction of tardive dyskinesia by metoclopramide-a D(2)receptor blocking agent suggest that D(2)receptors may be involved in the mediation of this syndrome.