ACTH-independent macronodular adrenocortical hyperplasia reveals prevalent aberrant in vivo and in vitro responses to hormonal stimuli and coupling of arginine-vasopressin type 1a receptor to 11ß-hydroxylase.

BACKGROUND: Adrenal Cushing's syndrome caused by ACTH-independent macronodular adrenocortical hyperplasia (AIMAH) can be accompanied by aberrant responses to hormonal stimuli. We investigated the prevalence of adrenocortical reactions to these stimuli in a large cohort of AIMAH patients, both in vivo and in vitro. METHODS: In vivo cortisol responses to hormonal stimuli were studied in 35 patients with ACTH-independent bilateral adrenal enlargement and (sub-)clinical hypercortisolism. In vitro, the effects of these stimuli on cortisol secretion and steroidogenic enzyme mRNA expression were evaluated in cultured AIMAH and other adrenocortical cells. Arginine-vasopressin (AVP) receptor mRNA levels were determined in the adrenal tissues. RESULTS: Positive serum cortisol responses to stimuli were detected in 27/35 AIMAH patients tested, with multiple responses within individual patients occurring for up to four stimuli. AVP and metoclopramide were the most prevalent hormonal stimuli triggering positive responses in vivo. Catecholamines induced short-term cortisol production more often in AIMAH cultures compared to other adrenal cells. Short- and long-term incubation with AVP increased cortisol secretion in cultures of AIMAH cells. AVP also increased steroidogenic enzyme mRNA expression, among which an aberrant induction of CYP11B1. AVP type 1a receptor was the only AVPR expressed and levels were high in the AIMAH tissues. AVPR1A expression was related to the AVP-induced stimulation of CYP11B1. CONCLUSIONS: Multiple hormonal signals can simultaneously induce hypercortisolism in AIMAH. AVP is the most prevalent eutopic signal and expression of its type 1a receptor was aberrantly linked to CYP11B1 expression.

In silico prediction of drug binding to CYP2D6: identification of a new metabolite of metoclopramide.

Patients with cancer often take many different classes of drugs to treat the effects of their malignancy and the side effects of treatment, as well as their comorbidities. The potential for drug-drug interactions that may affect the efficacy of anticancer treatment is high, and a major source of such interactions is competition for the drug-metabolizing enzymes, cytochromes P450 (P450s). We have examined a series of 20 drugs commonly prescribed to cancer patients to look for potential interactions via CYP2D6. We used a homology model of CYP2D6, together with molecular docking techniques, to perform an in silico screen for binding to CYP2D6. Experimental IC50 values were determined for these compounds and compared with the model predictions to reveal a correlation with a regression coefficient of r2= 0.61. Importantly, the docked conformation of the commonly prescribed antiemetic metoclopramide predicted a new site of metabolism that was further investigated through in vitro analysis with recombinant CYP2D6. An aromatic N-hydroxy metabolite of metoclopramide, consistent with predictions from our modeling studies, was identified by high-performance liquid chromatography/mass spectrometry. This metabolite was found to represent a major product of metabolism in human liver microsomes, and CYP2D6 was identified as the main P450 isoform responsible for catalyzing its formation. In view of the prevalence of interindividual variation in the CYP2D6 genotype and phenotype, we suggest that those experiencing adverse reactions with metoclopramide, e.g., extrapyramidal syndrome, are likely to have a particular CYP2D6 genotype/phenotype. This warrants further investigation.

Pharmacokinetics, toxicity, side effects, receptor affinities and in vitro radiosensitizing effects of the novel metoclopramide formulations, sensamide and neu-sensamide.

Metoclopramide is a drug which has experienced worldwide use in the clinic for over 30 years as an antiemetic. Recently, it has also been shown to possess radio- and chemosensitizing properties in both animal tumour models and humans at the higher dose of 2 mg/kg. Two new metoclopramide formulations are being clinically developed and they differ mainly in whether the pH of their formulations are acidic (pH 2.5-3.5) or neutral (pH 6.5-7.0). Here we report that intramuscular administration of neutral metoclopramide is about 100% bioavailable, safer and with reduced side effects compared to acidic metoclopramide delivered by intramuscular injection to rats within the dose range of 3.5 to 14 mg/kg. The intramuscular administration of metoclopramide was also about 100% bioavailable compared to the intravenous route of administration. Furthermore, neutral metoclopramide had significantly decreased affinity for dopamine D2 receptors and increased affinity for 5-hydroxytryptamine, receptors, but the radiosensitizing potency was the same, when compared to equimolar concentrations of acidic metoclopramide. Taken together these data support the continued development of neutral metoclopramide for high dose intramuscular administration of metoclopramide for future clinical use as both an antiemetic and radiosensitizer.

Pancopride, a potent and long-acting 5-HT3 receptor antagonist, is orally effective against anticancer drug-evoked emesis.

Pancopride ((+-)N-(1-azabicyclo-[2,2,2]-oct-3-yl)-2-cyclopropylmethoxy-4-ami no-5-chlorobenzamide) is a new potent and selective 5-HT3 receptor antagonist, orally and parenterally effective against cytotoxic drug-induced emesis. In vitro, pancopride displayed high affinity (Ki = 0.40 nM) for [3H]GR65630-labelled 5-HT3 recognition sites in membranes from the cortex of rat brains. In vivo, pancopride antagonized 5-HT-induced bradycardia in anaesthetized rats when administered i.v. 5 min (ID50 = 0.56 microgram/kg) or p.o. 60 min (ID50 = 8.7 micrograms/kg) before 5-HT challenge. A single oral dose (10 micrograms/kg) of pancopride produced a significant inhibition of the bradycardic reflex over an 8-h period. Pancopride dose dependently inhibited the number of vomiting episodes and delayed the onset of vomiting induced by cisplatin in dogs (ID50 = 3.6 micrograms/kg i.v. and 7.1 micrograms/kg p.o.). Pancopride was also effective in blocking mechlorethamine- and dacarbazine-induced emesis. Unlike metoclopramide, pancopride was shown to lack any measurable antidopaminergic activity both in vitro and in vivo. These results support clinical data, indicating that pancopride will be a useful drug for treating cytostatic-induced emesis in humans.

Pharmacokinetic comparison of intranasal, oral, and intramuscular metoclopramide in healthy volunteers.

This was a randomized, crossover study of the bioavailability and pharmacokinetics of metoclopramide given by intranasal (IN), oral (PO), and intramuscular (IM) routes. The formulations tested were 5 and 10 mg of IN gel, 10 mg PO, and 5 mg IM. The findings showed that metoclopramide follows similar absorption and elimination characteristics when given via these three extravascular routes. There were no statistically significant differences in the area under the drug concentration versus time curve (AUC) or peak metoclopramide plasma concentration (Cmax) data following PO, IM, or 10-mg IN administration. However, the 5-mg IN doses achieved an AUC that was 39.5% the AUC of the 10-mg IN dose. These data show consistent and relatively predictable metoclopramide plasma concentrations following IN administration. Further, 10-mg doses of IN and PO metoclopramide appear to be bioequivalent.

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.

Antiemetic effect and pharmacokinetics of high dose metoclopramide in cancer patients treated with cisplatin-containing chemotherapy regimens.

Fifteen cancer patients receiving cisplatin-containing chemotherapy participated in two antiemetic studies. In Study 1 they received standard antiemetics in low doses on demand, and in Study 2 the same patients participated in an open randomized cross-over study between metoclopramide 1 and 2 mg/kg i.v. X 5. Serum metoclopramide was determined by HPLC. Self-reporting of nausea using a visual analogue scale (VAS) was compared with observer rated scores. Tolerability and volume vomited were assessed by nurse observers. The biological half-life of metoclopramide was 9.9 h, the volume of distribution was 9.9 l/kg and the clearance was 0.68 l/h/kg. The pharmacokinetics of high dose metoclopramide was linear in the range 0.15-2 mg/kg X 5, with very little accumulation. Compared to standard antiemetics, both high dose regimens of metoclopramide had a significant effect on nausea, but no effect on the volume vomited. Self reports of nausea were significantly correlated with observer rated values. Tolerance of high dose metoclopramide was good except in 3 patients who left the study because of restlessness and trismus. It is concluded that high dose metoclopramide probably can be administered for several consecutive days without appreciable accumulation of the drug. Self-reporting of nausea by patients on VAS is a simple and feasible method of evaluation. The finding that metoclopramide affects nausea but not vomiting supports the hypothesis that nausea and vomiting should be evaluated separately in assessing antiemetic efficacy.

Oral bioavailability of high-dose metoclopramide.

The oral bioavailability of high-dose metoclopramide was studied in 12 patients, who received oral or intravenous (i.v.) metoclopramide in random order with each of 2 consecutive courses of cytotoxic chemotherapy. The terminal half-life of metoclopramide was 7.1 +/- 0.4 h (mean +/- SEM) and was not affected by the route of drug administration. Mean bioavailability was 86.6 +/- 4.7% and the range (65-118%) was less than that reported for standard doses. Neither half-life nor bioavailability was significantly correlated with age. Adverse effects were mild and were similar for both oral and iv metoclopramide. Oral high-dose metoclopramide, given in the same doses as for i.v. administration, should therefore be as effective as the i.v. regimen and may be easier to administer.

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)].

Pharmacokinetics and efficacy of high-dose metoclopramide given by continuous infusion for the control of cytotoxic drug-induced vomiting.

To avoid the accumulation of metoclopramide that occurs with repeated i.v. bolus doses, a new regimen for the administration of high-dose metoclopramide consisting of a loading dose followed by a continuous infusion was investigated to determine the pharmacokinetics and antiemetic efficacy of the drug when given in this manner. Nine patients with non-Hodgkin's lymphoma entered the study, of whom six completed the study, receiving each of three dosage schedules of metoclopramide during three consecutive courses of chemotherapy. In these six patients plasma metoclopramide half-life was 5.9 +/- 0.4 h (mean +/- s.e. mean) and plasma clearance was 25.4 +/- 4.8 l/h (mean +/- s.e. mean). Neither half-life nor clearance were dose-related. Steady-state was achieved during 9/18 infusions. Nausea and vomiting were completely controlled in 13/24 treatment courses (57%) and adverse effects were minimal. We conclude that steady-state plasma concentrations of metoclopramide can be achieved using a weight-related infusion regimen, though the optimum plasma concentration remains to be determined.

Metoclopramide: pharmacology and clinical application.

Metoclopramide antagonizes the effect of dopamine in the central nervous system and other organ systems. Metoclopramide's effect on the medullary chemoreceptor trigger zone makes it useful as a routine anti-emetic and in preventing vomiting induced by antineoplastic drugs, particularly cisplatin. Metoclopramide's gastrointestinal smooth muscle stimulatory effects are related to its ability to antagonize the inhibitory neurotransmitter, dopamine; to augment acetylcholine release and sensitize the muscarinic receptors of the gastrointestinal smooth muscle; and to coordinate gastric-pyloric-small intestinal motor function. The indications for which metoclopramide is approved in the United States are reviewed. Adverse effects, which may occur in up to 20% of patients, include drowsiness, lassitude, and akathisia; all are usually mild, transient, and reversible. Tremor, dystonic reactions, and extrapyramidal effects are infrequent; breast enlargement, galactorrhea, and menstrual irregularities are related to prolactin release.

Placental transfer and hormonal effects of metoclopramide.

In order to study the transplacental transfer of metoclopramide, and its endocrine effects, measurements were made of its concentration in maternal and fetal blood, and in the amniotic fluid, together with maternal and fetal plasma concentrations of prolactin, TSH and oestradiol, during delivery by selective Caesarean section. The drug, 10 mg, was injected i.m. 12 and 2 h and just before the onset of anaesthesia. Metoclopramide was detectable in all the umbilical arterial and venous and amniotic fluid samples, in mean concentrations of 50, 63 and 75 ng/ml, respectively. The mean ratio between the umbilical venous and maternal plasma concentrations was 0.63. Accurate maternal plasma half-lives could not be established but they must have averaged 2 to 4 h. The high amniotic fluid concentrations and relatively high umbilical venous and arterial concentrations soon after administration suggest that metoclopramide equilibrates relatively rapidly between the mother and fetus. Metoclopramide raised the maternal plasma prolactin levels from 315 +/- 128 ng/ml (SD) before therapy to 357 +/- 112 ng/ml at the time birth. No statistically significant difference in cord arterial or venous plasma prolactin levels was seen between the control and metoclopramide-treated groups. Metoclopramide did not affect maternal plasma TSH or oestradiol levels. The only change was a slight but significant increase in TSH level in cord blood taken from the umbilical artery after metoclopramide treatment.

Electron-capture gas chromatographic assay for metoclopramide in plasma.

An original electron-capture gas chromatographic assay has been developed for the quantiation of metoclopramide in human plasma. The method involves derivatization with heptafluorobutyryl imidazole after alkaline extraction, acid backwash, and a further alkaline extraction. Plasma levels of metoclopramide as low as 5 micrograms/l can be measured using 1 ml of plasma, and no interference from related substances or commonly prescribed drugs has been found. The percentage recovery of drug from plasma ranges from 88% to virtually 100%, and the between-run variation in the assay is 4.3%. The assay has been used for the study of metoclopramide pharmacokinetics in man following intravenous single-dose administration. The resultant plasma concentration vs. time curve was biexponential, with a terminal half-life of 5.0 h, and a distribution half-time of 0.3 h.

Metoclopramide: a review of its pharmacological properties and clinical use.

Metoclopramide, 4-amino-5-chloro-2-methoxy-N-(2-diethyl-aminoethyl) benzamide, is advocated for use in gastro-intestinal diagnostics, and in treating various types of vomiting and a variety of functional and organic gastro-intestinal disorders. Published data have indicated that metoclopramide assists radiological identification of lesions in the small intestine, facilitates duodenal intubation and small intestine biopsy, and eases emergency endoscopy in upper gastro-intestinal haemorrhage. Metoclopramide reduces post-operative vomiting and radiation sickness, and ameliorates some types of drug-induced vomiting. It may provide symptomatic relief in dyspepsia and possibly in vertigo, reflux oesophagitis and hiccups, but further controlled trials are needed to confirm the efficacy of metoclopramide in these proposed areas of use. It promotes gastric emptying prior to anaesthesia. Its effects in healing gastric ulcer and preventing relapse of duodenal ulcer remain unproven. Side-effects are few and transient, though alarming extrapyramidal reactions can occur in a small proportion of patients receiving therapeutic doses but more usually following excessive doses in young subjects. They respond rapidly to withdrawal of the drug.

Pharmacological effects on gastric emptying following laparotomy in the rat.

Alteration of the gastrointestinal motility following abdominal surgery is a well substantiated clinical observation. Clinical reports concerning the effect of drugs theoretically suitable for normalizing inhibited gastric emptying during the postoperative period have been conflicting, however. The effect of chlorpromazine, neostigmine and metoclopramide upon retarded gastric emptying following laparotomy was studied in experiments on rats. Metoclopramide (Primperan) considerably improved the emptying ability of the stomach as early as 24 hours after laparotomy. After 72 hours this effect was further accentuated. No improvement of postoperatively retarded motility resulted from treatment with chlorpromazine or with neostigmine during the first 3 postoperative days.