Comparative central nervous system effects and pharmacokinetics of neu-metoclopramide and metoclopramide in healthy volunteers

Interactions between metoclopramide and morphine: enhanced antinociception and motor dysfunction in rats

1. Opioid analgesics and anti-emetics are often used concomitantly to treat pain and nausea and vomiting in people with malignant disease. We investigated interactions between the opioid analgesic morphine and the anti-emetic metoclopramide, a dopamine D2 receptor antagonist, on nociception and gross motor function. 2. To assess for antinociceptive interactions, 11 Sprague-Dawley rats were injected intraperitoneally with morphine (5.0 mg/kg) or saline in combination with metoclopramide (0.5, 1.5 and 5.0 mg/kg) or saline and, 30 min later, the tail-flick latencies to a noxious thermal stimulus (49 degrees C water) were measured. Immediately thereafter we induced reperfusion hyperalgesia in the rats' tails using a tourniquet cuff and tested nociception again. Because, in addition to its ability to block D2 receptors, metoclopramide is also a weak 5-HT(3) receptor antagonist, we assessed in a further 11 rats whether any antinociceptive interactions occurred between morphine (5.0 mg/kg) and ondansetron (0.2 and 2.0 mg/kg), an anti-emetic that selectively antagonizes 5-HT(3) receptors. To assess for motor interactions, we injected another group of nine rats with morphine (5.0 mg/kg) or saline in combination with metoclopramide (0.5 and 5.0 mg/kg) or saline and tested the ability of the animals to run on an 80 mm diameter rod rotating at 25 r.p.m. for 30 min. 3. Metoclopramide was not inherently analgesic or antihyperalgesic, but the highest dose of metoclopramide (5.0 mg/kg) enhanced the analgesic and antihyperalgesic effects of morphine. Neither dose of ondansetron was analgesic or antihyperalgesic or enhanced the antinociceptive actions of morphine. 4. Only the high dose of metoclopramide compromised running performance when administered with saline. However, coadministering morphine with metoclopramide (both doses) decreased motor performance. 5. Therefore, metoclopramide, possibly through its actions on D2 receptors and not 5-HT(3) receptors, enhances the analgesic and antihyperalgesic effects of morphine, but morphine exacerbates metoclopramide-induced motor dysfunction in rats.

Presentation of a structurally diverse and commercially available drug data set for correlation and benchmarking studies

A multivariate analysis of drugs on the Swedish market was the basis for the selection of a small, physicochemically diverse set of 24 drug compounds. Factors such as structural diversity, commercial availability, price, and a suitable analytical technique for quantification were considered in the selection. Lipophilicity, pKa, solubility, and permeability across human Caco-2 cell monolayers were measured for the compiled data set. The results show that, by use of a physicochemically diverse data set, experimental responses over a wide range were obtained. The paper also shows how experimental difficulties due to the diversity of the data set can be overcome. We anticipate that this data set can serve as a benchmark set for validation of new experimental techniques or in silico models. It can also be used as a diverse starting data set for the development of new computational models.

Neutral metoclopramide sensitizes cytotoxicity induced by ionizing radiation in SCID mice xenografted with a human brain astrocytoma

A formulation of metoclopramide (MCA) conformationally altered by neutralization of pH (nMCA, Neu-Sensamide) has been shown to have the same efficacy of enhancing the cytotoxicity of a single dose of 1 Gy radiation as acidic formulations (e.g., Primperan, Sensamide) in a human lung adenocarcinoma (H2981) xenografted into SCID mice. In the present study, 2 x 1 Gy radiation was combined with 2 x 2 mg nMCA/kg body weight injected 2 hr before radiation treatment for evaluation of radiosensitization in SCID mice xenografted with a human brain astrocytoma (T24). Given in this treatment schedule, nMCA alone at 2 mg/kg showed no cytotoxic effect on tumor growth in vivo. When combined with 2 x 1 Gy of radiation, however, the cytotoxicity was significantly increased as measured by tumor growth delay over the radiation-only-treated group. Furthermore, nMCA was absorbed into brains of mice and rats as efficiently as acidic MCA (aMCA) when analyzed 45 min after i.m. injection by high-performance liquid chromatography.

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.