Metoclopramide in Parkinson's disease

Antipsychotic drug binding in the substantia nigra: an examination of high metoclopramide binding in the brains of normal, Alzheimer's disease, Huntington's disease, and Multiple Sclerosis patients, and its relation to tardive dyskinesia

This project was done in order to determine why the annual incidence of metoclopramide-associated tardive dyskinesia is much higher than that for the commonly used antipsychotics. To test the hypothesis that metoclopramide tardive dyskinesia may be associated with high concentrations of metoclopramide in the substantia nigra under clinical conditions, the nonspecific binding of tritiated antipsychotics to the dissected melaninized regions of postmortem human substantia nigra was measured. The nonspecific binding at 1 nM [³H]ligand was 7.3, 4.2, 2.6, 0.91 and 0.66 fmoles/mg for [³H]haloperidol, [³H]clozapine, [³H]raclopride, [³H]metoclopramide, and [³H]olanzapine, respectively. After adjusting these values for the known free concentrations of these drugs in plasma or spinal fluid, the amounts that would be bound under clinical conditions would be 231, 113, 15, 11, and 3.4 fmoles/mg for metoclopramide, clozapine, raclopride, haloperidol, and olanzapine, respectively. Using rat striatum as baseline to define antipsychotic binding to nonnigral tissue, the excess amount of binding to the Alzheimer nigral tissue under clinical conditions would be 209, 19, 0, 3.4 and 0.8 fmole/mg for metoclopramide, clozapine, raclopride, haloperidol, and olanzapine, respectively, with a similar pattern for nigral tissues from Huntington and Multiple Sclerosis patients. The high accumulation of metoclopramide is sufficiently high to cause nigral nerve cell membrane damage by metoclopramide's detergent-like action, possibly explaining metoclopramide's toxic ability to elicit early tardive dyskinesia. In addition, the nonspecific binding of metoclopramide was much higher in Alzheimer-diseased substantia nigra, consistent with the fact that older individuals are relatively more vulnerable to metoclopramide tardive dyskinesia.

The cardiovascular effects of metoclopramide in multiple system atrophy and pure autonomic failure

Metoclopramide (MCP), a central and peripheral dopaminergic blocker with cholinergic activity, has been proposed to treat orthostatic hypotension (OH) on the basis that it could antagonize the vasodilator and natriuretic effects of dopamine. The authors evaluated cardiovascular responses to MCP in 11 subjects with OH: 6 with multiple system atrophy (MSA) and 5 with pure autonomic failure (PAF), along with 6 healthy control subjects. Supine blood pressure (BP), heart rate (HR), and breathing were continuously monitored before, during, and after MCP infusion. The pre-MCP head-up tilt test was tolerated at 65 degrees for 10 minutes in all subjects except in one with PAF, who tolerated 30 degrees for only 5 minutes. Tilting confirmed the OH in patients with MSA (change in mean arterial pressure [deltaMAP] = -31 +/- 13 mm Hg) and PAF (AMAP = -34 +/- 8 mm Hg). Infusion of MCP was given in four 5-mg doses every 5 minutes, with the subject in a supine position. Infusion of MCP induced the following effects: (1) A transient hypotensive effect occurred after each infusion in both patients and control subjects, the fall in MAP being counteracted by an increase in HR in control subjects but not in patients; this acute MAP fall was mo resevere in patients. (2) A progressive reduction of MAP occurred during the test,which never returned to preinfusion levels in patients; this effect was so pronounced in two PAF patients as to prevent them from receiving the last dose. Post-MCP tilting was tolerated in control subjects but in only in 5 MSA patients and 4 PAF patients. In those patients who tolerated the test, the MAP fall was similar to, or worse than, that before MCP (MSA: deltaMAP = -28 +/- 16 mm Hg; PAF: deltaMAP = -38 +/- 16 mm Hg). The cardiovascular effect of MCP in normal subjects was a transient hypotension counterbalanced by reflex tachycardia. The lack of an HR increase and the progressive fall in supine BP in MSA and PAF patients, together with worsening orthostatic tolerance after MCP infusion, are effects that should strongly discourage the use of this drug in the treatment of OH.

Orphan neurones and amine excess: the functional neuropathology of Parkinsonism and neuropsychiatric disease

The aetiology and treatment of Parkinsonism is currently conceptualised within a dopamine (DA) deficiency-repletion framework. Loss of striatal DA is thought to cause motor impairment of which tremor, bradykinaesia and rigidity are prominent features. Repletion of deficient DA should at least minimise parkinsonian signs and symptoms. In Section 2, based on extensive pre-clinical and clinical findings, the instability of this approach to Parkinsonism is scrutinised as the existing negative findings challenging the DA deficiency hypothesis are reviewed and reinterpreted. In Section 3 it is suggested that Parkinsonism is due to a DA excess far from the striatum in the area of the posterior lateral hypothalamus (PLH) and the substantia nigra (SN). This unique area, around the diencephalon/mesencephalon border (DCMCB), is packed with many ascending and descending fibres which undergo functional transformation during degeneration, collectively labelled 'orphan neurones'. These malformed cells remain functional resulting in pathological release of transmitter and perpetual neurotoxicity. Orphan neurone formation is commonly observed in the PLH of animals and in man exhibiting Parkinsonism. The mechanism by which orphan neurones impair motor function is analogous to that seen in the diseased human heart. From this perspective, to conceptualise orphan neurones at the DCMCB as 'Time bombs in the brain' is neither fanciful nor unrealistic [E.M. Stricker, M.J. Zigmond, Comments on effects of nigro-striatal dopamine lesions, Appetite 5 (1984) 266-267] as the DA excess phenomenon demands a different therapeutic approach for the management of Parkinsonism. In Section 4 the focus is on this novel concept of treatment strategies by concentrating on non-invasive, pharmacological and surgical modification of functional orphan neurones as they affect adjacent systems. The Orphan neurone/DA excess hypothesis permits a more comprehensive and defendable interpretation of the interrelationship between Parkinsonism and schizophrenia and other related disorders.

Amelioration of experimental parkinsonism by intrahypothalamic administration of haloperidol

Accumulation of amines in the degenerating axons of ascending catecholamine-containing neurons in the hypothalamus has been proposed as a site of function neurotransmitter release and may thereby participate in the development of motor impairment seen after central dopamine-depleting lesions. To test this hypothesis further the dopamine receptor antagonist haloperidol (1 microL of a 14 nmol solution) was injected directly into the lateral hypothalamus (LH) in 6 different injection regimes to determine whether amphetamine-induced turning could be attenuated with this treatment. The injection of haloperidol at 1 and 24 h (group 1), 24 h (group 2) or 6+ 7 d (group 3) after 6-hydroxydopamine (6-OHDA) did not modify amphetamine-induced turning. However, the injection of haloperidol at 1 h, 24 h, 7 d, and 8 d (group 4), days 1-7 (group 5), or gradual infusion (14 nmol/microliters/h) for 7 days (group 6) all reduced the 6-OHDA-induced turning to a level similar to that of controls. These results add further support to the contention that amines are released from the axons of degenerating neurones in the hypothalamus and that this phenomenon participates in the elicitation of behavioral impairment attributed solely to the loss of functional neurotransmitters from terminal fields. Furthermore, the data emphasize the importance of hypothalamic pathology in the development of Parkinsonism and suggest that intrahypothalamic administration of dopamine blocking agents might be useful in the treatment of Parkinsonism.

Akinesia: a syndrome common to parkinsonism, retarded depression, and negative symptoms of schizophrenia

A distinct hypokinetic syndrome appears to exist across several different neuropsychiatric diagnoses, involving (1) slowed motor activity with difficulty initiating and sustaining behaviors, (2) anhedonia with depressed mood and reduced affective range, and (3) cognitive impairment. Specifically, three well-recognized states--parkinsonism, retarded depression, and the negative symptoms of schizophrenia--prominently feature the components of this syndrome, and reduced dopamine turnover in the brain has been hypothesized to play a part in the pathophysiology of each. While aspects of this conceptualization remain controversial, it generates testable hypotheses that could have implications for the understanding and treatment of these states.

The effects of domperidone on the absorption of levodopa in normal subjects

The effect of simultaneous oral administration of 20, 40, or 80 mg domperidone on the pharmacokinetics of an oral 500 mg dose of levodopa was studied in eight normal women. No significant differences in maximum plasma levodopa concentration, the time of its attainment, or the area under the plasma levodopa concentration versus time profile occurred. Domperidone significantly reduced the incidence of adverse gastrointestinal effects due to levodopa administration.

Potential uses for metoclopramide

Metoclopramide, a dopamine antagonist, is approved in the U.S. for the treatment of various gastrointestinal disorders. Its use has been investigated in a wide variety of diseases, including those not involving the intestinal tract. Although more study is required before routine clinical use of metoclopramide can be advocated, it may be effective in the treatment of tardive dyskinesia, in decreasing the risk factors associated with anesthetic-related aspiration, and as an adjunct in the treatment of gastric bezoars. It also may be used safely in patients with Parkinson's disease. The use of metoclopramide in the treatment of neurogenic bladder, orthostatic hypotension, tumor-associated gastroparesis, nonprolactinemic amenorrhea, failure to thrive, Tourette's syndrome, anorexia nervosa, and hiccups, as well as an adjunct to migraine therapy, has been investigated, but sufficient evidence has not been accumulated to advocate the use of metoclopramide in these disorders.

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.

Perhexiline maleate as a cause of reversible parkinsonism and peripheral neuropathy

In a 78-year-old woman receiving perhexiline maleate for intractable angina pectoris, a syndrome of parkinsonism and peripheral neuropathy developed. The neuropathy was confirmed by electromyographic and nerve conduction studies. The parkinsonism and peripheral neuropathy disappeared when perhexiline maleate was discontinued.

Selective permeation of the blood-brain barrier as a cause of the anomalous properties of 'atypical'neuroleptics

Metoclopramide is a widely used anti-emetic drug with potent dopamine-blocking effects on brain structures involved in emesis and prolactin secretion but it is apparently devoid of therapeutic effect in schizophrenia, thus calling into question the supposed role of dopamine blockade in the action of antischizophrenic drugs. This investigation compared the depression of hypothalamic self-stimulation produced by metoclopramide and by a 'typical' neuroleptic, spiroperidol (spiperone), when injected by different routes. Metoclopramide was found to9 be nearly 30 times more potent when administered directly into the brain via the cerebral ventricles than when injected intraperitoneally; on the other hand the potency of spiroperidol was virtually unaffected by the route of administration. The blood-brain barrier is known to be absent from brain sites controlling emesis and prolactin secretion; thus the potency of metoclopramide as an anti-emetic and in releasing prolactin, and its relative ineffectiveness as an antipsychotic can be accounted for by a failure to enter the brain freely except at privileged sites. Thus its anomalous properties are not necessarily inconsistent with the dopamine theory of schizophrenia.

Metoclopramide: antipsychotic efficacy of a drug lacking potency in receptor models

Metoclopramide is a substituted benzamide derivative, structurally similar to procainamide and sulpiride. In behavioral, biochemical, and neuroendocrine tests it displays classic neuroleptic dopamine (DA) antagonist properties; in contrast to other DA antagonists, it lacks potency in currently used DA receptor models. In clinical studies using low doses or dubious measures, it was considered not to be efficacious as an antipsychotic. We now find that it indeed has a clinical profile similar to known neuroleptics when used in a dose range predicted from animal models. The findings raise questions regarding the validity and universality of several predictive models, as well as hypotheses purporting to explain molecular mechanisms of action of neuroleptic agents. The drug's inactivity in receptor models suggests that an as yet unidentified DA receptor subpopulation may be important as the mediator of many DA dependent neurobiologic phenomena.

Metoclopramide and haloperidol in tardive dyskinesia

The effect of single intravenous doses of metoclopramide (10 mg, 20 mg and 40 mg) and haloperidol (5 mg and 10 mg) have been compared to placebo (saline) in a double blind randomised study in 8 patients with tardive dyskinesia secondary to neuroleptic therapy. Tardive dyskinesia rating scores were improved significantly (P less than 0.01) 6 hours after dosing by metoclopramide 40 mg, and haloperidol 5 mg and 10 mg, when compared to placebo. Single doses of dopamine receptor blocking agents improve tardive dyskinesia. The dose of metochlopramide required to show a beneficial effect was high, and this therefore suggests that it is unlikely to be of therapeutic value as the incidence of adverse reactions would be greatly increased. By monitoring the effects of single doses of dopamine receptor blocking drugs in patients with tardive dyskinesia it is possible to compare the relative potencies of these drugs on dopaminergic systems in vivo in man.