Pharmacokinetics, pharmacodynamics, safety, and tolerability of dopamine-receptor antagonists for the prevention of chemotherapy-induced nausea and vomiting.

INTRODUCTION: Dopamine (D)2,3-receptor antagonists (RAs) were the first antiemetics used in the prophylaxis of chemotherapy-induced nausea and vomiting (CINV). AREAS COVERED: Eight D2,3-RAs, amisulpride, domperidone, droperidol, haloperidol, metoclopramide, metopimazine, olanzapine and prochlorperazine are reviewed focusing on pharmacokinetics, pharmacodynamics, antiemetic effect and side effects. EXPERT OPINION: Since the introduction of D2,3-RAs, antiemetics such as corticosteroids, 5-hydroxytryptamine (5-HT)3-RAs and neurokinin (NK)1-RAs have been developed. The classical D2,3-RAs are recommended in the prophylaxis of CINV from low emetic risk chemotherapy, but not as a fixed component of an antiemetic regimen for moderately or highly (HEC) emetic risk chemotherapy. D2,3-RAs are also used in patients with breakthrough nausea and vomiting. It should be emphasized, that most of these drugs are not selective for dopamine receptors.The multi-receptor targeting agent, olanzapine, is recommended in the prophylaxis of HEC-induced CINV as part of a four-drug antiemetic regimen, including a 5-HT3-RA, dexamethasone and a NK1-RA. Olanzapine is the most effective agent to prevent chemotherapy-induced nausea.Side effects differ among various D2,3-RAs. Metopimazine and domperidone possess a low risk of extrapyramidal side effects. Domperidone and metoclopramide are prokinetics, whereas metopimazine delays gastric emptying and haloperidol does not influence gastric motility. Many D2,3-RAs increase the risk of prolonged QTc interval; other side effects include sedation and orthostatic hypotension.

High dose antipsychotic polypharmacy and dopamine partial agonists - time to rethink guidelines?

Guidelines for the treatment of schizophrenia limit the use of antipsychotic agents to clinically-established maximum doses. This acknowledges both the absence of additional efficacy of dopamine D2 receptor antagonists above a receptor occupancy threshold, and the increases in side effects that can occur at higher doses. These limits restrict the dosing of combinations of antipsychotics as they do single agents; drugs sharing the major antipsychotic mechanism of D2 receptor antagonism will act additively in blocking these receptors.Several newer antipsychotic drugs, including aripiprazole and cariprazine, act as partial agonists at the D2 receptor site and avoid action at several other receptors, effects at which are responsible for some non-dopaminergic adverse effects. This pharmacology imparts different characteristics to the drugs resulting often in a more favourable side effect profile. Their partial agonism, along with high affinities for the D2 receptor, also means that these drugs given adjunctively may in part replace, rather than enhance, the D2 antagonism of other antipsychotic agents. This can result in an improvement in certain side effects without loss of antipsychotic efficacy.This article makes the case for distinguishing the D2 partial agonists from antagonists in defining maximum doses of combined treatments, which would increase the options available to the prescriber, emphasising that pharmacological mechanisms need to be understood in identifying optimal treatments for psychotic illness.

Childhood dystonic reactions in the middle Black Sea region.

ABSTRACT: Acute dystonic reactions are a worrying reason for presentation to the pediatric emergency department and the pediatric neurology clinic in childhood. It must be diagnosed and treated quickly. The aim of this study was to examine the clinical presentations, etiological factors, and prognosis of patients presenting to our regional tertiary pediatric neurology clinic with a diagnosis of acute dystonic reactions in children.Nine pediatric patients who were treated for acute dystonic reactions between May, 2018 and May, 2020 and had adequate follow-up were included in the study. Medical record data were reviewed age, gender, etiology, features of family, treatment, and results.Three of the patients were female and 6 were male. Their average age was 11 years (4-17). All patients were evaluated as a drug-induced acute dystonic reaction. Of the 9 patients, 5 were due to metoclopramide, 3 were due to risperidone, and 1 was due to aripiprazole. It was learned that a similar situation against other drugs developed in the family history of 3 patients. As a treatment, all of them were intramuscularly applied biperiden suitable for their weight and 30 minutes dramatic improvement was observed. Additional dose had to be administered in only 1 case. All cases were discharged for 24 hours. No problem was observed in their follow-up.Drug-induced acute dystonic reaction can be diagnosed and has a clinical picture that completely resolves when effective treatment is applied. However, it should not be forgotten that it can reach life-threatening dimensions clinically.

Striatal TRPV1 activation by acetaminophen ameliorates dopamine D2 receptor antagonist-induced orofacial dyskinesia.

Antipsychotics often cause tardive dyskinesia, an adverse symptom of involuntary hyperkinetic movements. Analysis of the US Food and Drug Administration Adverse Event Reporting System and JMDC insurance claims revealed that acetaminophen prevented the dyskinesia induced by dopamine D2 receptor antagonists. In vivo experiments further showed that a 21-day treatment with haloperidol increased the number of vacuous chewing movements (VCMs) in rats, an effect that was inhibited by oral acetaminophen treatment or intracerebroventricular injection of N-(4-hydroxyphenyl)-arachidonylamide (AM404), an acetaminophen metabolite that acts as an activator of the transient receptor potential vanilloid 1 (TRPV1). In mice, haloperidol-induced VCMs were also mitigated by treatment with AM404 applied to the dorsal striatum, an effect not seen in TRPV1-deficient mice. Acetaminophen prevented the haloperidol-induced decrease in the number of c-Fos+preproenkephalin+ striatal neurons in wild-type mice but not in TRPV1-deficient mice. Finally, chemogenetic stimulation of indirect pathway medium spiny neurons in the dorsal striatum decreased haloperidol-induced VCMs. These results suggest that acetaminophen activates the indirect pathway neurons by activating TRPV1 channels via AM404.

Proarrhythmic potential of metoclopramide in a sensitive whole-heart model.

BACKGROUND: Metoclopramide (MCP) is a dopamine D2 -receptor antagonist, mainly used to treat post-operative or chemotherapy-induced nausea. While it is very effective in the cure of gastric symptoms, MCP can cause severe neurologic side effects. Furthermore, there is growing evidence for severe arrhythmic side effects resulting from inhibitory effects on cardiac sodium and potassium channels. METHODS AND RESULTS: Thirteen hearts of New Zealand white rabbits were retrogradely perfused, and electrophysiology studies were performed to obtain action potential duration (APD90 ) and effective refractory period (ERP). After generating baseline data, the hearts were perfused with increasing concentrations of metoclopramide (MCP 10 µM, MCP 50 µM, MCP 100 µM) and the standardized protocol was repeated for each concentration. Perfusion with MCP resulted in a significant prolongation of APD90 and QT interval. In parallel, the incidence of ventricular tachycardias was significantly increased by high doses of MCP. CONCLUSION: This is the first experimental study that investigated the effect of increasing doses of metoclopramide on a sensitive whole-heart model of proarrhythmia. MCP led to a significant increase in action potential duration and QT interval; meanwhile, the number of ventricular tachycardias was significantly increased.

Impaired Clearance From the Brain Increases the Brain Exposure to Metoclopramide in Elderly Subjects.

The antiemetic and gastroprokinetic drug metoclopramide is a weak substrate of the blood-brain barrier (BBB) efflux transporter P-gp and displays central nervous system (CNS) side effects (i.e., extrapyramidal symptoms and tardive dyskinesia) caused by dopamine D2 receptor blockade in the basal ganglia. These side effects occur with a higher incidence in elderly people. We used positron emission tomography to assess the brain distribution of [11 C]metoclopramide in young (n = 11, 26 ± 3 years) and elderly (n = 7, 68 ± 9 years) healthy men both after administration of a microdose (9 ± 7 µg) and a microdose co-injected with a therapeutic dose of unlabeled metoclopramide (10 mg). For both doses, elderly subjects had a significantly higher total volume of distribution (VT ) of [11 C]metoclopramide in the basal ganglia than young subjects (microdose: +26%, therapeutic dose: +41%). Increases in VT (= K1 /k2 ) were caused by significant decreases in the transfer rate constant of [11 C]metoclopramide from brain into plasma (k2 , microdose: -18%, therapeutic dose: -30%), whereas the distributional clearance from plasma into brain (K1 ) remained unaltered. This reduction in the clearance of [11 C]metoclopramide (k2 ) from the brains of elderly subjects may be caused by an age-related decrease in the activity of P-gp at the BBB and may contribute to the higher incidence of CNS side effects of metoclopramide in the aged population. Our data suggest that an age-associated decrease in the clearance properties of the BBB may modulate the CNS effects or side effects of clinically used P-gp substrates.

Pharmacological considerations in antipsychotic drug selection for prevention of drug-induced dysphagia.

Antipsychotic drugs have the ability to induce dysphagia. The aim of this study was to determine the association between the receptor affinity of antipsychotic drugs and the time-to-onset of dysphagia, and to identify factors that prevent antipsychotic drug-induced dysphagia. We used the receptor affinity of 13 antipsychotic drugs for which data were reported in an in vitro test using human receptors, extracted time-to-onset dysphagia from the Japan Adverse Drug Event Report database, and used data from 46 patients to evaluate the correlation between receptor affinity and time-to-onset of dysphagia. We found a negative correlation between D2 receptor affinity and time-to-onset of dysphagia (r = -0.4572, p = 0.0016), and a positive correlation between H1, M1, and M3 receptor affinity and time-to-onset of dysphagia (r = 0.5006, p = 0.0006; r = 0.4130, p = 0.0059; and r = 0.4149, p = 0.0057, respectively). Antipsychotic drugs with a strong D2 receptor-blocking action may accelerate the onset of dysphagia, whereas a strong H1, M1, and M3 receptor-blocking action may delay the onset of dysphagia. The current study revealed the relationship between the receptor affinity of antipsychotic drugs and the time-to-onset of dysphagia, which should aid in the selection of antipsychotic drugs, while preventing dysphagia.

The effectiveness of very slow switching to aripiprazole in schizophrenia patients with dopamine supersensitivity psychosis: a case series from an open study.

Dopamine supersensitivity psychosis (DSP) in patients with schizophrenia is induced by treatment with a high dosage of antipsychotics for a long time period, and it is characterized by unstable psychotic symptoms. The upregulation of dopamine D2 receptor (DRD2) provoked by antipsychotics underlies DSP. Aripiprazole does not cause an excessive blockade of DRD2 and is less likely to upregulate DRD2 by aripiprazole's dopamine partial agonistic profile. Aripiprazole; however, has a potential risk of inducing severe rebound psychosis in patients who have already developed dopamine supersensitivity. Recently, an animal model study suggested that aripiprazole could attenuate established dopamine supersensitivity. The present study was conducted to examine whether very slowly switching to aripiprazole could help patients with schizophrenia with dopamine supersensitivity while avoiding rebound psychosis. This study was a single-armed and open-labeled study in which patients were observed over a period of 2 years. Only 11 patients were ultimately recruited. Five patients were successfully switched to a sufficient dose of aripiprazole and completed the study protocol. These five patients did not present with severe DSP over the study period, but only one patient showed a large improvement in psychopathology. Five patients dropped out of the study, and one of these five showed a severe worsening of psychosis. The present study indicated that the introduction of aripiprazole in patients with DSP was difficult, but suggested that aripiprazole could contribute to attaining a stable state in psychosis if it was applied with careful observation.

A Randomized, Double-Dummy, Emergency Department-Based Study of Greater Occipital Nerve Block With Bupivacaine vs Intravenous Metoclopramide for Treatment of Migraine.

BACKGROUND: Greater occipital nerve blocks (GONB) are used increasingly to treat acute migraine. OBJECTIVE: We conducted a randomized controlled trial to determine whether GONB was as effective as intravenous metoclopramide for migraine. METHODS: This was a double-dummy, double-blind, parallel-arm, non-inferiority study conducted in 2 emergency departments (EDs). Patients with migraine of moderate or severe intensity were randomized to receive bilateral GONB with each side administered 3 mL of bupivacaine 0.5% or metoclopramide 10 mg IV, the putative standard of care. The primary outcome was improvement in pain on a 0-10 scale between time 0 and 1 hour later. To reject the null hypothesis that metoclopramide would be more efficacious in relieving pain, we required that the lower limit of the 95% CI for the difference in pain improvement between those randomized to GONB vs those randomized to metoclopramide be >-1.3, a validated minimum clinically important difference. Secondary outcomes included sustained headache relief, defined as achieving and maintaining for 48 hours a headache level of mild or none without the use of additional analgesic medication, and the use of rescue medication in the ED. RESULTS: Over a 2.5-year study period, 1358 patients were screened for participation and 99 were randomized, 51 to GONB and 48 to metoclopramide. All of these patients were included in the primary analysis. Patients who received the GONB reported mean improvement of 5.0 (95% CI: 4.1, 5.8) while those who received metoclopramide reported a larger mean improvement of 6.1 (95% CI: 5.2, 6.9). The 95% CI for the between group difference of -1.1 was -2.3, 0.1. Sustained headache relief was reported by 11/51 (22%) GONB and 18/47 (38%) metoclopramide patients (95% CI for rounded difference of 17%: -1, 35%). Of the 51 GONB patients, 17 (33%) required rescue medication in the ED vs 8/48 (17%) metoclopramide patients (95% CI for rounded difference of 17%: 0, 33%). An adverse event was reported by 16/51 (31%) GONB patients and 18/48 (38%) metoclopramide patients (95% CI for (rounded) difference of 6%: -13, 25%). CONCLUSION: GONB with bupivacaine was not as efficacious as IV metoclopramide for the first-line treatment of migraine in the ED.

Neuroleptic malignant syndrome in patients with cancer: a systematic review.

BACKGROUND: Antipsychotics potentially cause a low incidence of the side effect called neuroleptic malignant syndrome (NMS), which has a high mortality rate. However, few studies on NMS among patients with cancer exist. AIMS: We aimed to examine the characteristics of antipsychotic-induced NMS among patients with cancer. METHODS: We conducted a systematic review of published reports on NMS described during the treatment of patients with any type of cancer. Articles were identified by a comprehensive search of PubMed, Web of Science, the Cochrane Library and reference lists from relevant articles published until 25 December 2019. Original articles or case reports on humans published in English were included. This review summarises the symptoms, characteristics, treatment course and prognosis of patients with cancer with NMS. RESULTS: Eleven patients with various cancer types from ten case reports published from 1988 to 2013 met the eligibility criteria. Mean age of the 11 patients was 52.5 (range, 32-83) years. NMS developed mostly during the postoperative period, and haloperidol and D2 receptor antagonists were determined as the common causative drugs. Ten patients survived following treatment that mostly involved discontinuing the causative drugs and administering dantrolene, if necessary. CONCLUSION: Although NMS intrinsically has a low incidence and high mortality, only few reports were available, with most patients surviving after early detection and appropriate treatment. Healthcare providers should consider NMS development while prescribing antipsychotics to ensure prompt recognition of the condition and rapid treatment for preventing unnecessary deaths.

Hypermetabolic Syndrome and Dyskinesia After Neurologic Surgery for Labrune Syndrome: A Case Report.

A 20-year-old man with a rare neurodegenerative disease developed hypermetabolic symptoms with dyskinesia after a third ventriculostomy for hydrocephalus. The initial presentation was concerning for an acute dystonic reaction after metoclopramide was administered for nausea. He concurrently developed hypermetabolic symptoms, including hyperthermia, tachycardia, and a lactic acidosis. The diagnosis was broadened to include neuroleptic malignant syndrome, serotonin syndrome, and malignant hyperthermia. Although perhaps less intellectually satisfying but more true to clinical reality, we did not isolate a single diagnosis but treated effectively all 3 with dantrolene sodium and benzodiazepine.

Antipsychotic-induced Hyperprolactinemia in aging populations: Prevalence, implications, prevention and management.

This paper reviews the prevalence, implications, prevention and management of antipsychotic-induced hyperprolactinemia in aging populations. Antipsychotics are indicated mainly for the treatment of psychotic illness but are also used in other conditions. Complications induced by antipsychotics increase with age, due to age-related changes in drug metabolism and excretion. Almost all antipsychotics lead to hyperprolactinemia by blocking dopamine D2 receptors in the anterior pituitary gland, which counteracts dopamine's inhibitory action on prolactin secretion. The main findings of this narrative review are that, though many of the known side effects of high prolactin levels lose their salience with age, the risk of exacerbating osteoporosis remains critical. Methods of preventing antipsychotic-induced hyperprolactinemia in older individuals include using antipsychotic medication (AP) as sparingly as possible and monitoring AP serum levels, regularly measuring prolactin levels, closely monitoring bone density, treating substance abuse, and teaching patients stress management techniques. When hyperprolactinemia symptoms cannot be otherwise managed, adjunctive drugs are available. Potential helpful adjuncts are: dopamine agonists, antipsychotics with partial agonist properties (e.g. aripiprazole), selective estrogen receptor modulators, and metformin. Because a gold standard for prevention/treatment has not been established, clinical decisions need to be made based on safety and individual circumstance.

Structure-Kinetic Profiling of Haloperidol Analogues at the Human Dopamine D2 Receptor.

Haloperidol is a typical antipsychotic drug (APD) associated with an increased risk of extrapyramidal side effects (EPSs) and hyperprolactinemia relative to atypical APDs such as clozapine. Both drugs are dopamine D2 receptor (D2R) antagonists, with contrasting kinetic profiles. Haloperidol displays fast association/slow dissociation at the D2R, whereas clozapine exhibits relatively slow association/fast dissociation. Recently, we have provided evidence that slow dissociation from the D2R predicts hyperprolactinemia, whereas fast association predicts EPS. Unfortunately, clozapine can cause severe side effects independent of its D2R action. Our results suggest an optimal kinetic profile for D2R antagonist APDs that avoids EPS. To begin exploring this hypothesis, we conducted a structure-kinetic relationship study of haloperidol and revealed that subtle structural modifications dramatically change binding kinetic rate constants, affording compounds with a clozapine-like kinetic profile. Thus, optimization of these kinetic parameters may allow development of novel APDs based on the haloperidol scaffold with improved side-effect profiles.

Metoclopramide for the treatment of diabetic gastroparesis.

Introduction: Gastroparesis is a chronic disorder of the stomach characterized by delayed gastric emptying without mechanical obstruction. Diabetes is the most commonly known cause of gastroparesis. Management of diabetic gastroparesis involves lifestyle modifications, glycemic control, pharmacological drugs, and for refractory cases surgical treatments. Metoclopramide remains the only drug approved by the Food and Drug Administration for diabetic gastroparesis. The aim of this article is to provide a concise review of the pharmacology, clinical efficacy and tolerability of metoclopramide. Areas covered: We searched PubMed using the key words 'metoclopramide', 'diabetic gastroparesis', and 'gastric emptying'. The relevant articles and their bibliography were reviewed. Metoclopramide acts on several different receptors; primarily as a dopamine receptor antagonist, both peripherally improving gastric emptying, and centrally resulting in an anti-emetic effect. Metoclopramide side effects, mostly related to its ability to cross the blood-brain barrier, include drowsiness, restlessness, hyperprolactinemia, and tardive dyskinesia (TD), a movement disorder that may be irreversible. Expert opinion: Metoclopramide carries a black box warning for use >12 weeks due to the risk of TD. However, gastroparesis patients experience chronic symptoms often requiring prolonged treatments. Physicians and patients look forward to FDA approval of new agents for gastroparesis with better efficacy and safety profile.

Liability and Failure to Warn a Patient.

This medicolegal article examines a physician's liability when he or she has knowledge of adverse effects associated with a prescription medication and suggests ways to mitigate that liability risk. The article also discusses the circumstances under which pharmaceutical companies face liability for side effects such as tardive dyskinesia.

Acute Drug-Induced Symptoms of Restless Legs Syndrome in an Emergency Department.

ABSTRACT: Restless legs syndrome is a chronic disorder that is characterized by an urge to move the legs and unpleasant sensations in the lower extremities. Its symptoms develop slowly and a sudden onset is very unusual, which may be confusing for the emergency physician. We describe a case of an abrupt presentation of restless legs syndrome symptoms induced by infusion of metoclopramide during treatment of a migraine attack in settings of an emergency department. The patient shortly after infusion of metoclopramide started to experience rapid movements of the legs, claiming that it was the only way to relieve extremely unpleasant sensations in her legs. The symptoms subsided after saline infusion and did not appear again.

Gastroparesis, metoclopramide, and tardive dyskinesia: Risk revisited.

BACKGROUND: Metoclopramide is primarily a dopamine receptor antagonist, with 5HT3 receptor antagonist and 5HT4 receptor agonist activity, and used as an antiemetic and gastroprokinetic since almost 50 years. Regulatory authorities issued restrictions and recommendations regarding long-term use of the drug at oral doses exceeding 10 mg 3-4 times daily because of the risk for development of tardive dyskinesia. The aim of our study was to review mechanism(s) of action and pharmacokinetic-pharmacodynamic properties of metoclopramide, as well as the risk of metoclopramide-induced tardive dyskinesia, factors that may change drug exposure in humans, and to summarize the clinical context for appropriate use of the drug. METHODS: A PubMed, Google Scholar, and Cross Reference search was done using the key words and combined searches: drug-drug interaction, gastroparesis, metoclopramide, natural history, pharmacokinetics, pharmacodynamics, drug-drug interaction, outcome, risk factors, tardive dyskinesia. KEY RESULTS: Data show that the risk of tardive dyskinesia from metoclopramide is low, in the range of 0.1% per 1000 patient years. This is far below a previously estimated 1%-10% risk suggested in treatment guidelines by regulatory authorities. High-risk groups are elderly females, diabetics, patients with liver or kidney failure, and patients with concomitant antipsychotic drug therapy, which reduces the threshold for neurological complications. CONCLUSIONS & INFERENCES: The risk of tardive dyskinesia due to metoclopramide is far below approximated numbers in treatment guidelines. This risk and the influence of known risk factors should be considered when starting a course of metoclopramide for treatment of gastroparesis.

Two Cases of De Novo Pathological Gambling Associated With Aripiprazole.

OBJECTIVES: Pathological gambling can be potentiated by treatment with dopamine agonists. Aripiprazole, bearing a partial agonist activity at dopamine D2 and D3 receptors, has also been linked to such a behavioral aberration, usually on subjects predisposed with tendency of impulsive or addictive behaviors. METHODS: Review of patient's medical records and literature review. RESULTS: Two young patients' pathological gambling emerged simply due to exposure to aripiprazole, neither related to manic or psychotic symptoms nor with history of addictive or impulsive behaviors. Their pathological gambling disappeared soon after switching aripiprazole to other antipsychotics. One patient has tested such a relationship by reexposure to aripiprazole while his compulsion to gamble recurred. CONCLUSIONS: In addition to previously recognized risk factors, pathological gambling might occur in young patients whose history did not reveal an addictive tendency while they were sensitive to the pharmacological effect, as well as adverse effects, of psychotropic agents.