A case of sudden death after Japanese encephalitis vaccination

P-Glycoprotein-Mediated Interaction Is a Risk Factor for QT Prolongation in Concomitant Use of Antipsychotics and SSRIs as P-Glycoprotein-Mediated Inhibitors: Analysis of the Japanese Adverse Drug Event Report Database

The inhibition of human ether-a-go-go-related gene (hERG) channels is a known cause of QT prolongation triggered by antipsychotic drugs. Our previous studies suggest that P-glycoprotein (P-gp)-mediated drug interactions may lead to increased gastrointestinal absorption of pimozide and its accumulation in cardiomyocytes, thereby enhancing the inhibitory effect of hERG channels. There is a paucity of epidemiological studies examining the risk of QT prolongation by antipsychotic drugs in terms of P-gp-mediated interactions with concomitant drugs. Therefore, using the Japanese Adverse Event Reporting Database, we investigated whether the risk of QT prolongation triggered by antipsychotic drugs associated with hERG inhibition is affected by the concomitant use of selective serotonin reuptake inhibitors (SSRIs) associated with P-gp inhibition. The results showed that the frequency of QT prolongation increased when the antipsychotic drugs quetiapine and sulpiride, which are P-gp substrates, were combined with SSRIs with P-gp inhibition. In contrast, no association with QT prolongation was observed in patients on non-P-gp-substrate antipsychotics, irrespective of the P-gp inhibitory effect of the concomitant SSRI. These results suggest that P-gp-mediated interactions are a risk factor for antipsychotic-induced QT prolongation. There is a need for further investigation into the risks of specific drug combinations.

P-Glycoprotein-Mediated Pharmacokinetic Interactions Increase Pimozide hERG Channel Inhibition

Pimozide, an antipsychotic drug, is a potent inhibitor of the hERG channel. A case of death due to cardiac arrest has been reported in a boy who received pimozide together with sertraline and aripiprazole. In this study, we focused on drug-drug interactions and investigated the relationships between transporter-mediated intracellular accumulation and the hERG inhibitory effect of pimozide. The accumulation of pimozide in cardiomyocyte-derived AC16 cells was significantly increased by sertraline and aripiprazole, which are thought to have a P-glycoprotein (P-gp) inhibitory effect, and under P-gp siRNA conditions. These results suggest P-gp inhibition increases pimozide accumulation in AC16 cells. We introduced the hERG plasmid into AC16 cells and investigated the concentration-dependent hERG inhibitory effect of pimozide from within AC16 cells. Addition of 10 nM or more pimozide significantly inhibited the hERG current with concentration dependence. These results indicate P-gp-mediated pharmacokinetic interaction increases pimozide accumulation in AC16 cells, and the subsequent elevated pimozide levels within the cells may result in an increased risk of hERG channel inhibition. Our present study calls attention to the risks associated with the combined use of cardiotoxic P-gp substrate(s) and P-gp inhibitory medicines.

Gastrointestinal absorption of pimozide is enhanced by inhibition of P-glycoprotein

Drug-drug interaction was suggested to have played a role in the recent death due to cardiac arrest of a patient taking pimozide, sertraline and aripiprazole antipsychotic/antidepressant combination therapy. Here, we investigated the possible involvement of P-glycoprotein (P-gp)-mediated interaction among these drugs, using in vitro methods. ATPase assay confirmed that pimozide is a P-gp substrate, and might act as a P-gp inhibitor at higher concentrations. The maximum transport rate (J_max) and half-saturation concentration (K_t) for the carrier-mediated transport estimated by means of pimozide efflux assay using P-gp-overexpressing LLC-GA5-CoL150 cells were 84.9 ± 8.9 pmol/min/mg protein, and 10.6 ± 4.7 μM, respectively. These results indicate that pimozide is a good P-gp substrate, and it appears to have the potential to cause drug-drug interactions in the digestive tract at clinically relevant gastrointestinal concentrations. Moreover, sertraline or aripiprazole significantly decreased the efflux ratio of pimozide in LLC-GA5-CoL150 cells. Transport studies using Caco-2 cell monolayers were consistent with the results in LLC-GA5-CoL150 cells, and indicate that P-gp-mediated drug-drug interaction may occur in the gastrointestinal tract. Thus, P-gp inhibition by sertraline and/or aripiprazole may increase the gastrointestinal permeability of co-administered pimozide, resulting in an increased blood concentration of pimozide, which is known to be associated with an increased risk of QT prolongation, a life-threatening side effect.

Anti-NMDA Receptor Encephalitis and Vaccination

Anti-N-methyl-d-aspartate (Anti-NMDA) receptor encephalitis is an acute autoimmune neurological disorder. The cause of this disease is often unknown, and previous studies revealed that it might be caused by a virus, vaccine or tumor. It occurs more often in females than in males. Several cases were reported to be related to vaccination such as the H1N1 vaccine and tetanus/diphtheria/pertussis and polio vaccines. In this study, we reported an anti-NMDA receptor encephalitis case that may be caused by Japanese encephalitis vaccination. To investigate the association between anti-NMDA receptor encephalitis and vaccination, we analyzed the phylogenetic relationship of the microRNAs, which significantly regulate these vaccine viruses or bacteria, and the phylogenetic relationship of these viruses and bacteria. This reveals that anti-NMDA receptor encephalitis may be caused by Japanese encephalitis vaccination, as well as H1N1 vaccination or tetanus/diphtheria/pertussis and polio vaccinations, from the phylogenetic viewpoint.