title: Evaluation of antipsychotic drugs as inhibitors of multidrug resistance transporter P-glycoprotein.
abstract: BACKGROUND
  The multidrug resistance transporter, P-glycoprotein (P-gp), is involved in efflux transport of several antipsychotics in the blood-brain barrier (BBB).
  
  
  OBJECTIVE
  In the present study, we evaluated the inhibitory effect of the antipsychotics, i.e., risperidone, olanzapine, quetiapine, clozapine, haloperidol, chlorpromazine, a major metabolite of risperidone, 9-OH-risperidone, and a positive control inhibitor, PSC833, on the cellular uptake of a prototypic substrate of P-gp, rhodamine (Rhd) 123, in LLC-PK1 and L-MDR1 cells.
  
  
  METHODS
  After incubation of the antipsychotics (1-100 microM) and the positive (10 microM PSC833) or negative (1% dimethyl sulfoxide) controls with 5 microM Rhd 123 for 1 h, the effects of the antipsychotics on the intracellular accumulation of Rhd 123 were examined using a flow cytometric method.
  
  
  RESULTS
  All the antipsychotics showed various degrees of inhibitory effects on P-gp activity. The rank order of the concentration of inhibitor to cause 50% of the maximal increment of intracellular Rhd 123 fluorescence (EC(50)) was: PSC833 (0.5 microM) < olanzapine (3.9 microM) < chlorpromazine (5.8 microM) < risperidone (6.6 microM) < haloperidol (9.1 microM) < quetiapine (9.8 microM) < 9-OH-risperidone (12.5 microM) < clozapine (30 microM). Considering that the antipsychotics' plasma concentrations are generally lower than 1 microM, the present results suggest that olanzapine and risperidone are the only agents that may inhibit P-gp activity in the BBB. However, most of the antipsychotics are extensively accumulated in tissues. In addition, when given orally, the drug concentrations in the gastrointestinal tract are likely to be high.
  
  
  CONCLUSIONS
  Pharmacokinetic interactions due to inhibition of P-gp activity by the antipsychotics appear possible and warrant further investigation.
authors.affiliation: Laboratory of Drug Disposition and Pharmacogenetics, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, SC 29425, USA. wangjs@musc.edu
authors.forename: Jun-Sheng
authors.initials: JS
authors.lastname: Wang
authors.forename: Hao-Jie
authors.initials: HJ
authors.lastname: Zhu
authors.forename: John S
authors.initials: JS
authors.lastname: Markowitz
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Donovan
authors.forename: C Lindsay
authors.initials: CL
authors.lastname: DeVane
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology*; D001569:Benzodiazepines / Q000494:pharmacology; D002746:Chlorpromazine / Q000494:pharmacology; D003024:Clozapine / Q000494:pharmacology; D003524:Cyclosporins / Q000494:pharmacology; D003987:Dibenzothiazepines / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical / Q000379:methods; D004347:Drug Interactions; D005434:Flow Cytometry / Q000379:methods; D005456:Fluorescent Dyes / Q000378:metabolism; D006220:Haloperidol / Q000494:pharmacology; D007555:Isoxazoles / Q000494:pharmacology; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D018374:LLC-PK1 Cells; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D000077152:Olanzapine; D000068882:Paliperidone Palmitate; D011743:Pyrimidines / Q000494:pharmacology; D000069348:Quetiapine Fumarate; D020112:Rhodamine 123 / Q000378:metabolism; D018967:Risperidone / Q000494:pharmacology*; D013552:Swine; D014162:Transfection
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D014150:Antipsychotic Agents; D003524:Cyclosporins; D003987:Dibenzothiazepines; D005456:Fluorescent Dyes; D007555:Isoxazoles; D011743:Pyrimidines; D001569:Benzodiazepines; D020112:Rhodamine 123; D000069348:Quetiapine Fumarate; D003024:Clozapine; D006220:Haloperidol; D018967:Risperidone; D000077152:Olanzapine; C070272:valspodar; D000068882:Paliperidone Palmitate; D002746:Chlorpromazine