title: Influence of P-glycoprotein inhibition on the distribution of the tricyclic antidepressant nortriptyline over the blood-brain barrier.
abstract: The distribution of the antidepressant drug nortriptyline (NT) and its main metabolite E-10-hydroxy-nortriptyline (E-10-OH-NT) across the blood-brain barrier was considered in relation to inhibition of the multidrug transporter P-glycoprotein (P-gp). Rats received NT in doses of 25 mg/kg orally, 10 mg/kg i.p. or 25 mg/kg i.p. Half the rats were treated with the P-glycoprotein inhibitor cyclosporine A (CsA) (200 mg/kg) 2 h prior to NT administration, and the other half served as a control group. NT and the metabolite were extracted from brain and serum by liquid-liquid extraction and analysed by HPLC with UV-detection. The brain to serum ratio of NT was increased in the CsA treated groups (22.3-26.8) compared with the control groups (16.5-22.7), the difference being statistically significant in two of the three experiments (p<0.05). Increased brain-serum ratios were also found for E-10-OH-NT, but the differences were not statistically significant. These results suggest that inhibition of P-gp by CsA increases the accumulation of NT in the brain. Administration of the antipsychotic drug risperidone (0.5 mg/kg s.c.), which is a P-gp substrate, instead of CsA did not exert any measurable influence on the blood-brain ratio of NT concentrations. In conclusion, the results show that drug-drug interaction at P-gp may influence the intracerebral NT concentration, but apparently, a major inhibition of P-gp is necessary to attain a measurable effect.
authors.affiliation: Centre for Basic Psychiatric Research, Aarhus Psychiatric University Hospital, Skovagervej 2, DK-8240 Risskov, Denmark.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Ejsing
authors.forename: Kristian
authors.initials: K
authors.lastname: Linnet
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000284:Administration, Oral; D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D014150:Antipsychotic Agents / Q000008:administration & dosage / Q000494:pharmacology; D001812:Blood-Brain Barrier / Q000378:metabolism*; D001921:Brain / Q000378:metabolism; D016572:Cyclosporine / Q000008:administration & dosage / Q000494:pharmacology; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000494:pharmacology; D007274:Injections, Intraperitoneal; D007279:Injections, Subcutaneous; D008297:Male; D009661:Nortriptyline / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar; D018967:Risperidone / Q000008:administration & dosage / Q000494:pharmacology; D014018:Tissue Distribution
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000929:Antidepressive Agents, Tricyclic; D014150:Antipsychotic Agents; D007166:Immunosuppressive Agents; C013567:10-hydroxynortriptyline; D016572:Cyclosporine; D009661:Nortriptyline; D018967:Risperidone