PT  - JOURNAL ARTICLE
AU  - Tove Johansson
AU  - Lars Weidolf
AU  - Friedrich Popp
AU  - Reinhold Tacke
AU  - Ulrik Jurva
TI  - In Vitro Metabolism of Haloperidol and Sila-Haloperidol: New Metabolic Pathways Resulting from Carbon/Silicon Exchange
AID  - 10.1124/dmd.109.028449
DP  - 2010 Jan 01
TA  - Drug Metabolism and Disposition
PG  - 73--83
VI  - 38
IP  - 1
4099  - http://dmd.aspetjournals.org/content/38/1/73.short
4100  - http://dmd.aspetjournals.org/content/38/1/73.full
SO  - Drug Metab Dispos2010 Jan 01; 38
AB  - The neurotoxic side effects observed for the neuroleptic agent haloperidol have been associated with its pyridinium metabolite. In a previous study, a silicon analog of haloperidol (sila-haloperidol) was synthesized, which contains a silicon atom instead of the carbon atom in the 4-position of the piperidine ring. In the present study, the phase I metabolism of sila-haloperidol and haloperidol was studied in rat and human liver microsomes. The phase II metabolism was studied in rat, dog, and human hepatocytes and also in liver microsomes supplemented with UDP-glucuronic acid (UDPGA). A major metabolite of haloperidol, the pyridinium metabolite, was not formed in the microsomal incubations with sila-haloperidol. For sila-haloperidol, three metabolites originating from opening of the piperidine ring were observed, a mechanism that has not been observed for haloperidol. One of the significant phase II metabolites of haloperidol was the glucuronide of the hydroxy group bound to the piperidine ring. For sila-haloperidol, the analogous metabolite was not observed in the hepatocytes or in the liver microsomal incubations containing UDPGA. If silanol (SiOH) groups are not glucuronidated, introducing silanol groups in drug molecules could provide an opportunity to enhance the hydrophilicity without allowing for direct phase II metabolism. To provide further support for the observed differences in metabolic pathways between haloperidol and sila-haloperidol, the metabolism of another pair of C/Si analogs was studied, namely, trifluperidol and sila-trifluperidol. These studies showed the same differences in metabolic pathways as between sila-haloperidol and haloperidol. Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics