Introduction

1. Use of high doses of quetiapine in bipolar disorder episodes is not linked to high activity of cytochrome P4503A4 and/or cytochrome P4502D6 High dose Normal dose (n = 9) (n = 12) Age 44±12 43±12 p=0.86 Female 22% 75% p<0.001 Smokers 78% 75% p=0.6 Maximum quetiapine doses (mean; median)[mg/d] 1467;1200 433;350 p=0.002 Quetiapine serum/plasma concentrations (mean; median)[ng/ml] 303;287 64;44 p=0.006 Midazolam metabolic ratio 3.9;3.8 9.4;6.2 p=0.06 CYP2D6 ultrarapid metabolizer 11% 8.30% p=0.28 CYP2D6 Quetiapine CYP3A4 WHO Collaborating Center for Training and Research in Substance abuse Yasser Khazaal1, Daniele Fabio Zullino1, Chin Eap2 1Division of Substance Abuse, University Hospitals of Geneva 2Department of Psychiatry, University Hospitals of Lausanne Results Demographic and metabolic data measured in the high and normal dose groups are shown in Table one One patient in the high dose and one patient in the normal dose groups were genotyped as CYP2D6 ultrarapid metabolizers. CYP3A4 activities were not significantly different between the two groups, with even a trend for a higher CYP3A4 activity in the normal dose group as compared to the high dose group (midazolam metabolic ratio: 9.4 ± 8.2 ; 6.2; 1.7-26.8 versus 3.9 ± 2.3 ; 3.8; 1.5-7.6, respectively, p = 0.06). The results were not due to concomitant medications Table 1Group comparisons Limitations Lack of concomitant clinical data on mood episodes One recruitment center Sample size is too small to detect differences due to CYP2D6 Conclusions The present study shows that, the use of higher than licensed range of quetiapine cannot be explained by a high activity of CYP3A4 and/or CYP2D6, the two main enzymes involved in quetiapine metabolism. The present results did not contest that individual patients may receive a high quetiapine dose in relation to high activity of CYP3A4 and/or of CYP2D6. Further studies are needed to explore the influence of other genetic variability and of clinical factors (Khazaal et al., 2007) which could contribute to the interindividual variation of administered quetiapine doses for bipolar disorders and for schizoaffective episodes. Introduction Quetiapine as monotherapy (Vieta et al., 2005; Bowden et al., 2005; McIntyre et al., 2005) or in combination with other mood stabilizers (Sachs et al., 2004; Yatham et al., 2004) is efficacious in the treatment of acute mania, as well as monotherapy in bipolar depression (Calabrese et al., 2005). Although the maximal quetiapine doses in the published studies have been restricted to 800mg/day, higher quetiapine doses are not unusual in clinical practice. Quetiapine is predominantly metabolized by cytochrome P450 3A4 (CYP3A4) and to a lesser extent by CYP2D6. The large interindividual variability of these isozyme activities could contribute to the variability observed in quetiapine dosage. The aim of the present study was to evaluate if the use of high dosages of quetiapine clinical practice could be explained by a high activity of CYP3A4 and/or of CYP2D6 Methods CYP3A4 activities were determined using the midazolam metabolic ratio in 21 bipolar and schizoaffective bipolar patients genotyped for CYP2D6. 9 patients were treated with a high quetiapine dosage (mean ± SD, median; range: 1467 ± 625,1200; 1000-3000 mg/day) and 12 with a normal quetiapine dosage (433 ± 274, 350; 100-800 mg/day).  CYP3A4 activity was measured using the midazolam metabolic ratio (MR) as previously described (Eap et al., 2004). In summary, following oral administration, midazolam is oxidized to 1’-OH midazolam by CYP3A4. The test measures the 1’OH-midazolam / midazolam plasma MR half an hour after oral intake of 0.075 mg of midazolam (Eap et al., 2004) Genotyping of CYP2D6 was performed by real-time polymerase chain reaction with the use of 5’-nuclease allelic discrimination assays References Sachs G, Chengappa KN, Suppes T, Mullen JA, Brecher M, Devine NA, Sweitzer DE: Quetiapine with lithium or divalproex for the treatment of bipolar mania: a randomized, double-blind, placebo-controlled study. Bipolar Disord 2004, 6: 213-223. Yatham LN, Paulsson B, Mullen J, Vagero AM: Quetiapine versus placebo in combination with lithium or divalproex for the treatment of bipolar mania. J Clin Psychopharmacol 2004, 24: 599-606. Calabrese JR, Keck PE, Jr., Macfadden W, Minkwitz M, Ketter TA, Weisler RH, Cutler AJ, McCoy R, Wilson E, Mullen J: A randomized, double-blind, placebo-controlled trial of quetiapine in the treatment of bipolar I or II depression. Am J Psychiatry 2005, 162: 1351-1360. Eap CB, Buclin T, Cucchia G et al. Oral administration of a low dose of midazolam (75 microg) as an in vivo probe for CYP3A activity. Eur.J Clin.Pharmacol. 2004;60:237-46. Khazaal Y, Tapparel S, Chatton A, Rothen S, Preisig M, Zullino D. Quetiapine dosage in Bipolar disorder episodes and mixed states. Progress in Neuro-Psychopharmacology & Biological Psychiatry 2007 (in press). Service d’abus de substances Département de Psychiatrie