Quetiapine dosage

In patients with schizophrenia or bipolar disorder given quetiapine 300 mg twice daily, thioridazine 200 mg twice daily reduced the steady-state quetiapine AUC and its maximum and minimum plasma levels by about 41%, 48% and 33%, respectively. It was suggested that this was due to an increased metabolism of quetiapine, although the mechanism for this effect was unclear. These reductions are only moderate and their importance is not known, but until more information is available it would seem prudent to monitor concurrent use, being alert for the need to raise the quetiapine dosage. 

The manufacturers of quetiapine suggest that dosage adjustments [increases] may be necessary if quetiapine is given with carbamazepine, phenytoin or other enzyme inducers (such as barbiturates or rifampicin (rifampin). This is a reasonable prediction but no direct clinical evidence is yet available. However, be alert for the need to use an increased quetiapine dosage in patients given any of these drugs. 

Most antipsychotics have half-fives of elimination in the range of 20 to 40 hours. After dosage stabilization, most antipsychotics (except quetiapine and ziprasidone) can be dosed once daily. It may be possible to dose SGAs less often than their plasma kinetics would suggest. 

Usual dose When used as monotherapy or adjunct therapy (with lithium or divalproex), initiate quetiapine in twice-daily doses totaling 100 mg/day on day 1, increased to 400 mg/day on day 4 in increments of up to 100 mg/day in twice-daily divided doses. Further dosage adjustments up to 800 mg/day by day 6 should be in increments of no more than 200 mg/day. The safety of doses above 800 mg/day has not been evaluated in clinical trials. 

Take quetiapine as ordered do not abruptly discontinue the drug or increase the dosage... 

Using meta-analytic techniques based on the means and the standard errors presented graphically in the poster, we estimated pooled data of the four effective dosages of quetiapine both for the BPRS and the CGI severity of illness change scores from baseline to endpoint. Quetiapine produced an improvement of 0.43 effect-size units in comparison with placebo, a difference that was highly statistically significant and about the same improvement as haloperidol. Thus, based on the BPRS or PANSS, quetiapine was similar to neuroleptics in efficacy (i.e., differences were nonsignificant). Based on our meta-analysis, quetiapine is clearly superior to... 

Several studies have shown a relation between neuroleptic drug dosages, extrapyramidal adverse effects, and the degree of dopamine D2 receptor occupancy (SEDA-18, 48) (181,182). Atypical neuroleptic drugs, such as olanzapine, quetiapine, risperidone, and sertindole, which have lower affinities for D2 receptors, cause fewer extrapyramidal effects than typical neuroleptic drugs (183,185,186). However, there are reports of extrapyramidal effects associated with these atypical neuroleptic drugs (187-189). 

A 27-year-old woman had a seizure while taking a stable dosage of olanzapine 15 mg/day 1 day after the introduction of quetiapine 100 mg in the evening (130). She suddenly fell to the ground and had generalized shaking and inarticulate vocalization for about 30-60 seconds. 

CYP450 3A inhibitors and CYP450 2D6 inhibitors may reduce clearance of quetiapine and thus raise quetiapine plasma levels, but dosage reduction of quetiapine usually not necessary... 

I Sedation and Cognition. Sedation must be recognized as an antipsychotic side effect and not as an indication of therapeutic effect. It occurs more frequently with antipsychotics with antihistaminic properties. Chlorpromazine, thioridazine, mesoridazine, clozapine, olanzapine, and quetiapine are most frequently implicated. Administration of most or all of the daily dosage at bedtime (depending on the drug half-life) can decrease daytime sedation and in some patients eliminate the need for hypnotic agents. Sedation occurs early in treatment... 

A 38-year-old man with schizophrenia was given a combination of zotepine 100 mg/day and haloperidol ester 100 mg every 2 weeks and complained of spontaneous ejaculation, which became more severe when the dosage of zotepine was increased to 150 mg/day. Zotepine was discontinued and the spontaneous ejaculation no longer occurred with haloperidol monotherapy. A combination of haloperidol 100 mg every 2 weeks and quetiapine was then used, and spontaneous ejaculation did not recur. 

A case of steroid-induced psychosis and inappropriate sexual behaviour in an adolescent, as is the case of a 17-year-old boy who presented with inappropriate sexual behaviour, is reported. Quetiapine treatment was initiated at an initial dosage of 300 mg daily. The dosage was increased to 900mg/day on the fourth day of treatment. 

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