In clinical trials, quetiapine was not associated with a persistent increase in QT intervals. However, the QT effect was not systematically evaluated in a thorough QT study. In post marketing experience, there were cases reported of QT prolongation in patients who overdosed on quetiapine [see OVERDOSAGE ( 10.1)], in patients with concomitant illness, and in patients taking medicines known to cause electrolyte imbalance or increase QT interval [see DRUG INTERACTIONS ( 7.1)].
The use of quetiapine should be avoided in combination with other drugs that are known to prolong QTc including Class 1A antiarrythmics (e.g., quinidine, procainamide) or Class III antiarrythmics (e.g., amiodarone, sotalol), antipsychotic medications (e.g., ziprasidone, chlorpromazine, thioridazine), antibiotics (e.g., gatifloxacin, moxifloxacin), or any other class of medications known to prolong the QTc interval (e.g., pentamidine, levomethadyl acetate, methadone).
Quetiapine should also be avoided in circumstances that may increase the risk of occurrence of torsade de pointes and/or sudden death including (1) a history of cardiac arrhythmias such as bradycardia; (2) hypokalemia or hypomagnesemia; (3) concomitant use of other drugs that prolong the QTc interval; and (4) presence of congenital prolongation of the QT interval.
Caution should also be exercised when quetiapine is prescribed in patients with increased risk of QT prolongation (e.g. cardiovascular disease, family history of QT prolongation, the elderly, congestive heart failure and heart hypertrophy).
During clinical trials, seizures occurred in 0.5% (20/3490) of patients treated with quetiapine compared to 0.2% (2/954) on placebo and 0.7% (4/527) on active control drugs. As with other antipsychotics, quetiapine should be used cautiously in patients with a history of seizures or with conditions that potentially lower the seizure threshold, e.g., Alzheimer’s dementia. Conditions that lower the seizure threshold may be more prevalent in a population of 65 years or older.
Clinical trials with quetiapine demonstrated dose-related decreases in thyroid hormone levels. The reduction in total and free thyroxine (T 4 ) of approximately 20% at the higher end of the therapeutic dose range was maximal in the first six weeks of treatment and maintained without adaptation or progression during more chronic therapy. In nearly all cases, cessation of quetiapine treatment was associated with a reversal of the effects on total and free T 4 , irrespective of the duration of treatment. The mechanism by which quetiapine effects the thyroid axis is unclear. If there is an effect on the hypothalamic-pituitary axis, measurement of TSH alone may not accurately reflect a patient’s thyroid status. Therefore, both TSH and free T 4 , in addition to clinical assessment, should be measured at baseline and at follow-up.
In the mania adjunct studies, where quetiapine was added to lithium or divalproex, 12% (24/196) of quetiapine treated patients compared to 7% (15/203) of placebo-treated patients had elevated TSH levels. Of the quetiapine treated patients with elevated TSH levels, 3 had simultaneous low free T 4 levels (free T 4 <0.8 LLN).
About 0.7% (26/3489) of quetiapine patients did experience TSH increases in monotherapy studies. Some patients with TSH increases needed replacement thyroid treatment.
In all quetiapine trials, the incidence of shifts in thyroid hormones and TSH were 1: decrease in free T 4 (<0.8 LLN), 2.0% (357/17513); decrease in total T 4 (<0.8LLN), 4.0% (75/1861); decrease in free T 3 (<0.8LLN), 0.4% (53/13766); decrease in total T 3 (<0.8LLN), 2.0% (26/1312), and increase in TSH (>5mIU/L), 4.9% (956/19412). In eight patients, where TBG was measured, levels of TBG were unchanged.
1 Based on shifts from normal baseline to potentially clinically important value at anytime post-baseline. Shifts in total T 4 , free T 4, total T 3 and free T 3 are defined as <0.8 x LLN (pmol/L) and shift in TSH is > 5 mlU/L at any time.
Table 8 shows the incidence of these shifts in short-term placebo-controlled clinical trials.
1 Based on shifts from normal baseline to potentially clinically important value at any time post-baseline. Shifts in total T 4 , free T 4 , total T 3 and free T 3 are defined as <0.8 x LLN (pmol/L) and shift in TSH is >5 mIU/L at any time.
2 Includes quetiapine and quetiapine extended-release data.
|Total T 4||Free T 4||Total T 3||Free T 3||TSH|
|3.4% (37/1097)||0.6% (4/651)||0.7% (52/7218)||0.1% (4/3668)||0.5% (2/369)||0.0% (0/113)||0.2% (11/5673)||0.0% (1/2679)||3.2% (240/7587)||2.7% (105/3912)|
In short-term placebo-controlled monotherapy trials, the incidence of reciprocal, shifts in T 3 and TSH was 0.0 % for both quetiapine (1/4800) and placebo (0/2190) and for T 4 and TSH the shifts were 0.1% (7/6154) for quetiapine versus 0.0% (1/3007) for placebo.
Children and Adolescents
In acute placebo-controlled trials in children and adolescent patients with schizophrenia (6-week duration) or bipolar mania (3-week duration), the incidence of shifts for thyroid function values at any time for quetiapine treated patients and placebo-treated patients for elevated TSH was 2.9% (8/280) vs. 0.7% (1/138), respectively, and for decreased total thyroxine was 2.8% (8/289) vs. 0% (0/145, respectively). Of the quetiapine treated patients with elevated TSH levels, 1 had simultaneous low free T 4 level at end of treatment.
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