# 160 - Metabolic inhibition

# Metabolic inhibition

Schizophrenia and related psychoses
CHAPTER 1
Table 1.37  Non-­psychotropics associated with QT prolongation (see Crediblemeds.org for latest information; this 
is not a complete list).
Antibiotics
Erythromycin
Clarithromycin
Ampicillin
Co-­trimoxazole
Pentamidine
(Some 4 quinolones affect QTc – see manufacturers’ literature)
Antimalarials
Chloroquine
Mefloquine
Quinine
Antiarrhythmics
Quinidine
Disopyramide
Procainamide
Sotalol
Amiodarone
Bretylium
Others
Amantadine
Cyclosporin
Diphenhydramine
Hydroxyzine
Methadone
Nicardipine
Tamoxifen
Note: β2 agonists and sympathomimetics may provoke TdP in patients with prolonged QTc.
ECG monitoring
Measure QTc in all patients prescribed antipsychotics:
■
■on admission
■
■if previous abnormality or known additional risk factor, at annual physical health 
check.
Consider measuring QTc within a week of achieving a therapeutic dose of a newly 
prescribed antipsychotic that is associated with a moderate or high risk of QTc prolongation or of newly prescribed combined antipsychotics. Management of QT prolongation in patients receiving antipsychotic drugs is detailed in Table 1.38.
Metabolic inhibition
The effect of drugs on the QTc interval is usually plasma level dependent. Drug interactions are therefore important, especially when metabolic inhibition results in increased 
plasma levels of the drug affecting QTc. Commonly used metabolic inhibitors include 
fluvoxamine, fluoxetine, paroxetine and valproate.