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.