fluvoxamine × Theophylline

Fluvoxamine is the most potent CYP1A2 inhibitor among SSRIs, and CYP1A2 is the main theophylline metabolic route. Theophylline plasma levels rise 3-fold. Theophylline has a narrow therapeutic window.

Nausea, tachycardia, tremor, insomnia, agitation. At levels above 30 mg/L: seizures and ventricular arrhythmias. Older patients and chronic kidney disease: earlier symptoms.

Avoid the combination. Alternative antidepressants without CYP1A2 effect: sertraline, escitalopram, or agomelatine. If fluvoxamine is needed, reduce theophylline 3-fold and check level at 3–5 days.