Drug interactions between Adapin and Symbyax

doxepin ↔ fluoxetine

Applies to:Adapin (doxepin) and Symbyax (fluoxetine/olanzapine)

GENERALLY AVOID: Coadministration with fluoxetine may significantly increase the plasma concentrations of some tricyclic antidepressants (TCAs). The proposed mechanism is fluoxetine inhibition of CYP450 2D6, the isoenzyme responsible for the metabolic clearance of many antidepressant and psychotropic drugs. Seizures and delirium have been reported, as well as a fatality attributed to fluoxetine-induced chronic amitriptyline toxicity. Pharmacodynamically, the combination of fluoxetine (or any other selective serotonin reuptake inhibitor) and a TCA may potentiate the risk of serotonin syndrome, which is a rare but serious and potentially fatal condition thought to result from hyperstimulation of brainstem 5HT1A receptors.

MANAGEMENT: In general, the use of fluoxetine (or other SSRIs) with TCAs should be avoided if possible, or otherwise approached with caution if potential benefit is deemed to outweigh the risk. Pharmacologic response and plasma TCA levels should be monitored more closely whenever fluoxetine is added to or withdrawn from therapy in patients stabilized on their existing antidepressant regimen, and the TCA dosage adjusted as necessary. Patients should be monitored closely for signs and symptoms of TCA toxicity (e.g., sedation, dry mouth, blurred vision, constipation, urinary retention) and/or excessive serotonergic activity (e.g., CNS irritability, altered consciousness, confusion, myoclonus, ataxia, abdominal cramping, hyperpyrexia, shivering, pupillary dilation, diaphoresis, hypertension, and tachycardia). Due to the long half-life of fluoxetine and its active metabolite, norfluoxetine, the risk of interaction may persist for several weeks after discontinuation of fluoxetine.

doxepin ↔ olanzapine

Applies to:Adapin (doxepin) and Symbyax (fluoxetine/olanzapine)

MONITOR: Agents with anticholinergic properties (e.g., sedating antihistamines; antispasmodics; neuroleptics; phenothiazines; skeletal muscle relaxants; tricyclic antidepressants; disopyramide) may have additive effects when used in combination. Excessive parasympatholytic effects may result in paralytic ileus, hyperthermia, heat stroke, and the anticholinergic intoxication syndrome. Peripheral symptoms of intoxication commonly include mydriasis, blurred vision, flushed face, fever, dry skin and mucous membranes, tachycardia, urinary retention, and constipation. Central symptoms may include memory loss, disorientation, incoherence, hallucinations, psychosis, delirium, hyperactivity, twitching or jerking movements, stereotypy, and seizures. Central nervous system-depressant effects may also be additively or synergistically increased when these agents are combined, especially in elderly or debilitated patients. Use of neuroleptics in combination with other neuroleptics or anticholinergic agents may increase the risk of tardive dyskinesia.

MANAGEMENT: Caution is advised when agents with anticholinergic properties are combined, particularly in the elderly and those with underlying organic brain disease, who tend to be more sensitive to the central anticholinergic effects of these drugs and in whom toxicity symptoms may be easily overlooked. Patients should be advised to notify their physician promptly if they experience potential symptoms of anticholinergic intoxication such as abdominal pain, fever, heat intolerance, blurred vision, confusion, and/or hallucinations. Ambulatory patients should be counseled to avoid activities requiring mental alertness until they know how these agents affect them. A reduction in anticholinergic dosages may be necessary if excessive adverse effects develop.