Drug Interactions between Cyndal Expectorant and duloxetine

GENERALLY AVOID: Several case reports suggest that serotonin reuptake inhibitors may potentiate the pharmacologic response to sympathomimetic agents. The exact mechanism of interaction is unclear. In one case report, a patient experienced jitteriness, racing thoughts, stomach cramps, dry eyes, palpitations, tremors, and restlessness following a single dose of phentermine ingested approximately a week after she had discontinued fluoxetine. Because of the long half-life of fluoxetine and its metabolite, an interaction with fluoxetine is possible. Similar toxic reactions have been reported when fluoxetine was used concomitantly with amphetamine or phenylpropanolamine. Additionally, some sympathomimetic agents such as amphetamines may possess serotonergic activity and should generally not be administered with serotonin reuptake inhibitors because of the additive risk of serotonin syndrome, which is a rare but serious and potentially fatal condition thought to result from hyperstimulation of brainstem 5-HT1A and 2A receptors. The interaction was suspected in a patient treated with dexamphetamine who developed symptoms consistent with the serotonin syndrome approximately 2 weeks after the addition of venlafaxine. The medications were discontinued and the patient was given cyproheptadine for suspected serotonin syndrome, whereupon symptoms promptly resolved. A second episode occurred when dexamphetamine was subsequently resumed and citalopram added. The patient improved following cessation of citalopram on his own, and residual symptoms were successfully treated with cyproheptadine.

MANAGEMENT: In general, amphetamines and other sympathomimetic appetite suppressants should not be combined with selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs). Close monitoring for enhanced sympathomimetic effects and possible serotonin syndrome is recommended if these agents must be used together. Symptoms of the serotonin syndrome may include mental status changes such as irritability, altered consciousness, confusion, hallucinations, and coma; autonomic dysfunction such as tachycardia, hyperthermia, diaphoresis, shivering, blood pressure lability, and mydriasis; neuromuscular abnormalities such as hyperreflexia, myoclonus, tremor, rigidity, and ataxia; and gastrointestinal symptoms such as abdominal cramping, nausea, vomiting, and diarrhea.

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MONITOR: Drugs that are inhibitors of CYP450 2D6 may interfere with the analgesic effect of codeine. The mechanism is decreased in vivo conversion of codeine to morphine, a metabolic reaction mediated by CYP450 2D6. If an inhibitor is started after a stable dose of codeine is achieved, reduced analgesia and possible opioid withdrawal may result. Conversely, ceasing CYP450 2D6 inhibitor therapy may lead to increased morphine levels, increasing the risk of opioid-related adverse effects.

MANAGEMENT: The possibility of reduced or inadequate pain relief should be considered in patients receiving codeine with drugs that inhibit CYP450 2D6. An increase in the codeine dosage or a different analgesic agent may be necessary in patients requiring therapy with CYP450 2D6 inhibitors. If concurrent therapy is used and the CYP450 2D6 inhibitor is stopped, the dose of codeine may need to be reduced and the patient should be monitored for signs and symptoms of respiratory depression or sedation. In addition, it should be noted that rolapitant, a moderate CYP450 2D6 inhibitor, may interfere with the analgesic effects of codeine for at least 28 days after administration of rolapitant. The manufacturer's prescribing information should be consulted for further information.

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