Codeine and chlorpheniramine

No specific drug interaction studies have been conducted with TUXARIN ER. Phenytoin : Avoid concomitant use; may increase phenytoin levels. ( 7.4 ) Serotonergic drugs : Concomitant use may result in serotonin syndrome. Discontinue if serotonin syndrome is suspected. ( 7.6 ) Muscle relaxants : Avoid concomitant use. ( 7.8 ) Diuretics: Codeine may reduce the efficacy of diuretics. Monitor for reduced effect. ( 7.9 ) Anticholinergic drugs : Concurrent use may cause paralytic ileus. ( 5.10 , 7.10 )

7.1 Inhibitors of CYP3A4 The concomitant use of TUXARIN ER with CYP3A4 inhibitors, such as macrolide antibiotics (e.g., erythromycin), azole-antifungal agents (e.g. ketoconazole), or protease inhibitors (e.g., ritonavir), may result in an increase in codeine plasma concentrations with subsequently greater metabolism by cytochrome CYP2D6, resulting in greater morphine levels, which could increase or prolong adverse reactions and may cause potentially fatal respiratory depression, particularly when an inhibitor is added after a stable dose of TUXARIN ER is achieved [ see Warnings and Precautions (5.8) ].

After stopping a CYP3A4 inhibitor, as the effects of the inhibitor decline, it may result in lower codeine levels, greater norcodeine levels, and less metabolism via CYP2D6 with resultant lower morphine levels [ see Clinical Pharmacology (12.3) ], resulting in decreased opioid efficacy or a withdrawal syndrome in patients who had developed physical dependence to codeine. Avoid the use of TUXARIN ER while taking a CYP3A4 inhibitor. If concomitant use is necessary, monitor patients for respiratory depression and sedation at frequent intervals.

7.2 CYP3A4 Inducers The concomitant use of TUXARIN ER and CYP3A4 inducers, such as rifampin, carbamazepine, or phenytoin, can result in lower codeine levels, greater norcodeine levels, and less metabolism via 2D6 with resultant lower morphine levels [ see Clinical Pharmacology (12.3) ], resulting in decreased efficacy or onset of a withdrawal syndrome in patients who have developed physical dependence [ see Warnings and Precautions (5.8) ].

After stopping a CYP3A4 inducer, as the effects of the inducer decline, codeine plasma concentrations may increase with subsequently greater metabolism by cytochrome CYP2D6, resulting in greater morphine levels [ see Clinical Pharmacology (12.3) ], which could increase or prolong both the therapeutic effects and adverse reactions, and may cause serious respiratory depression. Avoid the use of TUXARIN ER in patients who are taking CYP3A4 inducers. If concomitant use of a CYP3A4 inducer is necessary, follow the patient for reduced efficacy.

7.3 Phenytoin Adverse event reports in the literature suggest a possible drug interaction involving increased serum phenytoin levels and phenytoin toxicity when chlorpheniramine and phenytoin are co-administered. The exact mechanism for this interaction is not known, however it is believed that chlorpheniramine may inhibit the hepatic metabolism of phenytoin. Avoid the use of TUXARIN ER while taking phenytoin.

7.4 Inhibitors of CYP2D6 Codeine is metabolized by CYP2D6 to form morphine. The concomitant use of TUXARIN ER and CYP2D6 inhibitors, such as paroxetine, fluoxetine, bupropion, or quinidine, can increase the plasma concentration of codeine, but can decrease the plasma concentration of active metabolite morphine, which could result in reduced efficacy [see Clinical Pharmacology (12.3) ].

After stopping a CYP2D6 inhibitor, as the effects of the inhibitor decline, the codeine plasma concentration will decrease but the active metabolite morphine plasma concentration will increase, which could increase or prolong adverse reactions and may cause potentially fatal respiratory depression [ see Clinical Pharmacology (12.3) ]. Avoid the use of TUXARIN ER in patients who are taking inhibitors of CYP2D6.

7.5 Benzodiazepines and Other CNS Depressants Due to additive pharmacologic effect, the concomitant use of benzodiazepines or other CNS depressants, including alcohol, other sedatives/hypnotics, anxiolytics, tranquilizers, muscle relaxants, general anesthetics, antipsychotics, and other opioids, can increase the risk of hypotension, respiratory depression, profound sedation, coma, and death. Avoid the use of TUXARIN ER in patients who are taking benzodiazepines or other CNS depressants. [ see Warnings and Precautions (5.9) ] .

7.6 Serotonergic Drugs The concomitant use of opioids with other drugs that affect the serotonergic neurotransmitter system has resulted in serotonin syndrome. If concomitant use is warranted, carefully observe the patient, particularly during treatment initiation. Discontinue TUXARIN ER if serotonin syndrome is suspected.

7.7 Monoamine Oxidase Inhibitors (MAOIs) TUXARIN ER is contraindicated in patients who are taking MAOIs (i.e., certain drugs used for depression, psychiatric or emotional conditions, or Parkinson's disease) or have taken MAOIs within 14 days [ see Contraindications (4) ]. MAOI interactions with opioids may manifest as serotonin syndrome or opioid toxicity (e.g., respiratory depression, coma) [ see Warnings and Precautions (5.13) ] .

7.8 Muscle Relaxants Codeine may enhance the neuromuscular blocking action of skeletal muscle relaxants and produce an increased degree of respiratory depression. Avoid the use of TUXARIN ER in patients taking muscle relaxants. If concomitant use is necessary, monitor patients for signs of respiratory depression that may be greater than otherwise expected.

7.9 Diuretics Opioids can reduce the efficacy of diuretics by inducing the release of antidiuretic hormone. Monitor patients for signs of diminished diuresis and/or effects on blood pressure and increase the dosage of the diuretic as needed.

7.10 Anticholinergic Drugs The concomitant use of anticholinergic drugs with TUXARIN ER may increase risk of urinary retention and/or severe constipation, which may lead to paralytic ileus [ see Warnings and Precautions (5.10) ]. Monitor patients for signs of urinary retention or reduced gastric motility when TUXARIN ER is used concomitantly with anticholinergic drugs. Additive adverse effects resulting from cholinergic blockade (e.g., xerostomia, blurred vision, or constipation) may occur when anticholinergic drugs are administered with chlorpheniramine .

8.1 Pregnancy Risk Summary TUXARIN ER is not recommended for use in pregnant women, including during or immediately prior to labor. Prolonged use of opioids during pregnancy may cause neonatal opioid withdrawal syndrome [see Warnings and Precautions (5.15) and Clinical Considerations ]. There are no available data with TUXARIN ER use in pregnant women to inform a drug-associated risk for adverse developmental outcomes. Published studies with codeine have reported inconsistent findings and have important methodological limitations ( see Data ). There are reports of respiratory depression when codeine is used during labor and delivery (see Clinical Considerations ) .

Reproductive toxicity studies have not been conducted with TUXARIN ER; however, studies are available with individual active ingredients ( see Data ). In animal reproduction studies, codeine administered by the oral route to pregnant rats during the period of organogenesis increased resorptions and decreased fetal weights at a dose approximately 15 times the maximum recommended human dose (MRHD) in the presence of maternal toxicity ( see Data ). Chlorpheniramine administered by the oral route to mice throughout pregnancy was embryolethal at a dose approximately 9 times the MRHD and decreased postnatal survival when dosing was continued after parturition.

Chlorpheniramine administered by the oral route to male and female rats prior to mating produced embryolethality at a dose approximately 9 times the MRHD ( see Data ). Based on the animal data, advise pregnant women of the potential risk to a fetus. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.

Clinical Considerations Fetal/Neonatal Adverse Reactions Prolonged use of opioid analgesics during pregnancy for medical or nonmedical purposes can result in physical dependence in the neonate and neonatal opioid withdrawal syndrome shortly after birth. Neonatal opioid withdrawal syndrome presents as irritability, hyperactivity and abnormal sleep pattern, high pitched cry, tremor, vomiting, diarrhea and failure to gain weight. The onset, duration, and severity of neonatal opioid withdrawal syndrome vary based on the specific opioid used, duration of use, timing and amount of last maternal use, and rate of elimination of the…