Acetaminopheninteractions

CYP2D6 Inhibitors Codeine is metabolized by CYP2D6 to form morphine. The concomitant use of acetaminophen and codeine phosphate oral solution and CYP2D6 inhibitors (e.g., paroxetine, fluoxetine, bupropion, quinidine) can increase the plasma concentration of codeine, but can decrease the plasma concentration of active metabolite morphine, which could result in reduced analgesic efficacy or symptoms of opioid withdrawal, particularly when an inhibitor is added after a stable dose of acetaminophen and codeine phosphate oral solution is achieved. 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. If concomitant use with a CYP2D6 inhibitor is necessary, or if a CYP2D6 inhibitor is discontinued after concomitant use, consider dosage adjustment of acetaminophen and codeine phosphate oral solution and evaluate patients closely at frequent intervals. If concomitant use with CYP2D6 inhibitors is necessary, assess the patient for reduced efficacy or signs and symptoms of opioid withdrawal and consider increasing the acetaminophen and codeine phosphate oral solution as needed. After stopping use of a CYP2D6 inhibitor, consider reducing the acetaminophen and codeine phosphate oral solution and evaluate the patient at frequent intervals for signs and symptoms of respiratory depression or sedation. CYP3A4 Inhibitors The concomitant use of acetaminophen and codeine phosphate oral solution and CYP3A4 inhibitors, such as macrolide antibiotics (e.g., erythromycin), azole-antifungal agents (e.g. ketoconazole), and 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 acetaminophen and codeine phosphate oral solution is achieved. 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, resulting in decreased opioid efficacy or a withdrawal syndrome in patients who had developed physical dependence to codeine. If concomitant use of CYP3A4 inhibitor is necessary, consider dosage reduction of acetaminophen and codeine phosphate oral solution until stable drug effects are achieved. Evaluate patients at frequent intervals for respiratory depression and sedation. If a CYP3A4 inhibitor is discontinued, consider increasing the acetaminophen and codeine phosphate oral solution dosage until stable drug effects are achieved. Assess for signs of opioid withdrawal. CYP3A4 Inducers The concomitant use of acetaminophen and codeine phosphate oral solution and CYP3A4 inducers (e.g., rifampin, carbamazepine, phenytoin) can result in lower codeine levels, greater norcodeine levels, and less metabolism via 2D6 with resultant lower morphine levels, resulting in decreased efficacy or onset of a withdrawal syndrome in patients who have developed physical dependence. 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, which could increase or prolong both the therapeutic effects and adverse reactions, and may cause serious respiratory depression. If concomitant use of a CYP3A4 inducer is necessary, evaluate the patient for reduced efficacy and signs of opioid withdrawal and consider increasing the acetaminophen and codeine phosphate oral solution dosage as needed. Assess for respiratory depression and sedation. If a CYP3A4 inducer is discontinued, consider an acetaminophen and codeine phosphate oral solution dose reduction and evaluate patients at frequent intervals for signs of respiratory depression and sedation. Benzodiazepines and Other Central Nervous System (CNS) Depressants Due to additive pharmacologic effect, the concomitant use of benzodiazepines or other CNS depressants, including alcohol, can increase the risk of hypotension, respiratory depression, profound sedation, coma, and death. Reserve concomitant prescribing of these drugs for use in patients for whom alternative treatment options are inadequate. Limit dosages and durations to the minimum required. Inform patients and caregivers of this potential interaction and educate them on the signs and symptoms of respiratory depression (including sedation). If concomitant use is warranted, consider recommending or prescribing an opioid overdose reversal agent. Benzodiazepines and other sedatives/hypnotics, anxiolytics, tranquilizers, muscle relaxants, general anesthetics, antipsychotics, gabapentinoids (gabapentin or pregabalin), other opioids, alcohol. Serotonergic Drugs The concomitant use of opioids with other drugs that affect the serotonergic neurotransmitter system has resulted in serotonin syndrome. Examples of these drugs include, selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), triptans, 5-HT3 receptor antagonists, drugs that effect the serotonin neurotransmitter system (e.g., mirtazapine, trazodone, tramadol), certain muscle relaxants (i.e., cyclobenzaprine, metaxalone), and monoamine oxidase (MAO) inhibitors (used to treat psychiatric disorders and also others, such as linezolid and intravenous methylene blue). If concomitant use is warranted, frequently evaluate the patient, particularly during treatment initiation and dose adjustment. Discontinue acetaminophen and codeine phosphate oral solution if serotonin syndrome is suspected. Monoamine Oxidase Inhibitors (MAOIs) The concomitant use of opioids and MAOIs, such as phenelzine, tranylcypromine, linezolid, may manifest as serotonin syndrome or opioid toxicity. Advise patients taking acetaminophen and codeine phosphate oral solution not to use MAOIs or within 14 days of stopping such treatment. If urgent use of an opioid is necessary, use test doses and frequent titration of small doses of other opioids (such as oxycodone, hydrocodone, oxymorphone, hydrocodone, or buprenorphine) to treat pain while closely monitoring blood pressure and signs and symptoms of CNS and respiratory depression. Mixed Agonist/Antagonist and Partial Agonist Opioid Analgesics The concomitant use of opioids with other opioid analgesics, such as butorphanol, nalbuphine, pentazocine, may reduce the analgesic effect of acetaminophen and codeine phosphate oral solution and/or precipitate withdrawal symptoms. Advise patient to avoid concomitant use of these drugs. Muscle Relaxants Codeine may enhance the neuromuscular blocking action of skeletal muscle relaxants and produce an increased degree of respiratory depression. If concomitant use is warranted, because respiratory depression may be greater than otherwise expected, decrease the dosage of acetaminophen and codeine phosphate oral solution and/or the muscle relaxant as necessary. Due to the risk of respiratory depression with concomitant use of skeletal muscle relaxants, (i.e., cyclobenzaprine, metaxalone) and opioids, consider recommending or prescribing an opioid overdose reversal agent. Diuretics Opioids can reduce the efficacy of diuretics by inducing the release of antidiuretic hormone. If concomitant use is warranted, evaluate patients for signs of diminished diuresis and/or effects on blood pressure and increase the dosage of the diuretic as needed. Anticholinergic Drugs The concomitant use of anticholinergic drugs may increase risk of urinary retention and/or severe constipation, which may lead to paralytic ileus. If concomitant use is warranted, evaluate patients for signs of urinary retention or reduced gastric motility when acetaminophen and codeine phosphate oral solution is used concomitantly with anticholinergic drugs.