Drug Interactions between fluconazole and MLK F2

GENERALLY AVOID: Additive toxicities may occur when bupivacaine is coadministered with other local anesthetics. The potential for increased risk of systemic toxicities such as methemoglobinemia and central nervous system and cardiovascular adverse reactions should be recognized.

MANAGEMENT: Additional use of local anesthetics should generally be avoided within 96 hours following administration of bupivacaine. If coadministration cannot be avoided, overall local anesthetic exposure through 72 hours must be considered in addition to monitoring for the development of methemoglobinemia as well as central nervous system and cardiovascular adverse reactions. Signs and symptoms of methemoglobinemia may be delayed some hours after drug exposure. Patients or their caregivers should be advised to seek medical attention if they notice signs and symptoms of methemoglobinemia such as slate-grey cyanosis in buccal mucous membranes, lips, and nail beds; nausea; headache; dizziness; lightheadedness; lethargy; fatigue; dyspnea; tachypnea; tachycardia; palpitation; anxiety; and confusion. In severe cases, patients may progress to central nervous system depression, stupor, seizures, acidosis, cardiac arrhythmias, syncope, shock, coma, and death. Early warning signs of central nervous system toxicity may include restlessness, anxiety, incoherent speech, dizziness, lightheadedness, numbness and tingling of the mouth and lips, metallic taste, tinnitus, blurred vision, tremors, twitching, depression, and drowsiness. Cardiovascular toxicity may include atrioventricular block, ventricular arrhythmias, cardiac arrest, and decreased cardiac output and arterial blood pressure due to depressed cardiac conductivity, excitability, and myocardial contractility. Patients should have cardiovascular and respiratory vital signs and state of consciousness constantly monitored while under treatment.

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MONITOR: Coadministration with moderate and potent inhibitors of CYP450 3A4 may increase the plasma concentrations of lidocaine, which is primarily metabolized by CYP450 3A4 and 1A2 isoenzymes to active metabolites (monoethylglycinexylidide (MEGX) and glycinexylidide). In addition, antiarrhythmic calcium channel blockers that also inhibit CYP450 3A4 (e.g., diltiazem, verapamil) may have additive negative inotropic effects on the heart when coadministered with lidocaine. A pharmacokinetic study of 9 healthy volunteers showed that the administration of lidocaine oral (1 mg/kg single dose) with itraconazole (200 mg daily), a combined potent CYP450 3A4 and P-gp inhibitor, increased lidocaine systemic exposure (AUC) and peak plasma concentration (Cmax) by 75% and 55%, respectively. However, no changes were observed in the pharmacokinetics of the active metabolite MEGX. In the same study, when the moderate CYP450 3A4 inhibitor erythromycin (500 mg three times a day) was administered, lidocaine AUC and Cmax increased by 60% and 40%, respectively. By contrast, when intravenous lidocaine (1.5 mg/kg infusion over 60 minutes) was administered on the fourth day of treatment with itraconazole (200 mg once a day) no changes in lidocaine AUC or Cmax were observed. However, when lidocaine (1.5 mg/kg infusion over 60 minutes) was coadministered with erythromycin (500 mg three times a day) in the same study, the AUC and Cmax of the active metabolite MEGX significantly increased by 45-60% and 40%, respectively. The observed differences between oral and intravenous lidocaine when coadministered with CYP450 3A4 inhibitors may be attributed to inhibition of CYP450 3A4 in both the gastrointestinal tract and liver affecting oral lidocaine to a greater extent than intravenous lidocaine. While the clinical significance of this interaction is unknown, increased exposure to lidocaine may lead to serious and/or life-threatening reactions including respiratory depression, convulsions, bradycardia, hypotension, arrhythmias and cardiovascular collapse.

MANAGEMENT: Caution and clinical monitoring are advised if lidocaine must be used concomitantly with moderate and potent CYP450 3A4 inhibitors. Monitoring of pharmacologic response and plasma lidocaine levels may be advised whenever a potent CYP450 3A4 inhibitor is added to or withdrawn from therapy, and the lidocaine dosage adjusted as necessary.

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MONITOR: Coadministration with fluconazole may increase the plasma concentrations of drugs that are substrates of CYP450 3A4. The mechanism is decreased clearance due to inhibition of CYP450 3A4-mediated metabolism by fluconazole, a moderate inhibitor of the isoenzyme. A 30% increase in serum carbamazepine has been observed during coadministration with fluconazole according to the product labeling. There have also been a few isolated case reports in the medical literature describing an approximate doubling of carbamazepine levels following the addition of fluconazole, resulting in toxicity. Other drugs metabolized by CYP450 3A4 whose plasma levels reportedly are increased by fluconazole include oral contraceptives (ethinyl estradiol and levonorgestrel), cyclosporine, tacrolimus, and cisapride. These interactions have usually been observed with higher dosages of fluconazole (200 mg/day or more).

MANAGEMENT: Caution is advised when fluconazole is used with medications that undergo metabolism by CYP450 3A4, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever fluconazole is added to or withdrawn from therapy.

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