Drug Interactions between dexamethasone / moxifloxacin and Robimycin

GENERALLY AVOID: Certain quinolones, including gatifloxacin and moxifloxacin, may cause dose-related prolongation of the QT interval in some patients. Theoretically, coadministration with other agents that can prolong the QT interval may result in additive effects and increased risk of ventricular arrhythmias including torsade de pointes and sudden death. During postmarketing surveillance, rare cases of torsade de pointes have been reported in patients taking gatifloxacin. These cases primarily involved patients with underlying medical conditions for which they were receiving concomitant medications known to prolong the QTc interval. Rare cases of tachycardia have been reported with moxifloxacin. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s).

MANAGEMENT: Coadministration of gatifloxacin or moxifloxacin with other drugs that can prolong the QT interval should generally be avoided. Caution and clinical monitoring are recommended if concomitant use is required. Since the magnitude of QTc prolongation increases with increasing plasma concentrations of the quinolone, recommended dosages and intravenous infusion rates should not be exceeded. Patients should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

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MONITOR CLOSELY: Concomitant administration of corticosteroids may potentiate the risk of tendinitis and tendon rupture associated with fluoroquinolone treatment. The mechanism is unknown. Tendinitis and tendon rupture have most frequently involved the Achilles tendon, although cases involving the rotator cuff (the shoulder), the hand, the biceps, and the thumb have also been reported. Some have required surgical repair or resulted in prolonged disability. Tendon rupture can occur during or up to several months after completion of fluoroquinolone therapy.

MANAGEMENT: Caution is recommended if fluoroquinolones are prescribed in combination with corticosteroids, particularly in patients with other concomitant risk factors (e.g., age over 60 years; recipient of kidney, heart, and/or lung transplant). Patients should be advised to stop taking the fluoroquinolone, avoid exercise and use of the affected area, and promptly contact their physician if they experience pain, swelling, or inflammation of a tendon. In general, fluoroquinolones should only be used to treat conditions that are proven or strongly suspected to be caused by bacteria and only if the benefits outweigh the risks.

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MONITOR: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations and pharmacologic effects of corticosteroids, which are primarily metabolized by the isoenzyme. The interaction has been reported with potent inhibitors such as clarithromycin, erythromycin, itraconazole, nefazodone, cobicistat, and ritonavir during concomitant use of various corticosteroids, including inhaled, nasal, and ophthalmic formulations. Systemic corticosteroid adverse effects may occur following intensive or long-term continuous ophthalmic corticosteroid therapy. Cushing's syndrome and adrenal insufficiency have been attributed to the interaction.

MANAGEMENT: The possibility of increased corticosteroid effects should be considered during coadministration with potent and moderate CYP450 3A4 inhibitors. Some authorities advise against concomitant use unless the potential benefit outweighs the risk. If the combination is considered necessary, a lower dosage of the corticosteroid may be required. When indicated for intranasal or inhalational use, alternative corticosteroids such as beclomethasone, which is less dependent on CYP450 3A4 metabolism, should be considered, particularly if long term treatment is required. Patients should be monitored for signs and symptoms of hypercorticism such as acne, striae, thinning of the skin, easy bruising, moon facies, dorsocervical "buffalo" hump, truncal obesity, increased appetite, acute weight gain, edema, hypertension, hirsutism, hyperhidrosis, proximal muscle wasting and weakness, glucose intolerance, exacerbation of preexisting diabetes, depression, and menstrual disorders. Other systemic glucocorticoid effects may include adrenal suppression, immunosuppression, posterior subcapsular cataracts, glaucoma, bone loss, and growth retardation in children and adolescents. Following extensive use with a potent CYP450 3A4 inhibitor, a progressive dosage reduction may be required over a longer period if the corticosteroid is to be withdrawn from therapy, as there may be a significant risk of adrenal suppression. Signs and symptoms of adrenal insufficiency include anorexia, hypoglycemia, nausea, vomiting, weight loss, muscle wasting, fatigue, weakness, dizziness, postural hypotension, depression, and adrenal crisis manifested as inability to respond to stress (e.g., illness, infection, surgery, trauma).

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