Drug Interactions between efavirenz and moxifloxacin / triamcinolone

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.

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.

MONITOR: Coadministration with efavirenz may decrease the plasma concentrations of drugs that are substrates of the CYP450 3A4 isoenzyme. The mechanism is accelerated clearance due to induction of CYP450 3A4 activity by efavirenz.

MONITOR: Administration of efavirenz can cause central nervous system (CNS) toxicity. In controlled studies, patients receiving efavirenz reported central nervous system and psychiatric symptoms. These CNS toxicity symptoms included, but were not limited to, dizziness, impaired concentration, somnolence, insomnia, abnormal dreams, and hallucinations. Combining efavirenz with other centrally-acting CNS agents may add to the neurotoxic effects of efavirenz.

MANAGEMENT: Caution is advised if efavirenz must be used concomitantly 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 efavirenz is added to or withdrawn from therapy. Additionally, patients treated with any medication that can cause CNS toxicity symptoms should be advised to seek prompt medical attention if they experience symptoms. Patients should be advised to avoid driving, operating machinery, or engaging in potentially hazardous activities requiring mental alertness and motor coordination until they know how the medications affect them.