Drug Interactions between dexamethasone / moxifloxacin and methoxsalen

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.

MONITOR: Concomitant use of methoxsalen with other known photosensitizing agents may increase the risk of photosensitivity reactions. These agents include anthralin, coal tar or coal tar derivatives, griseofulvin, hypericin extracts (e.g., St John's Wort), fluoroquinolones, phenothiazines, retinoids, halogenated salicylanilides (bacteriostatic soaps), sulfonamides, sulfonylureas, tetracyclines, thiazides, and certain organic staining dyes such as methylene blue, toluidine blue, rose bengal, and methyl orange.

MANAGEMENT: Caution is advised and pharmacologic response to methoxsalen therapy should be carefully monitored if concomitant use of other photosensitizing agents cannot be avoided. Patients should be advised to avoid sun exposure, even through window glass or cloud cover, for at least 8 hours after methoxsalen ingestion and during the 24 hours following photochemotherapy or photopheresis treatment. Protective devices should be used if sun exposure cannot be avoided, such as a hat and gloves and/or sunscreens containing ingredients that filter out UVA radiation (e.g., benzophenone and/or PABA esters). Sunscreens must be applied to all areas that might be exposed to the sun, including the lips. For the treatment of psoriasis, sunscreens should not be applied to areas affected by psoriasis until after treatment in the UVA chamber. In addition, UVA-absorbing wrap-around sunglasses should be worn during daylight for 24 hours after methoxsalen ingestion and during the 24 hours following photochemotherapy or photopheresis treatment to prevent the irreversible binding of methoxsalen to proteins and DNA components of the lens, which can lead to formation of cataracts. The glasses should be worn any time patients are exposed to direct or indirect sunlight, whether they are outdoors or exposed through a window. Because erythema and/or burning due to photochemotherapy and sunburn due to sun exposure are additive, patients should not sunbathe for 48 hours after photochemotherapy.