Drug Interactions between foscarnet 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.

MONITOR: The concomitant use of corticosteroids and agents that deplete potassium (e.g., potassium-wasting diuretics, amphotericin B, cation exchange resins) may result in increased risk of hypokalemia. Corticosteroids can produce hypokalemia and other electrolyte disturbances via mineralocorticoid effects, the degree of which varies with the agent (from most to least potent: fludrocortisone - cortisone/hydrocortisone - prednisolone/prednisone - other glucocorticoids) and route of administration (i.e. systemic vs. local). However, large systemic doses of any corticosteroid can demonstrate these effects, particularly if given for longer than brief periods. When used pharmacologically, adrenocorticotropic agents such as corticotropin have similar mineralocorticoid activities as cortisone and hydrocortisone.

MANAGEMENT: Patients receiving potassium-depleting agents with corticosteroids should be monitored closely for development of hypokalemia, particularly if fludrocortisone or large doses of another corticosteroid or adrenocorticotropic agent is given. Potassium supplementation may be necessary. Patients should be advised to notify their physician if they experience signs of electrolyte disturbances such as weakness, lethargy, and muscle pains or cramps.

MONITOR: Limited data suggest that coadministration of foscarnet and ciprofloxacin may potentiate the risk of seizures. Both agents are individually epileptogenic and may have additive effects when combined. Specifically, foscarnet can decrease the seizure threshold by chelating ionized calcium and magnesium, while ciprofloxacin inhibits gamma-aminobutyric acid (GABA). In a published report, two patients with AIDS developed generalized tonic-clonic seizures while receiving foscarnet and ciprofloxacin for the treatment of cytomegalovirus (CMV) retinitis and disseminated Mycobacterium avium complex (MAC) infection, respectively. The first patient developed seizures both during the first and second dose of foscarnet (60 mg/kg every 8 hours) while being treated with ciprofloxacin (750 mg twice a day) and some other medications, but experienced no further seizures after discontinuation of foscarnet therapy. The second patient had been receiving foscarnet without incident until he was given ciprofloxacin and various other antimicrobial agents for MAC sepsis. Shortly thereafter, he developed seizures upon the start of a foscarnet infusion and when the infusion was restarted following a brief interruption. A study in mice also found increased seizure potential associated with the combination of foscarnet and ciprofloxacin.

MANAGEMENT: Caution is advised during coadministration of foscarnet and ciprofloxacin, particularly in elderly patients and those with renal impairment, electrolyte and metabolic abnormalities, or underlying neurologic disorders. The same precaution may be applicable during therapy with other quinolones, although clinical data are lacking.