Drug Interaction Report

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: Coadministration of tenofovir with other nephrotoxic agents may increase the risk of renal impairment due to additive effects on the kidney. Additionally, renal impairment secondary to the use of these agents may reduce the clearance of tenofovir, which is primarily eliminated by a combination of glomerular filtration and active tubular secretion. The use of tenofovir has been associated with dose-related nephrotoxicity including acute renal failure and Fanconi syndrome characterized by renal tubular injury with severe hypophosphatemia, possibly as a result of mitochondrial toxicity. Cases of acute renal failure after initiation of high-dose or multiple nonsteroidal anti-inflammatory agents have been reported in HIV-infected patients with risk factors for renal dysfunction who appeared stable on tenofovir therapy. Some patients required hospitalization and renal replacement therapy. Available clinical data seem to suggest a lower risk of nephrotoxicity with tenofovir alafenamide fumarate (TAF) than with tenofovir disoproxil fumarate (TDF), presumably due to lower tenofovir systemic exposure following administration of TAF relative to TDF. Whereas TDF is metabolized in plasma to tenofovir and phosphorylated intracellularly to the active moiety tenofovir diphosphate, TAF is largely metabolized and phosphorylated intracellularly, resulting in substantially higher intracellular concentrations of tenofovir diphosphate and lower plasma levels of tenofovir at the therapeutic dose of 25 mg compared to TDF 300 mg. It has been further reported that tenofovir is actively transported into the proximal renal tubular cell by organic anion transporters (OAT) 1 and 3, but that TAF is not a substrate for these transporters and thus less likely to cause tubular injury. There have been no cases of Fanconi syndrome or proximal renal tubulopathy in clinical trials of various TAF-containing products according to the manufacturers.

MANAGEMENT: The use of tenofovir in patients who have recently received or are receiving treatment with other potentially nephrotoxic agents (e.g., aminoglycosides; polypeptide, glycopeptide, and polymyxin antibiotics; amphotericin B; aminosalicylates; antiviral agents such as acyclovir, adefovir, cidofovir, foscarnet, and ganciclovir; antineoplastics such as aldesleukin, cisplatin, clofarabine, ifosfamide, streptozocin, and high intravenous dosages of methotrexate; chelating agents such as deferasirox, deferoxamine, edetate disodium, and edetate calcium disodium; immunosuppressants such as cyclosporine, everolimus, sirolimus, and tacrolimus; intravenous bisphosphonates; intravenous pentamidine; high dosages and/or chronic use of nonsteroidal anti-inflammatory agents; gallium nitrate; lithium; penicillamine) should be avoided if possible. Renal function tests including serum creatinine, serum phosphorous, estimated creatinine clearance, urine glucose, and urine protein should be performed prior to and during therapy with tenofovir. Patients with renal insufficiency at baseline or during treatment may require dosage adjustment in accordance with the manufacturer's product labeling. Persistent or worsening bone pain, pain in extremities, fractures, and/or muscular pain or weakness may also be manifestations of proximal renal tubulopathy and should prompt an evaluation of renal function in at-risk patients.

MONITOR: The combined use of corticosteroids and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the potential for serious gastrointestinal (GI) toxicity, including inflammation, bleeding, ulceration, and perforation. In a large, case-control study of elderly patients, those who used corticosteroids and NSAIDs concurrently had an estimated relative risk (RR) for peptic ulcer disease and GI hemorrhage of 14.6 compared to those who used neither. Corticosteroid use was associated with a doubling of the risk (estimated RR = 2.0), but the risk was confined to those who also used NSAIDs. It is possible that both categories of agents are ulcerogenic and have additive effects on the GI mucosa during coadministration. Some investigators have also suggested that the primary effect of corticosteroids in this interaction is to delay healing of erosions caused by NSAIDs rather than cause de novo ulcerations.

MANAGEMENT: Caution is advised if corticosteroids and NSAIDs are used together, especially in patients with a prior history of peptic ulcer disease or GI bleeding and in elderly and debilitated patients. During concomitant therapy, patients should be advised to take the medications with food and to immediately report signs and symptoms of GI ulceration and bleeding such as severe abdominal pain, dizziness, lightheadedness, and the appearance of black, tarry stools. The selective use of prophylactic anti-ulcer therapy (e.g., antacids, H2-antagonists) may be considered.

MONITOR: Coadministration with nonsteroidal anti-inflammatory drugs (NSAIDs) may potentiate the risk of central nervous system toxicity sometimes associated with fluoroquinolone use. The interaction has been reported most often with enoxacin. It may occur with other fluoroquinolones as well, but is poorly documented. The exact mechanism of interaction is unknown. Some investigators suggest that the piperazine ring of fluoroquinolones may inhibit the binding of gamma-aminobutyric acid (GABA) to brain receptors and that NSAIDs may synergistically add to this effect. Patients with a history of seizures may be at greater risk.

MANAGEMENT: Clinical monitoring for signs of CNS stimulation such as tremors, involuntary muscle movements, hallucinations, or seizures is recommended if fluoroquinolone antibiotics are prescribed in combination with NSAIDs.

GENERALLY AVOID: The concurrent use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) and ethanol may lead to gastrointestinal (GI) blood loss. The mechanism may be due to a combined local effect as well as inhibition of prostaglandins leading to decreased integrity of the GI lining.

MANAGEMENT: Patients should be counseled on this potential interaction and advised to refrain from alcohol consumption while taking aspirin or NSAIDs.

Food enhances the oral absorption and bioavailability of tenofovir, the active entity of tenofovir disoproxil fumarate. According to the product labeling, administration of the drug following a high-fat meal increased the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of tenofovir by approximately 14% and 40%, respectively, compared to administration in the fasting state. However, administration with a light meal did not significantly affect the pharmacokinetics of tenofovir compared to administration in the fasting state. Food delays the time to reach tenofovir Cmax by approximately 1 hour. Tenofovir disoproxil fumarate may be administered without regard to meals.