Drug Interactions between cobicistat / elvitegravir / emtricitabine / tenofovir alafenamide and Gastrografin

GENERALLY AVOID: Concomitant use of intravascular radiocontrast media with other nephrotoxic agents may potentiate the risk of contrast-induced nephropathy and renal impairment. Contrast-induced nephropathy is most commonly defined as an increase in serum creatinine >=0.5 mg/dL or 25% from baseline within 24 to 72 hours of intravascular contrast administration in the absence of alternative etiologies, although nephropathy may occur up to a week after contrast exposure. Pathogenesis has not been fully elucidated, but may involve renal hypoperfusion and ischemia, direct cytotoxicity on tubular epithelial cells, and generation of reactive oxygen species. While the condition is usually transient and asymptomatic, it can be associated with increased risk of renal failure, dialysis, prolonged hospitalization, significant long-term morbidity, and mortality. Patients at increased risk of developing contrast-induced nephropathy include those with diabetes (especially diabetic nephropathy), preexisting renal insufficiency (serum creatinine >1.5 mg/dL or GFR <60 mL/min/1.73 m2), volume depletion (e.g., diuretic use), advanced age (>70 years), congestive heart failure, multiple myeloma, hypoalbuminemia, and concomitant use of nephrotoxic agents (e.g., aminoglycosides; polypeptide, glycopeptide, and polymyxin antibiotics; amphotericin B; aminosalicylates; antiviral/antiretroviral agents such as acyclovir, adefovir, cidofovir, foscarnet, and tenofovir; 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). The incidence has been reported to be approximately 10% to 30% in patients with risk factors, and as high as 90% in diabetics with chronic kidney disease. Intraarterial administration of contrast media is also associated with increased risk of nephropathy relative to intravenous administration.

MANAGEMENT: Alternative imaging techniques that do not require contrast should be considered in patients who are at increased risk for contrast-induced nephropathy. Otherwise, experts recommend discontinuing other nephrotoxic drugs 1 to 2 days before administration of contrast media, depending on the clinical feasibility of doing so. The smallest effective dose (100 mL or less) of a nonionic, low-osmolar (e.g., iohexol, iomeprol, iopamidol, iopental, iopromide, ioversol) or iso-osmolar (e.g., iodixanol, iotrolan) contrast medium should be used whenever possible, since the risk of nephrotoxicity may be increased with increasing contrast dose, osmolarity, and ionicity. Some studies suggest a lower risk for iso-osmolar contrasts compared to low-osmolar contrasts, although data are limited. Serum creatinine levels should be measured before contrast administration (if procedure is not urgent) and continued for 24 to 48 hours after. In addition, patients should be adequately hydrated with either intravenous normal saline or sodium bicarbonate starting 3 (outpatient) to 6 (inpatient) hours before and continued for 6 to 24 hours after procedure. Oral fluids are also beneficial, but not as effective as intravenous hydration. N-acetylcysteine the day before and day of contrast administration, or theophylline up to 30 minutes before contrast administration, have also been used in high-risk or critically ill patients. Preferably, a nephrologist should be consulted to optimize prophylactic measures for preventing contrast-induced nephropathy in high-risk patients and to guide treatment if the condition occurs. Any repeat procedures with contrast media, if necessary, should not occur until at least 48 to 72 hours after the previous contrast exposure and renal function has fully recovered.

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MONITOR: Concomitant use of tenofovir with cobicistat may increase the risk for tenofovir-related renal adverse effects, including renal impairment, renal failure, elevated creatinine, and Fanconi syndrome. The mechanism of this interaction has not been described. Cobicistat may decrease estimated creatinine clearance via inhibition of tubular secretion of creatinine; however, renal glomerular function does not appear to be affected. When given concomitantly with cobicistat, the systemic exposure (AUC) and trough plasma concentrations (Cmin) of tenofovir was also increased by 23% and 55%, respectively. However, data are lacking to determine whether concomitant use of tenofovir with cobicistat-containing regimens is associated with a greater risk of renal complications compared with regimens that do not include cobicistat.

MANAGEMENT: Initiation of cobicistat or cobicistat-containing regimens is not recommended in patients with CrCl less than 70 mL/min if any coadministered medicine requires dose adjustment based on renal function (including tenofovir), or is nephrotoxic. If concomitant therapy is necessary, monitoring of renal function is recommended, particularly in patients with risk factors for renal impairment.

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GENERALLY AVOID: Cobicistat may increase the plasma concentrations of antiretroviral agents. The plasma concentrations of cobicistat may also be increased or reduced in the presence of antiretroviral agents. The proposed mechanism is cobicistat inhibition of the CYP450 3A4 isoenzyme, of which antiretroviral agents may be substrates, and the inhibition or induction of CYP450 3A4 by concomitant antiretroviral medications. Cobicistat is a mechanism-based inhibitor and substrate of CYP450 3A4 with no antiretroviral activity of its own. Rather, it is indicated in its capacity as a pharmacokinetic booster of CYP450 3A4 to increase the systemic exposure of some antiretroviral medications such as atazanavir, darunavir, and elvitegravir, which are substrates of this isoenzyme. Concomitant use of other antiretroviral agents with cobicistat may also increase the plasma levels and risk of side effects associated with these medicines. In contrast, concomitant use of cobicistat-boosted atazanavir or darunavir with CYP450 3A4 inducers nevirapine, etravirine, or efavirenz may reduce the plasma concentrations of cobicistat, darunavir, and atazanavir, leading to a potential loss of therapeutic effect and development of resistance to darunavir and atazanavir. Pharmacokinetic data are not available.

MANAGEMENT: Cobicistat is not intended for use with more than one antiretroviral medication that requires pharmacokinetic enhancement, such as two protease inhibitors or elvitegravir in combination with a protease inhibitor. In addition, cobicistat should not be used concomitantly with ritonavir due to their similar effects on CYP450 3A4. According to some authorities, use of the antiretroviral combinations of atazanavir-cobicistat or darunavir-cobicistat concomitantly with the CYP450 3A4 inducers efavirenz, etravirine, or nevirapine is also not recommended. Other authorities consider the administration of atazanavir-cobicistat with efavirenz or nevirapine to be contraindicated. Since dosing recommendations have only been established for a number of antiretroviral medications, product labeling and current antiretroviral treatment guidelines should be consulted.

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