Ritonavir Fusidate

In a 32-year-old man infected with HIV plasma concentrations of ritonavir, saquinavir, and fusidic acid were significantly raised when these drugs were administered in combination, possibly from mutual inhibition of metabolism (23). 

Khahq Y, Galhcano K, Leger R, Foster B, Badley A. A dmg interaction between fusidic acid and a combination of ritonavir and saquinavir. Br J Clin Pharmacol 2000 50(l) 82-3. 

Clinically important, potentially hazardous interactions with amiodarone, atazanavir, azithromycin, bosentan, ciprofibrate, clarithromycin, clopidogrel, cyclosporine, darunavir, delavirdine, diltiazem, erythromycin, fosamprenavir, fusidic acid, gemfibrozil, grapefruit juice, imatinib, itraconazole, lopinavir, rabeprazole, ranolazine, red rice yeast, ritonavir, roxithromycin, selenium, St John s wort, tacrolimus, telithromycin, tipranavir, verapamil, warfarin... 

Indinavir levels are raised by interleukin-2, but not affected by influenza vaccine or quinidine. Protease inhibitors are predicted to increase quinidine levels. Nelfinavir does not appear to interact with pancreatic enzyme supplements. In one case report, the combination of ritonavir/saquinavir and fusidic acid raised plasma levels of all three drugs. 

A 32-year-old HIV-positive man was admitted with suspected fusidic acid toxicity after taking fusidic acid 500 mg three times daily for one week, with his usual treatment of ritonavir 400 mg twice daily, saquinavir 400 mg twice daily and stavudine 40 mg twice daily. His plasma fusidic acid level was found to be twice the expected level, and his ritonavir and saquinavir levels were also elevated. He improved spontaneously, but... 

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