Fosamprenavir drug interactions

Wire MB, Shelton MJ, Studenberg S (2006) Fosamprenavir Clinical pharmacokinetics and drug interactions of the amprenavir prodrug. Clin Pharmacokinet 45 137-168. 

The potential for drug interactions with fosamprenavir changes when fosamprenavir is coadministered with the potent CYP3A4 inhibitor ritonavir. Because ritonavir is a CYP2D6 inhibitor, clinically significant interactions with drugs metabolized by CYP2D6 are possible when coadministered with fosamprenavir plus ritonavir. 

Delavirdine is extensively metabolized to inactive metabolites by the CYP3A and CYP2D6 enzymes and also inhibits CYP3A4 and 2C9. Therefore, there are numerous potential drug-drug interactions to consider (Tables 49-3 and 49-4). The concurrent use of delavirdine with fosamprenavir and rifabutin is not recommended because of decreased delavirdine levels. 

Lopinavir/Ritonavir (Kaletra) [Anrirelroviral/Protease Inhibitor] Uses HIV Infxn Action Protease inhibitor Dose Adults. Tx naive 2 tab PO daily or 1 tab PO bid Tx experiencedpt 1 tab PO bid (T dose if w/ amprenavir, efavirenz, fosamprenavir, nelfinavir, nevirapine) Peds. 7-15 kg 12/3 mg/kg PO bid 15-40 kg 10/2.5 mg/kg PO bid >40 kg Adult dose w/ food Caution [C, /-] Numerous interactions Contra w/drugs dependent on CYP3A/CYP2D6 (Table VI-8) Disp Tab, soln SE Avoid disulfiram (soln has EtOH), metronidazole GI upset, asthenia, T cholesterol/triglycerides, pancreatitis protease metabolic synd Interactions T Effects Wl clarithromycin, erythromycin T effects OF amiodarone, amprenavir, azole andfungals, bepridil, cisapride, cyclosporine, CCBs, ergot alkaloids, flecainide, flurazepam, HMG-CoA reductase inhibitors, indinavir, lidocaine, meperidine, midazolam, pimozide, propafenone, propoxyphene, quinidine, rifabutin, saquinavir, sildenafil, tacrolimus, terfenadine, triazolam, zolpidem 1 effects Wl barbiturates, carbamazepine, dexamethasone, didanosine, efavirenz, nevirapine, phenytoin, rifabutin, rifampin, St. John s wort 1 effects OF OCPs, warfarin EMS Use andarrhythmics and benzodiazepines... 

Although information is limited, the pharmacokinetic interaction between the ethinylestradiol component of combined hormonal contraceptives and nelfinavir or ritonavir appears to be established and is likely to be clinically important. Similar decreases in plasma levels of ethinylestradiol caused by other drugs have resulted in reduced efficacy and reliability of combined oral contraceptives, and one retrospective report suggests that this has occurred with nelfinavir. It seem likely that the reduced contraceptive levels seen with fosamprenavir, lopinavir and tipranavir were due to the concurrent use of ritonavir (as would be common in practice). Similarly, although no interaction was reported with saquinavir, and raised contraceptive steroid levels were reported with amprenavir and atazanavir, in practice these drugs would be given with ritonavir (as a pharmacokinetic enhancer), and so the levels of combined hormonal contraceptives can reasonably be expected to be reduced. The Faculty ofFamily Planning... 

Drag-drag interactions Etravirine is metabolized by cytochrome P450 enzymes and interacts in vitro with high-dose ritonavir, atazanavir, fosamprenavir, rifampicin, and some antiepileptic drugs [159 ]. 

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