Protease inhibitors metabolism

Protease inhibitors [NE] Increased protease inhibitor metabolism. 

Zhang, Y., Hsieh, Y., Izumi, T., Lin, E. T., Benet, L. Z., EfFects of ketoconazole on the intestinal metabolism, transport and oral bioavailability of K02, a novel vinylsulfone peptidomimetic cysteine protease inhibitor and a P450 3A, P-glycoprotein dual substrate, in male Sprague-Dawley rats, J. Pharmacol. 

Fitzsimmons, M. E., Collins, J. M., Selective biotransformation of the human immunodeficiency virus protease inhibitor saquinavir by human small-intestinal cytochrome P4503A4 potential contribution to high first-pass metabolism, Drug. Metab. Dispos. 1997, 25, 256-266. 

Use of a hERG blocker in a patient also taking CYP3A4 inhibitors (e.g. antibacterial macrolides, azole antifungals, HIV protease inhibitors) or CYP2D6 inhibitors (quinidine, halofantrine, fluoxetine, paroxetine, thioridazine, terbinafine) the hERG blocker, if mostly metabolized by these CYP isoforms, may accumulate because... 

The major strategies to enhance transmucosal peptide and other drug absorption include (a) coadministration with protease inhibitors, (b) the use of membrane permeation enhancers, (c) coadministration with a combination of absorption enhancers and protease inhibitors, (d) modification of peptide structure to improve metabolic stability or membrane permeation, and (e) use of nano- or microparticles [27], Some of these strategies have been investigated using the in situ rat model. 

The example of amprenavir, an HIV-1 protease inhibitor, shows that intestinal metabolism can also be used as a strategy to enhance the bioavailability of compounds. In the biopharmaceutics classification system (BCS), amprenavir can be categorized as a class II compound it is poorly soluble but highly permeable [51]. Fosamprenavir, the water-soluble phosphate salt of amprenavir, on the other hand, shows poor transepithelial transport. However, after oral administration of fosamprenavir, this compound is metabolized into amprenavir in the intestinal lumen and in the enterocytes mainly by alkaline phosphatases, resulting in an increased intestinal absorption [51, 174],... 

Drug-drug interactions are often more problematic with carbamazepine than other mood stabilizers. Carbamazepine increases the activity of certain liver enzymes. Because these enzymes metabolize and eliminate medications and other substances introduced to the body, carbamazepine therapy can decrease the blood level and thereby reduce the effectiveness of itself (a phenomenon called autoinduction) and other medications that are metabolized by these enzymes. It is not unusual to find that the dose of carbamazepine must be increased after several weeks, because it has increased its own elimination. Other medications may likewise be less effective. Of particular concern are the oral contraceptives, Depo-Provera, and protease inhibitors used for the treatment of HI V+ patients. Oral contraceptives often require an increase in dose. 

The viral protease is inhibited by several drugs, including indinavir. Surprisingly, such protease inhibitors not only affect the virus but they also affect fat metabolism. They cause loss of adipose tissue in the hmbs and face, which is balanced by its accumulation in other areas, intraabdominal, breasts and over the cervical vertebrae, the last giving rise to the term buffalo hump , a change which is especially distressing for the patient. The cause of this effect is not known. 

Rifampin is known to induce the hepatic microsomal enzymes that metabolize various drugs such as acetaminophen, oral anticoagulants, barbiturates, benzodiazepines, beta blockers, chloramphenicol, clofibrate, oral contraceptives, corticosteroids, cyclosporine, disopyramide, estrogens, hydantoins, mexiletine, quinidine, sulfones, sulfonylureas, theophyllines, tocainide, verapamil, digoxin, enalapril, morphine, nifedipine, ondansetron, progestins, protease inhibitors, buspirone, delavirdine, doxycycline, fluoroquinolones, losartan, macrolides, sulfonylureas, tacrolimus, thyroid hormones, TCAs, zolpidem, zidovudine, and ketoconazole. The therapeutic effects of these drugs may be decreased. 

Pharmacology Lopinavir, an HIV protease inhibitor, prevents cleavage of the Gag-Pol polyprotein, resulting in the production of immature, noninfectious viral particles. As coformulated in the lopinavir/ritonavir combination, ritonavir inhibits the CYP3A-mediated metabolism of lopinavir, providing increased lopinavir plasma levels. 

The major isozymes that metabolize efavirenz are CYP3A4 and CYP2B6. In fact, after the administration of efavirenz, the CYP3A4 isozyme is upregulated, which is the same isoz5me responsible for the metabolism of protease inhibitors. As a result, the amoimt of protease inhibitor may need to be increased. The major primary metabolite is a result of hydroxylation at C-7 (compound 19). 

This class of antiretrovirals may be considered the most potent therapeutic agents for HIV to date. Protease inhibitors are used in combination regimens and combinations of reverse-transcriptase inhibitors and protease inhibitors have been proven most effective to decrease viral load and prolong survival. However, the protease inhibitors generally show poor penetration into the CNS and thus have no effect on aids dementia. The present Pis available for the treatment of HIV are indinavir, ritonavir, nel-finavir, saquinavir and (fos)amprenavir, atazanavir and lopinavir (in combination with ritonavir as ritonavir improves the bioavailability of lopinavir by inhibiting its metabolism in the liver by CYP3A). 

The protease inhibitors are partiaiiy metaboiized by the cytochrome P450 oxidase system and have a potentiai for serious interactions with a large number of commonly prescribed drug products metabolized by the same pathway. 

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