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Query: UMLS:C0019693 (HIV)
 170,526 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Treatment of HIV infection is a multi-drug issue. Not only are there drugs for the treatment of HIV but also concomitant drugs for opportunistic infections, complications arising from the anti-retroviral therapy and other conditions related to a chronic disease. To have any understanding of drug-drug interactions in HIV treatment we need to appreciate the importance of key pharmacological areas including: 1) how each drug in a regimen is eliminated; 2) the potential for a drug to either induce or inhibit metabolic enzymes and/or transporters; 3) the therapeutic index of each drug. It is impossible to memorise all the possible drug-drug interactions in HIV, therefore understanding how drugs are metabolised/eliminated and the potential for a particular drug to modify the pharmacokinetics of another has predictive value even when substantive data are unavailable. NNRTIs interact with cytochrome P450 (CYP450) enzymes both as substrates and inducers. Because of the inductive effects caution must be exercised when using with protease inhibitors (either boosted or un-boosted with ritonavir). In this situation therapeutic drug monitoring may play a role in optimising response. There needs to be care when using many drugs with NNRTIs e.g. methadone, oral contraceptives, rifampicin, and there are some definite contraindications. By understanding pharmacological principles, it is possible to optimise use of multi-drug regimens.
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PMID:Pharmacokinetic drug interactions with nevirapine. 1456 53

Tipranavir (TPV) is the first of a new class of non-peptidic protease inhibitors (NPPIs). It is a sulphonamide-containing dihydropyrone, which is highly selective for the HIV protease enzyme and demonstrates potent in vitro activity against wild-type HIV-1 and HIV-2. The IC90 for TPV was 0.1 microM against clinical HIV isolates. Since CYP3A is the major cytochrome P450 isoform for the phase I metabolism of TPV, its exposure is markedly enhanced in the presence of ritonavir (RTV). In one clinical study, using the new self emulsifying drug delivery system (SEDDS) formulation of TPV, plasma concentrations in excess of 20 microM were maintained for 12 hours, allowing for twice-a-day dosing following administration of TPV 300 mg/RTV(r) 200 mg twice a day. The 20 microM target represents 10-fold the IC90 for multiple protease inhibitor (PI)-resistant strains. Both in vitro data and pharmacokinetic results indicate that TPV will be active in vivo against PI-resistant viruses, when given twice a day in combination with low dose RTV. Of 105 HIV viral isolates taken from patients who had been heavily pretreated with PI-based regimens: 90% were fully susceptible to TPV; 8% exhibited intermediate resistance; and 2% were more than 10-fold resistant. In patients who had failed at least two PI-based regimens, only 12.2% of the HIV isolates exhibited four to 10-fold reduced susceptibility to TPV after one year of treatment with a regimen containing the NPPI (Study BI1182.2). A reduction of approximately 1.5 log10 copies/mL in the plasma viral load (pVL) was observed in treatment-naive patients after 15 days of monotherapy with TPV (300 or 1200 mg twice a day) co-administered with RTV (200 mg twice a day) (TPV/r) in a dose-ranging study (Study BI1182.3). The safety and efficacy of TPV (500 or 1250 mg) plus ritonavir (100 mg twice a day) plus two new nucleoside reverse transcriptase inhibitors (NRTIs) was studied in patients failing their first PI-containing regimen (Study BI1182.4). Similar decreases in pVLs (1.44-1.79 log10 copies/mL) were observed after 16 weeks of treatment with either dose of TPV/r. Two doses of TPV/r plus efavirenz (EFV) and a new NRTI have been studied in non-nucleoside reverse transcriptase inhibitor (NNRTI)-naive patients who had failed two or more PI-containing regimens (BI1182.2). Between 50% and 78.9% of patients maintained a pVL < 50 copies/mL for 48 weeks. Clinical studies have shown that TPV/r-associated adverse events are generally gastrointestinal-associated, transient and mild. A phase II study will define the optimal dose of TPV/r for highly treatment-experienced patients. The safety and efficacy of this dose of TPV/r will be evaluated in two phase III studies that will enroll more than 1300 patients worldwide. Tipranavir's robust activity against PI-resistant strains results from its molecular flexibility, which allows it to fit into the active pocket of the protease enzyme in viruses that have become resistant to other PIs.
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PMID:Tipranavir: a protease inhibitor from a new class with distinct antiviral activity. 1456 64

Rifampin is an important drug in the treatment of tuberculosis, but administration of rifampin in combination with protease inhibitors is complicated because of drug-drug interactions. A prospective, controlled, multiple-dose study involving 6 HIV-infected patients receiving a combination of indinavir (800 mg) and ritonavir (100 mg) twice a day was performed to evaluate whether the inducing effect of rifampin on the drug-metabolizing enzyme cytochrome P450 (CYP) 3A4 could be overcome by the inhibitory effect of ritonavir. Pharmacokinetic evaluations of steady-state concentrations of indinavir and ritonavir were performed before and after administration of rifampin (300 mg every day for 4 days). An 87% reduction (from 837 to 112 ng/mL) in median indinavir and a 94% reduction (from 431 to 27 ng/mL) in median ritonavir concentrations were seen 12 h after the last dose of rifampin was administered (P=.031). These results strongly indicate that the administration of rifampin with a combination of indinavir (800 mg) and ritonavir (100 mg) could lead to subtherapeutic concentrations of indinavir.
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PMID:Pharmacokinetic interaction between rifampin and the combination of indinavir and low-dose ritonavir in HIV-infected patients. 1472 16

Dyslipidemia, characterized by elevated serum levels of triglycerides and reduced levels of total cholesterol, low-density lipoprotein-cholesterol (LDL-C) and high-density lipoprotein-cholesterol, has been recognized in patients with human immunodeficiency virus (HIV) infection. It is thought that elevated levels of circulating cytokines, such as tumor necrosis factor-alpha and interferon-alpha, may alter lipid metabolism in patients with HIV infection. Protease inhibitors, such as saquinavir, indinavir and ritonavir, have been found to decrease mortality and improve quality of life in patients with HIV infection. However, these drugs have been associated with a syndrome of fat redistribution, insulin resistance, and hyperlipidemia. Elevations in serum total cholesterol and triglyceride levels, along with dyslipidemia that typically occurs in patients with HIV infection, may predispose patients to complications such as premature atherosclerosis and pancreatitis. It has been estimated that hypercholesterolemia and hypertriglyceridemia occur in greater than 50% of protease inhibitor recipients after 2 years of therapy, and that the risk of developing hyperlipidemia increases with the duration of treatment with protease inhibitors. In general, treatment of hyperlipidemia should follow National Cholesterol Education Program guidelines; efforts should be made to modify/control coronary heart disease risk factors (i.e. smoking; hypertension; diabetes mellitus) and maximize lifestyle modifications, primarily dietary intervention and exercise, in these patients. Where indicated, treatment usually consists of either pravastatin or atorvastatin for patients with elevated serum levels of LDL-C and/or total cholesterol. Atorvastatin is more potent in lowering serum total cholesterol and triglycerides compared with other hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, but it is also associated with more drug interactions compared with pravastatin. Simvastatin and lovastatin are significantly metabolized by cytochrome P450 enzymes (CYP3A4) and are therefore not recommended for coadministration with protease inhibitors. A fibric acid derivative (gemfibrozil or fenofibrate) should be used in patients with primary hypertriglyceridemia. However, it must be kept in mind that protease inhibitors, such as nelfinavir and ritonavir, induce enzymes involved in the metabolism of the fibric acid derivatives and may, therefore, reduce the lipid-lowering activity of coadministered gemfibrozil or fenofibrate. In certain patients HMG-CoA reductase inhibitors may be used in combination with fibric acid derivatives but patients should be carefully monitored for liver and skeletal muscle toxicity. Select patients may experience improvements in serum lipid levels when their offending protease inhibitor(s) is/are exchanged for efavirenz, nevirapine, or abacavir; however each patient's virologic and immunologic status must be taken closely into consideration.
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PMID:Management of protease inhibitor-associated hyperlipidemia. 1472 85

Two studies examined the pharmacokinetics of indinavir and rifabutin when coadministered in healthy subjects. Rifabutin, which induces the expression of cytochrome P450 (CYP) 3A, and indinavir, which inhibits that enzyme system, are frequently coadministered in patients infected with HIV. The second study was undertaken to determine if altering the dose of rifabutin coadministered with indinavir would minimize the drug interaction observed in the first study. Two studies, each with a three-period crossover design, were performed. In study 1, standard doses of rifabutin and indinavir (300 mg of rifabutin qd and 800 mg indinavir q8h) were administered as monotherapy (with placebo to the other drug) or in combination to 10 volunteers for 10 days. In study 2, 150 mg qd of rifabutin together with 800 mg q8h of indinavir, 300 mg qd of rifabutin alone, or 800 mg q8h of indinavir alone was administered to 14 volunteers for 10 days. In study 1, the geometric mean ratio (GMR) (90% confidence interval [CI]) of the AUC((0-8h)) of indinavir, coadministered with rifabutin 300 mg qd compared to indinavir alone (with rifabutin placebo), was 0.66 (0.56, 0.77), while that of the AUC((0-24h)) of rifabutin, coadministered with indinavir compared to rifabutin alone (with indinavir placebo), was 2.73 (1.99, 3.77). In study 2, the GMR (90% CI) of the AUC((0-8h)) of indinavir, coadministered with rifabutin 150 mg qd compared to indinavir alone, was 0.68 (0.60, 0.76), while that of the AUC((0-24h)) of rifabutin, when rifabutin 150 mg qd was coadministered with indinavir compared to rifabutin 300 mg qd alone, was 1.54 (1.33, 1.79). For both studies 1 and 2, indinavir and rifabutin administered alone or in combination were generally well tolerated. No clinical or laboratory adverse experience was serious. These data demonstrate the important pharmacokinetic interactions between indinavir and rifabutin when they are coadministered. Indeed, these observations formed the basis for the subsequent ACTG 365 study that explored dose adjustments for these agents in combination regimens to preserve the sustained antiviral activity of indinavir in the absence of adverse events as a result of elevated circulating levels of rifabutin.
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PMID:Indinavir and rifabutin drug interactions in healthy volunteers. 1497 5

S-1360, a 1,3-diketone derivative, was the first HIV integrase inhibitor to enter human trials. Clinical data suggested involvement of non-cytochrome P450 clearance pathways, including reduction and glucuronidation. Reduction of S-1360 generates a key metabolite in humans, designated HP1, and constitutes a major clearance pathway. For characterization of subcellular location and cofactor dependence of HP1 formation, [(14)C]-S-1360 was incubated with commercially available pooled human liver fractions, including microsomes, cytosol, and mitochondria, followed by HPLC analysis with radiochemical detection. Incubations were performed in the presence and absence of the cofactors NADH or NADPH. Results showed that the enzyme system responsible for generation of HP1 in vitro is cytosolic and NADPH-dependent, implicating aldo-keto reductases (AKRs) and/or short-chain dehydrogenases/reductases (SDRs). A validated LC/MS/MS method was developed for investigating the reduction of S-1360 in detail. The reduction reaction exhibited sigmoidal kinetics with a K(m,app) of 2 microM and a Hill coefficient of 2. The ratio of V(max)/K(m) was approximately 1 ml/(min mg cytosolic protein). The S-1360 kinetic data were consistent with positive cooperativity and a single enzyme system. The relative contributions of AKRs and SDRs were examined through the use of chemical inhibitors. For these experiments, non-radiolabeled S-1360 was incubated with pooled human liver cytosol and NADPH in the presence of inhibitors, followed by quantitation of HP1 by LC/MS/MS. Quercetin and menadione produced approximately 30% inhibition at a concentration of 100 microM. Enzymes sensitive to these inhibitors include the carbonyl reductases (CRs), a subset of the SDR enzyme family predominantly located in the cytosol. Flufenamic acid and phenolphthalein were the most potent inhibitors, with > 67% inhibition at a concentration of 20 microM, implicating the AKR enzyme family. The cofactor dependence, subcellular location, and chemical inhibitor results implicated the aldo-keto reductase family of enzymes as the most likely pathway for generation of the major metabolite HP1 from S-1360.
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PMID:Enzymology of a carbonyl reduction clearance pathway for the HIV integrase inhibitor, S-1360: role of human liver cytosolic aldo-keto reductases. 1501 15

Before highly active antiretroviral therapies (HAART) were available for the treatment of persons with HIV infection, disseminated Mycobacterium avium-intracellulare complex (MAC) infection was one of the most common opportunistic infections that affected people living with AIDS. Routine use of chemoprophylaxis with a macrolide has been advocated in guidelines for the treatment of HIV-infected individuals if they have a circulating CD4+ cell count of < or =50 cells/microL. In addition, lifelong prophylaxis for disease recurrence has been recommended for those with a history of disseminated MAC infection. The introduction of HAART has resulted in a remarkable decline in the incidence of opportunistic infections and death among persons living with AIDS. Considerable reconstitution of functional immune responses against opportunistic infections can be achieved with HAART. In the case of infection with MAC, there has been a substantial reduction in the incidence of disseminated infections in the HAART era, even in countries where the use of MAC prophylaxis was never widely accepted. Moreover, the clinical picture of MAC infections in patients treated with potent antiretroviral therapies has shifted from a disseminated disease with bacteraemia to a localised infection, presenting most often with lymphadenopathy and osteomyelitis. Data from several recently conducted randomised, double-blind, placebo-controlled trials led to the current practice of discontinuing primary and secondary prophylaxis against disseminated MAC infections at stable CD4+ cell counts >100 cells/microL. These recommendations are still conservative as primary or secondary disseminated MAC infections are only rarely seen in patients who respond to HAART, despite treatment initiation at very low CD4+ cell counts. Potential adverse effects of macrolide therapy and drug interactions with antiretrovirals also metabolised via the cytochrome P450 enzyme system must be critically weighed against the marginal benefit that MAC prophylaxis may provide in addition to treatment with HAART. These authors feel that, unless patients who initiate HAART at low CD4+ cell counts do not respond to HIV-treatment, routine MAC prophylaxis should not be recommended. Nevertheless, the patient population for whom MAC prophylaxis may still be indicated in the era of HAART needs to be identified in prospectively designed clinical trials.
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PMID:Disseminated mycobacterium avium-intracellulare complex (MAC) infection in the era of effective antiretroviral therapy: is prophylaxis still indicated? 1502 43

Combination antiretroviral therapy with two or more protease inhibitors has become the standard of care in the treatment of HIV infection. Dual protein inhibitor (PI) regimens, such as lopinavir/ritonavir, are commonly used as initial PI therapy. As viral resistance increases and the development of mechanistically novel protease inhibitors decreases, clinicians turn to ritonavir-enhanced dual PI therapy to treat salvage patients. Potency of these combination regimens is increased while pill burden, food restrictions and often, side effects are decreased. These clinical advantages result from the enhancement of their pharmacological properties, including alterations in the absorption and metabolism process. Alterations in the absorption and metabolism of protease inhibitors when co-administered with a cytochrome P450 (CYP) enzyme inhibitor, such as low dose ritonavir, are reflected by impressive changes in pharmacokinetic parameters. For example, the addition of ritonavir 100 or 200 mg to saquinavir 1200-1800 mg has been shown to increase saquinavir area under the concentration-time curve (AUC) by approximately 300-800% compared with saquinavir alone. The ability of ritonavir to increase plasma trough concentrations (C(min)) of concomitantly administered PIs is perhaps the greatest clinical benefit of dual or ritonavir-enhanced dual PI therapy since inadequate concentrations of antiretrovirals may support long term antiretroviral resistance. For example, lopinavir 400mg alone in healthy volunteers produced plasma concentrations that briefly exceeded the concentration required to inhibit 50% of viral replication (IC(50)). Yet, when low doses of ritonavir were added, C(min) values were 50- to 100-fold greater than the concentration required to produce 50% of the maximum effect for wild-type HIV (EC(50)). The following manuscript will discuss the rationale for combining protease inhibitors and will review pertinent pharmacokinetic and clinical data on these combination regimens.
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PMID:Pharmacokinetic enhancement of protease inhibitor therapy. 1508 Jul 63

The incidence of tuberculosis (TB) is currently increasing in HIV-infected patients living in Africa and Asia, where TB endemicity is high, reflecting the susceptibility of this group of patients to mycobacteria belonging to the TB group. In this population, extension of multiple resistance to anti-tuberculous drugs is also a matter of anxiety. HIV-induced immunosuppression modifies the clinical presentation of TB, resulting in atypical signs and symptoms, and more frequent extrapulmonary dissemination. The treatment of TB is also more difficult to manage in HIV-infected patients, particularly with regard to pharmacological interactions secondary to inhibition or induction of cytochrome P450 enzymes by protease inhibitors with rifampicin or rifabutin, respectively. Finally, immune restoration induced by highly active anti-retroviral therapy (HAART) in developed countries may be responsible for a paradoxical worsening of TB manifestations.
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PMID:Tuberculosis in HIV-infected patients: a comprehensive review. 1511 14

Enfuvirtide (Fuzeon) is an HIV fusion inhibitor, the first drug in a new class of antiretrovirals. The HIV protease inhibitors ritonavir and saquinavir both inhibit cytochrome P450 (CYP450) isoenzymes, and low-dose ritonavir is often used to boost pharmacokinetic exposure to full-dose protease inhibitors. These two studies were designed to assess whether ritonavir and ritonavir-boosted saquinavir influence the steady-state pharmacokinetics of enfuvirtide. Both studies were single-center, open-label, one-sequence crossover clinical pharmacology studies in 12 HIV-1-infected patients each. Patients received enfuvirtide (90 mg twice daily [bid], subcutaneous injection) for 7 days and either ritonavir (200 mg bid, ritonavir study, orally) or saquinavir/ritonavir (1000/100 mg bid, saquinavir/ritonavir study, orally) for 4 days on days 4 to 7. Serial blood samples were collected up to 24 hours after the morning dose of enfuvirtide on days 3 and 7. Plasma concentrations for enfuvirtide, enfuvirtide metabolite, saquinavir, and ritonavir were measured using validated liquid chromatography tandem mass spectrometry methods. Efficacy and safety were also monitored. Bioequivalence criteria require the 90% confidence interval (CI) for the least squares means (LSM) of C(max) and AUC(12h) to be between 80% and 125%. In the present studies, analysis of variance showed that when coadministered with ritonavir, the ratio of LSM for enfuvirtide was 124% for C(max) (90% confidence interval [CI]: 109%-141%), 122% for AUC(12h) (90% CI: 108%-137%), and 114% for C(trough) (90% CI: 102%-128%). Although the bioequivalence criteria were not met, the increase in enfuvirtide exposure was small (< 25%) and not clinically relevant. When administered with ritonavir-boosted saquinavir, the ratio of LSM for enfuvirtide was 107% for C(max) (90% CI: 94.3%-121%) and 114% for AUC(12h) (90% CI: 105%-124%), which therefore met bioequivalence criteria, and 126% for C(trough) (90% CI: 117%-135%). The pharmacokinetics of enfuvirtide are affected to a small extent when coadministered with ritonavir at a dose of 200 mg bid but not when coadministered with a saquinavir-ritonavir combination (1000/100 mg bid). However, previous clinical studies have shown that such increases in enfuvirtide exposure are not clinically relevant. Thus, no dosage adjustments are warranted when enfuvirtide is coadministered with low-dose ritonavir or saquinavir boosted with a low dose of ritonavir.
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PMID:Lack of interaction between enfuvirtide and ritonavir or ritonavir-boosted saquinavir in HIV-1-infected patients. 1519 84


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