Unexpected drug interactions and adverse events with antiretroviral drugs

Unconsented HIV testing in cases of occupational exposure: ethics, law, and policy

Postexposure prophylaxis (PEP) has substantially reduced the risk of acquiring human immunodeficiency virus (HIV) after an occupational exposure; nevertheless, exposure to HIV remains a concern for emergency department providers. According to published guidelines, PEP should be taken only when source patients are HIV-positive or have risk factors for HIV. Initiating PEP when source patients are uninfected puts exposed persons at risk from taking toxic drugs with no compensating benefit. Forgoing PEP if the source is infected results in increased risk of acquiring HIV. What should be done if source patients refuse HIV testing? Is it justifiable to test the blood of these patients over their autonomous objection? The authors review current law and policy and perform an ethical analysis to determine if laws permitting unconsented testing in cases of occupational exposure can be ethically justified.

Antiviral hepatitis and antiretroviral drug interactions

More and more HIV-infected patients are treated for viral hepatitis, increasing interactions. HEPATITIS C: The concomitant use of didanosine and ribavirin increases the risk of mitochondrial toxicity, responsible for pancreatitis and/or lactic acidosis. Lactic acidosis is characterized by a high mortality rate. Thus, didanosine, but also stavudine, should not be co-administered with ribavirin. Cases of hepatic decompensation have been reported in cirrhotics concomitantly receiving ribavirin and didanosine. Thus, this co-admininistration should be contraindicated in patients with advanced liver fibrosis. Anemia is a frequent side effect of ribavirin. In patients with zidovudine-related anemia, this drug should be discontinued before prescribing ribavirin. Erythropoietin may help to improve the haemoglobin level. HEPATITIS B: Adefovir significantly decreases the plasma levels of saquinavir. Pancreatitis may occur with the co-administration of didanosine and tenofovir. Thus this co-administration should be avoided. Atazanavir concentrations are decreased when tenofovir is co-administered. Thus, atazanavir should be boosted with ritonavir, when combined with tenofovir. Atazanavir increases the concentrations of tenofovir, with the potential risk of increasing the adverse events of tenofovir, including renal disorders. Tenofovir area under the curve is increased if lopinavir-ritonavir are co-administered. The main interactions, with a fatal risk, are observed with didanosine, when co-administered with ribavirin (hepatitis C) or with tenofovir (hepatitis B). Anemia is frequent, but usually moderate, when zidovudine is co-administered with ribavirin. Other interactions are usually easy to manage.

Acyclic nucleoside phosphonates: a key class of antiviral drugs

Almost 20 years after the broad antiviral activity spectrum of the first acyclic nucleoside phosphonates was described, several of these compounds have become important therapies for DNA virus and retrovirus infections. Here, we review the discovery and development of acyclic nucleoside phosphonates, focusing on cidofovir and its potential in the treatment of various herpes-, papilloma-, polyoma-, adeno- and pox-virus infections, adefovir for the treatment of hepatitis B and tenofovir for the treatment of AIDS and the prevention of HIV infections.

Blockade of HERG channels by HIV protease inhibitors

The HIV protease inhibitor class of antiretroviral drug causes unpredicted adverse effects by changing elements of normal cellular metabolism. A case of QT prolongation in a patient receiving protease inhibitors made us question whether these drugs might be responsible. We identified 24 patients with QT prolongation or torsade de pointes, or both, associated with protease inhibitors, using the Food and Drug Administration's voluntary adverse event reporting system. Attending physicians thought that protease inhibitors were the most probable cause of these symptoms in 14 of the patients. Drug-induced QT prolongation is usually caused by block of human ether-a-go-go-related gene (HERG) potassium channels, and we showed that lopinavir, nelfinavir, ritonavir, and saquinavir caused dose-dependent block of HERG channels heterologously expressed in HEK293 cells in vitro. We also recorded block by lopinavir of repolarising potassium current (I(Kr)) channels in neonatal mouse cardiac myocytes. Our data show that four protease inhibitors block HERG channels, suggesting that protease inhibitors could predispose individuals to QT prolongation and torsade de pointes.

Sex Differences in Antiretroviral Therapy-Associated Intolerance and Adverse Events

Although women account for a substantial proportion of the global population infected with HIV, most clinical trials evaluating the safety and efficacy of specific antiretroviral therapy regimens have been preformed in predominantly male cohorts. Our knowledge of the sex differences associated with responses to these treatments is therefore limited. Potentially sex-specific influences, such as endogenous or exogenous hormones, could impact antiretroviral tolerance. Women also have different pharmacokinetic profiles for selected antiretrovirals compared with men. These factors could influence how women respond and react to antiretrovirals. Several observational studies have described a higher frequency of antiretroviral-related adverse effects among women compared with men. Women appear to be at an especially high risk for lactic acidosis, nevirapine-associated rashes and hepatotoxicity, and fat redistribution after highly active antiretroviral therapy exposure. Although a statistical association between antiretroviral toxicity and pregnancy has not been described, pregnancy may provide an additional influence on the toxicity of several antiretrovirals or antiretroviral combinations. Potential tolerability should be an important component in discussions of antiretroviral options among women.