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Antiretroviral drugs are medications for the treatment of infection by retroviruses, primarily HIV. Different classes of antiretroviral drugs act at different stages of the HIV life cycle. Combination of several (typically three or four) antiretroviral drugs is known as Highly Active Anti-Retroviral Therapy (HAART). more...

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Organizations such as the National Institutes of Health (Bethesda, Maryland, USA) recommend offering antiretroviral treatment to all patients with HIV-related symptoms. However, because of the complexity of selecting and following a regimen, the severity of the side effects, and the importance of compliance to prevent viral resistance, such organizations emphasize the importance of involving patients in therapy choices and recommend analyzing the risks and the potential benefits to patients without symptoms.

Combination therapy

The life cycle of HIV can be as short as about 1.5 days: from viral entry into a cell; through replication, assembly, and release of additional viruses; to infection of other cells. HIV lacks proofreading enzymes to correct errors made when it converts its RNA into DNA via reverse transcription. Its short life cycle and high error rate cause the virus to mutate very rapidly, resulting in a high genetic variability of HIV. Most of the mutations either are inferior to the parent virus (often lacking the ability to reproduce at all) or convey no advantage, but some of them have a natural selection superiority to their parent and can enable them to slip past defenses such as the human immune system and antiretroviral drugs. The more active copies of the virus, the greater the possibility that one resistant to antiretroviral drugs will be made, so antiretroviral combination therapy defends against resistance by suppressing HIV replication as much as possible.

Combinations of antiretrovirals create multiple obstacles to HIV replication to keep the number of offspring low and reduce the possibility of a superior mutation. If a mutation arises that conveys resistance to one of the drugs being taken, the other drugs continue to suppress reproduction of that mutation. With rare exceptions, no individual antiretroviral drug has been demonstrated to suppress an HIV infection for long; these agents must be taken in combinations in order to have a lasting effect. As a result the standard of care is to use combinations of antiretroviral drugs.

Combinations of antiretrovirals are subject to positive and negative synergies, which limits the number of useful combinations. For example, ddI and AZT inhibit each other, so taking them together is less effective than taking either one separately. Other issues further limit some people's treatment options from antiretroviral drug combinations, including their complicated dosing schedules and often severe side effects.

Current treatment guidelines

Antiretroviral drug treatment guidelines have changed many times. Early recommendations attempted a "hit hard, hit early" approach. A more conservative approach followed, with a starting point somewhere between 350 and 500 CD4+ T cells/mm³. The current guidelines use new criteria to consider starting HAART, as described below. However, there remain a range of views on this subject and the decision of whether to commence treatment ultimately rests with the patient and their doctor.

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Vertex/Mitsubishi To Develop Hcv Oral Protease Inhibitor
From Worldwide Biotech, 8/1/04

Vertex Pharmaceuticals Incorporated (Nasdaq: VRTX), Cambridge, Mass., and Mitsubishi Pharma Corporation have signed an agreement to develop and commercialize VX-950,

Vertex's investigational oral protease inhibitor for the treatment of hepatitis C virus (HCV) infection, in Japan and certain Far East countries.

As part of the agreement, Mitsubishi will make pre-commercial payments to

Vertex to support clinical development of VX-950. Additionally, Mitsubishi will pay royalties to Vertex on commercial sales of VX-950 in Mitsubishi's territories. Vertex will retain exclusive development and marketing rights to VX-950 in the rest of the world, including North America and Europe.

"Vertex has selected hepatitis C as an important and rapidly growing therapeutic area in which to pursue independent development of its drug candidates in North America," stated Joshua Boger, Ph.D., chairman and CEO of Vertex. "This regional partnership provides financial support for the global development of this important product, recognizes the breakthrough potential of VX-950 as a direct antiviral therapy and provides important downstream opportunities for Vertex in one of the largest hepatitis C populations in the world."

"Current treatment alternatives for chronic hepatitis C infection provide

limited benefit to patients," said Akihiro Tobe, Ph.D., Executive Managing Officer, Division Manager of Strategic Planning at Mitsubishi Pharma Corporation. "Through this partnership with Vertex, a leader in the discovery and development of HCV protease inhibitors, we hope to accelerate the advancement of novel therapeutics for hepatitis C infection, and we are pleased to add VX-950 to our pipeline of innovative drugs in development."

Under the terms of the agreement, Mitsubishi will have exclusive rights to develop and commercialize VX-950 in Japan and certain Far East countries.

Vertex expects that Mitsubishi will make pre-commercialization payments to Vertex of up to $33 million under the agreement, consisting of license fees, a significant contribution to drug development costs through Phase II clinical development, and clinical milestone payments. Vertex anticipates that it could recognize the majority of these pre-commercial payments by the end of 2006. Further cost-sharing beyond Phase II clinical development will be determined by the parties based on the design of registration studies for VX- 950. Vertex will also receive royalties on VX-950 product sales by Mitsubishi and retains an option to supply bulk drug material to Mitsubishi for commercialization in its territories.

About VX-950

VX-950 is Vertex's lead oral HCV protease inhibitor and one of the most advanced of a new class of antivirals in development for HCV. Preclinical data have shown that VX-950 significantly reduces levels of HCV RNA in both the replicon system and infectious virus assays within days. Preclinical pharmacokinetic studies completed to date have indicated that VX-950 is orally bioavailable and achieves excellent exposure in the liver, the target organ

for HCV treatment. In early June 2004, Vertex initiated a Phase I clinical

trial for VX-950 in healthy volunteers.

Clinical Need and Market Opportunity in HCV Infection Chronic hepatitis C virus (HCV) infection is a serious public health concern affecting approximately 2.7 million people in the United States. HCV causes inflammation of the liver, which may lead to fibrosis and cirrhosis, liver cancer, and ultimately, liver failure. Cirrhosis of the liver resulting from chronic HCV infection is the leading indication for liver transplantation in the U.S. Due to the asymptomatic nature of HCV infection, it often goes undetected for up to 20 years following initial infection. Worldwide, the disease strikes as many as 185 million people. Each year, 8,000 to 10,000 people in the U.S. die from complications of HCV.

The current standard of care in HCV treatment is a treatment combination of pegylated interferon (peg-IFN), an injectable agent, and ribavirin. This combination therapy provides a sustained viral response for only 40 to 50 percent of patients chronically infected with genotype 1 HCV, the most difficult viral strain to treat and the most common form in the U.S.

Vertex's drug development portfolio includes two different approaches for advancing the future standard-of-care in HCV. In addition to VX-950, Vertex is developing merimepodib in combination with pegylated interferon alpha (peg-IFN) and ribavirin. The goal of combining merimepodib with standard therapy is to enhance antiviral efficacy and to increase the proportion of patients who

achieve a sustained response to treatment. Vertex owns worldwide development and commercialization rights for merimepodib.

About Vertex

Vertex Pharmaceuticals Incorporated is a global biotechnology company committed to the discovery and development of breakthrough small molecule drugs for

serious diseases. The company's strategy is to commercialize its products both independently and in collaboration with major pharmaceutical partners. Vertex's product pipeline is principally focused on viral diseases, inflammation, autoimmune diseases and cancer. Vertex co-promotes the new HIV protease inhibitor, Lexiva(TM), with GlaxoSmithKline.

About Mitsubishi

Mitsubishi Pharma Corporation was founded by the merger between former Welfide Corporation and Mitsubishi-Tokyo Pharmaceuticals, Inc., on October 1, 2001. The company is a global research-driven pharmaceutical company targeting the therapeutic areas of psychiatric and central nervous system diseases, cardiovascular and metabolic diseases, immunological and respiratory diseases, and cancer and hepatic disease. Mitsubishi Pharma Corporation has established a strong drug discovery infrastructure to engage in the development of innovative new drugs.

For more information, visit http://www.vrtx.com or call 617/444-6108.

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