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Description

Adefovir dipivoxil is the first nucleotide analog to be launched in the US as an oral treatment for hepatitis B virus (HBV) infections. It can be easily prepared in 4 steps from adenine. Adefovir dipivoxil acts as a bioavailable ester prodrug which is rapidly hydrolyzed to free adefovir and further anabolized to its active form, adefovir diphosphate, by two intracellular phosphotylation steps. The diphosphate competitively inhibits reverse transcriptase and/or causes chain termination when incorporated into growing DNA. Adefovir dipivoxil has a broad antiviral spectrum against retro-, herpes- and hepadnaviruses. The drug inhibits HBV replication, decreases HBV DNA levels and improves liver histology of patients infected with HBV wild type and resistant to other antivirals such as lamivudine. It also demonstrated activity in hepatitis B”e” antigennegative, or precore mutant, patients and in patients co-infected with HIV. To date, no adefovir dipivoxil-associated resistance mutations have been identified in patients up to 136 weeks with the drug. The oral bioavailability of adefovir after oral administration of its dipivoxil prodrug is approximately 30%. It is mainly excreted unchanged in the urine and its plasma elimination half-life is 4.2 h. However, a long intracellular half-life (17 h) of the active bisphosphorylated metabolite enables once-daily dosing. The most prominent adverse effect of adefovir dipivoxil is nephrotoxicity (which has prevented the drug from being marketed for HIV infections where the drug required administration at higher doses).

Chemical Properties

White Solid

Originator

Institute of Organic Chemistry and Biochemistry of the Academy of Sciences in the Czech Republic and the REGA Stichting Research (Czech Republic, Belgium)

Definition

ChEBI: Adefovir pivoxil is an organic phosphonate that is the dipivoxil ester of adefovir. A prodrug for adefovir, an HIV-1 reverse transcriptase inhibitor, adefovir pivoxil is used to treat chronic hepatitis B viral infection. It has a role as a prodrug, an antiviral drug, a DNA synthesis inhibitor, a HIV-1 reverse transcriptase inhibitor and a nephrotoxic agent. It is an organic phosphonate, a member of 6-aminopurines, an ether and a carbonate ester. It is functionally related to an adefovir.

Brand name

Hepsera (Gilead Sciences).

General Description

Adefovir is an orally active prodrug that is indicated for thetreatment of the chronic form of hepatitis B. The dipivoxil moieties are hydrolyzed by ubiquitous esterases to yieldadefovir, which is phosphorylated by adenylate kinase toyield adefovir diphosphate. This compound is inhibitory atHBV DNA polymerase. In addition, adefovir undergoes incorporationinto viral DNA and causes chain termination.Adefovir is poorly absorbed by the oral route, but the dipivoxilester groups cause the bioavailability to increase toapproximately 60%.

Mechanism of action

Adefovir dipivoxil is an orally active prodrug indicated for the treatment of chronic hepatitis B. The drug is hydrolyzed by extracellular esterases to produce adefovir, which in turn is phosphorylated by adenylate kinase to adefovir diphosphate, which inhibits HBV DNA polymerase. Incorporation of adefovir into viral DNA also leads to DNA chain termination. As shown in Figure 43.9, adefovir dipivoxyl is activated in two steps involving an esterase that exposes a free phosphate group (adefovir), followed by addition of a second phosphate by adenylate kinase to form adefovir diphosphate, the active form of the drug.

Clinical Use

Adefovir dipivoxil joins interferon and lamivudine in the treatment of chronic HBV. It can be used singly or in combination with lamivudine. Early clinical studies indicate benefit of the use of adefovir dipivoxil to treat lamivudine-resistant HBV with a low level of resistant virus developing to monotherapy with adefovir dipivoxil.

Synthesis

Steroidal dutasteride (5) was synthesized from 3-oxo-4- androstene-17β-carboxylic acid (55). Oxidation of 55 with potassium permanganate, sodium periodate and sodium carbonate in refluxing t-butyl alcohol and water gave secosteroid 56 which was cyclized with ammonium acetate in acetic acid to give 4-aza-steroid 57 in good yield. Stereoselective hydrogenation of 57 with H2 over PtO2 in hot acetic acid and in the presence of ammonium acetate yielded saturated azasteroid 58, which was dehydrogenated with DDQ in the presence of bis(trimethylsilyl)trifluoroacetamide (BSTFA) 59 in refluxing dioxane to give 60. Treatment of 60 with thionyl chloride gave the corresponding acyl chloride intermediate, which was then condensed with 2,5- bis(trifluoromethyl)aniline (61) by means of DMAP in heated toluene to give dutasteride (5) in 57% yield from intermediate 60.

Drug interactions

Potentially hazardous interactions with other drugs
Use with caution in combination with other nephrotoxins.
Antivirals: avoid concomitant administration with tenofovir
Interferons: use with caution with peginterferon alfa.

Metabolism

Adefovir is poorly absorbed orally, but the bioavailability of adefovir dipivoxil reaches approximately 59%. The drug is absorbed to an equal extent with or without the presence of food. Adefovir is excreted renally unchanged.

Questions And Answer

• Regulating human immune system

  Adefovir dipivoxil regulates the immune system and let the immune system to attack liver cells of the intrusion of HBV , and clear the virus, but this method will develop resistance, at the same time for patients with renal dysfunction or potential renal dysfunction risk, the use of adefovir dipivoxil chronic treatment will lead to renal toxicity. If eating 1 mg every day, in the three months will produce nephrotoxicity, this will lead to severe renal failure. These patients should be closely monitoring renal function and making appropriate dosage adjustments.
  Bisphosphonates is quick conversion of adefovir dipivoxil in vivo, adefovir dipivoxil is a kind of single adenosine monophosphate acyclic nucleoside analogues, became to activity of the metabolites of adefovir in cellular kinases by phosphorylation in cellular kinases. A Duff Vee two phosphate through the following two ways to suppress HBV DNA polymerase (reverse transcriptase); one is with the natural substrate of deoxyadenosine triphosphate competition, the second is the integration of viral DNA and induce DNA chain elongation terminated. A Duff Vee two phosphate to HBV DNA polymerase inhibition constant (KI) is 0.1μM, but of human DNA polymeraseα and γ is weak and Ki values were 1.18μM and 0.97 μM.
  Anti-viral activity: in the human hepatoma cell line transfected with HBV, the concentration of A Duff Vee inhibited 50% viral DNA replication (IC50) is from 0.2 to 2.5uM.
  Adefovir dipivoxil applies for the treatment of hepatitis B virus replication activity and serum amino acid transfer enzyme and persistently elevated liver decompensation adult patients with chronic hepatitis B patients.
  Liver injury is often encountered in the course of hepatitis B treatment, hepatitis B therapy is inappropriate, as well as long-term use of drugs on the liver damage, will lead to the occurrence of liver damage.
  After long-term taking adefovir dipivoxil tablets, once the withdrawal will aggravate the damage of liver function. Therefore, for stopping taking the patients should be monitored for liver function.
  Adefovir dipivoxil is more moderate suitable for long-term use, suitable for patients with lamivudine resistant patients, their chances of producing drug resistance is small, because the amount is less, side effects are small.
  Entecavir is new, antiviral effect is also strong, if not treated with lamivudine, the possible resistance is the smallest, but it and lamivudine have cross resistance, if treated with lamivudine to take entecavir produced resistance rate is much greater.
  The above information is Chemicalbook Hanya edited. ;

• Entecavir

  Entecavir is a new generation of guanine nucleoside analogues oral medicine for treatment of hepatitis B virus infection in, mainly for the treatment of adult patients with viral replication activity and serum transaminase continued to increase, or liver tissue for pathological activity of chronic hepatitis B, is currently down virus the fastest and the most powerful, the mutation rate lowest nucleoside analogues.
  Data show that different in patients with chronic hepatitis B, including nucleoside naive and nucleoside treated and liver cirrhosis patients, using well entecavir tablets in the treatment can control the disease rapidly and easily reach the treatment of reality end, namely the hepatitis B virus unmeasured; through adherence to treatment, a considerable portion of patients can be arrived at the end of treatment satisfaction, namely e antigen serology conversion, some patients can even reach the ideal for the treatment of end, namely surface antigen negative. ;

• Nephrotoxicity

  Nephrotoxicity is the most interesting problem in the clinical application of adefovir dipivoxil. In the global phase III clinical study and follow-up study, the general definition of renal toxicity to confirm≥0.5 mg/dL, increase serum creatinine compared with the baseline, and serum phosphorus <1.5mg/dl; the three years data show that HBeAg positive patients treat 144 weeks in no cases of renal toxicity; HBeAg negative patients are 3 cases (2.4%), appeared serum creatinine increasing, but not with phosphorus decreased subsequently (2 cases of drug withdrawal, 1 case to continue the medication) indexes returned to normal.
  For patients with chronic hepatitis B in liver transplantation, before and after transplantation taking adefovir dipivoxil, a part increase serum creatinine, but mostly with other multiple risk factors, such as the use of immunosuppressive agents and (or) other nephrotoxic drugs, leading to potential renal damage. In the these, many patients before treatment, most of them in the dose adjustment can still safe to use, about 2% of the patients have severe renal impairment and discontinuation.196 cases of YMDD positive chronic hepatitis B patients after transplantation, proportion of renal toxicity in receiving adefovir dipivoxil in the treatment is 13%, but these patients received cyclosporine or tacrolimus treatment, of which 13 cases had existed before the treatment of complications. 8 cases had renal insufficiency, 4 patients with decompensated cirrhosis, 2 cases received other nephrotoxic drugs treatment.
  Therefore, based in compensated chronic hepatitis B patients up to 3 years of research results, and in patients with liver transplantation results show that adefovir dipivoxil 10mg/d safety and placebo groups are similar, have no clinically significant renal events. There are patients with renal damage caused by drug taking at the same time, should close monitoring indexes of renal function during the medication use and before, and used with caution; according to creatinine clearance rate (ml/min) to adjust the dosing interval of patients with impaired renal function.
  ;

• Lamivudine

  Lamivudine is a new antiviral drug, belonging to nucleoside reverse transcriptase inhibitors, having a strong inhibitory effect in vitro and animal experimental infection of hepatitis B virus (HBV), can inhibit the synthesis of HIV virus; the drug produced by the GlaxoSmithKline Co. In the early 90s, they are used for the treatment of AIDS drugs in Europe and North American countries. In the middle of the 1990 medical experts found that they have inhibition to hepatitis B virus DNA, in 1998 the United States Food and Drug Administration (FDA) approved the first drug for treatment of hepatitis B treatment. In China, the State Food and Drug Administration approved the drug import mainly used as medicine in the treatment of hepatitis B, Chinese product name as "He Puding". In 1999, officially began on the mainland. Chinese sold after 10 years of clinical verification, lamivudine is the only proven to delay Hepatitis cirrhosis progress, fewer side effects, less cost of medication, currently has 2 million of the country's hepatitis B patients are using.
  Lamivudine can be metabolized to lamivudine three phosphate in HBV infection cells and normal cells, it is the active form of lamivudine, both inhibitors of HBV polymerase, and is polymerase substrate. Lamivudine three phosphate incorporation into viral DNA chain, can block the synthesis of viral DNA, and does not interfere with normal cell deoxynucleoside metabolism, having weak inhibition to mammalian DNA polymerase alpha and beta, almost no effect on mammalian cell DNA content, and without obvious toxicity to the structure of mitochondria, content and function of DNA. For Serum HBV-DNA detection results of most hepatitis B patients showed that lamivudine can rapidly inhibit the replication of HBV, its inhibitory effect lasted for the entire treatment process. At the same time the serum transaminase decreased to normal, long-term use can significantly improve the liver necrosis and inflammatory changes in relieve or prevent liver fibrosis. ;

• Appearance Properties

  White to white crystalline powder. ;

• Side Effects

  The following adverse reactions are often appearing, such as fatigue, headache, abdominal pain, nausea, flatulence, diarrhea and indigestion;
  Can produce nephrotoxicity. Therefore, when taking adefovir dipivoxil, should close observation of renal function, especially those that already exist in patients with kidney disease;
  Can cause blood lactic acid in the body, so that the body acid-base balance disorders, resulting in metabolic disorders;
  After stopping the drug, can cause hepatitis exacerbations, liver enlargement, liver area pain and so on. ;

• matters need attention

  1.Patients stop treating hepatitis B can occur acute exacerbation of hepatitis, including the cessation of the use of adefovir dipivoxil. So, stopping the treatment of hepatitis B patients should be monitored for liver function, if necessary, should reanti-hepatitis B therapy.
  2. Adefovir dipivoxil has slight kidney toxicity and before taking general medicine, should check renal function,and check for many times. For patients with renal dysfunction or potential renal dysfunction risk, should closely monitor renal function and serum phosphorus changes and according to the patient's age, weight and creatinine level calculated creatinine clearance rate, and creatinine clearance rate of appropriate dose adjustments. We should avoid as far as possible taking injection or other nephrotoxic drugs at the same time.
  3. The use of anti hepatitis B therapy with adefovir dipivoxil, will have an effect on the chronic hepatitis B patients, who carrying the unknown or untreated HIV, may be HIV drug resistance. Before treatment, all patients should be taken for human immunodeficiency virus (HIV) antibody test.
  4. Hepatitis B patients during antiviral therapy, taking the single with nucleoside analogues or in combination with other anti retroviral drugs will lead to lactic acidosis and severe associated with steatosis of hepatomegaly, including fatal events.
  5.Because the risk of developing human embryos is not clear, it is proposed that the treatment of women of childbearing age should take effective contraceptive measures. For already pregnant patients with hepatitis B should be in under the guidance of professional doctors consider to stop drug.
  ;

• Treatment of chronic hepatitis B can cause severe renal dysfunction

  American scholar's research shows that the treatment of adefovir dipivoxil (ADV) is an independent predictor of severe renal dysfunction in patients with chronic hepatitis B (CHB), for receiving the ADV treatment of patients with renal function monitoring, especially in the elderly, the baseline impairment of renal function or high blood pressure, diabetes patients. The study published in magazine of liver disease.
  ADV can cause renal dysfunction, but the occurrence rate and clinical significance are no long-term follow-up studies, nor clinical trials outside data. The study evaluate the clinical practice in ADV treatment caused the incidence and severity of renal dysfunction in patients with CHB.
  Two community health center of 290 cases of CHB patients were enrolled, the 145 cases of ADV (10 mg) received treatment, 145 patients did not receive ADV treatment and baseline characteristics of the two groups were similar, men accounted for 76.5%, baseline estimated glomerular filtration rate (EGFR) >50ml/min, baseline serum creatinine is 0.97~DL 0.99mg/, baseline creatinine clearance rate was 5.0~85.4ml/min.
  The incidence of ADV group of renal dysfunction (eGFR≤50ml/min) rate for 5 cases per 100 patients per year and the untreated group of 136 cases per 100 patients per year (P = 0.02), the relative risk is 3.68. ADV is significant predictors of risk factors of severe renal dysfunction (HR) =3.49, P = 0.03], age > 50 years old (HR=3.49, P = 0.087), baseline with mild renal impairment (HR=2.36, P = 0.074) for the 3.68.ADV, hypertension and (or) diabetes (HR=2.36, P = 0.074) and other factors increase trend of kidney damage. ;

• Curative effect of treating chronic hepatitis B

  There are at least 350 million people infected with hepatitis B virus (HBV) in the world. Hepatitis B treatment key to success is whether durable suppression of viral replication. α-interferon antiviral and immunomodulatory effects, clear effect, but its withdrawal after sustained response problems and more adverse reactions and injection therapy limits the clinical application.
  Adefovir dipivoxil is a new anti HBV drugs, due to less side effects of the drug, medication convenience and other advantages, so since birth it has been paid great attention. It is mainly used for the treatment of active viral, e antigen (HBeAg) positive chronic hepatitis B patients. And recently published in < New England Journal of Medicine > a report display, adefovir dipivoxil in HBeAg negative chronic hepatitis B patients were equally effective and long-term use can make curative effect has remained unchanged.
  In order to clarify the efficacy of chronic hepatitis B with negative e antigen and to prolong the duration of the drug, the researchers did the following experiments.
  Research process adopts the comparative method, the first step is that 185 HBeAg negative chronic hepatitis B patients were divided into two groups, the first group of 123 people, took adefovir dipivoxil of 10 mg/time/d; the second group of 62 people a day took the same dose of placebo, the treatment lasted for 48 weeks.
  The second step is after 48 weeks of treatment, received adefovir dipivoxil were randomly divided into two groups. One group continued taking, after treatment of the 96 weeks to continue treatment, and the remaining patients take placebo. Patients who taking placebo at the beginning, be substituted with adefovir dipivoxil.
  Results of the study showed that patients having been accepted for the treatment, medication 96 weeks and 144 weeks later, the amount of virus in the serum are significantly decreased. Treatment to the 96 week, 71% of the patients with viral levels below 1000 copies per milliliter; and after 144th week, 79% of the patients in vivo virus level below 1000 copies per milliliter. But patients after treatment of 144 weeks, have the emergence of low virus resistance.
  After 48 weeks, patients stopped the treatment and the therapeutic effect of most people disappeared, the virus also returned to the original level. To the 96 weeks and only 8% of patients with viral levels less than 1000 copies per milliliter, and until the 49 weeks to the 144th week, side effects are similar to the beginning of the 48 week, 144 weeks later, 5.9% of patients appear resistant mutations in the virus. ;

• Uses

  Has a broad spectrum of antiviral activity, can be used for the treatment of chronic hepatitis B. ;

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