Adefovir diphosphate functions as a DNA terminator in addition to targeting viral DNA polymerase. The first phosphorylation was found to be caused by adenylate oxidation, which was then followed by the oxidation of creatine and ADP to produce adefovir diphosphate [1].

Adefovir diaphragm has a 60% bioavailability and is not impacted by food. It has a 12-to 30-hour half-life. Adefovir has no discernible metabolites and is eliminated by the kidneys. In general, adefovir has no effect on cytochrome P450[3].

Absorption, Distribution and Excretion
Following oral administration of adefovir dipivoxil, the bioavailability of adefovir is approximately 59%. After a single oral dose of 10 mg adefovir dipivoxil in adults, peak plasma concentrations of adefovir are reached within 0.58–4 hours. The binding of adefovir to plasma or serum proteins is ≤4%. In vitro, the binding of adefovir to human plasma or serum proteins is ≤4% within the concentration range of 0.1–25 μg/mL. The steady-state volumes of distribution after intravenous administration of 1.0 or 3.0 mg/kg/day are 392 ± 75 mL/kg and 352 ± 9 mL/kg, respectively. Food does not affect the area under the concentration-time curve (AUC) of adefovir. For more complete data on absorption, distribution, and excretion of adefovir (10 parameters), please visit the HSDB records page.

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Metabolism/Metabolites
Oral administration of bis-POM PMEA only produces 9-(2-phosphonomethoxyethyl)adenine (PMEA). In rats, oral administration of bis-(phenyl)PMEA or bis-(o-ethoxyphenyl)PMEA resulted in the detection of three metabolites: PMEA, the corresponding monoester, and 2-adenosine. The major metabolite of bis(phenyl)PMEA is 2-adenosine following oral administration. 2-Adenosine appears to be formed from the intact drug prodrug via P450-mediated ethyl side-chain oxidation.
Adefovir dipivoxil is converted to active adefovir after oral administration.
PMEA is a known human metabolite of pradfovir.

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Biological Half-Life
Plasma adefovir concentration exhibits a biexponential decay, with a terminal elimination half-life of 7.48 ± 1.65 hours.
...Diphosphorylation...PMEA has a relatively long intracellular half-life (16–18 hours)...

Hepatotoxicity
Elevated serum transaminases are common during or after hepatitis B treatment, but this appears to be due to exacerbation of underlying hepatitis B virus (HBV) infection rather than hepatotoxicity. Abrupt discontinuation of adefovir treatment can lead to a rapid increase in viral load, triggering an acute hepatitis flare-up. These flare-ups are usually transient and self-limiting, but in rare cases, they can be severe and life-threatening, potentially leading to death or requiring a liver transplant. Moderate elevations in serum transaminases have been reported in clinical trials early in treatment, but these elevations are usually transient and asymptomatic, occurring in up to 25% of hepatitis B patients receiving nucleoside analogue therapy. Finally, the development of antiviral resistance can lead to underlying hepatitis B flare-ups due to elevated HBV DNA levels. Antiviral resistance is rare in the first 1-2 years of adefovir treatment, but resistance rates gradually increase with prolonged treatment. No cases of lactic acidosis with hepatic steatosis and liver failure have been reported with adefovir. Tenofovir is a nucleotide analogue similar to adefovir. Isolated cases of lactic acidosis have been reported, but only when used in combination with other antiretroviral drugs more likely to cause the syndrome. Because adefovir is contraindicated in HIV infection (due to its weaker anti-HIV activity), it is not used in combination with routine antiretroviral drugs. There is currently no conclusive evidence that adefovir causes lactic acidosis or significant liver damage with clinical symptoms or jaundice. Probability score: E (unlikely to be the cause of clinically significant specific liver damage). Pregnancy and Lactation Effects ◉ Overview of Use During Lactation Adefovir has not been studied in breastfeeding women receiving treatment for hepatitis B. Especially in breastfeeding newborns or premature infants, alternative medications may be preferred. There is no difference in infection rates between breastfed and formula-fed infants born to mothers with hepatitis B infection, provided the infant receives hepatitis B immunoglobulin and hepatitis B vaccine at birth. Mothers with hepatitis B are encouraged to breastfeed their infants after these preventative measures have been taken.
◉ Effects on breastfed infants
No published information found as of the revision date.
◉ Effects on lactation and breast milk
No published information found as of the revision date.

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Drug Interactions
Patients taking other nephrotoxic drugs (e.g., aminoglycosides, cyclosporine, tacrolimus, vancomycin, certain nonsteroidal anti-inflammatory drugs [NSAIDs]) may have an increased risk of nephrotoxicity; close monitoring is required.
Pharmacokinetic interactions (33% increase in peak plasma concentration and 23% increase in AUC with adefovir dipivoxil; no effect on the pharmacokinetics of ibuprofen). Clinical significance is unclear. May occur due to increased oral bioavailability of adefovir.
Tenofovir dipivoxil fumarate and adefovir dipivoxil should not be used concomitantly to treat chronic hepatitis B virus infection. The GS-02-531 study was an open-label, multicenter drug interaction trial designed to investigate potential drug interactions between adefovir and tacrolimus in stable post-transplant recipients. The study included 16 hepatitis B virus-free post-transplant recipients with a median age of 45.5 years (69% male, 44% Caucasian, 50% Hispanic, and 6% Black), who had stable hepatic and renal function while receiving a stable dose of tacrolimus (total daily dose 2–10 mg). The study was conducted before and after tacrolimus monotherapy, followed by daily administration of 10 mg adefovir for 14 days (days 1–14). Pharmacokinetic (PK) analysis was performed using a non-compartmental model. The median elimination half-life of tacrolimus was 14.47 hours on day 0 and 12.59 hours on day 14. The geometric mean odds ratios of tacrolimus on day 14 compared to day 0 were: Cmax 105.2% [90% confidence interval (90% CI): 89.8–123%], AUCτ 106.4% (90% CI: 92.9–122%). Both ratios' 90% CIs were within the pre-specified 80% and 125% limits for no interaction (i.e., within the limits of equivalence assessment), indicating that these PK parameters of tacrolimus were not significantly altered by co-administration with adefovir. Similarly, the pharmacokinetic parameters of adefovir observed after 14 days of co-administration with tacrolimus were comparable to those observed in non-transplant patients previously treated with adefovir monotherapy. Serum creatinine levels remained stable during the study. In liver transplant recipients, no significant pharmacokinetic interaction was observed after 14 days of co-administration of tacrolimus and adefovir.
Adefovir should not be used concurrently with VIREAD (tenofovir disoproxil fumarate) or products containing tenofovir disoproxil fumarate, including TRUVADA (emtricitabine/tenofovir disoproxil fumarate combination tablets), ATRIPLA (efavirenz/emtricitabine/tenofovir disoproxil fumarate combination tablets) and COMPLERA (emtricitabine/rilpivirine/tenofovir disoproxil fumarate).

[1]. 7.11 - Deoxyribonucleic Acid Viruses: Antivirals for Herpesviruses and Hepatitis B Virus. Comprehensive Medicinal Chemistry II. Volume 7, 2007, Pages 295-327.

[2]. Adefovir dipivoxil for the treatment of hepatitis B e antigen-positive chronic hepatitis B. N Engl J Med. 2003 Feb 27;348(9):808-16.

[3]. 155 - Drugs to Treat Viral Hepatitis. Infectious Diseases. Volume 2, 2017, Pages 1327-1332.

Therapeutic Uses
Phosphonates; Adenine/analogs and derivatives; Antiviral drugs; Reverse transcriptase inhibitors. Adefovir is indicated for the treatment of patients aged 12 years and older with chronic hepatitis B who have evidence of active viral replication and persistently elevated serum transaminases (ALT or AST) or evidence of histologically active disease. This indication is based on histological, virological, biochemical, and serological responses in HBeAg-positive and HBeAg-negative, compensated adult patients with chronic hepatitis B, as well as clinical evidence of lamivudine-resistant hepatitis B virus infection (whether compensated or decompensated). /US Product Label Includes/ For patients aged 12 to 18 years and younger, the indication is based on virological and biochemical responses in HBeAg-positive, compensated chronic hepatitis B virus-infected patients. /US Product Label Includes/
This study aimed to investigate the efficacy, safety, and pharmacokinetics of adefovir dipivoxil (ADV) in children and adolescents with chronic hepatitis B (CHB). A total of 173 treatment-naïve and treatment-experienced HBeAg-positive CHB patients were enrolled and randomly assigned to either the ADV or placebo group. Randomization was stratified by age (2–<7 years; >7–<12 years; >12–<18 years) and prior treatment history. In subjects aged 12–<18 years, the proportion of patients receiving adefovir dipivoxil (ADV) who achieved the primary efficacy endpoint (serum hepatitis B virus [HBV] DNA <1,000 copies/mL and normal alanine aminotransferase) was significantly higher in the ADV group than in the placebo group (23% vs 0%; P = 0.007). In the younger age groups, there was no statistically significant difference between the ADV and placebo groups at the end of double-blind treatment. The ADV treatment group had a higher HBeAg seroconversion rate: 18 out of 113 (15.9%) vs. 3 out of 57 (5.3%) (but P = 0.051), and more patients achieved the composite endpoint of HBeAg seroconversion, HBV DNA <1,000 copies/mL, and normal alanine aminotransferase (12 out of 113 vs. 0 out of 57; P = 0.009). None of the subjects had ADV-related mutations (i.e., rtN236T or rtA181V mutations) associated with HBV DNA rebound. ADV plasma concentrations were comparable across groups and within the target range. ADV treatment was well-tolerated, and no new safety issues were identified. Treatment-related adverse events were reported in 12% of subjects in the ADV treatment group and 10% in the placebo group. After 48 weeks of ADV treatment, the antiviral efficacy in HBeAg-positive chronic hepatitis B patients aged 12 to <18 years was similar to that of a study in treatment-naïve HBeAg-positive adult patients with chronic hepatitis B. Although plasma ADV exposure was adequate in all three age groups, there was no significant difference in ADV treatment efficacy compared to placebo in subjects aged 2 to 11 years. Conclusion: Adefovir demonstrated significant antiviral efficacy in HBeAg-positive chronic hepatitis B patients aged 12 to 17 years, but no difference compared to placebo in patients aged 2 to 11 years.

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Drug Warning
/Black Box Warning/ There have been reports of severe acute hepatitis exacerbations in patients who discontinued anti-hepatitis B treatment, including adefovir. Patients who discontinue anti-hepatitis B treatment should be closely monitored for liver function and followed up clinically and laboratory for at least several months. Reinstatement of anti-hepatitis B treatment may be considered if necessary.
/Warning with Black Box/ Long-term use of adefovir may lead to nephrotoxicity in patients at risk of or already suffering from renal impairment. Kidney function should be closely monitored in these patients, and dosage adjustments may be necessary.
/Warning with Black Box/ HIV resistance may develop in patients with chronic hepatitis B who also have unidentified or untreated human immunodeficiency virus (HIV) infection and are receiving anti-hepatitis B drugs such as adefovir. These anti-hepatitis B drugs may be effective against HIV.
There have been reports of lactic acidosis and severe hepatomegaly with steatosis, even leading to death, when used alone or in combination with other antiretroviral drugs.
For more complete data on drug warnings for adefovir (20 in total), please visit the HSDB records page.

C8H12N5O4P

273.18

273.062

106941-25-7

Adefovir-d4;1190021-70-5

60172

White to off-white solid powder

1.9±0.1 g/cm3

632.5±65.0 °C at 760 mmHg

>260°C

336.3±34.3 °C

0.0±2.0 mmHg at 25°C

1.769

-2.06

3

8

5

18

327

0

SUPKOOSCJHTBAH-UHFFFAOYSA-N

InChI=1S/C8H12N5O4P/c9-7-6-8(11-3-10-7)13(4-12-6)1-2-17-5-18(14,15)16/h3-4H,1-2,5H2,(H2,9,10,11)(H2,14,15,16)

((2-(6-amino-9H-purin-9-yl)ethoxy)methyl)phosphonic acid

GS-0393 GS-393 GS0393 GS393 GS 0393 GS 393 PMEA

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

0.1 M NaOH : ~10 mg/mL (~36.60 mM)
H2O : ~1 mg/mL (~3.66 mM)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)