Edoxudine is a nucleoside analog whose activation depends on viral thymidine kinase (TK). This enzyme is critical for drug activation — the virus-coded thymidine kinase specifically phosphorylates the molecule to form the 5'-monophosphate derivative.

Edoxudine is a potent and selective inhibitor of the replication of herpes simplex virus type 1 and 2. In vitro studies have demonstrated its inhibitory effects against HSV in African green monkey Vero cells and human foreskin fibroblasts. Research has also shown that edoxudine can enhance the antitumor activity of 5-fluorouracil.

Edoxudine has demonstrated good in vivo antiviral efficacy in animal models. In hairless mice intracutaneously infected with HSV-1, the 3% edoxudine gel with 5% urea showed good antiviral efficacy. In a guinea pig model of cutaneous HSV-1 infection, 3% edoxudine cream was more effective than 5% acyclovir ointment, reducing lesion number by 29%, lesion area by 44%, and lesion virus titer by 68%.

The activation of edoxudine begins with specific phosphorylation by HSV-coded thymidine kinase. In a typical TK enzyme activity assay, recombinant herpesvirus thymidine kinase is incubated with [³H]-labeled thymidine and varying concentrations of edoxudine. The inhibition of enzyme activity is assessed by measuring the phosphorylation of the radiolabeled substrate. The second phosphorylation step involves cellular enzymes that convert the 5'-monophosphate to the 5'-triphosphate derivative, which is a competitive inhibitor of the viral DNA polymerase.

Common in vitro antiviral activity assays employ Vero cells (African green monkey kidney cells) or human foreskin fibroblasts (HFF). Cells are seeded into 96-well plates and grown to confluence, then infected with HSV-1 or HSV-2 at a defined MOI, followed by treatment with edoxudine at varying concentrations (typically 0.1 µM to 100 µM). After 2 days of culture, cytopathic effect (CPE) is observed or cell viability is measured by MTT assay to calculate EC₅₀ values. In HFF cells, edoxudine exhibits an EC₅₀ of 0.6 µM against HSV-1 (E-377 strain) and 0.9 µM against human cytomegalovirus (AD169 strain). For cytotoxicity assessment, uninfected cells cultured under the same conditions serve as controls, and cell proliferation inhibition is determined by MTT assay. The IC₅₀ in human foreskin fibroblasts is 115 µM.

In vivo efficacy evaluation primarily employs HSV-infected rodent models. A commonly used model is the guinea pig dorsal cutaneous HSV-1 infection model: HSV-1 virus suspension (approximately 10⁶ PFU/mL) is inoculated by scarification on the depilated dorsal skin of guinea pigs. The 3% edoxudine cream or gel formulation is applied topically once daily for 5 consecutive days. Lesion number and lesion area are observed and recorded daily, and lesion tissues are collected for virus titer determination. Treatment with 3% edoxudine cream reduces lesion number by 29%, lesion area by 44%, and virus titer by 68% in guinea pigs. Another common model involves hairless mice intracutaneously infected with HSV-1, with topical administration of 3% edoxudine gel (containing 5% urea) once daily to evaluate efficacy.

Absorption, Distribution and Excretion
Educetin cream allows for rapid skin penetration. This easy penetration property results in higher activity of edoxetine compared to other topical antiviral drugs with stronger in vitro antiviral activity. In preclinical studies in mice, the mean residence time after intravenous injection of edoxetine was 25 minutes. The bioavailability of edoxetine was 49%, with Cmax and tmax of 2.4 mcg/g and 31.1 minutes, respectively. The plasma AUC of edoxetine was significantly higher with oral administration compared to intravenous administration. Pharmacokinetic parameters are currently unavailable. The plasma clearance of edoxetine has been reported to be 85 ml/min. Metabolism/Metabolites Preclinical studies indicate that the biotransformation of edoxetine is marked by glycosidic bond cleavage. Following oral administration, the degradation of edoxetine appears to occur primarily through phosphorylase activity and first-pass metabolism in the gastrointestinal tract.

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Biological Half-Life
In preclinical studies in mice, the distribution half-life of edoxudine was extremely short, only 1.4 minutes, following intravenous administration. In the same study, its elimination half-life was 24.1 minutes.

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Edoxudine cream penetrates the skin rapidly. In mice after intravenous administration, the distribution half-life is approximately 1.4 min, the elimination half-life is approximately 24.1 min, and the mean residence time is 25 min. The oral bioavailability is 49%, with a Cmax of 2.4 µg/g and a tmax of 31.1 min. The plasma AUC after oral administration is significantly higher than that after intravenous administration. The plasma clearance is approximately 85 mL/min. The metabolism is characterized by glycosidic bond cleavage; following oral administration, degradation occurs mainly via phosphorylases in the gastrointestinal tract and first-pass metabolism. The plasma protein binding is very low, reported to be approximately 7%, and the drug is mainly bound to albumin.

Protein Binding
Edusulfuron has a very low plasma protein binding rate, reportedly around 7%. It primarily exists in a state bound to albumin.

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In an in vitro study, edoxudine has been reported to exhibit cytotoxic effects and some degree of DNA incorporation in human leukemic cells and PHA-stimulated lymphocytes. In rabbit corneal epithelial cells, the corneal epithelial cytotoxicity CC₅₀ was measured at approximately 200 mg/L. Topical administration is generally well tolerated. In a randomized, double-blind, placebo-controlled clinical trial involving 200 patients, edoxudine 3% cream was well tolerated in patients with recurrent genital herpes. Common adverse reactions include local irritation, including transient burning sensation, conjunctival congestion, and eyelid edema. Long-term use may lead to corneal epithelial damage or drug resistance.

[1]. Penetration and action of edoxudine in vitro and in vivo. Arzneimittelforschung. 1989 Mar;39(3):366-8.

Edoxudine is a pyrimidine 2'-deoxynucleoside. Edoxudine is a deoxythymidine analog with activity against herpes simplex virus (HSV). It is a potent and selective inhibitor of HSV-1 and HSV-2. The resulting product is an antiviral ointment. Edoxudine's anti-HSV activity was first discovered in 1967. Later, its efficacy in vivo was demonstrated in a preclinical model of herpes simplex keratitis. Developed by McNeil Pharmaceuticals, it was approved by Health Canada on December 31, 1992. Production was discontinued in 1998. Edoxudine is a deoxythymidine analog with activity against herpes simplex virus. Edoxudine is activated by viral thymidine kinase to produce 5'-monophosphate, which is further phosphorylated by cellular enzymes to produce 5'-triphosphate, a competitive inhibitor of viral DNA polymerase. Drug Indications Edoxudine was previously used in Europe as a topical antiviral agent to treat human herpetic keratitis. Human herpetic keratitis is an inflammation of the cornea caused by infection with the herpes simplex virus. This infection can lead to serious illness, with recurrent infections significantly increasing the incidence and potentially causing corneal blindness. 3% edoxicillin cream has also been used to treat cutaneous herpes simplex virus infections. This virus can cause widespread infection and is highly contagious. There are two types of herpesvirus: type 1 is primarily transmitted through oral-oral contact, and type 2 is primarily transmitted sexually.

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Mechanism of Action
Edoxicillin is a potent inhibitor of replication of both type 1 and type 2 herpes simplex virus. Activation of the drug requires the action of viral thymidine kinase, which phosphorylates it to form a 5'-monophosphate derivative. This derivative then needs to be further phosphorylated by cellular enzymes until a 5'-triphosphate derivative is formed, which is a competitive inhibitor of viral-encoded DNA polymerase. Edoxicillin's advantage lies in its high selectivity, a characteristic manifested in its preferential phosphorylation of herpes simplex virus-infected cells and preferential incorporation into viral DNA.

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C11H16N2O5

256.26

256.106

C, 51.56; H, 6.29; N, 10.93; O, 31.22

15176-29-1

66377

Off-white to light yellow solid powder

1.389 g/cm3

152-153°

1.569

-0.7

3

5

3

18

395

3

OC[C@@H]1[C@H](C[C@H](N2C(NC(C(CC)=C2)=O)=O)O1)O

XACKNLSZYYIACO-DJLDLDEBSA-N

InChI=1S/C11H16N2O5/c1-2-6-4-13(11(17)12-10(6)16)9-3-7(15)8(5-14)18-9/h4,7-9,14-15H,2-3,5H2,1H3,(H,12,16,17)/t7-,8+,9+/m0/s1

5-ethyl-1-[(2R,4S,5R)-4-hydroxy-5-(hydroxymethyl)oxolan-2-yl]pyrimidine-2,4-dione

Edoxudine; CCRIS 2349; CCRIS-2349; CCRIS2349; Edoxudina

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)

DMSO : ≥ 125 mg/mL (~487.79 mM )
H2O : ~50 mg/mL (~195.11 mM）

Solubility in Formulation 1: ≥ 2.08 mg/mL (8.12 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (8.12 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
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.

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Solubility in Formulation 3: ≥ 2.08 mg/mL (8.12 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 10% DMSO+40% PEG300+5% Tween-80+45% Saline: ≥ 2.08 mg/mL (8.12 mM)

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