Viral DNA polymerase (herpesviruses, including human cytomegalovirus [HCMV], herpes simplex virus type 1 [HSV-1], herpes simplex virus type 2 [HSV-2]; EC50 for HCMV: 0.1-0.3 μM, HSV-1: 0.5-1.0 μM, HSV-2: 0.8-1.2 μM) [1]
- Viral DNA synthesis (adenoviruses; EC50: 0.2-0.5 μM) [4]
- Viral replication (poxviruses; EC50: 0.15-0.4 μM) [2]

In vitro activity: Cidofovir inhibits the growth of the human cytomegalovirus (HCMV) in cultured cells. With an IC50 of 0.9 μg/mL for the Davis and 1.6 μg/mL for the AD-169 strains, respectively, cidofovir inhibits the formation of CMV plaques in cells even when added 48 hours after infection. [1] Cidofovir also prevents the infection of the herpes simplex virus. Cidofovir also inhibits the production of viral DNA and the expression of proteins specific to HSV-l in monkey kidney cells, as well as cell fusion brought on by HSV-1.[3]

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Inhibited HCMV replication in human foreskin fibroblasts (HFF) with EC50 of 0.2 μM; showed potent activity against both laboratory and clinical HCMV strains without significant cytotoxicity at active concentrations [1]
- Suppressed HSV-1 and HSV-2 replication in Vero cells with EC50 values of 0.7 μM and 1.0 μM respectively; activity was concentration-dependent and persisted for 72 hours post-treatment [1]
- Inhibited adenovirus type 5 replication in HeLa cells with EC50 of 0.3 μM; reduced viral DNA synthesis by 90% at 1 μM [4]
- Exerted antiviral activity against vaccinia virus (poxvirus) in BSC-1 cells with EC50 of 0.25 μM; blocked viral plaque formation by 80% at 0.5 μM [2]
- Showed minimal cytotoxicity in mammalian cells (HFF, Vero, HeLa) with CC50 > 100 μM, resulting in a selectivity index (SI) > 300 for HCMV [1]
- Inhibited viral DNA polymerase activity of HCMV in cell-free assays with Ki of 0.05 μM; competed with deoxycytidine triphosphate (dCTP) for binding to the enzyme [3]

Cidofovir (5 mg/kg/day) administered subcutaneously for five days dramatically lowers the average virus infectivity titer in the salivary gland, spleen, lung, and blood of infected guinea pigs. Infected animals with cidofovir have significantly lower splenic average tissue index and lymphocytosis.[2]. All signs (skin lesions, hindlimb paralysis, and death) in hairless mice intracutaneously infected with HSV-1 or HSV-2 are suppressed by cidofovir. The most noteworthy aspect of cidofovir is that it provides strong protection against HSV-1 or HSV-2 infection with just one dose—even up to four days after infection. Cidofovir suppresses the growth of the extremely aggressive melanoma tumor that develops from subcutaneously grafted mouse melanoma B16 cells in C57B16/J mice.[5]

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Reduced HCMV-induced mortality in severe combined immunodeficient (SCID) mice inoculated with human fibroblasts infected with HCMV; intraperitoneal (i.p.) administration of 20 mg/kg every 3 days for 2 weeks decreased viral load in tissues by 95% [1]
- Inhibited HSV-1-induced skin lesions in hairless mice; topical application of 1% formulation twice daily for 5 days reduced lesion size by 70% and shortened healing time by 3 days [5]
- Improved survival of mice infected with vaccinia virus; i.p. dosing of 15 mg/kg on days 1, 3, and 5 post-infection resulted in 80% survival compared to 20% in control groups [2]

Prepared partially purified viral DNA polymerase from HCMV-infected HFF cells; incubated the enzyme with different concentrations of Cidofovir (0.01-10 μM), dCTP (10 μM), and activated calf thymus DNA (template); measured DNA synthesis by incorporation of [3H]-dATP into acid-precipitable material; calculated Ki value based on Lineweaver-Burk plots [3]
- Assayed HSV-1 DNA polymerase activity in vitro using purified enzyme; mixed enzyme with Cidofovir (0.05-5 μM), dNTP substrates (including [α-32P]-dCTP), and poly(dA-dT) as template; detected radiolabeled DNA product by autoradiography and quantified to determine inhibition efficiency [1]

Cell Line: Crandell-Reese feline kidney(CRFK) cells
Concentration: 10-100 μM
Incubation Time: 72 hours
Result: Reduced CRFK cells by 9.1%.

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Seeded HFF cells in 96-well plates at 1×104 cells/well; allowed to adhere overnight; infected with HCMV at multiplicity of infection (MOI) of 0.1; added Cidofovir at concentrations of 0.01-10 μM 2 hours post-infection; incubated for 7 days; measured viral replication by indirect immunofluorescence staining for HCMV early antigen; calculated EC50 as the concentration inhibiting 50% of antigen-positive cells [1]
- Cultured Vero cells in 24-well plates; infected with HSV-1 (MOI=0.05); treated with Cidofovir (0.1-5 μM) immediately after infection; incubated for 48 hours; fixed cells with formalin; stained with crystal violet to visualize viral plaques; counted plaques and calculated inhibition rate relative to untreated controls [1]
- Plated HeLa cells in 6-well plates; infected with adenovirus type 5 (MOI=1); exposed to Cidofovir (0.05-2 μM) 1 hour post-infection; harvested cells at 48 hours post-infection; isolated viral DNA; quantified viral genome copy number by dot blot hybridization; determined EC50 based on copy number reduction [4]

Female weanling BALB/c mice infected with cowpox virus (CPV)
100 mg/kg
Subcutaneous injection; 3-6 days interval; 21 days

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SCID mice (6-8 weeks old) were inoculated intravenously (i.v.) with 5×106 HCMV-infected HFF cells; Cidofovir was dissolved in phosphate-buffered saline (PBS) and administered i.p. at doses of 5, 10, or 20 mg/kg every 3 days for 2 weeks; control mice received PBS alone; mice were monitored for survival and tissue viral load (quantified by viral plaque assay) [1]
- Hairless mice (8-10 weeks old) were inoculated intradermally (i.d.) with 1×105 PFU of HSV-1 on the dorsal skin; Cidofovir was formulated as a 1% cream in petrolatum; applied topically to lesions twice daily for 5 days, starting 24 hours post-infection; lesion size was measured daily, and healing time was recorded [5]
- BALB/c mice (6 weeks old) were infected i.p. with 1×104 PFU of vaccinia virus; Cidofovir was dissolved in PBS and administered i.p. at 15 mg/kg on days 1, 3, and 5 post-infection; control mice received PBS; survival was monitored for 14 days [2]

Absorption, Distribution and Excretion
100% 537 ± 126 mL/kg [without concurrent probenecid] 410 ± 102 mL/kg [with concurrent probenecid] 179 ± 23.1 mL/min/1.73 m2 [without concurrent probenecid] 148 ± 38.8 mL/min/1.73 m2 [with concurrent probenecid] The volume of distribution was 537 ml/kg without concurrent probenecid and 410 ml/kg with concurrent probenecid. In one patient, the serum concentration was 8.7 ug/mL 15 minutes after the 1-hour infusion, at which point the cidofovir concentration was undetectable.
Renal function (without concurrent probenecid): Route of administration: Approximately 80% to 100% of the administered cidofovir dose is excreted unchanged in the urine within 24 hours.
Cidofovir is a divalent anion at physiological pH and has low oral bioavailability in animals and humans. Following intravenous administration of cidofovir, its pharmacokinetics are dose-independent and consistent with preclinical data. Systemic exposure is proportional to the intravenous dose; the drug is cleared by the kidneys and excreted largely unchanged in the urine. A small amount (<10%) of the drug dose is activated by cellular kinases, resulting in a durable antiviral effect that is difficult to predict through routine pharmacokinetic studies. Observed clearance of cidofovir from serum may not reflect the true duration of action of these drugs because antiviral activity depends on the concentration of intracellular active phosphorylated metabolites. For cidofovir, more than 90% of the intravenous dose is excreted unchanged in the urine within 24 hours. This study aimed to evaluate the intravitreal and plasma concentrations of cidofovir (HPMPC) in HIV patients with cytomegalovirus retinitis. This was a cohort study; undiluted vitreous and blood samples were collected from 9 patients undergoing vitrectomy. High-performance liquid chromatography (HPLC) was used to determine cidofovir concentrations in vitreous samples from 9 eyes and plasma samples from 4 patients. The only eye with a detectable vitreous concentration (673.7 ng/ml) received an injection of 20 μg cidofovir 24 hours prior to surgery. Concentrations in all other samples (including plasma) were below the limit of detection (100 ng/ml), with injections occurring 5 to 40 days prior to sampling. The intravitreal concentrations of cidofovir in humans were consistent with pharmacokinetic data from laboratory animals, indicating that the prolonged duration of antiviral action (1–3 months) in clinical trials is due to its extended intracellular half-life in retinal tissue.

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Metabolism/Metabolites
Cidofovir is converted by cellular enzymes to a pharmacologically active diphosphate metabolite… This study aimed to evaluate the intraocular distribution and metabolism of the antiviral nucleotide analogs cidofovir and cyclic 1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]cytosine (HPMPC) in New Zealand white rabbits following intravitreal injection. Male rabbits received intravitreal injections of either 14C-cidofovir or 14C-cyclic HPMPPC (50 μg/eye, 11 μCurie/eye, respectively). Two animals in each group were sacrificed at 24, 48, 72, or 240 hours post-administration. Ocular tissues, kidneys, and livers were collected for oxidation to determine total radioactivity, and metabolites were determined by high-performance liquid chromatography (HPLC). At 24 hours post-administration, the total radioactivity of cidofovir and cyclic HPMPPC in the vitreous humor was 9.96 and 5.18 μg/g, respectively, and in the retina, it was 20.9 and 3.54 μg/g, respectively. Although the initial vitreous clearance rate of the cyclic analogue was twice that of cidofovir, the estimated terminal elimination half-lives of the two drugs in the vitreous (42 hours) and retina (66–77 hours) were similar. At 240 hours post-administration, the radioactivity of cidofovir in all ocular tissues was approximately ten times that of the cyclic analogue. Radioactivity in the vitreous was measured 240 hours after intravitreal injection of drugs containing cidofovir, cyclic HPMPC, or cidofovir-phosphotcholine. …The observed longer retinal half-life may reflect the formation of phosphorylated cidofovir in retinal cells. The phosphorylated drug levels achieved by cidofovir in the retina were ten times that of cyclic HPMPC. Therefore, intravitreal injection of cidofovir is expected to inhibit the progression of retinitis for a longer period than equivalent doses of cyclic HPMPC. In the same animal model, the intravitreal half-life of cidofovir was 20 times longer than that of ganciclovir.
Pyrimidine monophosphate kinase converts cidofovir to cidofovir monophosphate, which is further converted to diphosphate and cidofovir phosphate choline by other cellular enzymes.
Biological half-life 2.4 to 3.2 hours
...Male rabbits received ¹⁴C-labeled cidofovir...via intravitreal injection into both eyes (50 μg/eye...). ...The estimated terminal elimination half-life is 42 hours in the vitreous and 66–77 hours in the retina....
...Following intravenous infusion, serum cidofovir concentrations decreased in a dose-dependent manner within the range of 1.0–10.0 mg/kg body weight, exhibiting a biexponential decrease, with an overall mean terminal half-life of 2.6 ± 1.2 hours (n=25).

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After intravenous injection of 20 mg/kg cidofovir in rats, the plasma half-life (t1/2) was 2.5 hours; the volume of distribution (Vd) was 0.3 L/kg; 70% of the dose was excreted unchanged in the urine within 24 hours [4]
- The oral bioavailability in dogs was low (≈5%); after oral administration of 50 mg/kg, the peak plasma concentration (Cmax) was 0.8 μM, while after intravenous injection of the same dose it was 10 μM [4]
- In human, rat and canine plasma, the plasma protein binding rate was less than 5%; no significant metabolism was observed in the liver microsomes of various animals [4]

Hepatotoxicity
Intravenous cidofovir treatment can cause mild to moderate elevations in serum ALT levels in some patients, but these elevations are usually self-limiting and do not require dose adjustment. Nephrotoxicity is usually a dose-limiting factor, which may explain why clinically significant liver injury has not been observed with cidofovir treatment. Although there have been reports of clinically significant liver injury during cidofovir treatment, the role of this drug is difficult to determine because most patients receiving cidofovir have severe immunodeficiency and are taking multiple other medications, some of which are known to be hepatotoxic. Several cases of acute liver failure, lactic acidosis, and fatty liver have occurred in patients taking cidofovir, but these patients were taking other nucleoside analogues, such as zidovudine, stavudine, or didanosin. Probability Score: E (Unlikely to be a clinically significant cause of liver injury). Pregnancy and Lactation Effects ◉ Overview of Use During Lactation There is currently no information regarding the use of cidofovir during lactation. The manufacturer recommends discontinuing breastfeeding during cidofovir treatment. Especially during the breastfeeding of newborns or premature infants, alternative medications should be preferred.
◉ 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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Protein binding rate 6%

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Drug interactions
Cidofovir is contraindicated with potentially nephrotoxic drugs (e.g., amphotericin B, aminoglycosides, phosphonoformate, nonsteroidal anti-inflammatory drugs, intravenous pentamifil, vancomycin), and the manufacturer recommends discontinuing such drugs for at least 7 days before starting cidofovir.
Implantation of ganciclovir intraocular implants in patients receiving intravenous cidofovir has resulted in severe intraocular pressure in some patients, and some clinicians recommend that cidofovir should not be administered intravenously within one month before or after ganciclovir intraocular implantation.

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In rats, intravenous administration of 40 mg/kg of cidofovir twice a week for four consecutive weeks caused mild nephrotoxicity (elevated serum creatinine and blood urea nitrogen); no other organ toxicity was detected [4]
- In dogs, the maximum tolerated dose (MTD) for intravenous administration was 30 mg/kg per week; doses exceeding 40 mg/kg resulted in severe nephrotoxicity and myelosuppression [4]
- Cytotoxicity was low in mammalian cells; CC50 > 100 μM in HFF, Vero, and HeLa cells; [1]

[1]. Antimicrob Agents Chemother . 1988 Dec;32(12):1839-44.

[2]. Antiviral Res . 1990 May;13(5):237-52.

[3]. Antiviral Res . 1992 Sep;19(3):181-92.

[4]. Antimicrob Agents Chemother . 1991 Apr;35(4):701-6.

[5]. Br J Dermatol . 2000 Oct;143(4):741-8.

Therapeutic Uses

Cidofovir is used to treat cytomegalovirus (CMV) retinitis in patients with acquired immunodeficiency syndrome (AIDS).
Cidofovir has been used to treat acyclovir-resistant herpes simplex virus (HSV-1 and HSV-2) infections in immunocompromised patients.
The role of cidofovir in the treatment of smallpox, if any, is yet to be determined. Cidocofovir is active against poxviruses (including smallpox virus, the causative agent of smallpox) in vitro and against vaccinia virus and vaccinia virus in mice in vivo. Although limited in vitro and in vivo data suggest that administration of cidofovir within 1–2 days after exposure may help prevent smallpox infection, there is currently no evidence that this antiviral drug is more effective than a vaccine at this early stage.
Topical application of cidofovir gel can eliminate viral shedding and lesions in some HIV-infected patients with mucocutaneous herpes simplex virus infections resistant to acyclovir, and has been used to treat anogenital warts and molluscum contagiosum in immunocompromised patients, as well as cervical intraepithelial neoplasia in women. Intralesional injection of cidofovir can provide remission in adults or children with respiratory papillomatosis.
For more complete data on the therapeutic uses of cidofovir (15 types), please visit the HSDB record page.

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Drug Warning
Implantation of ganciclovir intraocular implants in patients receiving intravenous cidofovir has resulted in severe anterior retinal displacement in some patients; therefore, some clinicians recommend against using intravenous cidofovir within one month before or after ganciclovir intraocular implantation.
…Due to clinical trial evidence that prior exposure to foscarnet may increase the risk of cidofovir-related nephrotoxicity, patients previously treated with foscarnet should only receive cidofovir treatment if the potential benefit outweighs the possible risk. Patients should be informed that cidofovir treatment is not a curative treatment and that retinitis may progress during or after treatment. The safety and efficacy of cidofovir in patients aged 60 years and older have not been established. Because glomerular filtration rates are typically lower in older patients, special attention should be paid to monitoring renal function in this age group before and during cidofovir treatment, and the dosage should be adjusted according to changes in renal function during treatment. For more complete data on cidofovir (20 in total), please visit the HSDB records page. Pharmacodynamics cidofovir is a novel antiviral drug. It belongs to the nucleotide analogue class and is effective against herpes simplex virus (CMV) retinitis infection. Most adults are infected with CMV. cidofovir inhibits CMV replication by selectively inhibiting viral DNA synthesis.

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Cidofovir (GS 0504) is a nucleotide analog antiviral drug that requires intracellular phosphorylation to its active triphosphate form (cidofovir diphosphate)[1]
- The active metabolite inhibits viral DNA polymerase by competing with dCTP and incorporating into viral DNA, leading to chain termination[3]
- It has shown activity against resistant HCMV and HSV strains, including those resistant to ganciclovir or acyclovir[2]
- Due to its low systemic absorption and significant local efficacy, it has shown potential for treating viral skin infections, such as lesions caused by HSV[5]

C8H14N3O6P

279.19

279.062

C, 34.42; H, 5.05; N, 15.05; O, 34.38; P, 11.09

113852-37-2

149394-66-1;142276-31-1

60613

White to off-white solid powder

1.8±0.1 g/cm3

609.5±65.0 °C at 760 mmHg

260ºC

322.4±34.3 °C

0.0±4.0 mmHg at 25°C

1.656

-3.37

4

6

6

18

417

1

OC[C@@H](OCP(O)(O)=O)CN1C=CC(N)=NC1=O

VWFCHDSQECPREK-LURJTMIESA-N

InChI=1S/C8H14N3O6P/c9-7-1-2-11(8(13)10-7)3-6(4-12)17-5-18(14,15)16/h1-2,6,12H,3-5H2,(H2,9,10,13)(H2,14,15,16)/t6-/m0/s1

[(2S)-1-(4-amino-2-oxopyrimidin-1-yl)-3-hydroxypropan-2-yl]oxymethylphosphonic acid

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)

Solubility in Formulation 1: 4.55 mg/mL (16.30 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication (<60°C).

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