Valganciclovir Hydrochloride

VALCYTE is a deoxynucleoside analogue cytomegalovirus (CMV) DNA polymerase inhibitor indicated for: Adult Patients ( 1.1 ) Treatment of CMV retinitis in patients with acquired immunodeficiency syndrome (AIDS). Prevention of CMV disease in kidney, heart, and kidney-pancreas transplant patients at high risk. Pediatric Patients ( 1.2 ) Prevention of CMV disease in kidney and heart transplant patients at high risk.

1.1 Adult Patients Treatment of Cytomegalovirus (CMV) Retinitis: VALCYTE is indicated for the treatment of CMV retinitis in patients with acquired immunodeficiency syndrome (AIDS) [see Clinical Studies (14.1) ] . Prevention of CMV Disease: VALCYTE is indicated for the prevention of CMV disease in kidney, heart, and kidney-pancreas transplant patients at high risk (Donor CMV seropositive/Recipient CMV seronegative [D+/R-]) [see Clinical Studies (14.1) ] .

1.2 Pediatric Patients Prevention of CMV Disease: VALCYTE is indicated for the prevention of CMV disease in kidney transplant patients (4 months to 16 years of age) and heart transplant patients (1 month to 16 years of age) at high risk [see Clinical Studies (14.2) ] .

VALCYTE tablets: 450 mg, pink, film-coated convex oval tablets with "VGC" on one side and "450" on the other side. VALCYTE for oral solution: 50 mg per mL, supplied as a white to slightly yellow powder for constitution, forming a colorless to brownish yellow tutti-frutti flavored solution. Available in glass bottles containing approximately 100 mL of solution after constitution. Tablets: 450 mg. ( 3 ) Oral Solution: 50 mg per mL. ( 3 )

VALCYTE is contraindicated in patients who have had a demonstrated clinically significant hypersensitivity reaction (e.g., anaphylaxis) to valganciclovir, ganciclovir, or any component of the formulation [see Adverse Reactions (6.1) ]. Hypersensitivity to valganciclovir or ganciclovir. ( 4 )

Acute renal failure: Acute renal failure may occur in elderly patients (with or without reduced renal function), patients who receive concomitant nephrotoxic drugs, or inadequately hydrated patients. Use with caution in elderly patients or those taking nephrotoxic drugs, reduce dosage in patients with renal impairment, and monitor renal function. ( 2.5 , 5.2 , 8.5 , 8.6 )

5.1 Hematologic Toxicity Severe leukopenia, neutropenia, anemia, thrombocytopenia, pancytopenia, and bone marrow failure including aplastic anemia have been reported in patients treated with VALCYTE or ganciclovir. VALCYTE should be avoided if the absolute neutrophil count is less than 500 cells/µL, the platelet count is less than 25,000/µL, or the hemoglobin is less than 8 g/dL. VALCYTE should also be used with caution in patients with pre-existing cytopenias and in patients receiving myelosuppressive drugs or irradiation. Cytopenia may occur at any time during treatment and may worsen with continued dosing. Cell counts usually begin to recover within 3 to 7 days after discontinuing drug. In patients with severe leukopenia, neutropenia, anemia and/or thrombocytopenia, treatment with hematopoietic growth factors may be considered. Due to the frequency of neutropenia, anemia, and thrombocytopenia in patients receiving VALCYTE [see Adverse Reactions (6.1) ] , complete blood counts with differential and platelet counts should be performed frequently, especially in infants, in patients with renal impairment, and in patients in whom ganciclovir or other nucleoside analogues have previously resulted in leukopenia, or in whom neutrophil counts are less than 1000 cells/µL at the beginning of treatment. Increased monitoring for cytopenias may be warranted if therapy with oral ganciclovir is changed to VALCYTE because of increased plasma concentrations of ganciclovir after VALCYTE administration [see Clinical Pharmacology (12.3) ] .

5.2 Acute Renal Failure Acute renal failure may occur in: Elderly patients with or without reduced renal function. Caution should be exercised when administering VALCYTE to geriatric patients, and dosage reduction is recommended for those with impaired renal function [see Dosage and Administration (2.5) , Use in Specific Populations (8.5 , 8.6) ] . Patients receiving potential nephrotoxic drugs. Caution should be exercised when administering VALCYTE to patients receiving potential nephrotoxic drugs. Patients without adequate hydration. Adequate hydration should be maintained for all patients.

5.3 Impairment of Fertility Based on animal data and limited human data, VALCYTE at the recommended human doses may cause temporary or permanent inhibition of spermatogenesis in males, and may cause suppression of fertility in females. Advise patients that fertility may be impaired with use of VALCYTE [see Use in Specific Populations (8.1 , 8.3) , Nonclinical Toxicology (13.1) ] .

5.4 Fetal Toxicity Ganciclovir may cause fetal toxicity when administered to pregnant women based on findings in animal studies. When given to pregnant rabbits at dosages resulting in 2 times the human exposure (based on AUC), ganciclovir caused malformations in multiple organs of the fetuses. Maternal and fetal toxicity were also observed in pregnant mice and rabbits. Therefore, VALCYTE has the potential to cause birth defects. Pregnancy should be avoided in female patients taking VALCYTE and in females with male partners taking VALCYTE. Females of reproductive potential should be advised to use effective contraception during treatment and for at least 30 days following treatment with VALCYTE because of the potential risk to the fetus. Similarly, males should be advised to use condoms during and for at least 90 days following treatment with VALCYTE [see Dosage and Administration (2.6) , Use in Specific Populations (8.1 , 8.3) , Nonclinical Toxicology (13.1) ].

5.5 Mutagenesis and Carcinogenesis Animal data indicate that ganciclovir is mutagenic and carcinogenic. VALCYTE should therefore be considered a potential carcinogen in humans [see Dosage and Administration (2.6) , Nonclinical Toxicology (13.1) ].

The following serious adverse reactions are discussed in greater detail in other sections of the labeling: Hematologic Toxicity [see Warnings and Precautions (5.1) ] . Acute Renal Failure [see Warnings and Precautions (5.2) ] . Impairment of Fertility [see Warnings and Precautions (5.3) ] . Fetal Toxicity [see Warnings and Precautions (5.4) ] . Mutagenesis and Carcinogenesis [see Warnings and Precautions (5.5) ] . The most common adverse reactions and laboratory abnormalities reported in at least one indication by greater than or equal to 20% of adult patients treated with VALCYTE tablets are diarrhea, pyrexia, fatigue, nausea, tremor, neutropenia, anemia, leukopenia, thrombocytopenia, headache, insomnia, urinary tract infection, and vomiting. The most common reported adverse reactions and laboratory abnormalities reported in greater than or equal to 20% of pediatric solid organ transplant recipients treated with VALCYTE for oral solution or tablets are diarrhea, pyrexia, upper respiratory tract infection, urinary tract infection, vomiting, neutropenia, leukopenia, and headache. Adult patients: Most common adverse reactions and laboratory abnormalities (reported in at least one indication by greater than or equal to 20% of patients) are diarrhea, pyrexia, fatigue, nausea, tremor, neutropenia, anemia, leukopenia, thrombocytopenia, headache, insomnia, urinary tract infection, and vomiting. ( 6.1 ) Pediatric patients: Most common adverse reactions and laboratory abnormalities (reported in greater than or equal to 20% of pediatric solid organ transplant recipients) are diarrhea, pyrexia, upper respiratory tract infection, urinary tract infection, vomiting, neutropenia, leukopenia, and headache. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact 1-866-946-3684 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect rates observed in practice. Valganciclovir, a prodrug of ganciclovir, is rapidly converted to ganciclovir after oral administration. Adverse reactions known to be associated with ganciclovir usage can therefore be expected to occur with VALCYTE. Adverse Reactions in Adults: Treatment of CMV Retinitis in AIDS Patients: In a clinical study for the treatment of CMV retinitis in HIV-infected patients, the adverse reactions reported by patients receiving VALCYTE tablets (n=79) or intravenous ganciclovir (n=79) for 28 days of randomized therapy (21 days induction dose and 7 days maintenance dose), respectively, included diarrhea (16%, 10%), nausea (8%, 14%), and headache (9%, 5%). The incidence of adverse reactions was similar between the group who received VALCYTE tablets and the group who received intravenous ganciclovir. The frequencies of neutropenia (ANC less than 500/µL) were 11% for patients receiving VALCYTE tablets compared with 13% for patients receiving intravenous ganciclovir. Anemia (Hgb less than 8 g/dL) occurred in 8% of patients in each group. Other laboratory abnormalities occurred with similar frequencies in the two groups. Adverse reactions and laboratory abnormalities are available for 370 patients who received maintenance therapy with VALCYTE tablets 900 mg once daily in two open-label clinical trials. Approximately 252 (68%) of these patients received VALCYTE tablets for more than nine months (maximum duration was 36 months). Table 3 and Table 4 show pooled selected adverse reactions and abnormal laboratory values from these patients. Table 3 Pooled Selected Adverse Reactions Reported in greater than or equal to 5% of Patients who Received VALCYTE Tablets Maintenance Therapy for CMV Retinitis Patients with CMV Retinitis Adverse Reactions according to Body System VALCYTE Tablets (N=370) % Gastrointestinal system Diarrhea 41 Nausea 30 Vomiting 21 Abdominal pain 15 General disorders and administrative site conditions Pyrexia 31 Nervous system disorders Headache 22 Insomnia 16 Neuropathy peripheral 9 Paresthesia 8 Eye disorders Retinal detachment 15 Table 4 Pooled Selected Laboratory Abnormalities Reported in Patients Who Received VALCYTE Tablets Maintenance Therapy for the Treatment of CMV Retinitis Patients with CMV Retinitis Laboratory Abnormalities VALCYTE Tablets (N=370) % Neutropenia: ANC/µL < 500 19 500 – < 750 17 750 – < 1000 17 Anemia: Hemoglobin g/dL < 6.5 7 6.5 – < 8.0 13 8.0 – < 9.5 16 Thrombocytopenia: Platelets/µL < 25000 4 25000 – < 50000 6 50000 – < 100000 22 Serum Creatinine: mg/dL > 2.5 3 > 1.5 – 2.5 12 Prevention of CMV Disease in Solid Organ Transplant Patients: Table 5 shows selected adverse reactions regardless of severity with an incidence of greater than or equal to 5% from a clinical trial (up to 28 days after study treatment) where heart, kidney, kidney-pancreas and liver transplant patients received VALCYTE tablets (N=244) or oral ganciclovir (N=126) until Day 100 post-transplant. The majority of the adverse reactions were of mild or moderate intensity. Table 5 Percentage of Selected Grades 1–4 Adverse Reactions Reported in greater than or equal to 5% of Adult Patients From a Study of Solid Organ Transplant Patients Adverse Reactions VALCYTE Tablets (N=244) % Oral Ganciclovir (N=126) % Gastrointestinal disorders Diarrhea 30 29 Nausea 23 23 Vomiting 16 14 Nervous system disorders Tremors 28 25 Headache 22 27 Insomnia 20 16 General disorders and administration site conditions Pyrexia 13 14 Table 6 shows selected adverse reactions regardless of severity with an incidence of greater than or equal to 5% from another clinical trial where kidney transplant patients received either valganciclovir once daily starting within 10 days post-transplant until Day 100 post-transplant followed by 100 days of placebo or valganciclovir once daily until Day 200 post-transplant. The overall safety profile of VALCYTE did not change with the extension of prophylaxis until Day 200 post-transplant in high risk kidney transplant patients. Table 6 Percentage of Selected Grades 1–4 Adverse Reactions Reported in greater than or equal to 5% of Adult Patients from a Study of Kidney Transplant Patients Adverse Reactions VALCYTE Tablets Day 100 Post-transplant (N=164) % VALCYTE Tablets Day 200 Post-transplant (N=156) % Gastrointestinal disorders Diarrhea 26 31 Nausea 11 11 Vomiting 3 6 Nervous system disorders Tremors 12 17 Headache 10 6 Insomnia 7 6 General disorders and administration site conditions Pyrexia 12 9 Table 7 and Table 8 show selected laboratory abnormalities reported with VALCYTE tablets in two trials in solid organ transplant patients. […]

In vivo drug-drug interaction studies were not conducted with valganciclovir. However, because valganciclovir is rapidly and extensively converted to ganciclovir, drug-drug interactions associated with ganciclovir will be expected for VALCYTE. Drug-drug interaction studies with ganciclovir were conducted in patients with normal renal function. Following concomitant administration of VALCYTE and other renally excreted drugs, patients with impaired renal function may have increased concentrations of ganciclovir and the coadministered drug. Therefore, these patients should be closely monitored for toxicity of ganciclovir and the coadministered drug. Established and other potentially significant drug interactions conducted with ganciclovir are listed in Table 9 . Table 9 Established and Other Potentially Significant Drug Interactions with Ganciclovir Name of the Concomitant Drug Change in the Concentration of Ganciclovir or Concomitant Drug Clinical Comment Imipenem-cilastatin Unknown Coadministration with imipenem-cilastatin is not recommended because generalized seizures have been reported in patients who received ganciclovir and imipenem-cilastatin. Cyclosporine or amphotericin B Unknown Monitor renal function when VALCYTE is coadministered with cyclosporine or amphotericin B because of potential increase in serum creatinine [see Warnings and Precautions (5.2) ]. Mycophenolate mofetil (MMF) ↔ Ganciclovir (in patients with normal renal function) ↔ MMF (in patients with normal renal function) Based on increased risk, patients should be monitored for hematological and renal toxicity. Other drugs associated with myelosuppression or nephrotoxicity (e.g., adriamycin, dapsone, doxorubicin, flucytosine, hydroxyurea, pentamidine, tacrolimus, trimethoprim/ sulfamethoxazole, vinblastine, vincristine, and zidovudine) Unknown Because of potential for higher toxicity, coadministration with VALCYTE should be considered only if the potential benefits are judged to outweigh the risks. Didanosine ↔ Ganciclovir ↑ Didanosine Patients should be closely monitored for didanosine toxicity (e.g., pancreatitis) Probenecid ↑ Ganciclovir VALCYTE dose may need to be reduced. Monitor for evidence of ganciclovir toxicity. Imipenem-cilastatin: Seizures were reported in patients receiving ganciclovir and imipenem-cilastatin. Concomitant use is not recommended unless the potential benefits outweigh the risks. ( 7 ) Cyclosporine or amphotericin B: When coadministered with valganciclovir, the risk of nephrotoxicity may be increased. Monitor renal function. ( 5.2 , 7 ) Mycophenolate mofetil (MMF): When coadministered with valganciclovir, the risk of hematological and renal toxicity may be increased. Monitor for ganciclovir and MMF toxicity. ( 7 ) Other drugs associated with myelosuppression or nephrotoxicity: Due to potential for increased toxicity, consider for concomitant use with valganciclovir only if the potential benefits are judged to outweigh the risks. ( 7 ) Didanosine: Ganciclovir coadministered with didanosine may increase didanosine levels. Monitor for didanosine toxicity (e.g., pancreatitis). ( 7 ) Probenecid: May increase ganciclovir levels. Monitor for evidence of ganciclovir toxicity. ( 7 )

Drug Interactions: In vivo drug-drug interaction studies were not conducted with valganciclovir. However, because valganciclovir is rapidly and extensively converted to ganciclovir, interactions associated with ganciclovir will be expected for VALCYTE [see Drug Interactions (7) ]. Table 15 and Table 16 provide a listing of established drug interaction studies with ganciclovir. Table 15 provides the effects of coadministered drug on ganciclovir plasma pharmacokinetic parameters, whereas Table 16 provides the effects of ganciclovir on plasma pharmacokinetic parameters of coadministered drug. Table 15 Results of Drug Interaction Studies with Ganciclovir: Effects of Coadministered Drug on Ganciclovir Pharmacokinetic Parameters Coadministered Drug Ganciclovir Dosage N Ganciclovir Pharmacokinetic (PK) Parameter Mycophenolate mofetil (MMF) 1.5 g single dose 5 mg/kg IV single dose 12 No effect on ganciclovir PK parameters observed (patients with normal renal function) Trimethoprim 200 mg once daily 1000 mg every 8 hours 12 No effect on ganciclovir PK parameters observed Didanosine 200 mg every 12 hours simultaneously administered with ganciclovir 5 mg/kg IV twice daily 11 No effect on ganciclovir PK parameters observed 5 mg/kg IV once daily 11 No effect on ganciclovir PK parameters observed Probenecid 500 mg every 6 hours 1000 mg every 8 hours 10 AUC ↑ 53 ± 91% (range: -14% to 299%) Ganciclovir renal clearance ↓ 22 ± 20% (range: -54% to -4%) Table 16 Results of Drug Interaction Studies with Ganciclovir: Effects of Ganciclovir on Pharmacokinetic Parameters of Coadministered Drug Coadministered Drug Ganciclovir Dosage N Coadministered Drug Pharmacokinetic (PK) Parameter Oral cyclosporine at therapeutic doses 5 mg/kg infused over 1 hour every 12 hours 93 In a retrospective analysis of liver allograft recipients, there was no evidence of an effect on cyclosporine whole blood concentrations. Mycophenolate mofetil (MMF) 1.5 g single dose 5 mg/kg IV single dose 12 No PK interaction observed (patients with normal renal function) Trimethoprim 200 mg once daily 1000 mg every 8 hours 12 No effect on trimethoprim PK parameters observed Didanosine 200 mg every 12 hours 5 mg/kg IV twice daily 11 AUC 0-12 ↑70 ± 40% (range: 3% to 121%) C max ↑49 ± 48% (range: -28% to 125%) Didanosine 200 mg every 12 hours 5 mg/kg IV once daily 11 AUC 0-12 ↑50 ± 26% (range: 22% to 110%) C max ↑36 ± 36% (range: -27% to 94%)

Lactation: Breastfeeding is not recommended with use of VALCYTE. ( 8.2 )

8.1 Pregnancy Risk Summary After oral administration, valganciclovir (prodrug) is converted to ganciclovir (active drug) and, therefore, VALCYTE is expected to have reproductive toxicity effects similar to ganciclovir. In animal studies, ganciclovir caused maternal and fetal toxicity and embryo-fetal mortality in pregnant mice and rabbits as well as teratogenicity in rabbits at exposures two-times the human exposure. There are no available human data on use of VALCYTE or ganciclovir in pregnant women to establish the presence or absence of drug-associated risk. The background risk of major birth defects and miscarriage for the indicated populations is unknown. However, the background risk in the U.S. general population of major birth defects is 2–4% and the risk of miscarriage is 15–20% of clinically recognized pregnancies. Advise pregnant women of the potential risk to the fetus [see Warnings and Precautions (5.3) , Use in Specific Populations (8.3) ]. Clinical Considerations Disease-associated maternal and/or embryo/fetal risk Most maternal CMV infections are asymptomatic or they may be associated with a self-limited mononucleosis-like syndrome. However, in immunocompromised patients (i.e., transplant patients or patients with AIDS) CMV infections may be symptomatic and may result in significant maternal morbidity and mortality. The transmission of CMV to the fetus is a result of maternal viremia and transplacental infection. Perinatal infection can also occur from exposure of the neonate to CMV shedding in the genital tract. Approximately 10% of children with congenital CMV infection are symptomatic at birth. Mortality in these infants is about 10% and approximately 50–90% of symptomatic surviving newborns experience significant morbidity, including mental retardation, sensorineural hearing loss, microcephaly, seizures, and other medical problems. The risk of congenital CMV infection resulting from primary maternal CMV infection may be higher and of greater severity than that resulting from maternal reactivation of CMV infection. Data Animal Data Doses resulting in two-times the human exposure of ganciclovir (based on the human AUC following a single intravenous infusion of 5 mg per kg of ganciclovir) resulted in maternal and embryo-fetal toxicity in pregnant mice and rabbits as well as teratogenicity in the rabbits. Fetal resorptions were present in at least 85% of rabbits and mice. Rabbits showed increased embryo-fetal mortality, growth retardation of the fetuses and structural abnormalities of multiple organs of the fetuses including the palate (cleft palate), eyes (anophthalmia/microphthalmia), brain (hydrocephalus), jaw (brachygnathia), kidneys and pancreas (aplastic organs). Increased embryo-fetal mortality was also seen in mice. Daily intravenous doses of approximately 1.7 times the human exposure (based on AUC) administered to female mice prior to mating, during gestation, and during lactation caused hypoplasia of the testes and seminal vesicles in the male offspring, as well as pathologic changes in the nonglandular region of the stomach. Data from an ex-vivo human placental model showed that ganciclovir crosses the human placenta. The transfer occurred by passive diffusion and was not saturable over a concentration range of 1 to 10 mg/mL.

8.2 Lactation Risk Summary No data are available regarding the presence of valganciclovir (prodrug) or ganciclovir (active drug) in human milk, the effects on the breastfed infant, or the effects on milk production. Animal data indicate that ganciclovir is excreted in the milk of lactating rats. The Centers for Disease Control and Prevention recommend that HIV-infected mothers not breastfeed their infants to avoid risking postnatal transmission of HIV. Advise nursing mothers that breastfeeding is not recommended during treatment with VALCYTE because of the potential for serious adverse events in nursing infants and because of the potential for transmission of HIV [see Boxed Warning , Warnings and Precautions (5.1 , 5.3 , 5.4 , 5.5) , Nonclinical Toxicology (13.1) ] .

8.3 Females and Males of Reproductive Potential Pregnancy Testing Females of reproductive potential should undergo pregnancy testing before initiation of VALCYTE [see Use in Specific Populations (8.1) ] . Contraception Females Because of the mutagenic and teratogenic potential of VALCYTE, females of reproductive potential should be advised to use effective contraception during treatment and for at least 30 days following treatment with VALCYTE [see Dosage and Administration (2.6) , Warnings and Precautions (5.4 , 5.5) , Nonclinical Toxicology (13.1) ] . Males Because of its mutagenic potential, males should be advised to use condoms during and for at least 90 days following, treatment with VALCYTE [see Dosage and Administration (2.6) , Warnings and Precautions (5.3 , 5.5) , Nonclinical Toxicology (13.1) ]. Infertility VALCYTE at the recommended doses may cause temporary or permanent female and male infertility [see Warnings and Precautions (5.3) , Nonclinical Toxicology (13.1) ]. Data Human Data In a small, open-label, non-randomized clinical study, adult male renal transplant patients receiving VALCYTE for CMV prophylaxis for up to 200 days post-transplantation were compared to an untreated control group. Patients were followed-up for six months after VALCYTE discontinuation. Among 24 evaluable patients in the VALCYTE group, the mean sperm density at the end of treatment visit decreased by 11 million/mL from baseline; whereas, among 14 evaluable patients in the control group the mean sperm density increased by 33 million/mL. However, at the follow-up visit among 20 evaluable patients in the VALCYTE group the mean sperm density was comparable to that observed among 10 evaluable patients in the untreated control group (the mean sperm density at the end of follow-up visit increased by 41 million/mL from baseline in the VALCYTE group and by 43 million/mL in the untreated group).

8.4 Pediatric Use VALCYTE for oral solution and tablets are indicated for the prevention of CMV disease in pediatric kidney transplant patients 4 months to 16 years of age and in pediatric heart transplant patients 1 month to 16 years of age at risk for developing CMV disease [see Indications and Usage (1.2) , Dosage and Administration (2.3) ]. The use of VALCYTE for oral solution and tablets for the prevention of CMV disease in pediatric kidney transplant patients 4 months to 16 years of age is based on two single-arm, open-label, non-comparative studies in patients 4 months to 16 years of age. Study 1 was a safety and pharmacokinetic study in pediatric solid organ transplant patients (kidney, liver, heart, and kidney/pancreas). VALCYTE was administered once daily within 10 days of transplantation for a maximum of 100 days post-transplantation. Study 2 was a safety and tolerability study where VALCYTE was administered once daily within 10 days of transplantation for a maximum of 200 days post-transplantation in pediatric kidney transplant patients. The results of these studies were supported by previous demonstration of efficacy in adult patients [see Adverse Reactions (6.1) , Clinical Pharmacology (12.3) , Clinical Studies (14.2) ]. The use of VALCYTE for oral solution and tablets for the prevention of CMV disease in pediatric heart transplant patients 1 month to 16 years of age is based on two studies (Study 1 described above and Study 3) and was supported by previous demonstration of efficacy in adult patients [see Clinical Pharmacology (12.3) , Clinical Studies (14.2) ] . Study 3 was a pharmacokinetic and safety study of VALCYTE in pediatric heart transplant patients less than 4 months of age who received a single dose of VALCYTE oral solution on each of two consecutive days. […]

Valganciclovir is an antiviral drug with activity against CMV [see Microbiology (12.4) ] .

Mechanism of Action: Valganciclovir is an L-valyl ester (prodrug) of ganciclovir that exists as a mixture of two diastereomers. After oral administration, both diastereomers are rapidly converted to ganciclovir by intestinal and hepatic esterases. Ganciclovir is a synthetic analogue of 2'-deoxyguanosine, which inhibits replication of human CMV in cell culture and in vivo. In CMV-infected cells, ganciclovir is initially phosphorylated to ganciclovir monophosphate by the viral protein kinase, pUL97. Further phosphorylation occurs by cellular kinases to produce ganciclovir triphosphate, which is then slowly metabolized intracellularly (half-life 18 hours). As the phosphorylation is largely dependent on the viral kinase, phosphorylation of ganciclovir occurs preferentially in virus-infected cells. The virustatic activity of ganciclovir is due to inhibition of the viral DNA polymerase, pUL54 by ganciclovir triphosphate.