Population pharmacokinetics of ganciclovir after intravenous ganciclovir and oral valganciclovir administration in solid organ transplant patients infected with cytomegalovirus

Evidence supporting the use of therapeutic drug monitoring of ganciclovir in transplantation

PURPOSE OF REVIEW

This review describes current knowledge of ganciclovir (GCV) and valganciclovir (ValGCV) pharmacokinetic/pharmacodynamic characteristics, highlighting the likely contribution from host genetic factors to interpatient variability. The evidence and challenges surrounding optimization of drug dosing through therapeutic drug monitoring (TDM) are examined, with recommendations made.

RECENT FINDINGS

Pharmacokinetic studies of current dosing guidelines have shown high interindividual and intraindividual variability of GCV concentrations. This is sometimes associated with a slow decline in cytomegalovirus (CMV) viral load in some transplant recipients. A high incidence of GCV-associated myelosuppression has limited the use of this drug in the transplant setting. Patient groups identified to benefit from GCV TDM include pediatric patients, cystic fibrosis with lung transplantation, obese with kidney transplantation, and patients with fluctuating renal function or on hemodialysis. The emergence of refractory resistant CMV, particularly in immune compromised patients, highlights the importance of appropriate dosing of these antivirals. Host genetic factors need to be considered where recently, two host genes were shown to account for interpatient variation during ganciclovir therapy. Therapeutic Drug Monitoring has been shown to improve target antiviral-level attainment. The use of TDM may guide concentration-based dose adjustment, potentially improving virological and clinical outcomes. However, evidence supporting the use of TDM in clinical practice remains limited and further study is needed in the transplant cohort.

SUMMARY

Further studies examining novel biomarkers are needed to guide target concentrations in prophylaxis and treatment. The use of TDM in transplant recipients is likely to improve the clinical efficacy of current antivirals and optimize outcomes in transplant recipients.

Establishment and Evaluation of a Parametric Population Pharmacokinetic Model Repository for Ganciclovir and Valganciclovir

BACKGROUND

Ganciclovir and valganciclovir are used for prophylaxis and treatment of cytomegalovirus infection. However, there is great interindividual variability in ganciclovir's pharmacokinetics (PK), highlighting the importance of individualized dosing. To facilitate model-informed precision dosing (MIPD), this study aimed to establish a parametric model repository of ganciclovir and valganciclovir by summarizing existing population pharmacokinetic information and analyzing the sources of variability. (2) Methods: A total of four databases were searched for published population PK models. We replicated these models, evaluated the impact of covariates on clearance, calculated the probability of target attainment for each model based on a predetermined dosing regimen, and developed an area under the concentration-time curve (AUC) calculator using maximum a posteriori Bayesian estimation. (3) Results: A total of 16 models, one- or two-compartment models, were included. The most significant covariates were body size (weight and body surface area) and renal function. The results show that 5 mg/kg/12 h of ganciclovir could make the AUC_0-24h within 40-80 mg·h/L for 50.03% pediatrics but cause AUC_0-24h exceeding the exposure thresholds for toxicity (120 mg·h/L) in 51.24% adults. (4) Conclusions: Dosing regimens of ganciclovir and valganciclovir should be adjusted according to body size and renal function. This model repository has a broad range of potential applications in MIPD.

Comparison of Three Renal Function Formulas for Ganciclovir/Valganciclovir Dose Individualization in CMV-Infected Solid Organ Transplantation Patients Using a Population Approach

BACKGROUND AND OBJECTIVE

The gold standard treatment of established cytomegalovirus infection or prevention in solid organ transplantation is the intravenous administration of ganciclovir (GCV) or oral administration of valganciclovir (VGCV), both adjusted to the renal function. In both instances, there is a high interindividual pharmacokinetic variability, mainly owing to the wide range of variation of both the renal function and body weight. Therefore, accurate estimation of the renal function is crucial for GCV/VGCV dose optimization. This study aimed to compare three different formulas for estimating the renal function in solid organ transplantation patients with cytomegalovirus infection, for individualizing antiviral therapy with GCV/VGCV, using a population approach.

METHODS

A population pharmacokinetic analysis was performed using NONMEM 7.4. A total of 650 plasma concentrations obtained after intravenous GCV and oral VGCV administrations were analyzed, from intensive and sparse sampling designs. Three different population pharmacokinetic models were built with the renal function given by Cockcroft-Gault, Modification of Diet in Renal Disease, or Chronic Kidney Disease EPIdemiology Collaboration (CKD-EPI) formulas. Pharmacokinetic parameters were allometrically scaled to body weight.

RESULTS

The CKD-EPI formula was identified as the best predictor of between-patient variability in GCV clearance. Internal and external validation techniques showed that the CKD-EPI model had better stability and performed better compared with the others.

CONCLUSIONS

The model based on the more accurate estimation of the renal function with the CKD-EPI formula and body weight as a size metric most used in the clinical practice can refine initial dose recommendations and contribute to GCV and VGCV dose individualization when required in the prevention or treatment of cytomegalovirus infection in solid organ transplantation patients.

Population Pharmacokinetics of Ganciclovir in Allogeneic Hematopoietic Stem Cell Transplant Patients

Treatment of cytomegalovirus (CMV) infection in allogeneic hematopoietic stem cell transplantation (alloHCT) patients with ganciclovir is complicated by toxicity and resistance. This study aimed to develop an intravenous ganciclovir population pharmacokinetic model for post-alloHCT patients and to determine dosing regimens likely to achieve suggested therapeutic exposure targets. We performed a prospective observational single-center pharmacokinetic study in adult alloHCT patients requiring treatment with intravenous ganciclovir for CMV viremia or disease. Samples were analyzed using a validated ultraperformance liquid chromatography method. Population pharmacokinetic analysis and Monte Carlo simulations (n = 1000) were performed using Pmetrics for R. Twenty patients aged 18 to 69 years were included in the study. A 2-compartment model with linear elimination from the central compartment and between occasion variability best described the data. Incorporating creatinine clearance (CLCR) estimated by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and presence of continuous renal replacement therapy as covariates for ganciclovir clearance improved the model. Compared to current dosing recommendations, simulations demonstrated loading doses were required to achieve a target AUC24 of 80 to 120 mg.h/L on day 1 of induction therapy. Increased individualization of post-loading induction and maintenance doses based on CLCR is required to achieve the suggested exposures for efficacy (AUC24 >80/>40 mg.h/L for induction/maintenance) while remaining below the exposure thresholds for toxicity (AUC24 <120/<60 mg.h/L for induction/maintenance). Intravenous ganciclovir dosing in alloHCT patients can be guided by CLCR estimated by CKD-EPI. Incorporation of loading doses into induction dosing regimens should be considered for timely achievement of currently suggested exposures.

Detection of Ganciclovir-Resistant Cytomegalovirus in a Prospective Cohort of Kidney Transplant Recipients Receiving Subtherapeutic Valganciclovir Prophylaxis

Cytomegalovirus infection during antiviral prophylaxis occurs in transplant recipients despite individualized regimens based on renal function. Fifty kidney transplant recipients were assessed between 2016 and 2019 for valganciclovir dosing, ganciclovir exposure, cytomegalovirus infection, and genotypic resistance markers during the first year posttransplant. Ganciclovir plasma concentrations were measured using mass spectrometry. Population pharmacokinetics was used to determine individual ganciclovir exposure and to evaluate the ability of manufacturer dosing guidelines to meet therapeutic target daily area under the curve (AUC24) of 40 to 50 μg·h/mL. Full-length UL54 and UL97 were assessed using high-throughput sequencing in cytomegalovirus DNA-positive patient specimens. Valganciclovir doses administered to recipients with creatinine clearance of <40 mL/min were higher than specified by guidelines, and they were lower for recipients with creatinine clearance of ≥40 mL/min. The mean ganciclovir AUC24 was 33 ± 13 μg·h/mL, and 82% of subjects did not attain the therapeutic target. Pharmacokinetic simulations showed that the guidelines similarly could not attain the therapeutic target in 79% of individuals. Cytomegalovirus breakthrough occurred in 6% (3/50) of recipients, while 12% (6/50) developed late-onset infection. The mean AUC24s of recipients with (n = 3) and without (n = 47) infection were not significantly different (P = 0.528). However, one recipient with an AUC24 of 20 μg·h/mL acquired two UL97 ganciclovir resistance mutations. Current prophylaxis guidelines resulted in subtherapeutic ganciclovir exposure in several study recipients, including the emergence of resistance genotypes. IMPORTANCE This study examined the pharmacokinetics and viral genomic data from a prospective cohort of kidney transplant recipients undergoing valganciclovir prophylaxis for cytomegalovirus (CMV) prevention. We showed for the first time using high-throughput sequencing the detection of ganciclovir resistance mutations in breakthrough CMV infection during subtherapeutic plasma ganciclovir as indicated by the pharmacokinetic parameter daily area under the curve (AUC24). In addition, we found that current valganciclovir dosing guidelines for CMV prophylaxis are predicted to attain therapeutic targets in only 21% of recipients, which is consistent with previous pharmacokinetic studies. The novel findings of resistance mutations during subtherapeutic ganciclovir exposure presented here can inform future studies investigating the dynamics of drug selection pressure and the emergence of resistance mutations in vivo.

Standard ganciclovir dosing results in slow decline of cytomegalovirus viral loads

BACKGROUND

Cytomegalovirus (CMV) can cause severe disease, including rejection in transplant recipients. Ganciclovir and its oral prodrug valganciclovir have been used as first-line therapy for CMV disease in transplant recipients. The exposure targets of ganciclovir are not exactly known, and toxicity and resistance have interfered with ganciclovir therapy.

OBJECTIVES

To evaluate the pharmacokinetics (PK) and pharmacodynamics (PD) of ganciclovir in transplant recipients.

METHODS

We used patient data from a previous observational study on ganciclovir therapeutic drug monitoring (TDM) in prophylaxis and therapy. The ganciclovir concentrations and CMV viral loads were determined during routine clinical care. The PK/PD population modelling and simulations were done with non-parametric methodology using the Pmetrics program.

RESULTS

Eighty-five patients were included in the PK modelling. The final PK model was a two-compartment model with first-order absorption and elimination. A subset of 17 patients on CMV therapy were included in the PD modelling. A median of 4 (range 2-8) viral loads were obtained per patient. A simulation of 10 000 patients showed that an approximately 1 log10 reduction of CMV viral load will be observed after 12.5 days at the current recommended dose.

CONCLUSIONS

The developed linked PK/PD population model and subsequent PD simulations showed slow decline of CMV viral load and it appears that dosing of (val)ganciclovir in this study might have been inadequate to achieve fast reduction of viral load. It is clear that further studies are needed to specify the PD effects of ganciclovir by performing systematic measurements of both ganciclovir concentrations and CMV viral loads.

Therapeutic Drug Monitoring of Ganciclovir: Where Are We?

BACKGROUND

Ganciclovir is the mainstay of therapy for the prophylaxis and treatment of Cytomegalovirus. However, therapy with this antiviral agent is hindered by side effects such as myelosuppression, which often leads to therapy cessation. Underdosing, as an attempt to prevent side effects, can lead to drug resistance and therapy failure. Therapeutic drug monitoring (TDM) has been used to overcome these problems. The purpose of this narrative review was to give an overview of ganciclovir TDM, available assays, population pharmacokinetic models, and discuss the current knowledge gaps.

METHODS

For this narrative review, a nonsystematic literature search was performed on the PubMed database in April 2021. The following search terms were used: ganciclovir, valganciclovir, pharmacokinetics, pharmacodynamics, population pharmacokinetics, therapeutic drug monitoring, bioassay, liquid chromatography coupled with tandem mass spectrometry, liquid chromatography, chromatography, spectrophotometry, and toxicity. In addition, the reference lists of the included articles were screened.

RESULTS

The most common bioanalysis method identified was liquid chromatography coupled with tandem mass spectrometry. There are different models presenting ganciclovir IC50; however, establishing a pharmacokinetic/pharmacodynamic target for ganciclovir based on preclinical data is difficult because there are no studies combining dynamic drug exposure in relation to inhibition of viral replication. The data on ganciclovir TDM show large interindividual variability, indicating that TDM may play a role in modifying the dose to reduce toxicity and prevent treatment failure related to low concentrations. The main hurdle for implementing TDM is the lack of robust data to define a therapeutic window.

CONCLUSIONS

Although the pharmacokinetics (PK) involved is relatively well-described, both the pharmacodynamics (PD) and pharmacokinetic/pharmacodynamic relationship are not. This is because the studies conducted to date have mainly focused on estimating ganciclovir exposure, and owing to the limited therapeutic options for CMV infections, future studies on ganciclovir are warranted.

Pharmacokinetics, Pharmacodynamics, and Therapeutic Drug Monitoring of Valganciclovir and Ganciclovir in Transplantation

Ganciclovir and valganciclovir are first choice drugs for the prevention and treatment of cytomegalovirus infection and disease in solid organ and stem cell transplant recipients. Only a few studies on the pharmacokinetics and exposure/efficacy or exposure/safety relationships of ganciclovir and valganciclovir in transplant recipients have been published so far, and there are still controversies about the exposure parameter to use for therapeutic drug monitoring (TDM). We performed an extensive literature review of the clinical pharmacokinetics data, the exposure/effect relationships in terms of efficacy and safety, and the available tools for valganciclovir and ganciclovir TDM in adults and pediatrics transplant recipients. The pharmacokinetics of ganciclovir and valganciclovir is well described in adults and children, and a high interindividual variability is commonly observed. In contrast, the drug pharmacodynamics has been poorly described in adults and barely in children. The average 24-hour area under the concentration-time curve (AUC_0-24h ) seems to be the best predictor of efficacy and toxicity. The benefit of TDM remains controversial in adult patients but should be considered in children due to higher interindividual variability and lower probability of target attainment. Several bayesian estimators based on limited sampling strategies have been developed with this aim and may be used in clinical practice for the AUC-based individual dose adjustment of ganciclovir and valganciclovir.

Population Pharmacokinetics of Ganciclovir in Critically Ill Patients

BACKGROUND

The pharmacokinetic (PK) data of ganciclovir (GCV), a first-line antiviral treatment for cytomegalovirus infections, in critically ill patients are limited. This study aimed at characterizing GCV population PK and interindividual variability (IIV) in intensive care unit (ICU) patients. Secondary objectives were to identify patient characteristics responsible for IIV and simulate GCV exposure for different dosing regimens.

METHOD

In this retrospective observational study, clinical data and serum GCV levels were collected from ICU patients on intravenous GCV. PK modeling, covariate analyses, and explorative Monte Carlo dosing simulations (MCS) were performed using nonlinear mixed-effects modeling. Bootstrap and visual predictive checks were used to determine model adequacy.

RESULTS

In total, 128 GCV measurements were obtained from 34 patients. GCV PK conformed to a 1-compartment model with first-order elimination. After multivariate analyses, only the estimated glomerular filtration rate calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula (P < 0.001) was included as a covariate. In the final model, the estimated clearance (CL) and volume of distribution (V1) were 2.3 L/h and 42 L, respectively, for a patient with the median CKD-EPI of the population (65 mL/min per 1.73 m). The association between CKD-EPI and CL decreased the residual variability from 0.56 to 0.43 and V1-IIV from 114% to 80%, whereas CL-IIV changed from 43% to 47%. MCS revealed that a substantial number of patients may not achieve the GCV PK/pharmacodynamic target trough level (>1.5 mg/L) when administering the label-recommended dose reductions for patients with CKD-EPI <50 mL/min.

CONCLUSIONS

A large IIV was observed in GCV PK among ICU patients. CKD-EPI could partially explain the IIV, although a large part of the variability remains unclear. MCS suggested that recommended dose reductions for CKD-EPI <50 mL/min may lead to subtherapeutic plasma GCV levels in these patients.

Population Pharmacokinetics of Intravenous Ganciclovir and Oral Valganciclovir in a Pediatric Population To Optimize Dosing Regimens

Ganciclovir is indicated for curative or preventive treatment of cytomegalovirus (CMV) infections. This study aimed to characterize ganciclovir pharmacokinetics, following intravenous ganciclovir and oral valganciclovir administration, to optimize dosing schemes. All children aged <18 years receiving ganciclovir or valganciclovir were included in this study. Pharmacokinetics were described using nonlinear mixed-effect modeling. Monte Carlo simulations were used to optimize the dosing regimen to maintain the area under the concentration-time curve (AUC) in the preventive or therapeutic target. Among the 105 children (374 concentration-time observations) included, 78 received intravenous (i.v.) ganciclovir, 19 received oral valganciclovir, and 6 received both drugs. A two-compartment model with first-order absorption for valganciclovir and first-order elimination best described the data. An allometric model was used to describe the bodyweight (BW) effect. Estimated glomerular filtration rate (eGFR) and medical status of critically ill children were significantly associated with ganciclovir elimination. Recommended doses were adapted for prophylactic treatment. To obtain a therapeutic exposure, doses should be increased to 40 mg/kg of body weight/day oral or 15 to 20 mg/kg/day i.v. in children with normal eGFR and to 56 mg/kg/day oral or 20 to 25 mg/kg/day i.v. in children with augmented eGFR. These doses should be prospectively confirmed, and therapeutic drug monitoring could be used to refine them individually. (This study has been registered at ClinicalTrials.gov under identifier NCT02539407.).

Population pharmacokinetics of ganciclovir and valganciclovir in paediatric solid organ and stem cell transplant recipients

AIMS

Ganciclovir (GCV) and its prodrug valganciclovir (VGCV) are first-line agents to prevent and treat cytomegalovirus in transplant recipients. There is high pharmacokinetic (PK) interindividual variability and PK data are scarce, especially in paediatric stem cell transplant (SCT) recipients. We sought to determine the optimal GCV and VGCV dosing in transplanted children.

METHODS

We conducted a single-centre retrospective population PK (POPPK) study of IV GCV and enteral VGCV in paediatric solid organ transplant (SOT) and SCT recipients. We included children who were transplanted and had available plasma GCV concentrations, done per standard of care. POPPK analysis was performed using a nonlinear mixed effects modelling approach with NONMEM. Optimal dosing was determined based on the achievement of the surrogate efficacy target: GCV 24 h area under the concentration-time curve (AUC_0-24h ) of 40-60 mg.h.L^-1 .

RESULTS

Fifty children with a median [range] age of 7.5 years [0.5-17.4] contributed 580 PK samples. A two-compartment model with first-order absorption with a lag time and first-order elimination fit the data well. Creatinine clearance and body weight (WT) were significant covariates for GCV clearance (CL); and WT for the volumes of distribution. IV GCV 15-20 mg.kg^-1 .day^-1 divided every 12 hours achieved the highest probability of target achievement (PTA) (33.0-33.8%). Enteral VGCV 30 and 40 mg.kg^-1 .day^-1 divided every 12 hours in children 0-<6 years, and 6-18 years, respectively, achieved the highest PTA (29.1-33.0%).

CONCLUSION

This is the first POPPK model developed in children with either SOT or SCT. Concentration target achievement was low, suggesting a potential benefit for therapeutic drug monitoring to ensure optimal exposure.

Population Pharmacokinetics and Bayesian Estimation of the Area Under the Concentration-Time Curve for Ganciclovir in Adult Chinese Renal Allograft Recipients After Valganciclovir Administration

Valganciclovir (VGCV) is the prodrug of ganciclovir (GCV). The objective of this study was to establish a population pharmacokinetic model (PPK) of GCV to investigate the PK characteristics of GCV after administration of VGCV in adult Chinese renal allograft recipients. Seventy Chinese renal allograft recipients were given 450 mg (n = 41) or 900 mg (n = 29) VGCV daily. Blood samples were drawn 0-24 hours after 5 days' therapy, and GCV plasma levels were determined. The PPK model was constructed using nonlinear mixed-effects modeling, and the Bayesian estimation of AUC_0-24h was constructed for an individual patient based on limited plasma samples. The PK of GCV was best described by a 2-compartment model with a first-order absorption process. The CL/F, V₂ /F, Q/F, V₃ /F, K_a , and lag time of GCV were 15.8 ± 0.71 L/h, 10.9 ± 2.38 L, 3.98 ± 0.40 L/h, 167 ± 44.0 L, 0.23 ± 0.0078 1/h, and 0.93 ± 0.017 hours, respectively. Clearance of creatinine was found to have a significant impact on the CL/F of GCV (P < .01). Sampling strategies consisted of plasma concentrations 0 and 2 and 0, 2, and 4 hours after VGCV administration were shown to be suitable for the estimation of the GCV AUC_0-24h . The PPK model was acceptable and can describe the PK of GCV in Chinese renal transplant patients administered VGCV. The AUC_0-24h of GCV in Chinese renal transplant patients can be calculated by a limited sampling strategy method.

Intensive Hemodiafiltration Successfully Removes Ganciclovir Overdose and Largely Exceeds Reported Elimination During Hemodialysis-A Case Report and Review of the Literature

We present the case of a kidney transplant patient (Cockroft-Gault estimated creatinine clearance 14 ml/min) who was inadvertently eight-fold overdosed with a single dose of 500 mg intravenous ganciclovir. To prevent the immunosuppressed patient from being exposed to severe risks of prolonged ganciclovir overdosing, including potentially fatal bone marrow suppression and severe neurotoxicity, the patient was treated with hemodiafiltration (HDF) to enhance drug elimination. Since the product label reports a 50% decrease of ganciclovir plasma concentrations after intermittent hemodialysis (HD), two HDF sessions were considered necessary to achieve a ≥75% elimination of the drug by precaution, despite targeted intense HDF prescription. Ganciclovir plasma concentration data were obtained during both HDF sessions and were analyzed retrospectively. Pharmacokinetic analysis revealed that prescribed HDF successfully decreased drug plasma concentrations by ≥90%. This ganciclovir reduction ratio matched the urea reduction ratio achieved (≥92%). Model-based assessment of ganciclovir dialysis clearance (estimated to be 445 ml/min), accounting for its two-compartmental kinetics, was higher than urea dialysis clearance (estimated to be 310 ml/min). This suggests potential relevant accumulation of ganciclovir into blood cells, at least in this patient after overdosing. The amount (fraction) of drug removed by 1st HDF was estimated to 269 mg (93% of total amount of 288 mg eliminated during the 1st HDF session; estimated amount in the body prior to 1st HDF: 380 mg). A literature review was performed to summarize and systematically compare available information on ganciclovir elimination during intermittent renal replacement therapy. In conclusion, the high ganciclovir HDF clearance measured in our patient largely exceeded previously reported elimination during HD, meaning that HDF prescription was highly efficient in the present case, and that a second HDF session might not have been necessary. This finding may be considered to guide renal replacement therapy in the scope of drug overdosing. It may also be evaluated for ganciclovir dose adjustment in patients on chronic HD or HDF with high small solute clearance, since a strong correlation between ganciclovir and urea elimination efficiency was observed.

Construction of a flow chart-like risk prediction model of ganciclovir-induced neutropaenia including severity grade: A data mining approach using decision tree

WHAT IS KNOWN AND OBJECTIVE

Haematological toxicities such as neutropaenia are a common side effect of ganciclovir (GCV); however, risk factors for GCV-induced neutropaenia have not been well established. Decision tree (DT) analysis is a typical technique of data mining consisting of a flow chart-like framework that shows various outcomes from a series of decisions. By following the flow chart, users can estimate combinations of risk factors that may increase the probability of certain events. In our previous study, we demonstrated the usefulness of this approach in the evaluation of adverse drug reactions. Therefore, we aimed to construct a risk prediction model of GCV-induced neutropaenia including severity grade.

METHODS

We performed a retrospective study at the Hokkaido University Hospital and enrolled patients who received GCV between April 2008 and March 2018. Neutropaenia was defined as an absolute neutrophil count (ANC) <1500 cells/mm³ and a decrease to <75% relative to baseline. We classified the patients who developed neutropaenia in three groups (Grades 2-4) based on the National Cancer Institute-Common Terminology Criteria for Adverse Events. Data collection was achieved through the retrieval of medical records. We employed a chi-squared automatic interaction detection algorithm to construct the DT model and compared the accuracies to the logistic regression model (a conventional statistical method) to evaluate the established model.

RESULTS AND DISCUSSION

In total, 396 adult patients were included in the study; 61 (15.4%) developed neutropaenia. Three predictive factors (hematopoietic stem cell transplantation, baseline ANC <3854 cells/mm³ and duration of therapy ≥15 days) were extracted using the DT analysis to produce five subgroups, the incidence of neutropaenia ranged between 1.7% and 52.8%. In each subgroup, patients who developed neutropaenia were categorized based on the severity. The accuracies of each model were the same (84.6%), which indicated precision.

WHAT IS NEW AND CONCLUSION

We successfully built a risk prediction model of GCV-induced neutropaenia including severity grade. This model is expected to assist decision-making in the clinical setting.

Relationship of Ganciclovir Therapeutic Drug Monitoring with Clinical Efficacy and Patient Safety

The clinical utility of ganciclovir therapeutic drug monitoring (TDM) is unknown. We retrospectively analyzed adult patients treated for cytomegalovirus (CMV) infection with ganciclovir with TDM between 2005 and 2015. The primary outcome was an association between ganciclovir TDM and clinical efficacy endpoints within 30 days, defined by viral load and symptomatology. Secondary outcomes included safety endpoints, evaluated within 7 days of the last administered dose of ganciclovir. Of 175 patients evaluated, 82 patients with CMV infection were included in our analysis with a median (interquartile range) baseline CMV viral load of 5,500 (3,000 to 15,200) copies/ml. The majority achieved undetectable or reduced CMV viral load below the lower limit of quantification (74.4%) with improvement in symptomatology (70.7%) at 30 days. Among patients with detectable CMV viremia at 30 days, the viral load had declined to a median of 1,000 (1,000 to 3,090) copies/ml. We did not observe significant associations between the efficacy outcomes and ganciclovir trough (P = 0.20 and P = 0.20, respectively) or peak concentrations (P = 0.14 and P = 0.14, respectively). Similarly, there was no significant association between ganciclovir trough or peak concentrations and safety endpoints, including leukopenia (P = 0.48 and P = 0.69), neutropenia (P = 0.59 and P = 0.69), thrombocytopenia (P = 0.29 and P = 0.37), anemia (P = 0.51 and P = 0.35), nephrotoxicity (P = 0.41 and P = 0.57), and neurotoxicity (P = 0.22 and P = 0.48). We did not observe any associations between ganciclovir TDM and clinical efficacy or safety endpoints. Routine ganciclovir TDM may be of limited value. Future studies may be warranted to identify specific populations with unpredictable pharmacokinetic and pharmacodynamics profiles in whom ganciclovir TDM may be of benefit.

Systematic review of ganciclovir pharmacodynamics during the prevention of cytomegalovirus infection in adult solid organ transplant recipients

Human cytomegalovirus (CMV) represents the most common infection among recipients of solid organ transplants (SOTs). Previous meta-analysis showed 0.8% of SOT recipients developed CMV disease whilst receiving valganciclovir (ValGCV) prophylaxis. However, the clinical utility of monitoring ganciclovir (GCV) blood concentrations is unclear. We systematically reviewed the association between GCV concentrations during prophylaxis and the incidence of CMV. MEDLINE and EMBASE databases were searched for studies between 1946 and 2018, where GCV pharmacokinetics and incidence of CMV viraemia or disease in SOT were available. Research designs included randomised trials, comparative, prospective cohort, retrospective, or case report studies. Only human adult studies were included, with English language restriction. The 11 studies that met the eligibility criteria included 610 participants receiving GCV or ValGCV prophylaxis. Quality assessment showed 2/4 randomised trials, 4/6 cohort studies, and 1/1 case report were of high quality. Despite dose adjustments for renal impairment, mean GCV exposures for patients were heterogeneous and ranged between 28 and 53.7 μg·h/mL across three randomised trials. The incidence of CMV infection and disease ranged from 0% to 50% and 0% to 3.1%, respectively, with follow up between 3 to 9 months. One study showed statistical power in determining relationship, where GCV exposure at 40 to 50 μg·h/mL in high-risk SOT recipients was associated with a reduced risk of viraemia. Clinical monitoring for GCV exposure can be applied to high-risk SOT recipients during ValGCV prophylaxis; however, further studies are needed to determine the utility of monitoring in all SOT recipients.

Ganciclovir

Ganciclovir is synthetic nucleoside analog of guanine closely related to acyclovir but has greater activity against cytomegalovirus. This comprehensive profile on ganciclovir starts with a description of the drug: nomenclature, formulae, chemical structure, elemental composition, and appearance. The uses and application of the drug are explained. The methods that were used for the preparation of ganciclovir are described and their respective schemes are outlined. The methods which were used for the physical characterization of the dug are: ionization constant, solubility, X-ray powder diffraction pattern, crystal structure, melting point, and differential scanning calorimetry. The chapter contains the spectra of the drug: ultraviolet spectrum, vibrational spectrum, nuclear magnetic resonance spectra, and the mass spectrum. The compendial methods of analysis of ganciclovir include the United States Pharmacopeia methods. Other methods of analysis that were reported in the literature include: high-performance liquid chromatography alone or with mass spectrometry, electrophoresis, spectrophotometry, voltammetry, chemiluminescence, and radioimmunoassay. Biological investigation on the drug includes: pharmacokinetics, metabolism, bioavailability, and biological analysis. Reviews on the methods used for preparation or for analysis of the drug are provided. The stability of the drug in various media and storage conditions is reported. More than 240 references are listed at the end of the chapter.

Feasibility and applicability of antimicrobial stewardship in immunocompromised patients

PURPOSE OF REVIEW

Antimicrobial stewardship is the primary intervention in the battle against antimicrobial resistance, but clinicians do not always apply many key antimicrobial stewardship principles to patients with significant immune defects due to lack of data and fear of bad outcomes. We review evidence regarding the application of stewardship principles to immunocompromised patients, with a focus on solid organ and hematopoietic stem cell transplant recipients.

RECENT FINDINGS

Antimicrobial stewardship programs (ASPs), targeting immunocompromised patient populations such as oncology and transplant, are gaining traction. Emerging literature suggests that several stewardship interventions can be adapted to immunocompromised hosts and improve antimicrobial utilization, but data supporting improved outcomes is very limited.

SUMMARY

The application of antimicrobial stewardship principles to immunocompromised patients is feasible, necessary, and urgent. As antimicrobial stewardship programs gain momentum across a diverse range of healthcare settings more immunocompromised patients will fall under their purview. It is imperative that centers applying antimicrobial stewardship principles share their experience and establish collaborative research efforts to advance our knowledge base in applying antimicrobial stewardship initiatives to immunocompromised host populations, both in terms of programmatic success and patient outcomes.

Effect of Ganciclovir on IL-6 Levels Among Cytomegalovirus-Seropositive Adults With Critical Illness: A Randomized Clinical Trial

IMPORTANCE

The role of cytomegalovirus (CMV) reactivation in mediating adverse clinical outcomes in nonimmunosuppressed adults with critical illness is unknown.

OBJECTIVE

To determine whether ganciclovir prophylaxis reduces plasma interleukin 6 (IL-6) levels in CMV-seropositive adults who are critically ill.

DESIGN, SETTING, AND PARTICIPANTS

Double-blind, placebo-controlled, randomized clinical trial (conducted March 10, 2011-April 29, 2016) with a follow-up of 180 days (November 10, 2016) that included 160 CMV-seropositive adults with either sepsis or trauma and respiratory failure at 14 university intensive care units (ICUs) across the United States.

INTERVENTIONS

Patients were randomized (1:1) to receive either intravenous ganciclovir (5 mg/kg twice daily for 5 days), followed by either intravenous ganciclovir or oral valganciclovir once daily until hospital discharge (n = 84) or to receive matching placebo (n = 76).

MAIN OUTCOMES AND MEASURES

The primary outcome was change in IL-6 level from day 1 to 14. Secondary outcomes were incidence of CMV reactivation in plasma, mechanical ventilation days, incidence of secondary bacteremia or fungemia, ICU length of stay, mortality, and ventilator-free days (VFDs) at 28 days.

RESULTS

Among 160 randomized patients (mean age, 57 years; women, 43%), 156 patients received 1or more dose(s) of study medication, and 132 patients (85%) completed the study. The mean change in plasma IL-6 levels between groups was -0.79 log10 units (-2.06 to 0.48) in the ganciclovir group and -0.79 log10 units (-2.14 to 0.56) in the placebo group (point estimate of difference, 0 [95% CI, -0.3 to 0.3]; P > .99). Among secondary outcomes, CMV reactivation in plasma was significantly lower in the ganciclovir group (12% [10 of 84 patients] vs 39% [28 of 72 patients]); absolute risk difference, -27 (95% CI, -40 to -14), P < .001. The ganciclovir group had more median VFDs in both the intention-to-treat (ITT) group and in the prespecified sepsis subgroup (ITT group: 23 days in ganciclovir group vs 20 days in the placebo group, P = .05; sepsis subgroup, 23 days in the ganciclovir group vs 20 days in the placebo group, P = .03). There were no significant differences between the ganciclovir and placebo groups in duration of mechanical ventilation (5 days for the ganciclovir group vs 6 days for the placebo group, P = .16), incidence of secondary bacteremia or fungemia (15% for the ganciclovir group vs 15% for the placebo group, P = .67), ICU length of stay (8 days for the ganciclovir group vs 8 days for the placebo group, P = .76), or mortality (12% for the ganciclovir group vs 15% for the placebo group, P = .54).

CONCLUSIONS AND RELEVANCE

Among CMV-seropositive adults with critical illness due to sepsis or trauma, ganciclovir did not reduce IL-6 levels and the current study does not support routine clinical use of ganciclovir as a prophylactic agent in patients with sepsis. Additional research is necessary to determine the clinical efficacy and safety of CMV suppression in this setting.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01335932.

Management of Viral Central Nervous System Infections: A Primer for Clinicians

Viruses are a common cause of central nervous system (CNS) infections with many host, agent, and environmental factors influencing the expression of viral diseases. Viruses can be responsible for CNS disease through a variety of mechanisms including direct infection and replication within the CNS resulting in encephalitis, infection limited to the meninges, or immune-related processes such as acute disseminated encephalomyelitis. Common pathogens including herpes simplex virus, varicella zoster, and enterovirus are responsible for the greatest number of cases in immunocompetent hosts. Other herpes viruses (eg, cytomegalovirus, John Cunningham virus) are more common in immunocompromised hosts. Arboviruses such as Japanese encephalitis virus and Zika virus are important pathogens globally, but the prevalence varies significantly by geographic region and often season. Early diagnosis from radiographic evidence and molecular (eg, rapid) diagnostics is important for targeted therapy. Antivirals may be used effectively against some pathogens, although several viruses have no effective treatment. This article provides a review of epidemiology, diagnostics, and management of common viral pathogens in CNS disease.

Treatment of alpha and beta herpesvirus infections in solid organ transplant recipients

INTRODUCTION

Human herpesviruses frequently cause infections in solid organ transplant (SOT) recipients. Areas covered: We provide an overview of the clinical impact of alpha and beta herpesviruses and highlight the mechanisms of action, pharmacokinetics, clinical indications, and adverse effects of antiviral drugs for the management of herpes simplex virus, varicella zoster virus and cytomegalovirus. We comprehensively evaluated key clinical trials that led to drug approval, and served as the foundation for management guidelines. We further provide an update on investigational antiviral agents for alpha and beta herpesvirus infections after SOT. Expert commentary: The therapeutic armamentarium for herpes infections is limited by the emergence of drug resistance. There have been major efforts for discovery of new drugs against these viruses, but the results of early-phase clinical trials have been less than encouraging. We believe, however, that more antiviral drug options are needed given the adverse side effects associated with current antiviral agents, and the emergence of drug-resistant virus populations in SOT recipients. Likewise, optimized use and strategies are needed for existing and novel antiviral drugs against alpha and beta-herpesviruses in SOT recipients.

Bottom-up Meets Top-down: Complementary Physiologically Based Pharmacokinetic and Population Pharmacokinetic Modeling for Regulatory Approval of a Dosing Algorithm of Valganciclovir in Very Young Children

Population pharmacokinetic (PopPK) and physiologically based pharmacokinetic (PBPK) models are frequently used to support pediatric drug development. Both methods have strengths and limitations and we used them complementarily to support the regulatory approval of a dosing algorithm for valganciclovir (VGCV) in children <4 months old. An existing pediatric PBPK model was extended to neonates and showed that potential physiological differences compared with older children are minor. The PopPK model was used to simulate ganciclovir (GCV) exposures in children with population typical combinations of body size and renal function and to assess the effectiveness of an alternative dosing algorithm suggested by the US Food and Drug Administration. PBPK and PopPK confirmed that the proposed VGCV dosing algorithm achieves similar GCV exposures in children of all ages and that the alternative dosing algorithm leads to underexposure in a substantial fraction of patients. Our approach raised the confidence in the VGCV dosing algorithm for children <4 months old and supported the regulatory approval.

A Physiologically Based Pharmacokinetic Model for Ganciclovir and Its Prodrug Valganciclovir in Adults and Children

A physiologically based pharmacokinetic (PBPK) model has been developed for ganciclovir and its prodrug valganciclovir. Initial bottom-up modeling based on physicochemical drug properties and measured in vitro inputs was verified in preclinical animal species, and then, a clinical model was verified in a stepwise fashion with pharmacokinetic data in adult, children, and neonatal patients. The final model incorporated conversion of valganciclovir to ganciclovir through esterases and permeability-limited tissue distribution of both drugs with active transport processes added in gut, liver, and kidney. A PBPK model which accounted for known age-related tissue volumes, composition and blood flows, and renal filtration clearance was able to simulate well the measured plasma exposures in adults and pediatric patients. Overall, this work illustrates the stepwise development of PBPK models which could be used to predict pharmacokinetics in infants and neonates, thereby assisting drug development in a vulnerable patient population where clinical data are challenging to obtain.

Contribution of Population Pharmacokinetics to Dose Optimization of Ganciclovir-Valganciclovir in Solid-Organ Transplant Patients

Treatment of solid-organ transplant (SOT) patients with ganciclovir (GCV)-valganciclovir (VGCV) according to the manufacturer's recommendations may result in over- or underexposure. Bayesian prediction based on a population pharmacokinetics model may optimize GCV-VGCV dosing, achieving the area under the curve (AUC) therapeutic target. We conducted a two-arm, randomized, open-label, 40% superiority trial in adult SOT patients receiving GCV-VGCV as prophylaxis or treatment of cytomegalovirus infection. Group A was treated according to the manufacturer's recommendations. For group B, the dosing was adjusted based on target exposures using a Bayesian prediction model (NONMEM). Fifty-three patients were recruited (27 in group A and 26 in group B). About 88.6% of patients in group B and 22.2% in group A reached target AUC, achieving the 40% superiority margin (P< 0.001; 95% confidence interval [CI] difference, 47 to 86%). The time to reach target AUC was significantly longer in group A than in group B (55.9 ± 8.2 versus 15.8 ± 2.3 days,P< 0.001). A shorter time to viral clearance was observed in group B than in group A (12.5 versus 17.6 days;P= 0.125). The incidences of relapse (group A, 66.67%, and group B, 9.01%) and late-onset infection (group A, 36.7%, and group B, 7.7%) were higher in group A. Neutropenia and anemia were related to GCV overexposure. GCV-VCGV dose adjustment based on a population pharmacokinetics Bayesian prediction model optimizes GCV-VGCV exposure. (This study has been registered at ClinicalTrials.gov under registration no. NCT01446445.).

Liquid chromatography tandem mass spectrometry quantitation of intracellular concentrations of ganciclovir and its phosphorylated forms

Ganciclovir (GCV) is prescribed for cytomegalovirus infection which is a major issue in immunodepressed patients. It is however characterized by hematological toxicity. A better understanding of GCV concentration-effects relationships implies the measurement of intracellular forms. The objective of this study was to develop a method to measure GCV and its derivatives in cells. A four-stage procedure was developed with the following strategy: (1) to separate into different fractions the different intracellular forms of GCV (GCV itself and its phosphorylated forms) by solid-phase extraction (SPE) from blood cells, (2) to dephosphorylate the different phosphorylated forms into GCV, (3) to perform a second SPE to desalt samples and concentrate GCV, and (4) to measure GCV concentrations in the different extracts using a triple-quadrupole, linear ion trap mass spectrometer. Finally, the procedure was tested in 17 patients receiving GCV. From lysed cells, the different forms of GCV were fractionated, the phosphorylated forms were eluted with different KCl solutions, and the obtained fractions were treated with acid phosphatase to transform the phosphorylated metabolites back into GCV. The method was validated from 5 to 500 μg L(-1) with a limit of detection of 1 μg L(-1). The whole procedure was validated according to the US Food and Drug Administration guidelines and successfully applied in 17 patients receiving GCV. The method liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) allowing the measurement of GCV and its phosphorylated forms in blood cells was developed and can be used in developing clinical studies to explore the role of these biomarkers in the event of toxicity.

Optimal sparse sampling for estimating ganciclovir/valganciclovir AUC in solid organ transplant patients using NONMEN

BACKGROUND

Ganciclovir and valganciclovir (GCV/VGCV) are used for the treatment and prophylaxis of cytomegalovirus in solid organ transplant (SOT) patients. An area under the time-concentration curve of 40-50 μg × h/mL is related to efficacy. Therapeutic drug monitoring could prevent suboptimal drug exposure and adverse events, but obtaining full concentration profiles is not feasible. Sampling optimization by developing a reliable and clinically applicable limited sampling strategy (LSS) may simplify dose adjustment.

METHODS

An LSS was developed using an original pharmacokinetic (PK) data set of 40 full profiles from 20 adult SOT patients. The LSS was developed based on population and Bayesian prediction approaches. Population PK parameters from a previous model were used for simulation or as priors (NONMEM version 7.2). Median percentage of prediction error and median of absolute percentage prediction error were calculated for plasma clearance (CL) and central compartment distribution volume (V(2)). Bias and precisions were compared using 1-way analysis of variance (SPSSv19.0).

RESULTS

Sampling windows were designed according to the PK profile previously observed with the entire set of data. The 4 windows selected were distributed from 0.5 to 1.5 hours, 2 to 3 hours, 4 to 5 hours, and 6 to 8 hours. Predose and concentrations beyond 8 hours were not considered in any case because simulated negative concentrations occurred in both cases. Predicted exposure using 3 sampling times (0.5-1.5, 4-5, and 6-8 hours) showed the best predictive performance, by either the population or Bayesian approaches. Bias and imprecision for CL and V(2) were 0 and 0.60%, and -0.78% and 0.78%, respectively.

CONCLUSIONS

GCV/VCG area under the time-concentration curve in SOT patients could be predicted with acceptable accuracy for clinical management and dose individualization using LSS. The estimator of GCV/VGC, using 3 concentrations measured at 0.5-1.5, 4-5, and 6-8 hours after drug intake, could be used for dose adjustment.

Clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir in children with cytomegalovirus infection

INTRODUCTION

Among infants and immunocompromised children cytomegalovirus (CMV) is associated with significant morbidity and mortality.

AREAS COVERED

This review describes the clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir for the treatment and prevention of CMV infection in children.

EXPERT OPINION

A 24-h ganciclovir area under the concentration versus time curve (AUC₀₋₂₄) of 40 - 60 μg h/ml decreased the risk of CMV infection for adults undergoing CMV prophylaxis. For adults undergoing treatment for active CMV disease, a target AUC₀₋₁₂ of 40 - 60 μg h/ml has been suggested. The applicability of these targets to children remains uncertain; however, with the most sophisticated dosing regimens developed to date only 21% of patients are predicted to reach these targets. Moving forward, identification of optimal pediatric ganciclovir and valganciclovir dosing regimens may involve the use of an externally validated pediatric population pharmacokinetic model for empirical dosing, an optimal sampling strategy for collecting a minimal number of blood samples for each patient and Bayesian updating of the dosing regimen based on an individual patient's pharmacokinetic profile.

Pharmacokinetics of ganciclovir during continuous venovenous hemodiafiltration in critically ill patients

Ganciclovir is an antiviral agent that is frequently used in critically ill patients with cytomegalovirus (CMV) infections. Continuous venovenous hemodiafiltration (CVVHDF) is a common extracorporeal renal replacement therapy in intensive care unit patients. The aim of this study was to investigate the pharmacokinetics of ganciclovir in anuric patients undergoing CVVHDF. Population pharmacokinetic analysis was performed for nine critically ill patients with proven or suspected CMV infection who were undergoing CVVHDF. All patients received a single dose of ganciclovir at 5 mg/kg of body weight intravenously. Serum and ultradiafiltrate concentrations were assessed by high-performance liquid chromatography, and these data were used for pharmacokinetic analysis. Mean peak and trough prefilter ganciclovir concentrations were 11.8 ± 3.5 mg/liter and 2.4 ± 0.7 mg/liter, respectively. The pharmacokinetic parameters elimination half-life (24.2 ± 7.6 h), volume of distribution (81.2 ± 38.3 liters), sieving coefficient (0.76 ± 0.1), total clearance (2.7 ± 1.2 liters/h), and clearance of CVVHDF (1.5 ± 0.2 liters/h) were determined. Based on population pharmacokinetic simulations with respect to a target area under the curve (AUC) of 50 mg · h/liter and a trough level of 2 mg/liter, a ganciclovir dose of 2.5 mg/kg once daily seems to be adequate for anuric critically ill patients during CVVHDF.

Combinatorial targeting of 2 different steps in adenoviral DNA replication by herpes simplex virus thymidine kinase and artificial microRNA expression for the inhibition of virus multiplication in the presence of ganciclovir

BACKGROUND

Human adenoviruses are a frequent threat to immunocompromised patients, and disseminated disease is associated with severe morbidity and mortality. Current drugs are not capable of preventing all fatalities, thus indicating the need for alternative treatment strategies. Adenoviruses can be rendered susceptible to antiherpetic prodrugs such as ganciclovir (GCV), upon expression of the herpes simplex virus thymidine kinase (HSV-TK) gene in adenovirus-infected cells. Furthermore, adenoviruses are amenable to post-transcriptional gene silencing via small interfering RNAs (siRNAs) or artificial micro RNAs (amiRNAs).

RESULTS

In this study, we combined these 2 approaches by constructing a combinatorial gene expression cassette that comprises the HSV-TK gene and multiple copies of an amiRNA directed against the mRNA encoding the adenoviral preterminal protein (pTP). HSV-TK gene expression was controlled by the adenoviral E4 promoter, which is activated in the presence of the adenoviral E1 gene products (i.e., when adenovirus is present in the cell). When inserted into a replication-deficient (E1-, E3-deleted) adenoviral vector, this cassette effectively inhibited the replication of wild-type adenovirus in vitro. The reduction rate mediated by the combinatorial approach was higher compared to that achieved by either of the 2 approaches alone, and these obvious additive effects became most pronounced when the GCV concentration was low.

CONCLUSIONS

The concept presented here has the potential to aid in the inhibition of wild-type adenovirus replication. Furthermore, the combinatorial expression cassette may constitute a safeguard to potentially control unintended replication of adenoviral vectors and to prevent immune responses provoked by them.

Targeted expression of herpes simplex virus thymidine kinase in adenovirus-infected cells reduces virus titers upon treatment with ganciclovir in vitro

BACKGROUND

Adenoviruses are a frequent cause of life-threatening infections in immunocompromised patients. Available therapeutics still cannot completely prevent fatal outcomes. By contrast, herpes viruses are well treatable with prodrugs such as ganciclovir (GCV), which are selectively activated in virus-infected cells by virus-encoded thymidine kinases. This effective group of prodrugs is not applicable to adenoviruses and other DNA viruses because they lack those kinases.

METHODS

To render adenoviruses amenable to GCV treatment, we generated an adenoviral vector-based delivery system for targeted expression of herpes simplex virus thymidine kinase (HSV-TK) in wild-type adenovirus 5 (wt Ad5)-infected cells. HSV-TK expression was largely restricted to wt virus-infected cells by transcription of the gene from the Ad5 E4 promoter. Its activity is dependent on the adenoviral E1A gene product which is not produced by the vector but is only provided in cells infected with wt adenovirus. The anti-adenoviral effect of HSV-TK expression and concomitant treatment with GCV was assessed in vitro in four different cell lines or primary cells.

RESULTS

E4 promoter-mediated HSV-TK background expression was sufficiently low to prevent cytotoxicity in the presence of low-levels GCV in cells not infected with wt Ad5. However, expression was several-fold increased in wt Ad5-infected cells and treatment with low levels of GCV efficiently inhibited wt Ad5 DNA replication. Genome copy numbers and output of infectious particles were reduced by up to > 99.99% and cell viability was greatly increased.

CONCLUSIONS

We extended the concept of enzyme/prodrug therapy to adenovirus infections by selectively sensitizing adenovirus-infected cells to treatment with GCV.

Evaluation of valganciclovir pharmacokinetics in lung transplant recipients

BACKGROUND

Valganciclovir is commonly used for cytomegalovirus prevention after lung transplantation. The pharmacokinetic profile of valganciclovir in lung transplant patients has not been well described or linked to efficacy and safety.

METHODS

This prospective, randomized, crossover study determined the steady-state pharmacokinetic profile of 2 different doses of valganciclovir in lung transplant recipients and compared these profiles with intravenous ganciclovir.

RESULTS

Ten patients were evaluated. Patients were 56.8 ± 3.4 years old and had a mean creatinine clearance of 69 ± 9 ml/min. Oral bioavailability of ganciclovir after administration of valganciclovir was 59%, and mean half-life was 3.73 ± 1.15 hours. The maximal concentration after intravenous 5 mg/kg ganciclovir was significantly higher than after 450 mg valganciclovir (8.37 ± 3.03 mg/liter vs. 5.3 ± 2.09 mg/liter, respectively; p = 0.02) and similar to 900 mg valganciclovir (7.93 ± 3.97 mg/liter; p = 0.78). A higher area under the curve at 0-24 hours (AUC(0-24)) was found with 900 mg valganciclovir compared with intravenous 5 mg/kg/day ganciclovir (47.8 ± 19.7 vs 32.9 ± 10.8 mg · hour/liter, respectively; p = 0.049). The AUC(0-24) for 450 mg valganciclovir twice daily was 45.5 ± 22.9 mg · hour/liter.

CONCLUSION

Valganciclovir at 900 mg/day resulted in the equivalent of a mean daily dose of 7.7 mg/kg intravenous ganciclovir. Higher systemic ganciclovir exposures occurred after 900 mg/day valganciclovir compared with intravenous 5 mg/kg/day ganciclovir. Valganciclovir therapeutic drug monitoring may be warranted in select lung transplant patients to avoid increased toxicity.

Valganciclovir to prevent or treat cytomegalovirus disease in organ transplantation

Cytomegalovirus (CMV) is generally considered the most significant pathogen to infect patients following organ transplantation. Significant improvements have been achieved in the management of CMV disease over recent years, especially since the introduction of oral drugs such as oral ganciclovir followed by valganciclovir (VGC), a prodrug of ganciclovir with enhanced bioavailability. Several randomized controlled trials have shown that VGC is an efficacious and convenient oral drug to prevent or treat CMV disease in solid-organ transplant recipients. In this article, we discuss the clinical and pharmacological experience with the use of VGC for the management of CMV in solid-organ transplant recipients. Finally, novel strategies to further reduce the incidence of CMV disease after transplantation are also reviewed.

Determination of ganciclovir in human plasma by ultra performance liquid chromatography-UV detection

OBJECTIVES

Implement a sensitive UHPLC method for the assay of ganciclovir in human plasma.

DESIGN AND METHODS

We developed and validated a chromatographic method coupled to ultraviolet detection for quantification of ganciclovir, with a short run time using a small volume of human plasma. Comparison of system performance was made with respect to analysis time, efficiency and sensitivity.

RESULTS

Correlation coefficients (r) of the calibration curves ranged from 0.999744 to 0.999784. Within-day and between-day imprecision and inaccuracy, specificity and recovery were also evaluated for validation. The method was precise and accurate and the retention time was 0.7 min. The calibration curves were linear between 0.5 and 30 μg/mL. There was a good correlation between HPLC and UHPLC techniques.

CONCLUSIONS

We developed a method that is currently applied in a clinical study assessing GCV plasma concentration variability after ganciclovir and valganciclovir administration.

Antiviral drugs for viruses other than human immunodeficiency virus

Most viral diseases, with the exception of those caused by human immunodeficiency virus, are self-limited illnesses that do not require specific antiviral therapy. The currently available antiviral drugs target 3 main groups of viruses: herpes, hepatitis, and influenza viruses. With the exception of the antisense molecule fomivirsen, all antiherpes drugs inhibit viral replication by serving as competitive substrates for viral DNA polymerase. Drugs for the treatment of influenza inhibit the ion channel M(2) protein or the enzyme neuraminidase. Combination therapy with Interferon-α and ribavirin remains the backbone treatment for chronic hepatitis C; the addition of serine protease inhibitors improves the treatment outcome of patients infected with hepatitis C virus genotype 1. Chronic hepatitis B can be treated with interferon or a combination of nucleos(t)ide analogues. Notably, almost all the nucleos(t) ide analogues for the treatment of chronic hepatitis B possess anti-human immunodeficiency virus properties, and they inhibit replication of hepatitis B virus by serving as competitive substrates for its DNA polymerase. Some antiviral drugs possess multiple potential clinical applications, such as ribavirin for the treatment of chronic hepatitis C and respiratory syncytial virus and cidofovir for the treatment of cytomegalovirus and other DNA viruses. Drug resistance is an emerging threat to the clinical utility of antiviral drugs. The major mechanisms for drug resistance are mutations in the viral DNA polymerase gene or in genes that encode for the viral kinases required for the activation of certain drugs such as acyclovir and ganciclovir. Widespread antiviral resistance has limited the clinical utility of M(2) inhibitors for the prevention and treatment of influenza infections. This article provides an overview of clinically available antiviral drugs for the primary care physician, with a special focus on pharmacology, clinical uses, and adverse effects.

High efficacy and low toxicity of short-course oral valganciclovir as pre-emptive therapy for hematopoietic stem cell transplant cytomegalovirus infection

BACKGROUND

Cytomegalovirus (CMV) infection is a major infectious complication post-allogeneic hematopoietic stem cell transplantation (HSCT). CMV seropositivity in Eastern Mediterranean and certain Asian countries is reported to be close to 100%; hence, the need for effective pre-emptive treatment strategy that has low toxicity. Valganciclovir (VGC) is a prodrug of ganciclovir with high bioavailability.

PATIENTS AND METHODS

HSCT patients with documented CMV infection (as defined by positive CMV antigenemia) were treated as outpatients with VGC at a starting dose of 900 mg twice daily for 1 week. Those who were antigenemia negative after one week received 900 mg once daily for another week and treatment was subsequently discontinued. Those who were positive after one week of therapy continued on the twice-daily treatment schedule for another week and changed to a daily schedule once they converted to antigenemia negativity.

RESULTS

From January 2004 to December 2007, 47 HSCT patients received preemptive treatment with VGC for 61 episodes of CMV infection. The antigenemia range was 1 to 700 infected cells/slide. Complete responses were observed in 92% and 97% after the 1st and 2nd week of treatment, respectively. Three percent of the episodes were considered refractory, requiring alternative therapy. No CMV disease was observed in this cohort.

CONCLUSION

Neutropenia was the main observed toxicity, requiring granulocyte-colony stimulating factor in 8 episodes. Outpatient treatment of CMV infection with "short-course oral VGC" given as a one-week twice-daily treatment and one week once daily maintenance is a highly effective therapy with minimal toxicity. These results require validation in a larger, randomized study.