The importance of drug exposure in the development of cytomegalovirus resistance

Objective

Human cytomegalovirus (CMV) is a widespread pathogen which remains asymptomatic in healthy individuals. However, CMV disease can be life-threatening in immunocompromised individuals, particularly in transplant patients. This disease is routinely managed by antiviral agents, including (val)ganciclovir, foscarnet, cidofovir, letermovir, and maribavir. Subtherapeutic antiviral drug exposure is a common occurrence and can lead to drug-resistant CMV development, a key contributor to disease progression. Breakthrough CMV often results in graft loss, end-organ failure, or death. By optimizing intracellular exposure levels of antiviral therapies, it may be possible to improve patient outcomes. Therefore, this review aims to explore the relationship between antiviral exposure and the development of drug-resistant CMV.

Methods

A literature search was conducted in Pubmed database including keywords “cytomegalovirus”, “resistance”, “pharmacokinetics”, “pharmacodynamics”, “drug exposure”, “ganciclovir”, “foscarnet”, “maribavir”, “letermovir”, “cidofovir”.

Results

There are several challenges to achieving optimal concentrations of current and novel CMV therapies. Narrow therapeutic indices and toxicity profiles of current CMV therapeutics contribute to their subtherapeutic exposure and, hence, suboptimal clinical outcomes. Alternately, novel antivirals such as letermovir and maribavir offer improved pharmacokinetic profiles. However, these agents are associated with rapid resistance development. Overall, a distinct gap exists in understanding the relationship between antiviral exposure and resistance development. As a result, current clinical markers used to predict clinical efficacy lack reliability. In future, resistance development in relation to drug exposure should be included as a clinical trial endpoint to gain understanding of exposure-resistance relationships.

Conclusions

With solid knowledge of exposure-resistance relationships, more predictive in vitro and in vivo markers of clinical efficacy can be identified. PK/PD targets that account for free EC50/EC90 and viral load should be defined to improve clinical outcomes and reduce the risk for emergence of R/R CMV.