Pharmacokinetic considerations in the use of antivirals in neonates

The use of antiviral drugs in children

Viral infections are particularly common among children. They often have a mild course, are self-limiting and do not need any specific treatment. However, in some cases, the disease can be severe and lead to permanent disabilities. A variety of antiviral drugs are available for the treatments of certain infectious agents: for instance, acyclovir is used to treat herpes simplex virus encephalitis. Recommendations for flu treatment may change according to the current epidemiological surveillance data, on the basis of which antiviral sensibility can be forecast: recommended drugs for the 2020-21 flu season are oseltamivir, zanamivir, peramivir and baloxavir. Some drugs are used to treat congenital infections, such as valganciclovir and ganciclovir in congenital cytomegalovirus infection. Antiretroviral prophylaxis in newborns from HIV-1 infected mothers must be initiated as soon as possible, with one or more drugs according to therapeutic regimens based on the baby's risk category. According to the most recent guidelines, antiretroviral therapy must be started at diagnosis. Several antiretroviral drugs are available today and approved for use in children, so several combinations can be made. However, out of the 29 antiretroviral drugs approved for adults, only 38% (11/29) are approved for children under the age of two and about 60% (18/29) for children under the age of twelve. Treatment with direct antiviral agents against hepatitis C virus is approved for children over the age of three; it consists in different therapeutic regimens chosen on the basis of the viral genotype (ledipasvir/sofosbuvir for genotypes 1, 4, 5 and 6, sofosbuvir/ribavirin for genotypes 2 and 3, sofosbuvir/velpatasvir and glecaprevir/pibrentasvir for all genotypes) and it has dramatically changed the course of the illness. Many molecules have been studied in order to treat SARS-CoV-2 infection, but only remdesivir seems to play a role in shortening recovery time, although inclusion criteria are very specific and data on the use in children is limited.

Extrapolation and dosing recommendations for raxibacumab in children from birth to age <18 years

AIMS

The US Food and Drug Administration's Animal Rule allows for the approval of drugs when human efficacy studies are not ethical. While the therapeutic doses of raxibacumab, a monoclonal antibody for the prophylaxis and treatment of inhalational anthrax, have been based on pharmacokinetic data from adult subjects, its disposition in children has not been investigated in clinical trials. Here we evaluate the effect of demographic covariates and maturation processes on the pharmacokinetics of raxibacumab and explore opportunities for the optimisation of paediatric doses.

METHODS

A population pharmacokinetic model was used as basis for the extrapolation of raxibacumab disposition from adults to children. Different extrapolation scenarios, including weight-banded dosing regimens, were considered to assess the effect of growth and maturation on the pharmacokinetic parameters of interest. Area under the concentration-time curve, maximum plasma concentration and the time of serum raxibacumab concentrations greater than or equimolar to the highest serum protective antigen concentrations observed for at least 28 days in any monkey challenged with Bacillus anthracis that died were derived and compared with the currently approved US doses.

RESULTS

Based on practical considerations, a weight-banded dosing regimen consisting of 4 dose levels (75 mg/kg for individuals ≤1.5 kg, 55 mg/kg for individuals <10 kg, 45 mg/kg for individuals <50 kg, 40 mg/kg for all individuals >50 kg) was required to optimise target exposure across the paediatric population.

CONCLUSIONS

Age-related maturation processes may affect raxibacumab clearance in very young patients. The proposed dosing regimens take into account effects of body weight and maturation processes on the elimination of raxibacumab.

The emerging role of physiologically based pharmacokinetic modelling in solid drug nanoparticle translation

The use of solid drug nanoparticles (SDN) has become an established approach to improve drug delivery, supporting enhancement of oral absorption and long-acting administration strategies. A broad range of SDNs have been successfully utilised for multiple products and several development programmes are currently underway across different therapeutic areas. With some approaches, a large range of material space is available with diversity in physical characteristics, excipient choice and pharmacological behaviour. The selection of SDN lead candidates is a complex process including a broad range of in vitro and in vivo data, and a better understanding of how physical characteristics relate to performance is required. Physiologically-based pharmacokinetic (PBPK) modelling is based upon a comprehensive integration of experimental data into a mathematical description of drug distribution, allowing simulation of SDN pharmacokinetics that can be qualified in vivo prior to human prediction. This review aims to provide a description of how PBPK can find application into the development of SDN. Integration of predictive PBPK modelling into SDN development allows a better understanding of the SDN dose-response relationship, supporting a framework for rational optimisation while reducing the risk of failure in developing safe and effective nanomedicines.