The bioavailability and maturing clearance of doxapram in preterm infants

The effects of doxapram and its potential interactions with K2P channels in experimental model preparations

The channels commonly responsible for maintaining cell resting membrane potentials are referred to as K2P (two-P-domain K+ subunit) channels. These K+ ion channels generally remain open but can be modulated by their local environment. These channels are classified based on pharmacology, pH sensitivity, mechanical stretch, and ionic permeability. Little is known about the physiological nature of these K2P channels in invertebrates. Acidic conditions depolarize neurons and muscle fibers, which may be caused by K2P channels given that one subtype can be blocked by acidic conditions. Doxapram is used clinically as a respiratory aid known to block acid-sensitive K2P channels; thus, the effects of doxapram on the muscle fibers and synaptic transmission in larval Drosophila and crawfish were monitored. A dose-dependent response was observed via depolarization of the larval Drosophila muscle and an increase in evoked synaptic transmission, but doxapram blocked the production of action potentials in the crawfish motor neuron and had a minor effect on the resting membrane potential of the crawfish muscle. This indicates that the nerve and muscle tissues in larval Drosophila and crawfish likely express different K2P channel subtypes. Since these organisms serve as physiological models for neurobiology and physiology, it would be of interest to further investigate what types of K2P channel are expressed in these tissues. (212 words).

When will the Glomerular Filtration Rate in Former Preterm Neonates Catch up with Their Term Peers?

AIMS

Whether and when glomerular filtration rate (GFR) in preterms catches up with term peers is unknown. This study aims to develop a GFR maturation model for (pre)term-born individuals from birth to 18 years of age. Secondarily, the function is applied to data of different renally excreted drugs.

METHODS

We combined published inulin clearance values and serum creatinine (Scr) concentrations in (pre)term born individuals throughout childhood. Inulin clearance was assumed to be equal to GFR, and Scr to reflect creatinine synthesis rate/GFR. We developed a GFR function consisting of GFRbirth (GFR at birth), and an Emax model dependent on PNA (with GFRmax, PNA50 (PNA at which half ofGFR max is reached) and Hill coefficient). The final GFR model was applied to predict gentamicin, tobramycin and vancomycin concentrations.

RESULT

In the GFR model, GFRbirth varied with birthweight linearly while in the PNA-based Emax equation, GA was the best covariate for PNA50, and current weight for GFRmax. The final model showed that for a child born at 26 weeks GA, absolute GFR is 18%, 63%, 80%, 92% and 96% of the GFR of a child born at 40 weeks GA at 1 month, 6 months, 1 year, 3 years and 12 years, respectively. PopPK models with the GFR maturation equations predicted concentrations of renally cleared antibiotics across (pre)term-born neonates until 18 years well.

CONCLUSIONS

GFR of preterm individuals catches up with term peers at around three years of age, implying reduced dosages of renally cleared drugs should be considered below this age.

Doxapram versus placebo in preterm newborns: a study protocol for an international double blinded multicentre randomized controlled trial (DOXA-trial)

BACKGROUND

Apnoea of prematurity (AOP) is one of the most common diagnoses among preterm infants. AOP often leads to hypoxemia and bradycardia which are associated with an increased risk of death or disability. In addition to caffeine therapy and non-invasive respiratory support, doxapram might be used to reduce hypoxemic episodes and the need for invasive mechanical ventilation in preterm infants, thereby possibly improving their long-term outcome. However, high-quality trials on doxapram are lacking. The DOXA-trial therefore aims to investigate the safety and efficacy of doxapram compared to placebo in reducing the composite outcome of death or severe disability at 18 to 24 months corrected age.

METHODS

The DOXA-trial is a double blinded, multicentre, randomized, placebo-controlled trial conducted in the Netherlands, Belgium and Canada. A total of 396 preterm infants with a gestational age below 29 weeks, suffering from AOP unresponsive to non-invasive respiratory support and caffeine will be randomized to receive doxapram therapy or placebo. The primary outcome is death or severe disability, defined as cognitive delay, cerebral palsy, severe hearing loss, or bilateral blindness, at 18-24 months corrected age. Secondary outcomes are short-term neonatal morbidity, including duration of mechanical ventilation, bronchopulmonary dysplasia and necrotising enterocolitis, hospital mortality, adverse effects, pharmacokinetics and cost-effectiveness. Analysis will be on an intention-to-treat principle.

DISCUSSION

Doxapram has the potential to improve neonatal outcomes by improving respiration, but the safety concerns need to be weighed against the potential risks of invasive mechanical ventilation. It is unknown if the use of doxapram improves the long-term outcome. This forms the clinical equipoise of the current trial. This international, multicentre trial will provide the needed high-quality evidence on the efficacy and safety of doxapram in the treatment of AOP in preterm infants.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04430790 and EUDRACT 2019-003666-41. Prospectively registered on respectively June and January 2020.

The Effects of Doxapram Blocking the Response of Gram-Negative Bacterial Toxin (LPS) at Glutamatergic Synapses

Lipopolysaccharides (LPS) associated with Gram-negative bacteria are one factor responsible for triggering the mammalian immune response. Blocking the action of LPS is key to reducing its downstream effects. However, the direct action of LPS on cells is not yet fully addressed. LPS can have rapid, direct effects on cells in the absence of a systemic immune response. Recent studies have shown that doxapram, a blocker of a subset of K2P channels, also blocks the acute actions of LPS. Doxapram was evaluated to determine if such action also occurs at glutamatergic synapses in which it is known that LPS can increase synaptic transmission. Doxapram at 5 mM first enhanced synaptic transmission, then reduced synaptic response, while 10 mM rapidly blocked transmission. Doxapram at 5 mM blocked the excitatory response induced by LPS. Enhancing synaptic transmission with LPS and then applying LPS combined with doxapram also resulted in retarding the response of LPS. It is possible doxapram and LPS are mediated via a similar receptor or cellular responses. The potential of designing pharmacological compounds with a similar structure to doxapram and determining the binding of such compounds can aid in addressing the acute, direct actions by LPS on cells.

Recent research advances in ATX inhibitors: An overview of primary literature

The autoglobulin gene is the main enzyme for circulating LPA production and has lysophosphatidylcholine D activity, which catalyzes the production of lysophosphatidic acid and choline with lysophosphatidylcholine as substrate. A growing body of experimental evidence suggests that autoglobulin is involved in the pathogenesis of a variety of diseases. This review summarizes the different structural ATX inhibitors classified according to their binding mode to the ATX triple orientation site, and summarizes the conformational relationships and molecular docking of each type with ATX structure, hoping to contribute to the development of novel ATX inhibitors.

The Pharmacokinetics of Caffeine in Preterm Newborns: No Influence of Doxapram but Important Maturation with Age

BACKGROUND

Apnea of prematurity can persist despite caffeine therapy in preterm infants. Doxapram may additionally support breathing. Although multiple small studies have reported the efficacy of doxapram, the structural co-treatment with caffeine impedes to ascribe the efficacy to doxapram itself or to a pharmacokinetic (PK) interaction where doxapram increases the exposure to caffeine. We examined whether there is a PK drug-drug interaction between doxapram and caffeine by developing a PK model for caffeine including infants with and without doxapram treatment.

METHODS

In preterm neonates receiving caffeine, we determined caffeine plasma concentrations before, during, and directly after doxapram co-treatment and used these to develop a population PK model in NONMEM 7.3. Patient characteristics and concomitant doxapram administration were tested as covariates.

RESULTS

166 plasma samples were collected from 39 preterm neonates receiving caffeine (median gestational age 25.6 [range 24.0-28.0] weeks) of which 65 samples were taken during co-treatment with doxapram (39%, from 32/39 infants). Clearance of caffeine was 9.99 mL/h for a typical preterm neonate with a birth weight of 0.8 kg and 23 days postnatal age and increased with birth weight and postnatal age, resulting in a 4-fold increase in clearance during the first month of life. No PK interaction between caffeine and doxapram was identified.

DISCUSSION

Caffeine clearance is not affected by concomitant doxapram therapy but shows a rapid maturation with postnatal age. As current guidelines do not adjust the caffeine dose with postnatal age, decreased exposure to caffeine might partly explain the need for doxapram therapy after the first week of life.