Fetal and neonatal rats paracetamol dosage and the perinatal human setting: Lost in translation?

Interleukin-1β-induced inflammation and acetaminophen during infancy: Distinct and interactive effects on social-emotional and repetitive behavior in C57BL/6J mice

Acetaminophen (APAP) exposure early in life has been associated with increased risk of neurodevelopmental disorders in epidemiological studies. In rodent models, early-life APAP has similarly been shown to produce long-term changes in brain and behavior, including altered activity levels and social behavior. Most rodent studies to date have, nevertheless, attempted to model early-life APAP without considering that most APAP exposure occurs in a context of immune activation and/or fever. To mimic the repeated infections common during infancy, we employed the cytokine interleukin-1β (IL-1β) to induce immune activation three times during early postnatal development (i.e., day 5, 8, and 11). On these days, C57BL/6J pups were administered either IL-1β (0.2 μg/kg) or saline vehicle followed, after 45 min, by either APAP (103.9 mg/kg) or vehicle. Mice were subsequently administered a battery of tests of social-emotional and repetitive behavior. A number of distinct long-term effects of IL-1β and APAP treatments were found, including sex-specific shifts in repetitive behavior and emotional hyperthermia following early-life IL-1β and increased social caution in males following early-life APAP. We also observed significant interaction between IL-1β and APAP: as adults, 'two-hit' IL-1β + APAP females displayed greater anxiety-related thigmotaxis across a number of tests, including an open field. 'Two hit' males, in turn, showed elevated levels of avoidance of an unfamiliar social partner during a social interaction test. Our results highlight that IL-1β-induced inflammation and APAP have both distinct effects and significant interactions during early life, with enduring sex-specific effects on phenotypes relevant to neurodevelopmental disorders.

Paracetamol (Acetaminophen) and its Effect on the Developing Mouse Brain

Paracetamol, or acetaminophen (AAP), is the most commonly used analgesic during pregnancy and early life. While therapeutic doses of AAP are considered harmless during these periods, recent findings in both humans and rodents suggest a link between developmental exposure to AAP and behavioral consequences later in life. The aim of this study is to evaluate the impact of neonatal exposure to clinically relevant doses of AAP on adult spontaneous behavior, habituation, memory, learning, and cognitive flexibility later in life using a mouse model. Markers of oxidative stress, axon outgrowth, and glutamatergic transmission were also investigated in the hippocampus during the first 24 h after exposure. In addition, potential long-term effects on synaptic density in the hippocampus have been investigated. In a home cage setting, mice neonatally exposed to AAP (30 + 30 mg/kg, 4 h apart) on postnatal day 10 displayed altered spontaneous behavior and changed habituation patterns later in life compared to controls. These mice also displayed reduced memory, learning and cognitive flexibility compared to control animals in the Morris water maze. An increase of markers for oxidative stress was observed in the hippocampus 6 h after AAP exposure. As AAP is the first choice treatment for pain and/or fever during pregnancy and early life, these results may be of great importance for risk assessment. Here we show that AAP can have persistent negative effects on brain development and suggest that AAP, despite the relatively low doses, is capable to induce acute oxidative stress in the hippocampus.

Narcotic-Sparing Approaches and the Shift Toward Paracetamol in Neonatal Intensive Care

Effective analgesia in neonates is relevant not only because of ethical aspects or empathy, but it is a crucial and integral part of medical and nursing care. However, there is also emerging evidence - although mainly in animal models - on the relation between the exposure to narcotics and impaired neurodevelopmental outcome, resulting in a CATCH-22 scenario. Consequently, a balanced approach is needed with the overarching intention to attain adequate pain management with minimal side effects. Despite the available evidence-based guidance on narcotics in ventilated neonates, observations on drug utilization still suggest an overall increase in exposure with extensive variability between units. This increased exposure over time and the extensive variability is concerning given the limited evidence of benefits and potential harm.Implementation strategies are effective to reduce exposure to narcotics but result in increased paracetamol exposure. We therefore summarized the evidence on paracetamol use in procedural pain management, in minor to moderate as well as major pain syndromes in neonates. While there are sufficient data on short-term safety, there are still concerns on long-term side effects. These concerns relate to neurobehavioral outcome, atopy or fertility, and are at present mainly driven by epidemiological perinatal observations, together with postulated mechanisms.We conclude that future clinical research objectives should still focus on the need to develop better assessment tools to quantify pain and on the need for high-quality data on long-term outcome of therapeutic interventions - also for paracetamol - and exploration of the mechanisms involved.