Fentanyl is an opioid drug used as analgesic and anaesthetic also in Neonatal Intensive Care Units (NICU), according to the last national and international recommendations, during invasive life support strategies such as mechanical ventilation. Opioids manifest their sedative effect through activation of μ-opioid receptors, which are abundant both in the central and peripheral nervous system. Comparing fentanyl to morphine we can appreciate a much more powerful effect (75-220 major) with lower doses to obtain similar analgesic effect; these characteristics are due to the high lipophilicity of the molecule which easily crosses the blood-brain barrier (BBB). At the same time, fentanyl shows less adverse effects than morphine such as vomiting, nausea, gastrointestinal constipation, respiratory depression, dependence and tolerance. The drug is extensively metabolized by liver enzymes.

In routinary clinical practice it has been observed that large interindividual differences are found in the daily dosages needed to achieve pain control. Literature evidences that pharmacodynamic variation related to genotypes in receptor signalling or pain modulators may play an important role in this variability. Many genes are related to fentanyl pharmacodynamics and pharmacokinetics. Some polymorphism in these genes are already known to correlate with toxicity or efficacy of the drug, also in the paediatric population. More polymorphisms could be involved in abnormal pharmacodynamic or pharmacokinetics of fentanyl, therefore studies are necessary to better explain the possible role of pharmacogenetics in precision medicine especially in a very specific population as newborn.

Inclusion Criteria:

1. all newborns on mechanical ventilation receiving fentanyl
2. parental written informed consent for participation in the study must be obtained

Exclusion Criteria:

1. Concurrent or previous opioid and/or midazolam administration (72 h interval required)
2. Known genetic or chromosomal anomaly
3. Probable rapid extubation

All newborns admitted in NICU and mechanically ventilated (MV) who received fentanyl administration for procedural pain.