NeoFent-I Study; Fentanyl Treatment in Newborn Infants; a Pharmacokinetic, Pharmacodynamic and Pharmacogenetic Study

Inclusion Criteria: * Clinical indication for analgesia before any of following procedures; 1. insertion of peripheral IV-catheter 2. insertion of arterial cannula 3. insertion of chest tube 4. other skin breaking procedure. * Possibility to obtain blood samle after the procedure (indwelling line) * Infants all gestational ages. * Postnatal age 0-28 days * Informed written parental concent Exclusion Criteria: * Concurrent or previous opioid administration (72 h interval required) * Abdominal surgery * Major chromosomal anomaly * Neonatal encephalopathy * Use of muscle relaxant * Hypothermia treatment after hypoxic-ischemic insult * Clinical or biochemical evidence of hepatic failure * Participation in other intervention trial