Final answer:
Increased toxicity risk from bupivacaine injection in neonates is primarily due to decreased alpha1 acid-glycoprotein, along with immature blood-brain barrier and decreased hepatic clearance.
Step-by-step explanation:
The increased risk of toxicity in a 2-week old neonate inadvertently injected with bupivacaine compared to an adult is primarily due to decreased alpha1 acid-glycoprotein. Neonates have lower levels of plasma proteins, including alpha1 acid-glycoprotein, which binds to local anesthetics like bupivacaine. This reduced protein binding leads to a higher free concentration of the drug in plasma, increasing the risk of systemic toxicity. Additionally, neonates have an immature blood-brain barrier, which allows easier penetration of drugs compared to adults. Furthermore, decreased hepatic clearance in neonates also contributes to the heightened risk of bupivacaine toxicity because their liver enzymes are not fully developed, limiting the metabolism and clearance of the drug from their system.