Final answer:
Newborns are most at risk for drug interaction because of their immature renal function, which is still developing and can't efficiently concentrate urine.
Step-by-step explanation:
Newborns are most at risk for drug interaction because of their immature renal function. During fetal development, the kidneys begin to function by filtering blood and producing urine, but after birth, the neonatal kidneys are still developing and have a reduced ability to concentrate urine efficiently. Consequently, newborns produce very dilute urine necessitating the need for adequate hydration through breast milk or formula.
Factors such as homeostatic imbalances, an Apgar score assessment immediately after birth, and the presence of teratogens like prescription medicines can influence the health and development of a newborn.
Other aspects such as the size of the skull due to fontanelles, which allow for growth and ease during birth, and the differences in fetal hemoglobin, do not directly contribute to the increased risk of drug interactions as does the neonate's renal function.