Final answer:
The infant's kidney function significantly affects their physiological response to medications due to the immature state of the kidneys in neonates. This immaturity impacts the excretion of drugs and requires careful consideration when administering medications to ensure safety and efficacy.
Step-by-step explanation:
The factor that can affect an infant's physiological response to medications is the infant's kidney function. The kidneys are critical for filtering blood, maintaining homeostasis, regulating blood pressure, and balancing electrolytes. Since neonatal kidneys are still maturing and are inefficient at concentrating urine, infants' drug clearance can be significantly affected. This immaturity means that infants are unable to remove medicines from their body as effectively as adults can. Consequently, dosage and frequency of medication administration have to be carefully tailored to avoid toxicity and ensure drugs are effective.
In the context of the question specified, the factors such as body surface area, gastrointestinal pH, and liver function also play a role in the way medications are absorbed and processed, but kidney function is particularly significant due to the immature nature of these organs in infants, which can directly influence drug pharmacokinetics. Additionally, the kidneys work in concert with other systems such as the urinary system and the endocrine system, and any damage to these organs can impair the kidney's ability to maintain homeostasis and properly excrete drugs.