Final answer:
In monitoring an infant for gentamicin toxicity, the nurse should first check the blood urea nitrogen levels to assess renal function, as gentamicin can cause kidney damage.
Step-by-step explanation:
When monitoring an 8 month-old infant receiving gentamicin (Cidomycin) for drug toxicity, the nurse should primarily review the blood urea nitrogen (BUN) levels. Gentamicin is known to potentially cause nephrotoxicity (kidney damage), hence checking renal function is crucial. Assessing BUN and plasma creatinine levels provides valuable information about the kidneys' ability to filter waste from the blood and maintain proper electrolyte balance.
Normal BUN levels range from 8-20 mg/dl and plasma creatinine levels for infants should be lower than those for adults, around 0.2-0.4 mg/dl. If these levels are elevated, it could suggest renal impairment possibly due to gentamicin toxicity. The nurse should observe for signs of toxicity and report any abnormal findings to the physician immediately for further management.