A patient with a severe infection is given gentamicin, the only antibiotic shown to be effective in culture and sensitivity tests. A few hours after the drug is started intravenously, the patient becomes very restless and develops edema. Blood tests reveal abnormal electrolytes and elevated blood urea nitrogen. This reaction was most likely caused by 

a. An anaphylactic reaction. 

b. Renal toxicity associated with gentamicin. 

c. Superinfection related to the antibiotic. 

d. Hypoglycemia.