17.6 pounds is 8.07 kilograms.
The ordered dose is 160 mg per kilogram, every 4 hours prn.
Therefore, the nurse should give 8.07 x 160 = 1,290.2 mg of the drug.
Since the drug is in a concentration of 160 mg per 5 mls, the nurse should give 1,290.2 / 160 = 8.0625 mls of the drug.
Therefore, the nurse should give 8.0625 mls (or 8 ml) of the drug.