What patient feature causes a concern for renal injury when administering IV acyclovir too rapidly?

When administering intravenous acyclovir, a rapid infusion rate can lead to renal injury due to precipitation of the drug in the renal tubules, which can cause crystal nephropathy. Acyclovir is eliminated primarily through the kidneys, and if the drug is infused too quickly, especially in the context of dehydration or pre-existing renal impairment, it can exceed the solubility limit in the renal tubules. This leads to the formation of crystals, which can occlude the tubules and result in acute kidney injury.

It is essential to administer acyclovir at an appropriate rate and to maintain adequate hydration in patients receiving this medication to reduce the risk of nephrotoxicity. This is why the infusion rate is the feature of concern regarding renal injury when administering IV acyclovir.