-Tinnitus Trough and peak levels that exceed the expected reference range indicate toxicity, with manifestations that include nausea, vertigo, unsteadiness, and tinnitus. These are signs of ototoxicity, which is generally irreversible. -Persistent headache Trough and peak levels that exceed the expected reference range indicate toxicity, with manifestations that include nausea, vertigo, unsteadiness, and a persistent headache. These are signs of ototoxicity, which is generally irreversible. |