A 32-year-old woman was diagnosed with schizophrenia approximately 4 years ago. She has been stable on haloperidol for 1 year, following trials with several atypical antipsychotics. Two weeks ago, she began exhibiting mild pseudo-Parkinson's disease symptoms. Because she did not achieve symptom control on so many medications, the PMHNP is reluctant to discontinue the haloperidol and instead chooses to treat the side effect. Which class of medications is the most appropriate for treating these side effects?