PRECAUTIONS General Patients with cardiac, liver, or kidney disorders, or with hypertension, should be closely monitored. Since trihexyphenidyl has atropine-like properties, patients on long-term treatment should be carefully monitored for untoward reactions. Since trihexyphenidyl has parasympatholytic activity, it should be used with caution in patients with glaucoma, obstructive disease of the gastrointestinal or genitourinary tracts, and in elderly males with possible prostatic hypertrophy. Incipient glaucoma may be precipitated by parasympatholytic drugs such as trihexyphenidyl. Tardive dyskinesia may appear in some patients on long-term therapy with antipsychotic drugs or may occur after therapy with these drugs has been discontinued. Antiparkinsonism agents do not alleviate the symptoms of tardive dyskinesia, and in some instances may aggravate them. However, parkinsonism and tardive dyskinesia often coexist in patients receiving chronic neuroleptic treatment, and anticholinergic therapy with trihexyphenidyl may relieve some of these parkinsonism symptoms. Trihexyphenidyl is not recommended for use in patients with tardive dyskinesia unless they have concomitant Parkinson's disease. Patients with arteriosclerosis or with a history of idiosyncrasy to other drugs may exhibit reactions of mental confusion, agitation, disturbed behavior, or nausea and vomiting. Such patients should be allowed to develop a tolerance through the initial administration of a small dose and gradual increase in dose until an effective level is reached. If a severe reaction should occur, administration of the drug should be discontinued for a few days and then resumed at a lower dosage. Psychiatric disturbances can result from indiscriminate use (leading to overdosage) to sustain continued euphoria. (See DRUG ABUSE AND DEPENDENCE ). Abrupt withdrawal of treatment for parkinsonism may result in acute exacerbation of parkinsonism symptoms; therefore, abrupt withdrawal should be avoided (See DOSAGE AND ADMINISTRATION ). Information for Patients Trihexyphenidyl may impair mental and/or physical abilities required for performance of hazardous tasks, such as operating machinery or driving a motor vehicle. Patients should be cautioned about operating machinery, including automobiles, until they are reasonably certain that trihexyphenidyl therapy does not adversely affect their ability to engage in such activities. Because of increased sedative effects, patients should be cautioned to avoid the use of alcohol or other CNS depressants while taking trihexyphenidyl. Since this medication may increase the susceptibility to heat stroke (gastrointestinal (GI) problems, fever, heat intolerance), use with caution during hot weather. (See WARNINGS ). Patients should be advised to report the occurrence of GI problems, fever, or heat intolerance promptly since paralytic ileus, hyperthermia, or heat stroke may occur. If GI upset occurs, trihexyphenidyl may be taken with food. Patients should have close monitoring of intraocular pressure. (See WARNINGS ). Drug Interactions Cannabinoids, barbiturates, opiates, and alcohol may have additive effects with trihexyphenidyl, and thus, an abuse potential exists. Concurrent use of alcohol or other CNS depressants with trihexyphenidyl may cause increased sedative effects. Monoamine oxidase inhibitors and tricyclic antidepressants possessing significant anticholinergic activity may intensify the anticholinergic effects of antidyskinetic agents because of the secondary anticholinergic activities of these medications. Prophylactic administration of anticholinergic agents, such as trihexyphenidyl, as a prevention of drug-induced parkinsonism during neuroleptic therapy is not recommended. There may be an increased risk for the development of tardive dyskinesia during concomitant administration of anticholinergics and neuroleptics (See PRECAUTIONS, General ). The usual dose of either trihexyphenidyl or levodopa may need to be reduced during concomitant therapy, since concomitant administration may increase drug-induced involuntary movements (See DOSAGE AND ADMINISTRATION ). Carcinogenesis, Mutagenesis, Impairment of Fertility No carcinogenicity studies or adequate genotoxicity or fertility studies have been conducted for trihexyphenidyl. Pregnancy TERATOGENIC EFFECTS PREGNANCY CATEGORY C Animal reproduction studies to evaluate teratogenic and embryotoxic potential have not been conducted with trihexyphenidyl. It is also not known whether trihexyphenidyl can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Trihexyphenidyl should be given to a pregnant woman only if clearly needed. Nursing Mothers It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when trihexyphenidyl is administered to a nursing woman. As with other anticholinergics, trihexyphenidyl may cause suppression of lactation. Therefore, trihexyphenidyl should only be used if the expected benefit to the mother outweighs the potential risk to the infant. Pediatric Use Safety and effectiveness in pediatric patients have not been established. (See also ADVERSE REACTIONS ). Geriatric Use Sensitivity to the actions of parasympatholytic drugs may increase with age, particularly over the age of 60; therefore, elderly patients generally should be started on low doses of trihexyphenidyl and observed closely. Trihexyphenidyl has been shown to cause some cognitive dysfunctions in the elderly, including confusion and memory impairment. (See ADVERSE REACTIONS and DOSAGE AND ADMINISTRATION ).