Biperiden HCl is an anticholinergic drug [1].
As an anticholinergic drug, biperiden is first used in the treatment of Parkinson's disease. It is a competitive antagonist of muscarinic receptor. It has been believed that in the patients of PD, a reduction of intranigral dopamine concentrations results in a relative imbalance between the dopaminergic and cholinergic neurological pathways. The anticholinergics can correct the imbalance through reducing the degree of neurotransmission mediated by neostriatal acetylcholine. Biperiden is also used to treat extrapyramidal side effects of antipsychotic drugs. In addition, the misuse of biperiden causing delirium has been reported in several clinical settings [1, 2].
References:
[1] Brocks D R. Anticholinergic drugs used in Parkinson’s disease: an overlooked class of drugs from a pharmacokinetic perspective. J Pharm Pharm Sci, 1999, 2(2): 39-46.
[2] Espi Martinez F, Espi Forcen F, Shapov A, et al. Biperiden Dependence: Case Report and Literature Review. Case reports in psychiatry, 2012, 2012.