Blood-Brain Barrier Permeation and Efflux Exclusion of Anticholinergics Used in the Treatment of Overactive Bladder

• Published in: Drugs & aging 2012-04, Vol.29 (4), p.259-273
• Main Authors: Chancellor, Michael B., Staskin, David R., Kay, Gary G., Sandage, Bobby W., Oefelein, Michael G., Tsao, Jack W.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Biological Transport - drug effects; Bladder; Blood-brain barrier; Blood-Brain Barrier - drug effects; Blood-Brain Barrier - metabolism; Brain; Cerebrospinal fluid; Chemical Phenomena; Cholinergic Antagonists - adverse effects; Cholinergic Antagonists - chemistry; Cholinergic Antagonists - metabolism; Cholinergic Antagonists - therapeutic use; Cognitive ability; Constipation; Geriatrics/Gerontology; Humans; Internal Medicine; Medical sciences; Medicine; Medicine & Public Health; Nephrology. Urinary tract diseases; Nervous system; Older people; Permeability; Pharmacology. Drug treatments; Pharmacology/Toxicology; Pharmacotherapy; Review Article; Urinary Bladder, Overactive - drug therapy; Urinary Bladder, Overactive - metabolism; Urinary system involvement in other diseases. Miscellaneous; Urinary tract. Prostate gland
• ISSN: 1170-229X; 1179-1969
• DOI: 10.2165/11597530-000000000-00000

Overactive bladder (OAB) is a common condition, particularly in the elderly. Anticholinergic agents are the mainstay of pharmacological treatment of OAB; however, many anticholinergics can cross the blood-brain barrier (BBB) and may cause central nervous system (CNS) effects, including cognitive deficits, which can be especially detrimental in older patients. Many anticholinergics have the potential to cause adverse CNS effects due to muscarinic (M 1 ) receptor binding in the brain. Of note, permeability of the BBB increases with age and can also be affected by trauma, stress, and some diseases and medications. Passive crossing of a molecule across the BBB into the brain is dependent upon its physicochemical properties. Molecular characteristics that hinder passive BBB penetration include a large molecular size, positive or negative ionic charge at physiological pH, and a hydrophilic structure. Active transport across the BBB is dependent upon protein-mediated transporter systems, such as that of permeability-glycoprotein (P-gp), which occurs only for P-gp substrates, such as trospium chloride, darifenacin and fesoterodine. Reliance on active transport can be problematic since genetic polymorphisms of P-gp exist, and many commonly used drugs and even some foods are P-gp inhibitors or are substrates themselves and, due to competition, can reduce the amount of the drug that is actively transported out of the CNS. Therefore, for drugs that are preferred not to cross into the CNS, such as potent anticholinergics intended for the bladder, it is optimal to have minimal passive crossing of the BBB, although it may also be beneficial for the drug to be a substrate for an active efflux transport system. Anticholinergics demonstrate different propensities to cross the BBB. Darifenacin, fesoterodine and trospium chloride are substrates for P-gp and, therefore, are actively transported away from the brain. In addition, trospium chloride has not been detected in cerebrospinal fluid assays and does not appear to have significant CNS penetration. This article reviews the properties of anticholinergics that affect BBB penetration and active transport out of the CNS, discusses issues of increased BBB permeability in patients with OAB, and examines the clinical implications of BBB penetration on adverse events associated with anticholinergics.