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Peripherally selective drugs have their primary mechanism of action outside of the central nervous system (CNS), usually because they are excluded from the CNS by the blood–brain barrier. By being excluded from the CNS, drugs may act on the rest of the body without producing side-effects related to their effects on the brain or spinal cord. For example, most opioids cause sedation when given at a sufficiently high dose, but peripherally selective opioids can act on the rest of the body without entering the brain and are less likely to cause sedation. These peripherally selective opioids can be used as antidiarrheals, for instance loperamide (Imodium).
Mechanisms of peripheral selectivity include physicochemical hydrophilicity and large molecular size, which prevent drug permeation through the lipid bilayer cell membranes of the blood–brain barrier, and efflux out of the brain by blood–brain barrier transporters such as P-glycoprotein among many others. Transport out of the brain by P-glycoprotein is thought to be responsible for the peripheral selectivity of many drugs, including loperamide, domperidone, fexofenadine, bilastine, cetirizine, ivermectin, and dexamethasone, among others.
Entacapone is a potent and specific peripheral catechol-O-methyltransferase inhibitor. [...] Entacapone has no antiparkinsonian activity as a sole agent. Therefore, it must be given as an adjunct to LD and a peripherally acting DDC inhibitor, such as carbidopa. Entacapone acts peripherally and does not penetrate the blood-brain barrier (BBB). [...] It is poorly lipophilic and does not penetrate the BBB to any significant extent. Its clinical effects are thus due to peripheral COMT inhibition only (Nutt, 1998; Fahn et al, 2004). [...] Entacapone is poorly lipophilic. Therefore, its clinical effects are due to peripheral COMT inhibition alone. [...] Entacapone is a potent, specific, and reversible COMT inhibitor. The drug has been shown to act peripherally, but not centrally, when given at clinically effective doses.
{{cite journal}}: CS1 maint: periodical has ISBN (link)Opicapone (OPC) is a novel, long-acting, peripherally selective, once daily, third-generation catechol-O-methyl transferase inhibitor.
The efficacy of tolcapone as an adjunct to levodopa in patients with Parkinson's disease has primarily been attributed to its ability to inhibit peripheral it is thought that tolcapone enters the CNS to a minimal extent only.[16] However, results [17] of a study in patients with Parkinson's disease, as well as results of animal studies,[18-21] suggest that tolcapone also has central activity.
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