Brain histamine H1 receptor occupancy of orally administered antihistamines, bepotastine and diphenhydramine, measured by PET with 11C-doxepin
Article first published online: 11 APR 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
British Journal of Clinical Pharmacology
Volume 65, Issue 6, pages 811–821, June 2008
How to Cite
Tashiro, M., Duan, X., Kato, M., Miyake, M., Watanuki, S., Ishikawa, Y., Funaki, Y., Iwata, R., Itoh, M. and Yanai, K. (2008), Brain histamine H1 receptor occupancy of orally administered antihistamines, bepotastine and diphenhydramine, measured by PET with 11C-doxepin. British Journal of Clinical Pharmacology, 65: 811–821. doi: 10.1111/j.1365-2125.2008.03143.x
- Issue published online: 11 APR 2008
- Article first published online: 11 APR 2008
- Received 3 April 2007Accepted17 January 2008
- first-generation antihistamine;
- histamine H1 receptor occupancy;
- placebo-controlled crossover study design;
- positron emission tomography;
- second-generation antihistamine
WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT
• ‘Bepotastine besilate’ is a novel second-generation antihistamine developed in Japan and its antiallergic effects have already been demonstrated by various studies.
• However, only a few clinical studies regarding its sedative property are available.
• In addition, histamine H1 receptor occupancy (H1RO) of this new antihistamine has never been measured by positron emission tomography (PET).
WHAT THIS STUDY ADDS
• This paper provides the first measurement result of cerebral H1RO of bepotastine besilate (approximately 15%) as determined by PET.
• This result is in accordance with the clinical classification of bepotastine as a second-generation antihistamine.
• In addition, the relationship between subjective sleepiness and cerebral H1RO of this second-generation antihistamine is demonstrated for the first time using a placebo-controlled crossover study design.
Antihistamines are frequently used for treating various allergic diseases, but often induce sedation. The degree of sedation can be evaluated by measuring histamine H1 receptor occupancy (H1RO) in the brain using positron emission tomography (PET). The aim was to measure H1RO of bepotastine, a new second-generation antihistamine, and to compare it with that of diphenhydramine.
Eight healthy male volunteers (mean age ± SD 24.4 ± 3.3 years) were studied after single oral administration of bepotastine (10 mg), diphenhydramine (30 mg) or placebo, by PET imaging with 11C-doxepin in a crossover study design. Binding potential ratio and H1ROs were calculated using placebo data and were compared between bepotastine and diphenhydramine in the anterior and posterior cingulate gyri (ACG and PCG, respectively), superior and inferior frontal cortices (SFC and IFC, respectively), orbitofrontal cortex (OFC), insular cortex (IC), lateral and medial temporal cortices (LTC and MTC, respectively), parietal cortex (PC), occipital cortex (OC) and sensorimotor cortex (SMC). Plasma concentration of each antihistamine was measured, and its correlation to H1RO was examined.
H1RO after bepotastine treatment was significantly lower than that after diphenhydramine treatment in all cortical regions (P < 0.001). Mean H1ROs of bepotastine and diphenhydramine were 14.7% and 56.4%, respectively. H1ROs of both bepotastine and diphenhydramine correlated to their respective drug plasma concentration (P < 0.001).
Oral bepotastine (10 mg), with its relatively low H1RO and thus minimal sedation, has the potential for use as a mildly or slightly sedative antihistamine in the treatment of various allergic disorders.