H1 antihistamines and benzodiazepines. Pharmacological interactions and their impact on cerebral function

Antihistamines (AH) have been classified into first and second generation according to their pharmacokinetic properties, structural characteristics and adverse effects. The effects on the central nervous system (CNS) are determined basically by their capacity to cross the hematoencephalic barrier and attach to central H1 receptors. Benzodiazepines (BZD) are drugs with effects on the CNS following their union to the specific location of GABA receptors type A. At low doses, the BZD have sedative and anticonvulsive effects, and as the dose increases it leads to sedation, amnesia and finally unconsciousness. Various studies have been made on the possible interaction between the BZD and the AH H1 with special attention to their effect on the CNS. In some cases these were studies to assess the safety of this association and in others, the aim was different: to see if their joint administration gives a better therapeutic result in pathology related with anxiety syndrome or insomnia. In general it can be said that first generation AH interact with the BZD increasing the sedative effects of the latter. However, second generation AH do not increase these sedative effects, which makes them the chosen drugs to treat allergic rhinitis/rhino-conjunctivitis and urticaria in patients also receiving BZD.