Comparison of diphenhydramine and modafinil on arousal and autonomic functions in healthy volunteers.
Arousal is regulated by the interplay between wakefulness- and sleep-promoting nuclei. Major wakefulness-promoting nuclei are the histaminergic tuberomamillary nucleus (TMN) of the hypothalamus and the noradrenergic locus coeruleus (LC) of the pons, which also play a role in autonomic regulation. First generation antihistamines, such as diphenhydramine, are likely to cause sedation by blocking excitatory H1 histamine receptors in the cerebral cortex, and the anti-narcolepsy drug modafinil may promote wakefulness by activating the locus coeruleus. We compared the effects of single doses of diphenhydramine (75 mg) and modafinil (200 mg) on arousal and autonomic functions in 16 healthy male volunteers, using a placebo-controlled, balanced, double-blind design. Arousal was assessed by critical flicker fusion frequency (CFFF), visual analogue scales (VAS) and pupillary fatigue waves (Pupillographic Sleepiness Test (PST)). Autonomic functions measured included resting pupil diameter, light and darkness reflex responses, blood pressure, heart rate and salivation. Data were analysed with ANOVA, with multiple comparisons. Diphenhydramine had sedative effects as shown by reductions in CFFF, VAS alertness ratings and increases of the indices of pupillary fatigue. Modafinil had alerting effects as indicated by reductions in the measures of pupillary fatigue. Comparison of pre-post medication changes in pupil diameter showed a decrease after diphenhydramine and an increase after modafinil. Diphenhydramine reduced salivation, and modafinil increased systolic blood pressure. In conclusion, diphenhydramine and modafinil evoked opposite effects on arousal and sympathetic functions, which are likely to reflect their interaction with the central histaminergic and noradrenergic systems. Hyposalivation by diphenhydramine is likely to be due to its additional anticholinergic property.
Hou
R H
RH
Psychopharmacology Section, Division of Psychiatry, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, UK.
Langley
R W
RW
Szabadi
E
E
Bradshaw
C M
CM
D000284:Administration, Oral; D000328:Adult; D000339:Affect / Q000187:drug effects; D001143:Arousal / Q000187:drug effects*; D001288:Attention / Q000187:drug effects; D001341:Autonomic Nervous System / Q000187:drug effects*; D001559:Benzhydryl Compounds / Q000008:administration & dosage / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000494:pharmacology*; D018592:Cross-Over Studies; D004155:Diphenhydramine / Q000008:administration & dosage / Q000494:pharmacology*; D004311:Double-Blind Method; D005425:Flicker Fusion / Q000187:drug effects; D006634:Histamine H1 Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D008297:Male; D000077408:Modafinil; D012016:Reference Values; D012025:Reflex, Pupillary / Q000187:drug effects; D012472:Salivation / Q000187:drug effects
D001559:Benzhydryl Compounds; D000697:Central Nervous System Stimulants; D006634:Histamine H1 Antagonists; D004155:Diphenhydramine; D000077408:Modafinil