Sedation Without Somnolence with Antihistamines


Am Fam Physician. 2004 Jun 15;69(12):2906.

Clinical Question: Does cetirizine cause sedation that is unnoticed by children?

Setting: Outpatient (specialty)

Study Design: Crossover trial (randomized)

Synopsis: Sedation results in slower reaction times and impaired performance in activities that require diligent attention. Drowsiness is the subjective feeling of being tired. The two are not always connected; sedation can occur without drowsiness, and vice versa. Cetirizine has been shown not to have a sedative effect in adults, but it had not been studied in children. This study included 24 children (14 boys, 10 girls) with allergic rhinitis who were not taking medications that could affect central nervous system function.

In a research setting, the children were given a single dose of placebo, cetirizine, or chlorpheniramine in a randomized fashion. In succesive weeks, they were given the second and third options, so each child served as his or her own control subject. Sedation was measured before each dose and two hours after the dose using the P300 event-related potential neuropsychologic test. This test measures changes in brain waves and response time when the child is presented with different auditory stimuli. Drowsiness was measured using a 10-cm visual analog scale ranging from “wide awake” to “cannot stay awake.”

Compared with baseline, a significant delay in auditory response occurred when the children children received chlorpheniramine (P <.05) or cetirizine (P <.05). Chlorpheniramine has been documented to cause sedation; it was included in this study to serve as a positive control to ensure sensitivity of the outcome measures. The placebo group experienced no change. A change of at least 5 percent (a clinically relevant change) occurred in one in three of the children when they received cetirizine. However, subjective feelings of drowsiness were not significantly different in any of the groups.

Bottom Line: Some antihistamines can cause sedation without causing a subjective feeling of drowsiness. Compared with placebo, cetirizine causes changes in response time, a measure of sedation, in children. However, subjective feelings of drowsiness are not reported by those children. Although not evaluated in this study, sedation may affect learning ability. (Level of Evidence: 1c)


Ng KH, et al. Central nervous system side effects of first- and second-generation antihistamines in school children with perennial allergic rhinitis: a randomized, doubleblind, placebo-controlled comparative study. Pediatrics. February 2004;113:e116–21.

Used with permission from Shaughnessy AF. Sedation without somnolence with antihistamines. Accessed online March 29, 2004, at: http://www.InfoPOEMs.com.



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