Example of non sedating antihistamine
General practitioners are also asked to indicate whether the event was considered to be related to the drug, although they are not required to make this connection.
Additionally, the prescribers are asked to indicate whether the drug has been stopped and, if so, the reason for this.
Main outcome measure: Reporting of sedation or drowsiness.
Results: The odds ratios (adjusted for age and sex) for the incidence of sedation were 0.63 (95% confidence interval 0.36 to 1.11; P=0.1) for fexofenadine; 2.79 (1.69 to 4.58; P Antihistamines are often used to treat the symptoms of allergies such as seasonal and perennial allergic rhinitis and urticaria.
The first generation antihistamines have been associated with side effects, particularly sedation.1 Second generation antihistamines are therefore favoured over the first generation drugs, not because of greatly improved efficacy but because they have fewer side effects, especially sedation.24 Although the second generation antihistamines are known to all have similar efficacy,3 the extent of their sedative effects is not well established.
To further examine the sedative effects of four commonly prescribed antihistamines—loratadine, cetirizine, fexofenadine, and acrivastine—we analysed the results of four non-interventional observational cohort studies of these drugs performed by the Drug Safety Research Unit.
It has been recognised for over 30 years that drug safety depends not only on preclinical studies but also on post-marketing surveillance.6 Post-marketing prescription-event monitoring studies observe large cohorts and aim to provide data on around 10 000 patients for each drug.
The response rates (number of green forms returned/number of green form sent) were 50.7% for loratadine, 50.9% for fexofenadine, 56.5% for acrivastine, and 57.4% for cetirizine.Incidence densities were calculated for all of the events reported, to give an indication of which events were reported significantly more frequently in the first month of exposure.We calculated non-adjusted and age and sex adjusted odds ratios for drowsiness or sedation for fexofenadine, cetirizine, and acrivastine using loratadine as baseline.The methods of prescription-event monitoring have been previously described in detail.5 In brief, the general practitioner writes a prescription which the patient takes to the pharmacist.The pharmacist sends all these prescriptions to the Prescription Pricing Authority, which under conditions of full confidentiality, provides electronic copies of the exposure data to the Drug Safety Research Unit.