PubMed · 9614025
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B Sibbald, C Roberts. 1998-06-06. Understanding controlled trials. Crossover trials.. https://doi.org/10.1136/bmj.316.7146.1719
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PURPOSE: Sildenafil is the first member of a new class of oral drugs effective for erectile dysfunction. However, approximately 20% of patients complain about nasal congestion after sildenafil administration. MATERIALS AND METHODS: Because nasal airflow and olfaction are closely linked, the sense of smell was evaluated in 20 young, healthy volunteers after the administration of 50 and 100 mg sildenafil, and placebo in a double-blinded, crossover study. Olfactory function was evaluated using a standardized and validated test (Sniffin' Sticks). To investigate a possible impact of G-protein beta3 subunit C825T polymorphism on the effect of sildenafil on olfaction the genotype of all subjects was determined. RESULTS: The effect of sildenafil on olfaction was only present at a dose of 100 mg but not at a dose of 50 mg sildenafil. The genotypes TT, CC and TC of the G-protein beta3 C825T polymorphism had no impact on the change in olfactory function. CONCLUSIONS: Higher sildenafil doses may produce decreased olfactory sensitivity.
The randomised experiment in a single patient, the N-of-1 trial, is the best study design for demonstrating causality, for example between agent and effect. Despite this, this type of study is only encountered sporadically in medical journals. One reason for this is that even this type of design cannot definitively demonstrate causality, because different points in time are compared with one another. Moreover, the design is rather inefficient, since the results correspond with those from observation without randomisation, placebo control or blinding. Even so, the N-of-1 trial is the ultimate form of verification in, for example, the individualisation of treatment. For this reason, this form of study might be used more often.
OBJECTIVE: To determine whether there was a connection between the complaint of restless legs and the ingestion of artificial sweeteners in a patient with these symptoms after drinking certain 'light' beverages. DESIGN: Randomised, double-blind, placebo-controlled N-of-1 trial with a cross-over design. METHOD: During a period of 48 days, the patient took 4 capsules per day containing either 150 mg of cyclamate, 22.5 mg of saccharine, both sweeteners, or placebo on two successive days. Between each of these 2-day periods there was a 2-day rest period during which no capsules were taken. The hospital pharmacist had prepared the capsules and determined the sequence of the 2-day periods on a random basis. The patient did not know which capsules he was taking. Every day on arising, starting 3 weeks before the trial period, the patient noted the intensity and duration of the symptoms in the late evening and previous night. For this notation he used an 11-point scale, from 0 (= no restless legs) to 10 (= almost total inability to sleep because of restless legs). RESULTS: A score of 1-3 corresponded to mild symptoms that had no effect on the patient's sleep; at a score of 4-6 his sleep was disturbed and at a score of 7-10 the patient hardly slept at all. The patient had symptoms more often while using saccharine or the combination of saccharine and cyclamate than when taking the placebo (4 and 4 versus 2 ofthe 6 nights); moreover, the average score was then statistically significantly higher (5.2 and 5.8 versus 3.3). CONCLUSION: There was a connection between the patient's complaints of restless legs and the use of saccharine, but not the use of cyclamate.