Clinical trials parallel groups

Parallel Track Some patients do not fulfill the criteria to be enrolled in clinical trials, but their conditions quahfy them to be treated in parallel with an ongoing chnical trial. AIDS patients are an example for this group. 

The sample size calculation should be detailed in the trial publication, indicating the estimated outcomes in each of the treatment groups (and this will define, in particular, the clinically relevant difference to be detected), the type I error, the type II error or power and, for a continuous primary outcome variable in a parallel group trial, the within-group standard deviation of that measure. For time-to-event data details on clinically relevant difference would usually be specified in terms of the either the median event times or the proportions event-free at a certain time point. 

Gadow et al. (1995), however, found no increase in tics in a placebo-controlled trial of methylphenidate in children with ADHD and a tic disorder. Other trials of stimulants in such children have found little or no average increase in tic severity scores, but clinically significant increases of tics in a handful of subjects severe enough to prompt discontinuation of the stimulant (Castellanos et al., 1997 Law and Schachar, 1999) or to require addition of a medication to control their tic symptoms (Gadow et al., 1999). A multicenter, doubleblind, placebo-controlled, parallel group study of methylphenidate and clonidine, used alone or in combination in 136 children with ADHD and a comorbid... 

Numerous clinical trials have also attested to the anxiolytic efficacy of hydroxyzine. Controlled trials have confirmed its efficacy and safety at a fixed dose of 50 mg in GAD (64). In a double-blind, parallel-group, multicenter study in France and Great Britain, a total of 244 patients with GAD were allocated randomly to treatment with hydroxyzine (12.5 mg t.i.d.), buspirone 5 mg morning and midday and 10 mg in the evening, or placebo. The results showed both hydroxyzine and buspirone to be more efficacious than placebo, indicating that hydroxyzine can be a useful treatment for GAD (65). 

Two common statistical techniques that are typically used to analyze efficacy data in superiority trials are f-tests and ANOVA. In parallel group trials, the independent groups Mest and the independent groups ANOVA discussed in Chapter 7 would be used. Another important aspect of the statistical methodology employed in superiority trials, the use of CIs (confidence intervals) to estimate the clinical significance of a treatment effect, was discussed in Chapter 8. These discussions are not repeated here. Instead, some additional aspects of statistical methodology that are relevant to superiority trials are discussed. 

The simplest and probably most frequently used design for a clinical trial is the parallel-group design. Eligible patients are randomly assigned to receive one and only one of several treatments or treatment regimens. 

Chosidow O, Drouault Y, Leconte-Vavriac F, et al. Famciclovir vs. aciclovir in immunocompetent patients with recurrent genital herpes infections a parallel-groups, randomized, double-blind clinical trial. BrJ Dermatol 2001 144(4) 818-824. 

In a multicenter, double-blind, randomized, parallel-group, placebo-controlled trial in 22 European centers for specialist diabetes care over 6 months, sibutramine, in conjunction with moderate caloric restriction, enabled obese patients with type 2 diabetes taking sulfonylureas to achieve clinically significant weight loss (7). This was... 

The tests for two independent groups are appropriate when separate groups in which the patients have not been matched in pairs have been used in the study, as, for example in a randomised, parallel group clinical trial. 

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