Trials of agents with high risk profiles or for which the risk profile is largely unknown often require more visits selleck chemical 17-DMAG to ensure patient safety. For example, early-phase studies (phase I or IIa) are often shorter (on the order of weeks to months) and require more frequent study visits than later-phase studies. Phase II AD trials of gamma secretase inhibitors have commonly used every-other-week study visits [1], making participation more daunting, especially for individuals who travel great distances to participate. In contrast, late-phase studies (phase IIb or III) that aim to evaluate efficacy are commonly at least 18 months long. These trials generally use study visits every 3 months. Less commonly, the intervention itself necessitates a more frequent rate of study visits.

Ongoing trials of some immunotherapies for AD use medication infusions once or twice per month. Selection of the targeted Alzheimer’s disease population The target population is defined by the inclusion and exclusion criteria that participants must meet to enroll. Inclusion criteria should be designed to enroll only patients who truly suffer from AD and to maximize the likelihood of demonstrating a difference between drug and placebo when one exists [2]. Inclusion criteria generally identify a patient population of a specific disease severity. This is most often defined by a range of scores on the Mini-Mental State Examination (MMSE) [3]. Challenges in enrollment are not limited to trials of specific disease severities.

As can be seen in the sample of published AD trials described in Table ?Table1,1, examples of studies with fast rates of enrollment (for example, RR >1) exist for all disease severities. Similarly, slow enrollment can occur in trials in all stages of disease severity. Trials that fail to complete enrollment are also likely to go unpublished, given the probability that they will fail to meet the primary outcome [4]. To be clear, recruitment of participants with more severe disease faces unique challenges in comparison with studies of milder disease. Careful design and unique recruitment Carfilzomib strategies, however, can be undertaken to overcome such challenges [5]. Besides disease severity, other specifications selleck chem Trichostatin A related to the population to be recruited can impact the rate of enrollment. For example, the Alzheimer’s Disease Co-operative Study (ADCS) trial of estrogen replacement enrolled only women who had mild-to-moderate AD and who had undergone hysterectomy. Despite a somewhat wider range of MMSE inclusion criteria (12 to 28) than is typical, this trial enrolled only an average 10 subjects per month across 39 sites, and it took more than 3 years to complete enrollment [6].