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1.  Alzheimer’s disease drug-development pipeline: few candidates, frequent failures 
Introduction
Alzheimer’s disease (AD) is increasing in frequency as the global population ages. Five drugs are approved for treatment of AD, including four cholinesterase inhibitors and an N-methyl-D-aspartate (NMDA)-receptor antagonist. We have an urgent need to find new therapies for AD.
Methods
We examined Clinicaltrials.gov, a public website that records ongoing clinical trials. We examined the decade of 2002 to 2012, to better understand AD-drug development. We reviewed trials by sponsor, sites, drug mechanism of action, duration, number of patients required, and rate of success in terms of advancement from one phase to the next. We also reviewed the current AD therapy pipeline.
Results
During the 2002 to 2012 observation period, 413 AD trials were performed: 124 Phase 1 trials, 206 Phase 2 trials, and 83 Phase 3 trials. Seventy-eight percent were sponsored by pharmaceutical companies. The United States of America (U.S.) remains the single world region with the greatest number of trials; cumulatively, more non-U.S. than U.S. trials are performed. The largest number of registered trials addressed symptomatic agents aimed at improving cognition (36.6%), followed by trials of disease-modifying small molecules (35.1%) and trials of disease-modifying immunotherapies (18%). The mean length of trials increases from Phase 2 to Phase 3, and the number of participants in trials increases between Phase 2 and Phase 3. Trials of disease-modifying agents are larger and longer than those for symptomatic agents. A very high attrition rate was found, with an overall success rate during the 2002 to 2012 period of 0.4% (99.6% failure).
Conclusions
The Clinicaltrials.gov database demonstrates that relatively few clinical trials are undertaken for AD therapeutics, considering the magnitude of the problem. The success rate for advancing from one phase to another is low, and the number of compounds progressing to regulatory review is among the lowest found in any therapeutic area. The AD drug-development ecosystem requires support.
doi:10.1186/alzrt269
PMCID: PMC4095696  PMID: 25024750
2.  Advances in designs for Alzheimer’s disease clinical trials 
There is an urgent need to identify new treatments for the rapidly growing population of people with Alzheimer’s disease (AD). Innovations in clinical trial designs many help to reduce development time, provide more definitive answers regarding drug efficacy, and facilitate prioritizing compounds to be advanced to Phase III clinical trials. Standard designs compare drug and placebo changes from baseline on a rating scale. Baysian adaptive clinical trials allow the use of data collected in the trial to modify doses, sample size, trial duration, and entry criteria in an ongoing way as the data are collected. Disease-modification is supported by findings on staggered start and delayed withdrawal designs. Futility designs can use historical controls and may shorten trial duration. Combination therapy designs may allow investigation of additive or synergistic treatment effects. Novel trial selection criteria allow investigation of treatment effects in asymptomatic or minimally symptomatic, prodromal AD populations. The Clinical Dementia Rating-Sum of Boxes (CDR-SOB) can be considered as a single trial outcome in early disease populations. Alternate forms of the Alzheimer’s Disease Assessment Scale-Cognitive Portion (ADAS-cog), computerized measures, and pharmacoeconomic scales provide new and relevant information on drug effects. Comparative dose strategies are used in trials of symptomatic agents, and novel methods including withdrawal designs, symptom emergence analyses, and sequential designs are being utilized to assess the efficacy of putative psychotropic agents. The choice of trial design is driven by the question to be answered by the clinical trial; an increasing number of design approaches are available and may be useful in accelerating and refining AD drug development.
PMCID: PMC3560467  PMID: 23383393
Clinical trials; Alzheimer’s disease; designs; drug development
3.  Globalization of Alzheimer's disease clinical trials 
Alzheimer's disease (AD) therapies are increasingly being tested in global clinical trials. A search of ClincalTrials.gov revealed that of 269 currently active trials, 28% are currently being conducted in the United States; the majority of trials and the majority of trial sites are ex-US. The US has the largest number of trial sites of any single country; cumulatively, nearly half of all sites are outside the US. The US conducts more trials in all phases of drug development but has a greater proportion of phase 3 trials. The increasing importance of global participants in clinical trials emphasizes the importance of considering the ethnic and international factors that may influence trial outcome. The International Conference on Harmonization guidelines divide ethnic factors that may affect drug development into intrinsic and extrinsic influences. These include language, cultural factors, educational levels, the general level of health and standard of care, as well as nutrition and diet. Ethnic influences on pharmacokinetics are known for some metabolic pathways. The biology of AD may also differ among the world's populations. The frequency of the apolipoprotein e4 allele, a major risk factor for AD, differs internationally. Genetic variations might also affect inflammatory, excitotoxic, and oxidative components of AD. Diagnostic standards and experience vary from country to country. Levels of practitioner training and experience, diagnostic approaches to AD, and attitudes regarding aging and AD may differ. Experience and sophistication with regard to clinical trial conduct also vary within and between countries. Experience with conducting the necessary examinations, as well as the linguistic and cultural validity of instrument translations, may affect trial outcomes. Operational and regulatory aspects of clinical trials vary and provide important barriers to seamless conduct of multiregional clinical trials. Collection and testing of biological samples, continuous provision of drug substance, and protection of the integrity of supply lines may be difficult in some international circumstances. Attention to these potential influences on clinical trials will determine the success of global drug development programs and the utility of global trials for developing new AD therapeutics.
doi:10.1186/alzrt86
PMCID: PMC3226279  PMID: 21861855

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