On May 15, 2007, news outlets all over the world reported results from a recent clinical trial on the effects of Coenzyme Q10 (CoQ10) in Parkinson's disease. Specifically, researchers found that CoQ10 does not exert a beneficial effect on PD symptoms. This information may seem surprising in light of the results of an earlier Phase II clinical trial suggesting that CoQ10 slowed functional decline in Parkinson's, which has prompted the National Institute of Neurological Disorders and Stroke (NINDS) to support a Phase III trial (the “QE3 Trial”).

As a service to its constituents seeking more information on these seemingly contradictory results, The Michael J. Fox Foundation offers the following Q&A with Brian Fiske, PhD, associate director of research programs.

Q: What is the difference between the earlier trial and this one?

BF: The earlier phase II trial of CoQ10 was looking for possible effects of the drug on slowing disease progression. It tested several doses of drug (300mg, 600mg and 1200mg) in patients with relatively early PD who had not yet begun levodopa therapy. They were followed for up to 16 months or until they developed enough disability to require initiation of levodopa. Results of that trial demonstrated that CoQ10, in particular the 1200mg dose, reduced the amount of disability that developed in patients over the study period. Although the evidence was not definitive, the authors suggested that CoQ10 might be slowing the progression of the disease.

The new trial had a slightly different goal: to determine whether CoQ10 had any effect specifically on PD symptoms (a “symptomatic” effect). The study looked at patients with later-stage PD who were already on levodopa therapy to see if CoQ10 had any benefit on symptoms. They used a slightly different formulation of CoQ10 at a dose estimated to be similar to the 1200mg dose of the earlier study. They also followed the patients only for three months. 

Q: Any particular reason for the differences?

BF: The authors of the new trial wondered if some of the benefit seen in the earlier trial could have been due to a symptomatic effect. This was particularly important because much of the benefit previously seen related to improvements in patients’ activities of daily living (one of the clinical outcome measures used in PD trials) and not really in motor symptoms. Thus, they surmised that CoQ10 could be having a general functional or anti-depressive effect in patients rather than an effect on the underlying disease process itself. 

They designed their trial to test this hypothesis, and in fact the results suggest that CoQ10 does not have any major short-term impact on symptoms relative to placebo. This does not rule out the possibility of a protective effect of CoQ10 over the long term, which is what the QE3 trial will look at.

Q: So we may still learn that CoQ10 exerts a protective effect?

BF: Yes, that remains a possibility. The results reported this week are not negative findings about possible protective or disease-modifying effects of CoQ10. If anything, they may suggest that any benefit seen in QE3 could be a protective effect of some kind because we now know that CoQ10 does not have any obvious symptomatic effects.