Combination Therapies and the Theoretical Limits of Evidence-Based Medicine

BACKGROUND

Advances in molecular pharmacology and surgical, endovascular, and radiation techniques have yielded multiple effective or promising, and potentially complementary, classes of treatments for virtually every major medical disorder. Consequently, determining the optimum combination of therapies for a condition is a burgeoning challenge to clinical trialists and practicing physicians.

METHODS

General phase III trial strategies for testing combination regimens are described, and then applied to two illustrative conditions, Alzheimer disease and ischemic stroke.

RESULTS

Strategies for testing combination regimens include: head to head trials of all combinations, which lead to unwieldy trial numbers; very large multi-arm trials, which impractically delay interval information on regimen utility; and hierarchical, serial clinical trials. Systematic literature review revealed seven classes of agents already approved or in late phase III testing for preventing the development or slowing the progression of Alzheimer disease and five for ischemic stroke prevention. Possible combination regimens number 128 (2(7)) for Alzheimer disease and 32 (2(5)) for ischemic stroke. Hierarchical, serial clinical trials would permit identification of the optimum combination of these agent classes for Alzheimer disease through 127 trials, enrolling 63,500 patients, requiring 286 years; for ischemic stroke through 31 trials, enrolling 186,000 patients, requiring 155 years.

CONCLUSIONS

Marked limitations in the ability of clinical trials to interrogate varied treatment combinations to determine the most effective ensemble exist, and their scope is widely underappreciated. Steps that may attenuate, though not eliminate, the challenge of a surfeit of combination treatment regimens include preclinical testing to identify the most promising regimens, use of surrogate outcome measures in exploratory clinical trials, and use of hierarchical, serial and factorial phase III trials.

Thrombolytic reversal of acute human cerebral ischemic injury shown by diffusion/perfusion magnetic resonance imaging

Diffusion magnetic resonance imaging provides an early marker of acute cerebral ischemic injury. Thrombolytic reversal of diffusion abnormalities has not previously been demonstrated in humans. Serial diffusion and perfusion imaging studies were acquired in patients experiencing acute hemispheric cerebral ischemia treated with intra-arterial thrombolytic therapy within 6 hours of symptom onset. Seven patients met inclusion criteria of prethrombolysis and postthrombolysis magnetic resonance studies, presence of large artery anterior circulation occlusion at angiography, and achievement of vessel recanalization. Mean diffusion-weighted imaging lesion volume at baseline was 23 cm3 (95% confidence interval [95% CI], 8-38 cm3) and decreased to 10 cm3 (95% CI, 3-17 cm3) 2.5 to 9.5 hours after thrombolysis. Mean apparent diffusion coefficient lesion volume decreased from 9 cm3 (95% CI, 2-16 cm3) at baseline to 1 cm3 (95% CI, 0.4-2 cm3) early after thrombolysis. A secondary increase in diffusion volumes was seen in 3 of 6 patients at day 7. In all 4 patients in whom perfusion imaging was obtained before and after treatment, complete resolution of the perfusion deficit was shown. Diffusion magnetic resonance signatures of early tissue ischemic injury can be reversed in humans by prompt thrombolytic vessel recanalization. The ischemic penumbra includes not only the region of diffusion/perfusion mismatch, but also portions of the region of initial diffusion abnormality.

Cranial computed tomography interpretation in acute stroke: physician accuracy in determining eligibility for thrombolytic therapy

CONTEXT

Intracranial hemorrhage must be excluded prior to administration of thrombolytic agents in acute stroke.

OBJECTIVE

To evaluate physician accuracy in cranial computed tomography scan interpretation for determining eligibility for thrombolytic therapy in acute stroke.

DESIGN

Administration of randomly selected, randomly ordered series of 15 computed tomography scans from a pool of 54 scans that demonstrated intracerebral hemorrhage, acute infarction, intracerebral calcifications (impostor for hemorrhage), old cerebral infarction (impostor for acute infarction), and normal findings.

PARTICIPANTS

A convenience sample of 38 emergency physicians, 29 neurologists, and 36 general radiologists.

MAIN OUTCOME MEASURES

Physician determination of eligibility for thrombolytic therapy based on computed tomography scan interpretation.

RESULTS

Average correct score by all physicians on all computed tomography scans was 77% (95% confidence interval, 74%-80%). Of 569 computed tomography readings by emergency physicians, 67% were correct; of 435 readings by neurologists, 83% were correct; and of 540 readings by radiologists, 83% were correct. Overall sensitivity for detecting hemorrhage was 82% (95% confidence interval, 78%-85%); 17% of emergency physicians, 40% of neurologists, and 52% of radiologists achieved 100% sensitivity for identification of hemorrhage.

CONCLUSION

Physicians in this study did not uniformly achieve a level of sensitivity for identification of intracerebral hemorrhage sufficient to permit safe selection of candidates for thrombolytic therapy.

Multiple cerebral pseudoaneurysms and hemorrhages: the expanding spectrum of metastatic cerebral choriocarcinoma

Cerebral metastases occur in 10-20% of patients with choriocarcinoma. Although single oncotic and pseudoaneurysms have been reported, multiple pseudoaneurysms and hemorrhages are rare. A 33-year-old woman developed 10 intracerebral hemorrhages over a 30-day period. Angiogram showed multiple focal areas of delayed contrast washout in distal vessels. Autopsy revealed intravascular choriocarcinoma without true aneurysm formation. A diagnosis of choriocarcinoma should be considered for women of childbearing age presenting with cerebrovascular syndromes, especially those found to have cerebral aneurysm pseudoaneurysm and/or hemorrhage.

Peripheral measures of arginine vasopressin, atrial natriuretic peptide and adrenocorticotropic hormone in premenstrual syndrome

Because of the unique combination of physical (e.g. bloating, water retention) and psychological (e.g. mood, memory) symptoms associated with premenstrual syndrome (PMS), various hypothalamic and pituitary hormones have been implicated in the pathophysiology of PMS. We measured plasma adrenocorticotropic hormone (ACTH), arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) across the menstrual cycle in 19 women with PMS and 12 normal women. AVP concentrations were lower throughout the menstrual cycle in symptomatic PMS patients compared with PMS patients during asymptomatic cycles and normal women. No differences in ACTH and ANP were observed between patients and controls. However, ACTH and ANP were positively and significantly correlated with each other in women with PMS but not in controls. These findings contribute to a growing list of menstrual cycle-independent findings in women with PMS and suggest that there may be an underlying neurobiological vulnerability that predisposes some women to experience somatic and mood dysregulation in the luteal phase of the menstrual cycle.