A comparison of crossover versus parallel-group design in the evaluation of analgesic efficacy after molar extraction

Testosterone for Androgen Deficiency-Like Symptoms in Men Without Pathologic Hypogonadism: A Randomized, Placebo-Controlled Cross-over With Masked Choice Extension Clinical Trial

BACKGROUND

Off-label testosterone prescribing for androgen deficiency (AD)-like sexual and energy symptoms of older men without pathologic hypogonadism has increased dramatically without convincing evidence of efficacy.

METHODS

In a randomized, double-blind, placebo-controlled study with three phases, we entered 45 men aged at least 40 years without pathologic hypogonadism but with AD-like energy and/or sexual symptoms to either daily testosterone or placebo gel treatment for 6 weeks in a cross-over study design with a third, mandatory extension phase in which participants chose which previous treatment they preferred to repeat while remaining masked to their original treatment. Primary endpoints were energy and sexual symptoms as assessed by a visual analog scale (Lead Symptom Score [LSS]).

RESULTS

Increasing serum testosterone to the healthy young male range produced no significant benefit more than placebo for energy or sexual LSS. Covariate effects of age, body mass index, and pretreatment baseline serum testosterone on quality-of-life scales were detected. Only 1 out of 22 indices from seven quality-of-life scales was significantly improved by testosterone treatment over placebo. Participants did not choose testosterone significantly more than placebo as their preferred treatment in the third phase.

CONCLUSIONS

Six-week testosterone treatment does not improve energy or sexual symptoms more than placebo in symptomatic men without pathologic hypogonadism.

Which treatment is better? Ascertaining patient preferences with crossover randomized controlled trials

CONTEXT

The difference in patient-reported outcomes between study arms can often be difficult to ascertain in randomized controlled trials (RCTs) using a parallel design because of wide interindividual variations in baseline characteristics and how patients interpret the outcome measures. Furthermore, the minimal clinically significant difference is often not available for many outcomes, and even when available, not individualized for each patient. Crossover RCTs are designed for intraindividual comparisons, which can address these issues by asking patients to directly compare the interventions with regard to effectiveness, adverse effects, and ease of use and to provide an overall choice.

OBJECTIVES

We discuss the key design elements for crossover trials, their advantages and disadvantages relative to parallel designs, and their utility in palliative care research using a number of case examples.

METHODS

This is a narrative review.

RESULTS

Crossover studies randomize patients to a sequence of treatments. In addition to facilitating intraindividual comparisons, they often require a smaller sample size for the same statistical power compared with parallel designs and are thus less costly. However, crossover studies are only feasible when the condition being studied is relatively stable and the intervention has a short-term effect. Crossover studies with inadequate washout periods may be difficult to interpret. The risk of attrition also may increase because of prolonged study duration.

CONCLUSION

By facilitating intraindividual comparisons and eliciting patient preferences, crossover studies can provide unique information on the superior intervention. Crossover designs should be considered for selected palliative care studies.

Proof of efficacy trials: cross-over versus parallel-group

In recent years, most of the published trials of new antiepileptic drugs (AEDs) have had a parallel-group design rather than cross-over. Nevertheless, in some situations the cross-over trial does have advantages, and therefore, its role needs re-appraisal. The crossover design requires a much smaller number of patients for a similar statistical power because patients act as their own controls, which is a particular advantage when the type or severity of epilepsy varies widely in the patients recruited. As a result, the financial cost is smaller and fewer patients are exposed to the new agent, perhaps with ethical arguments in favour of this type of design in proof-of-efficacy trials. Within-patient analysis also makes the detection of drug interactions more robust. On the other hand, there is a theoretical risk that the beneficial effects of the first treatment (or conversely, withdrawal seizures on stopping it) might carry over into the second treatment period and thereby confound the detection of treatment effects. The parallel-group design is more versatile in that a stable disease state is not a pre-requisite, and therefore, trials in newly diagnosed patients are possible. Multiple treatment limbs are also more practical. The duration of a parallel-group trial may be shorter because only one treatment period is involved, although this may be offset by the much larger number of patients needed to be recruited and the time involved in doing so. Parallel-group trials almost always require a multicentre approach, with the inevitable logistic problems involved. It is argued that proof-of-principle and add-on proof-of-efficacy trials of a new drug are more efficiently undertaken using a cross-over design but that subsequent evaluation will require the versatility of trials with a parallel-group design.