Understanding Clinical Trial Data

Trial experience can provide a window on the efficacy and safety of new agents or products.

By Agustin L. Gonzalez, OD, FAAO

When a new medication or device is introduced to the market, it faces a hurdle in that practitioners lack clinical experience with the product. Before the newly approved product can gain wide adoption, it is to be expected that clinicians less familiar with the new technology will take a conservative approach to it. They may wait to see what their peers’ reactions are before, for example, adopting a new drug or contact lens.

Yet is it undeniable that the advent of a new technology has the potential to bring an improved treatment option for managing a disease entity, treating an otherwise neglected population, or expanding a patient population, which can in turn potentially increase our patient base.

For clinicians eager to adopt a new medication or device, information from clinical trials can often provide a window into how to use the product and how best to select patients to ensure improved outcomes. Clinical trial data can provide a guide to the use, effectiveness, and safety of a product. Closely evaluating data from the clinical trials of a medication requires a knowledge of how to interpret the published data. Information from these studies, from patient selection criteria to study results, can serve to guide both our clinical adoption and proper use of the new device or medication. This article reviews key points that clinicians should keep in mind when evaluating data from clinical trials.


In the United States, new ophthalmic drugs must undergo scrutiny by the FDA, and a fundamental part of this scrutiny is the clinical trial process. Data from clinical trials determines a product’s labeling and demonstrates both its safety and efficacy. The approval process generates an extensive amount of information, and clinical trial data are often shared through publication in peer-reviewed journals multiple times before a given product reaches the market. A careful review of clinical trial data and a basic understanding of the FDA approval process can guide the eager clinician in the adoption and use of an innovative product.

Clinical trial data can help predict patient acceptance and develop in-office patient selection and disease management and care protocols. The data can aid in deciding whether a new pharmacologic agent would be of clinical utility to the practitioner and would benefit his or her patient base.


In examining clinical trial data, one of the first things that should be considered is the overall number of study subjects. The higher the number of enrolled subjects (the “N”), the more reliable the predictive outcomes, and the N should play an important role in the clinician’s consideration of whether to adopt a product. The clinical trial should have a large enough sample size to provide realistic conclusions on the effectiveness and safety of the medication or device being studied.

Another number to consider is the percentage of subjects completing the trial. A high discontinuation rate often signals problems relating to one or more factors, most commonly including compliance, study design, adverse events, or safety.

When assessing a device’s performance or efficacy in a trial, note the probability value, or P value. The calculated probability value helps to demonstrate that the results of a trial were not reached by chance but rather are statistically significant. It is worthwhile to note differences in P values among studies and groups, as this can help to validate whether there are sufficient data to statistically back up trial outcomes.

Confidence in study design is imperative for FDA approval, and, because of this, an examination of study design is critical. Clinical trials for new medications are often randomized to offer greater confidence in the efficacy and safety data generated.

When making comparisons with other clinical trials and to better understand and compare a study’s design, it is important to understand selection criteria for study participants, as this defines the population for which the drug would theoretically provide the most benefit. By matching our initial patient selection for a medication to the study selection criteria, clinicians will be more likely to have a positive result in line with those of the clinical trial.

Patient exclusion and inclusion criteria for enrollment can be a helpful predictive factor for clinical results when we first use a device or medication. It is useful to note whether patients included in a trial were symptomatic or asymptomatic, as this will give us a better guide for initial patient selection criteria and what results we can expect in our patient population.

When reading clinical trials we should also make sure to analyze closely the differences in the main outcome measures for the study. For example, a glaucoma drug will likely produce a reduction in intraocular pressure, but it is also important to understand the outcomes in measurements over specific time points.


Critically assessing new technology allows clinicians to pick and choose medications that showcase their innovative spirit and achieve enhanced patient outcomes. Often new therapies and devices can improve treatment outcomes without negatively affecting costs. It is important to be knowledgeable about the products we use in our clinical practice. When we decide to adopt a new device or prescribe a new medication, a good understanding of the published literature and studies, including clinical trials, is invaluable. When reviewed from a clinical perspective, clinical trial data should be a compass guiding our adoption of new technologies.

Promotional presentations and product mentions during conferences are also helpful for indirectly gathering experience with new products. These opportunities offer ways to interact with clinicians who have had extensive experience with the new medication or device. Often published after product approval, postmarketing or so-called phase 4 studies can also give us a better understanding of the use of the product after its initial FDA approval.

Being able to understand clinical trial data is a crucial first step in judging a new product’s performance, safety, and efficacy. Clinical trials provide a clinical compass and become useful in understanding new products and how these products will perform in well-defined populations. The astute clinician still realizes that reading clinical trial data is no substitute for clinical experience; day-to-day experience is essential for a comprehensive assessment of how and when new products will be appropriate for our practices and how to use them to best help our patients.

Agustin L. Gonzalez, OD, FAAO
• Optometric glaucoma specialist and therapeutic optometrist in practice at Eye & Vision in Richardson, Texas