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Orphan Drugs and Single Trials

Posted by Joseph Watson on Thu, Dec 12, 2019 @ 09:00 AM

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Joseph Watson, PhD, RAC, Research Scientist at Rho, has experience in both regulatory submissions and clinical document preparation, with over fifteen years of experience in scientific writing and editing jwatsonclinical and nonclinical documents, including numerous publications in peer-reviewed journals.  Dr. Watson has led the preparation, review, and coordination of a variety of regulatory and clinical documents, including protocols; clinical study reports; integrated summaries of biopharmaceutics, safety, and efficacy; CMC and nonclinical documents; draft product labels; and 120‑day safety updates.  His writing and editing experience covers a broad range of therapeutic areas, including drug addiction, middle ear disorders, infectious diseases, psychiatric disorders, acute and chronic pain, multiple sclerosis, hemophilia, and oncology. 

Since the enactment of the Orphan Drug Act in 1983, the number of orphan drug approvals has risen steadily. In 2018 alone, 34 out of 59 approved novel medications were for orphan diseases. Consistent with the increase in orphan applications reviewed by the Agency, Rho has received an increasing number of sponsor requests for support of programs working towards an orphan drug approval. Our sponsors often think that their product can be approved with support from a single trial, but how realistic is this stance? To better understand when a single trial approval is possible, we look to FDA guidances.Conceptual image with ladder reaching increasing graph-1

In the 1998 Guidance for Industry Providing Clinical Evidence of Effectiveness for Human Drug and Biological Products, FDA spells out the potential circumstances in which a single clinical trial for a novel therapeutic could be sufficient to support an efficacy claim. The guidance states “reliance on only a single study will generally be limited to situations in which a trial has demonstrated a clinically meaningful effect on mortality, irreversible morbidity, or prevention of a disease with potentially serious outcome and confirmation of the result in a second trial would be practically or ethically impossible.”

The key points outlined in the guidance are:

1.   The condition must be serious. If the FDA doesn’t believe the condition is serious, they will not consider a single adequate and well controlled trial for a novel therapy.
2.   A second adequate and well-controlled trial is practically or ethically impossible to conduct. This situation could apply for an orphan indication given limited patient populations (and likely assuming point 1 above).

Both points could apply to an orphan indication; an orphan indication has, by definition, a limited patient population, and many orphan indications are serious. A serious orphan indication falls into the “sweet spot” in which FDA may be willing to show flexibility and accept a single adequate and well-controlled trial.

After considering points 1 and 2 below, FDA must review the single adequate and well controlled trial to determine if it is sufficiently robust and compelling; i.e., does it feature any of 5 characteristics that could make it adequate to support an effectiveness claim (in other words, sufficiently robust & persuasive; FDA’s typical prior to reviewing the data is that the determination will be a review issue):

1.   A large multicenter study
2.   Consistency across study subsets (large trial)
3.   Multiple studies in a single study (e.g., properly designed factorial studies)
4.   Multiple endpoints involving different events (i.e., prospectively identified primary and  secondary endpoints representing different beneficial effects)
5.   Statistically very persuasive findings

For orphan indications, characteristics 1 and 2 are difficult to achieve due to the need for large trials. Characteristic 3 is situational; the example provided by FDA highlights a combination therapy tested as both the combination and as individual parts. Characteristic 4 is typically incorporated into the study designs Rho reviews. Often, this item can be interpreted by sponsors as the “everything but the kitchen sink” approach. In our experience, multiple well thought out, differentiated endpoints can help FDA assess approvability; however, FDA will stress that these endpoints should be independent of each other.

Additionally, FDA will often request that the endpoints be hierarchically ranked; this preserves the overall alpha for the study by preventing companies from fishing for an acceptable endpoint should the primary fail. If the program hits on multiple, well-thought out, agreed upon endpoints, improves significantly on current therapies, and the disease is serious, FDA may consider a single trial appropriate.

Clinical Trial written in search barCharacteristic 5 is likely the most realistic situation orphan drug sponsors can achieve, in spite of the small sample sizes typically observed in orphan trials. Assuming the orphan indication is for a serious indication (as defined above), FDA will at times negotiate with a sponsor those outcomes considered sufficient to support approval with a single clinical trial. Such a strategy should be discussed prospectively with FDA prior to initiating the pivotal trial; assuming FDA agrees with the design, FDA may be willing to consider allowing the filing to proceed if either 1) a highly statistically persuasive and clinically meaningful outcome is achieved or 2) at FDA’s discretion, dependent on FDA’s review of the efficacy data, the severity of the disease, and medical need. In practice, this approach has a high chance of failure, as most companies who work on orphan products move into their pivotal study with either 1) very small proof of concept Phase 1/2 trials that hint at efficacy but are not robust or 2) uncontrolled Phase 2 studies that show efficacy versus natural history data but fail to achieve statistically significant results when conducted as randomized, double-blind studies.

That aside, recently, FDA has taken an active approach for approving products based on a single trial with certain therapeutic paths, particularly anti-infectives. The Limited Population Antibacterial Drug (LPAD) pathway allows antibiotics to be approved and labeled for small populations with unmet needs. As of October 2019, two products have been approved using this pathway with single clinical studies:

•   Arikayce (amikacin liposome inhalation suspension), for the treatment of lung disease caused by a group of bacteria, Mycobacterium avium complex, in a limited population of patients with the disease who do not respond to conventional treatment, approved with a single trial on a surrogate endpoint (sputum conversion); and
•   Pretomanid Tablets in combination with bedaquiline and linezolid for the treatment of a specific type of highly treatment-resistant tuberculosis of the lungs, which was approved with a single trial that showed significant benefit relative to historical controls.

The success of these programs demonstrates FDA’s willingness to be flexible when the benefit can be properly assessed and truly outweighs the risk in a specific patient population. However, companies should be cautious when developing an orphan product. Prospectively planning to properly assess efficacy outcomes in reasonably sized, randomized, double-blind Phase 2 trials will help companies make appropriate go/no go decisions earlier in a product’s life cycle, ultimately helping companies spend less time and money on unapprovable products.