Beyond Approval: Why Drug Development Doesn’t End at FDA Sign-Off

For many neuromuscular community members — and clinicians — who are waiting for a new treatment, a drug’s approval by the US Food and Drug Administration (FDA) marks the finish line. Years of discovery, testing, and clinical trials can result in a regulatory green light and, finally, patient access.

But for researchers, FDA approval may just be the beginning of a new chapter.

Continuing drug development after approval — whether through new indications, formulations, or delivery methods — is a lesser-known part of the process. But it is especially common in fields such as neuromuscular disease, where patient populations are small and treatment needs are complex. In fact, for rare diseases, this post-approval work can be transformative.

Why study drugs that are already approved?

There are several reasons researchers continue to investigate therapies that are already on the market:

Expanding to new indications

A drug initially approved for one condition may also have beneficial effects on other diseases.

For example, eculizumab (Soliris) was originally developed for the rare blood disorder paroxysmal nocturnal hemoglobinuria (PNH). It was later approved for generalized myasthenia gravis (gMG) in certain patients to help ease gMG symptoms.

This is because Soliris works by inhibiting a protein called C5. In PNH, blocking C5 reduces the breakdown of red blood cells. Blocking C5 is also helpful in gMG, though for different reasons — it helps preserve neuromuscular function and improve muscle strength.

Optimizing dosing, delivery, and therapeutic impact

Clinical trials conducted before approval can be limited in duration and scope. Given the urgent need for a treatment, researchers may prioritize getting approval of a safe and effective dose level quickly, rather than fully optimizing the dosing paradigm.

In some cases, as an approved drug is used over time by more people, doctors become aware of side effects or practical challenges that lead to adherence issues.

After approval, researchers may explore extended-release formulations, alternative routes of delivery (e.g., oral medication instead of injection), or different dosing regimens to improve tolerability, convenience, and even outcomes.

One example is nusinersen (Spinraza^®), which was approved by the FDA in 2016 for the treatment of spinal muscular atrophy (SMA) in all ages. In April 2026, the FDA approved a new high-dose regimen of Spinraza for all ages.

“It is designed to deliver much more of the drug and to do so more quickly, reflecting a growing recognition that maintaining motor neurons early and as robustly as possible may translate into improved long-term outcomes,” says Stephanie Fradette, PharmD, head of the Neuromuscular Development Unit at Biogen.

The FDA based its approval on data from new studies showing that symptomatic infants given the high-dose regimen of Spinraza, rather than the original dosing regimen, experienced statistically significant improvements in motor function. The study also generated supportive data in older patients.

“Development of the high-dose regimen reflects our long-term commitment to the SMA community and our willingness to critically evaluate and acknowledge the remaining needs in the current treatment landscape so that we can work to address them,” Stephanie says.

Addressing unmet needs

Initial approvals may focus on specific age groups or disease stages. That’s because drug developers generally focus on a particular disease population when designing and testing their drug.

“If I’m trying to design a drug, I’m going to do a clinical trial in which the probability of being able to measure a difference is highest,” explains Thomas Crawford, MD, a neurologist at Johns Hopkins, an MDA Care Center. “That means I’m going to cut eligibility criteria very carefully, which often ends up with an indication that’s kind of narrow.”

But when researchers believe a drug could be useful to a broader group of people than it is approved for, they may conduct subsequent studies to expand access to more diverse populations.

For example, last year, the FDA approved onasemnogene abeparvovec-brve (Itvisma), a version of onasemnogene abeparvovec-xioi (Zolgensma) that can be used in children, teens, and adults with SMA to stabilize or improve motor function. Zolgensma was approved only for children up to 23 months old.

In neuromuscular diseases, where progressive decline is common, these types of refinements can significantly alter the disease trajectory.

How the process differs from developing novel drugs

At a glance, post-approval drug development resembles pre-approval drug development: clinical trials, regulatory submissions, and ongoing monitoring. But some key differences set it apart:

Leveraging existing compounds and data

When researchers develop a brand-new (novel) drug, they take several steps in the lab — identifying a target, screening compounds, and conducting preclinical testing — before reaching human clinical trials. In post-approval development, the drug compound has already completed much of this journey. Developers can focus directly on new questions, then hold additional, more targeted studies.

Researchers can also build on an existing foundation of clinical knowledge, drawing from earlier trials, long-term safety data, and real patient experience to guide the next phase of study.

This was the case in the recent development of high-dose Spinraza. “We were able to leverage our understanding of nusinersen to move directly into a phase 2/3 study after completing the necessary preclinical work,” Stephanie says. “In some ways, development of the high-dose regimen was more streamlined given the established understanding of nusinersen.”

Post-approval commitments and phase 4 studies

In some cases, the FDA requires ongoing studies as a condition of drug approval. These can include long-term safety monitoring, pediatric studies of a therapy approved for adults, or collecting additional data on a drug’s performance. Biogen, for example, is conducting a long-term extension study, called ONWARD, to observe the safety and efficacy of their new high-dose Spinraza regimen.

In essence, post-approval drug development is more iterative and data-informed, building on an existing evidence base rather than constructing one from the ground up.

A continuous cycle of innovation

Drug approval is not a static conclusion but is often the beginning of a continuous cycle. Therapies must evolve as clinicians gain experience, new scientific insights emerge, and patient needs change. This is especially true in neuromuscular medicine, where even small improvements in muscle strength, respiratory function, or fatigue can significantly enhance someone’s life.

By conducting careful studies, collaborating with regulators, and designing with patients in mind, researchers can refine existing drugs to be more effective, accessible, and precisely targeted. This ensures that innovation continues even after the initial approval.