Clinical trials in children: why kids are not small adults
When a new drug is developed, it is tested in adults first, sometimes for years, before anyone thinks about giving it to a child. Here is the problem: children are not miniature adults. Their bodies are growing, their organs are developing, and their metabolism changes almost yearly. Giving a child the adult dose scaled down by weight is not just imprecise. It can be dangerous. Figuring out what is actually safe is what pediatric clinical trials are for, and they come with their own challenges and safeguards.
The biology is different
Children process drugs differently at nearly every level. The liver enzymes that break down medications develop gradually over the first years of life. A newborn's kidney function is only about 30 percent of an adult's. Body composition, more water and less fat, changes how drugs are distributed. The blood-brain barrier is not fully formed in infants, so some drugs that are safe for adults can be toxic in babies. And children are growing: a drug that affects bone growth, hormone development, or brain formation can leave consequences that last a lifetime.
A history of guessing
For most of the 20th century, doctors simply guessed, taking the adult dose, dividing by weight, and hoping for the best. The results were often tragic. The sulfanilamide elixir disaster of 1937, when a toxic solvent killed more than 100 children because nobody tested the liquid formulation, helped trigger modern drug regulation. Thalidomide in the 1950s and 60s caused severe birth defects because it was never tested in pregnant women. Even after those disasters, pediatric testing stayed rare. As late as the 1990s, more than 70 percent of drugs prescribed to children had never been tested in children at all.
Two laws changed the field
That changed in the late 1990s and early 2000s thanks to two US laws. The Best Pharmaceuticals for Children Act (BPCA), passed in 2002, gives drug companies an extra six months of market exclusivity, essentially extended patent protection, if they voluntarily conduct pediatric studies (FDA on the pediatric exclusivity provision). The Pediatric Research Equity Act (PREA), passed in 2003, is mandatory: companies developing a new drug must also study it in children unless they get a waiver. Together the laws transformed pediatric drug development. Before BPCA and PREA, only about 20 percent of drugs had pediatric labeling. Today it is over 50 percent.
Under PREA, a company submitting a new drug application for adults must also submit a pediatric study plan covering ages, doses, and safety endpoints, which the FDA reviews and can expand (FDA guidance on complying with PREA and BPCA). There are also requirements for pediatric formulations: if the adult version is a large tablet, the company may need a liquid or chewable version for children.
Waivers and deferrals
Not every drug needs pediatric testing right away. The FDA has two tools. A full waiver excuses pediatric studies entirely, for example when the condition does not occur in children or the drug would be unsafe at any pediatric dose. A partial waiver might excuse testing in one age group, like newborns, while requiring it in older children. A deferral means the studies are required but can be done after adult approval, which is common when a disease is rare in children and enrollment would take years, or when the adult formulation needs to be reformulated. Deferrals balance timely adult access against eventual pediatric data.
Consent and assent
Children cannot legally consent to research. That is a fundamental ethical protection. Instead, parents or legal guardians give parental permission. But that is not the whole story. For children old enough to understand, usually around age seven and up, researchers must also obtain the child's assent: agreement given in a way that fits the child's age and maturity. For a seven-year-old that might be a conversation with a picture book. For a teenager it is closer to adult informed consent. A child can withdraw assent at any time. If they say they want to stop, they stop, even if the parents say it is okay.
Parental consent has its own layers. One parent's consent is usually enough, but for higher-risk research the FDA and institutional review boards may require both parents, so that neither objects. Special rules cover children in foster care, where the state is the legal guardian, and emancipated minors who can consent for themselves. There is also the therapeutic misconception: parents may believe their child will personally benefit from research that is designed to gather knowledge, not provide treatment. Researchers have an ethical duty to make that distinction clear.
Designing around small numbers
Pediatric trials are designed differently from adult trials. Sample sizes are much smaller because there simply are not as many children with a given condition, so researchers use statistical methods that work with smaller numbers. Many pediatric trials use adaptive designs, where the dose or treatment is adjusted based on interim results. There is also greater reliance on extrapolation: if the disease is similar in adults and children and the drug works the same way, regulators may accept adult trial data combined with smaller pediatric pharmacokinetic studies, reducing how many children are exposed to experimental treatments.
Dosing is one of the trickiest parts. A dose that works for a six-year-old may be wrong for a six-month-old. Many drugs must be dosed by body surface area rather than weight. Pediatric drugs need liquid formulations that taste acceptable, stay stable, and contain appropriate preservatives; a bitter drug may simply be refused, making compliance impossible. And then there are neonates, premature babies who weigh less than a kilogram, where a single drop of fluid can be a significant dose.
Reducing the burden
Minimizing pain and discomfort is a top priority. Children cannot tolerate multiple blood draws, long clinic visits, or uncomfortable procedures the way adults can. Researchers use numbing creams before injections, smaller blood volumes, child life specialists who use play and distraction, and home visits instead of clinic visits. Some pediatric studies use pharmacokinetic scavenging: collecting small leftover blood samples from routine clinical tests rather than drawing extra blood for the study. A child's negative research experience can affect their willingness to engage with medical care for the rest of their lives, so every effort is made to keep it non-traumatic.
Successes that prove the point
Despite the challenges, pediatric trials have delivered remarkable results. Childhood leukemia survival was under 10 percent in the 1960s; today it exceeds 90 percent for some forms. Antiretroviral drugs extended the lives of HIV-infected children from months to decades. Surfactant therapy for premature babies, tested in infants weighing less than a kilogram, cut newborn respiratory distress deaths by 50 percent. These are measurable impacts on children's lives, and they would not exist without pediatric clinical research.
The bottom line
Children are not small adults. Their developing bodies, legal status, and vulnerabilities require a different approach to research, governed by BPCA and PREA, built on parental permission plus age-appropriate assent, and designed with smaller samples, adaptive methods, and a relentless focus on reducing pain and burden. The result is safer, more effective medicines for the youngest patients, and a system that keeps improving.
This article is based on the Clarity Clinical Solutions video "Clinical Trials in Children: Why Kids Are Not Small Adults." Watch it here: Clinical Trials in Children: Why Kids Are Not Small Adults
References
- Clarity Clinical Solutions — "Clinical Trials in Children: Why Kids Are Not Small Adults" (source video). https://www.youtube.com/watch?v=Wz94ofmoTEo
- FDA — Pediatric exclusivity provision (BPCA incentives). https://www.fda.gov/science-research/pediatrics/pediatric-exclusivity-provision
- FDA guidance — Pediatric drug development: regulatory considerations for complying with PREA and BPCA. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/pediatric-drug-development-regulatory-considerations-complying-pediatric-research-equity-act-and
- NIH — Clinical research trials and you (why people participate and how trials protect participants). https://clinicaltrials.gov/