Noses are like caverns – twisting, turning, no two exactly the same. But if you nose past anyone’s nostrils, you’ll discover a surprisingly sprawling space.
“The size of the nasal cavity is about the same as a large handkerchief,” said Hugh Smyth, PhD, a professor of molecular pharmaceutics and drug delivery at the University of Texas at Austin.
“It’s very accessible tissue, and it has a lot of blood flow,” said Dr. Smyth. “The speed of onset can often be as fast as injections, sometimes even faster.”
It’s nothing new to get medicines via your nose. For decades, we’ve squirted various sprays into our nostrils to treat local maladies like allergies or infections. Even the ancients saw wisdom in the nasal route.
But recently, the nose has gained scientific attention as a gateway to the rest of the body – even the brain, a notoriously difficult target.
The upshot: Someday, inhaling therapies could be as routine as swallowing pills.
The nasal route is quick, needle free, and user friendly, and it often requires a smaller dose than other methods, since the drug doesn’t have to pass through the digestive tract, losing potency during digestion.
But there are challenges.
How hard can it be?
Old-school nasal sprayers, mostly unchanged since the 1800s, aren’t cut out for deep-nose delivery. “The technology is relatively limited because you’ve just got a single spray nozzle,” said Michael Hindle, PhD, a professor of pharmaceutics at Virginia Commonwealth University, Richmond.
These traditional devices (similar to perfume sprayers) don’t consistently push meds past the lower to middle sections inside the nose, called the nasal valve – if they do so at all: In a 2020 Rhinology study (doi: 10.4193/Rhin18.304) conventional nasal sprays only reached this first segment of the nose, a less-than-ideal spot to land.
Inside the nasal valve, the surface is skin-like and doesn’t absorb very well. Its narrow design slows airflow, preventing particles from moving to deeper regions, where tissue is vascular and porous like the lungs. And even if this structural roadblock is surpassed, other hurdles remain.
The nose is designed to keep stuff out. Nose hair, cilia, mucus, sneezing, coughing – all make “distributing drugs evenly across the nasal cavity difficult,” said Dr. Smyth. “The spray gets filtered out before it reaches those deeper zones,” potentially dripping out of the nostrils instead of being absorbed.
Complicating matters is how every person’s nose is different. In a 2018 study, Dr. Smyth and a research team created three dimensional–printed models of people’s nasal cavities. They varied widely. “Nasal cavities are very different in size, length, and internal geometry,” he said. “This makes it challenging to target specific areas.”
Although carefully positioning the spray nozzle can help, even something as minor as sniffing too hard (constricting the nostrils) can keep sprays from reaching the absorptive deeper regions.
Still, the benefits are enough to compel researchers to find a way in.
“This really is a drug delivery challenge we’ve been wrestling with,” said Dr. Hindle. “It’s not new formulations we hear about. It’s new devices and delivery methods trying to target the different nasal regions.”