When you have a headache and reach for a pain reliever, you’re probably not thinking about your body position when you swallow that pill. But a new study by Johns Hopkins engineers finds your posture can make a big difference in how quickly your body absorbs the medicine.
The findings are based on what’s thought to be the first model to simulate the mechanics of drug dissolution in a human stomach.
“We were very surprised that posture had such an immense effect on the dissolution rate of a pill,” says senior author Rajat Mittal, a professor of mechanical engineering and expert in fluid dynamics whose team’s work appeared in Physics of Fluids.
In recent years, models have been created to authentically represent the workings of several major organs, notably the heart. The model developed by the team, called StomachSim, appears to be one of the first to be able to conduct a realistic simulation of the human stomach. Blending physics with biomechanics and fluid mechanics, StomachSim mimics what is happening inside a stomach as it digests food or—in this case—medicine.
Most pills do not start working until the stomach ejects their contents into the intestine. So the closer a pill lands to the lower part of the stomach, the antrum, the faster it starts to dissolve and empty its contents through the pylorus into the duodenum, the first part of the small
intestine. If you’re aiming a pill for this part of the stomach, posture is critical to both gravity and the natural asymmetry of the stomach.
The team tested four postures. Taking pills while lying on the right side was by far the best, sending pills into the deepest part of the stomach to achieve a dissolution rate 2.3 times faster than even an upright posture. Lying on the left side was the worst. The team was very surprised to find that if a pill takes 10 minutes to dissolve on the right side, it could take 23 minutes to dissolve in an upright posture and over 100 minutes when laying on the left side.
“For elderly, sedentary, or bedridden people, whether they’re turning to the left or to the right can have a huge impact,” Mittal says.
Standing upright was a decent second choice, essentially tied in effectiveness with lying straight back.
The team also considered what stomachs that aren’t functioning at full strength meant for pill dissolution. The impact of stomach disease, such as gastroparesis caused by diabetes or Parkinson’s disease, on drug dissolution was similar to that of posture—which underscores how significant a difference posture makes.
“Posture itself has such a huge impact, it’s equivalent to somebody’s stomach having a very significant dysfunction as far as pill dissolution is concerned,” Mittal says.