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Though studies evaluating the effects of posture on the absorption of drugs have been conducted, a systematized review revealed critical gaps in methodology.

Of 18 original research articles selected for review, only 43.9% met the methodology criteria identified as essential to include in a pharmacokinetics study, reported Brittany Walsh-Reed, PharmD, BCPS, an independent consultant in Cleveland, during a poster presentation at the Midyear American Society of Health-System Pharmacists meeting.

"You can really see methodologies aren't clearly defined and how that is impacting ... drug absorption and then your drug regimen," Walsh-Reed told MedPage Today.

She and her colleagues used multiple search engines to identify 18 original research studies related to posture and drug pharmacokinetics, evaluating each study for 11 pre-selected "fundamental questions/components":

• What posture positions were studied -- standing, sitting, supine, prone, right-lateral decubitus, and left-lateral decubitus?
• Was position maintained for the entire sampling period?
• Was head-position mentioned?
• Was overnight fast specified?
• Was presence of caffeine specified?
• What fluid volume was given with drug?
• What type of fluid?
• Was intra-gastric volume measured at start?
• Was length of time of blood sampling given?
• Was number of samples drawn over the absorption period given?
• Which pharmacokinetic metrics were measured?

Overall, none of the studies answered all 11 questions/components, and none identified starting intra-gastric volumes among patients.

Most did answer questions related to sampling time, number of samples, and metrics measured (95.5%), but few answered questions about fluid administration or caffeine intake (16.6%).

Furthermore, no study was conducted that compared the six postures. Surprisingly, some of the studies didn't even have their subject maintain their position for the entirety of the sampling period after the drug was administered, Reed-Walsh noted.

"One of the studies in here that I assessed, it said, 'position was maintained,' but then you read on and it says, 'patients were allowed to get up to use the toilet.' So, I'm like, 'well, then technically it wasn't maintained,'" she said.

Many factors can impact pharmacokinetics, but are better understood: weight, age, pregnancy, genetics, and diet. Some of the studies that Walsh-Reed and colleagues looked at gave patients fluids other than water, like milk, which the body can recognize as a nutrient, slowing absorption. Slowing or speeding absorption can be beneficial, but is very drug-dependant, Walsh-Reed noted.

Because most drugs are absorbed through the intestines, posture may make a difference in how rapidly a drug is absorbed, she explained. For example, according to , laying on the left side versus the right side may slow gastric emptying of non-nutrient fluids. One potential explanation is that fluids may have a harder time getting to the pylorus, which leads to the nutrient-absorbing small intestine, because of how the stomach is positioned laying on the left.

Walsh-Reed noted some instances of paramedics laying patients experiencing overdose on their left side to slow gastric emptying. However, research this strategy. Laying on the right versus sitting can also speed up gastric water emptying, suggested.

She said that she was initially interested in migraine therapy, and thought about how some patients with migraines lay down right away. "If they take a migraine med, they're not getting relief, and some patients have to take a second [dose of medication]," she added. "Was that because they went and laid down?"

Much of the research evaluating these effects is not new, but, according to Walsh-Reed, it's not rigorous enough. "They're not looking holistically. They're not even thinking of it," she said.

Because of the lack of methodologically sound studies, it's unclear to what extent posture plays a role in how well a drug works, she noted. "Some of them have statistical significance," she said, but "is it playing a factor clinically? We don't know yet, because all of this criteria is not described."

The researchers used PubMed, Google Scholar, and Scopus to identify relevant studies that evaluated effects of posture on absorption of a wide range of drugs, including theophylline, phenytoin (Dilantin), amoxicillin, acetaminophen, and imipramine, among others. All studies occurred in a clinical setting. Some looked at the effects of only posture on pharmacokinetics, but others included posture among other elements affecting pharmacokinetics.

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