Why Gut Motility is Key to Properly Delivering the Parkinson's Disease Drug 'Levodopa' to the Brain

For patients with Parkinson's disease, medication is not just a supplement but a core factor that determines their quality of life. However, even when taking medication at set times every day, many complain of frustration because the drug's effect does not appear or symptoms are not controlled. This is because a problem occurs at one of the complex stages in the path the drug must take from being ingested through the mouth to reaching its final destination, the brain.

According to a video from Uihak Channel Biondwi, Professor Lee Woong-woo of the Department of Neurology at Nowon Eulji University Hospital explained the process by which 'Levodopa', a key agent in Parkinson's disease treatment, is delivered to the brain, and emphasized that to make the drug work as a 'real medicine', it is important to understand the gastrointestinal state and the characteristics of the blood-brain barrier (BBB).

The reason why only a tiny fraction of 100mg of Levodopa is delivered to the brain

Levodopa, which forms the basis of Parkinson's disease treatment, is converted into dopamine in the brain to alleviate motor symptoms. Professor Lee Woong-woo compared dopamine production to a flour factory and movement to a snack factory. Since Parkinson's disease is a condition where the factory producing the 'flour' called dopamine is broken, supplying the raw material called Levodopa from the outside allows it to turn into dopamine in the brain and create movement.

However, the process of Levodopa reaching the brain is very arduous. The professor explains that if Levodopa is taken alone, the ratio of the amount ingested orally that is delivered to the brain is only 1–3%. Even if 100mg of the drug is taken, the actual amount going to the brain is limited to the level of 1–3mg. To compensate for this, it is currently standard to take an 'AADC inhibitor (e.g., Carbidopa)' together to help the absorption of Levodopa.

The AADC inhibitor plays the role of preventing Levodopa from being converted into dopamine prematurely in the periphery (intestines or blood) before it reaches the brain. This is because if Levodopa turns into dopamine in the periphery before it can even reach the brain, the enlarged dopamine cannot pass through the 'blood-brain barrier (BBB)', which is the brain's protective shield, and is lost. The blood-brain barrier acts as a defense shield to prevent external substances from entering the brain recklessly. By co-administering an AADC inhibitor, the amount delivered to the brain when taking 100mg can be increased to about 12mg.

The hidden obstacles blocking drug efficacy: 'Constipation' and 'Gastrointestinal Environment'

For the drug to reach the brain, it must be swallowed through the mouth, pass through the stomach and intestines, be absorbed in the small intestine, and then travel through the blood. In this process, the patient's gastrointestinal state has a decisive impact on the drug's efficacy. The professor warns that the drug must move quickly from the stomach to the small intestine for absorption to begin, and if this flow is blocked, the drug's effect will not appear.

The most representative interfering factor is 'constipation'. If the intestines are full of stool that has not been discharged, intestinal motility is inhibited, slowing down the speed at which the drug moves down to the small intestine. Additionally, cases where bacteria in the small intestine convert Levodopa into dopamine prematurely, or where Helicobacter pylori interferes with drug metabolism, also cause a decrease in drug efficacy. In severe cases, if gastric emptying is delayed, the patient ends up in a state where the brain has not received the drug despite having taken it, to the extent that it can be confirmed through gastroscopy that the drug is staying in the stomach as is. This is like a situation where rice was ordered, but because the rice delivered to the kitchen was not moved to the dining table, it does not become cooked rice.

Lifestyle rules for maximizing drug efficacy: Activating intestinal motility

Ultimately, for Parkinson's disease medication to function properly, all paths from the stage of swallowing the medicine to the stage of reaching the brain must be smooth. Professor Lee cited 'activation of intestinal motility' as a key management method to increase drug efficacy. He stated that the intestinal environment must be improved so that the drug can quickly reach its target destination, the small intestine.

To this end, patients should promote intestinal motility through sufficient activity. Exercises such as steady walking help improve intestinal motility and aid drug absorption. Also, if constipation is severe, constipation treatment should be carried out in parallel, and if Helicobacter is present, reorganizing the intestinal environment through eradication treatment helps maintain drug efficacy. For patients with difficulty swallowing (dysphagia), the drug may not be properly processed in the esophagus or stomach, so meticulous management, such as adjusting the form of administration through consultation with medical staff, is necessary.