When you take aspirin for a headache, how does aspirin get to the head and relieve the pain? The short answer is no: molecules cannot be transported through the body and have no control over where they end up. So how do medicines know where to get their body?
But researchers can chemically modify the molecules of medicament to make sure that it is strongly connected to the places we want and weakly to the places we don’t want.
Pharmaceuticals contain more than one active drug that directly affects the body. Medicines also include “inactive ingredients” or molecules that increase the stability, absorption, aroma and other qualities that are essential to enable the medicine to do its job. For example, the aspirin you swallow also has ingredients that prevent the tablet from breaking during transport and help it break down in your body.
To better understand the thinking behind the way different medicines are designed, let’s look at a medicine from the moment it first enters the body to where it finally arrives.
When you swallow it tablet, it will initially dissolve in the stomach and intestines before the drug molecules are absorbed into the blood. Once in the blood, it can circulate throughout the body to access various organs and tissues. Drug molecules affect the body by binding to various receptors on the cells that can trigger a certain response.
Medicines and their circulation in the body
Even if drugs are designed to target specific receptors to produce a desired effect, it is impossible to prevent them from continuing to circulate in the blood and bind to non-target sites that can cause unwanted side effects.
The drug molecules that circulate in the blood also degrade over time and eventually leave the body in the urine. A classic example is the strong smell that your urine can have after eating asparagus, because of how quickly your kidneys eliminate asparagusic acid. Similarly, multivitamins usually contain riboflavin or vitamin B2, which makes the urine bright yellow when cleaned.
Because how effectively the drug molecules can cross the intestinal mucosa may vary depending on the chemical properties of the drug, some of the drugs you swallow are never absorbed and are excreted in the feces. Moreover, because not all of the medicine is absorbed, this is why some medicines, such as those used to treat high blood pressure and allergies, are taken repeatedly to replace the removed drug molecules and to maintain a level. high enough drug in the blood to maintain its effects on the body.
Compared to pills and tablets, a more effective way to introduce a drug into the blood is to inject it directly into a vein. In this way, all the medicine is in the body and prevents degradation in the stomach. Many medicines that are given intravenously are ‘biological’ or ‘biotechnological medicines’, which include substances derived from other organisms.
The most common of these is a type of cancer drug called monoclonal antibodies, a protein that binds and kills tumor cells. These drugs are injected directly into a vein because your stomach can’t tell the difference between digesting a therapeutic protein and digesting protein in a cheeseburger.
In other cases, medicines that require very high concentrations to be effective, such as antibiotics for severe infections, can only be given by infusion.
While increasing the concentration of the drug can help ensure that enough molecules bind to the right places to have a therapeutic effect, it also increases the binding to non-target places and the risk of side effects.
One way to get a high concentration of the medicine in the right place is to apply the medicine exactly where it is needed, such as rubbing an ointment on a rash or using eye drops for allergies. While some drug molecules will be absorbed into the bloodstream, they will be diluted enough that the amount of drug that reaches elsewhere is very small and is unlikely to cause side effects.
Similarly, an inhaler delivers the drug directly to the lungs and prevents damage to the rest of the body.
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