If you take aspirin for a headache, how does the aspirin know it’s getting into your head and relieving the pain?
The short answer is no: molecules cannot transport themselves throughout the body, and they have no control over where they ultimately end up.
But researchers can chemically modify drug molecules to ensure they bind strongly where we want them and weakly where we don’t have them.
Pharmaceutical products contain more than just the active ingredient that acts directly on the body. Drugs also contain “inactive ingredients” or molecules that enhance stability, absorption, taste, and other properties that are critical for the drug to be effective.
For example, the aspirin you swallow also contains ingredients that both prevent the pill from breaking during transit and help it break apart in your body.
As a pharmaceutical scientist, I have been involved with drug delivery for 30 years. That means developing methods and designing non-drug components that help get a drug to where it needs to go in the body.
To better understand the thought process behind the development of different drugs, let’s follow a drug from its first entry into the body to its final destination.
How drugs are absorbed into the body
When you swallow a pill, it first dissolves in your stomach and intestines before the drug molecules are absorbed into your bloodstream. Once in the blood, it can circulate throughout the body to gain access to various organs and tissues.
Drug molecules affect the body by binding to various receptors on cells that can trigger a specific response.
Although 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 potentially cause unwanted side effects.
Drug molecules circulating in the blood also break down over time and eventually leave the body in your urine. A classic example is the strong odor your urine might have after eating asparagus because your kidneys break down asparagus acid so quickly. Similarly, multivitamins typically contain riboflavin or vitamin B2, which causes your urine to turn bright yellow when cleared.
Because the effectiveness of drug molecules that can pass through the intestinal lining can depend on the chemical properties of the drug, some of the drugs you swallow are never absorbed and are excreted in your stool.
Because not all of the drug is absorbed, some drugs, such as those used to treat high blood pressure and allergies, are taken repeatedly to replace excreted drug molecules and maintain high enough drug levels in the blood to maintain its effects in the body.
Bring medicines to the right place
Getting a drug into the blood by injecting it directly into a vein is more efficient than pills and tablets. This way, all of the drug is circulated throughout the body and avoids breakdown in the stomach.
Many drugs that are given intravenously are “biologics” or “biotechnological drugs” that contain substances derived from other organisms.
The most common of these are a type of cancer drug called monoclonal antibodies, proteins that attach to tumor cells and kill them. These drugs are injected directly into a vein because your stomach cannot tell the difference between digesting a therapeutic protein and digesting the proteins in a cheeseburger.
In other cases, drugs that require very high concentrations to be effective, such as B. antibiotics for severe infections, can only be administered by infusion.
While increasing drug concentration can help ensure enough molecules bind to the right sites to produce a therapeutic effect, it also increases binding to non-target sites and the risk of side effects.
One way to get a high drug concentration in the right place is to apply the drug exactly where it is needed, e.g. B. rubbing an ointment on a skin rash or using eye drops for allergies. As some drug molecules are eventually absorbed into the bloodstream, they become diluted so that the amount of drug that reaches other sites is very small and side effects are unlikely to occur.
Similarly, an inhaler delivers the medication directly to the lungs and avoids affecting the rest of the body.
Finally, a key aspect of drug development is simply getting patients to take the right amount of medication at the right time.
Because many people find it difficult to remember to take a drug multiple times a day, researchers are trying to design drug formulations so that they only need to be taken once a day or less.
Likewise, pills, inhalers, or nasal sprays are more convenient than an IV, which requires a trip to a clinic to have a trained doctor inject it into your arm.
The less complicated and costly it is to administer a medication, the more likely it is that patients will take their medication when they need it.
However, sometimes IV fluids or injections are the only effective way to administer certain medications.
Even with all the science that goes into understanding a disease to develop an effective drug, it’s often up to the patient to make sure everything works as intended.
Tom Anchordoquy, Professor of Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus.
This article was republished by The Conversation under a Creative Commons license. Read the original article.