When you take aspirin for a headache, how does aspirin get to your head and ease the pain?
The short answer is that they don’t. Molecules cannot travel through the body and they have no control over where they end up. But researchers can chemically modify drug molecules to ensure that they bind strongly where we want them and weakly where we don’t.
Pharmaceuticals contain more than the active drug that directly affects the body. Drugs also include “inactive ingredients,” or molecules that enhance stability, absorption, flavor, and other qualities essential to allowing the drug to do its job. For example, the aspirin you swallow also contains ingredients that both prevent the tablet from fracturing during transport and help it break down in your body.
Like a pharmaceutical scientistI’ve studied drug administration for 30 years. That is, to develop methods and design 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 design of different drugs, let’s follow a drug from its entry into the body to its arrival.
How drugs are absorbed by the body
When you swallow a tablet, it initially dissolves in your stomach and intestines before the drug molecules are absorbed into your bloodstream. Once in the blood, it can travel throughout the body to access different organs and tissues.
Drug molecules act on the body by binding to different receptors on the cells that can trigger a particular response. Even though drugs are designed to target specific receptors to produce the desired effect, there is no way to prevent them from continuing to circulate in the blood and binding to off-target sites that can cause unwanted side effects.
Many factors, such as your age, genetics, and diet, can affect how your body processes a drug.
Drug molecules circulating in the blood also break down over time and eventually leave the body in your urine. A classic example is a strong smell your urine might have after eating asparagus due to how quickly your kidneys cleanse themselves. asparagus acid. In the same way, multivitamins usually contain riboflavin, or vitamin B2, which causes your urine to turn bright yellow when passed. Since the efficiency with which drug molecules can cross the intestinal lining can vary depending on the chemical properties of the drug, some of the drugs you swallow are never absorbed and are eliminated in your stool.
Because not all of the medicine is absorbed, which is why some medicines, such as those used to treat high blood pressure and allergies, are taken several times to replace removed drug molecules and maintain a high enough level of the drug in the blood to sustain its effects in the body.
Getting medications to the right place
Compared to pills and tablets, a more efficient way to get drugs into the bloodstream is to inject them directly into a vein. In this way, all the medicine circulates throughout the body and avoids degradation in the stomach.
Many medications given intravenously arebiologics” or “biotech drugswhich include substances derived from other organisms. The most common of these is a type of cancer medicine called monoclonal antibodies, proteins that bind to tumor cells and kill them. These drugs are injected directly into a vein because your stomach can’t tell the difference between digesting therapeutic protein and digesting the protein in a cheeseburger.
In other cases, drugs that require very high concentrations to be effective, such as antibiotics for serious infections, can only be administered by infusion. Although increasing drug concentration can help ensure that enough molecules bind to the appropriate sites to have a therapeutic effect, it also increases binding to non-target sites and the risk of side effects.
One way to get a high concentration of medicine in the right place is to apply the medicine where it’s needed, such as by rubbing ointment on a rash or using eye drops for allergies. While some drug molecules will eventually be absorbed into the bloodstream, they will be sufficiently diluted that the amount of drug that reaches other sites is very small and unlikely to cause side effects. Similarly, an inhaler delivers the medicine directly to the lungs and avoids affecting the rest of the body.
Finally, a key aspect of any drug design is simply getting patients to take the right amount of drugs at the right time.
Since it is difficult for many people to remember to take a drug several times a day, researchers are trying to design drug formulations that need to be taken once a day or less.
Likewise, pills, inhalers, or nasal sprays are more convenient than an infusion that requires traveling to a clinic to have a trained clinician inject it into your arm. The less difficult and expensive it is to administer a drug, the more likely it is that patients will take their drugs when they need them. However, infusions or injections are sometimes the only effective way to deliver certain medications.
Even with all the science needed to understand a disease well enough to develop an effective drug, it’s often up to the patient to make everything work as intended.