A medication’s movement through the body is a complex process influenced by a variety of factors, from the medication’s own chemical properties to variations in individual metabolism. Read on to learn about the key phases of this process as well as what steps you can take to experience the full therapeutic benefits of a medication.
ADME: A Medication’s Journey
The journey of a medication through the body is sometimes referred to by the acronym of ADME, which stands for the phases of absorption, distribution, metabolism, and excretion. Here’s what happens at each stage.
Absorption
This is how a medication moves into your bloodstream. There are two aspects to it: the rate of absorption and the amount that is absorbed. Both qualities depend on the following factors.
Delivery method
A medication can be taken orally, topically, or as an injection. There are several types of injection techniques:
Intramuscular, in which a medication is injected into muscle
Subcutaneous, in which a medication is injected just beneath the skin
Intravenous, in which a medication is injected directly into a vein
Medication absorption is fastest with intravenous administration, a method that immediately delivers all of a medication’s active ingredients into the bloodstream. The efficiency of this method is one reason it’s often used in critical care settings.
On the other hand, oral medications, which account for most prescription medications taken at home in the United States, must be absorbed in the stomach or gastrointestinal tract before they can enter the bloodstream.
Medication properties
A medication’s chemistry and composition also impact the duration and ease of absorption. Aspirin is one of many medications that can be absorbed in the acidity of the stomach, but others must be absorbed in the less acidic environment of the gut. The latter takes more time, as the medication needs to travel through the stomach and into the gut.
Interactions with food
The digestive process is accompanied by many physiological effects, like changes in your levels of stomach acid, and food can affect medication absorption. While a full stomach often delays the process of absorption, some medications are better absorbed when taken with food. Your pharmacist can explain how to take your medication.
Distribution
Distribution is how a medication, now absorbed into the bloodstream, reaches various tissues throughout the body. Much of this depends on the medication’s chemical make-up. Fat-soluble medications and vitamins — like the commonly prescribed steroid prednisone as well as vitamins A, D, E, and K — can be absorbed by fats that you’ve eaten, which allows for relatively easy access to cell membranes.
The process is slightly more complicated for water-soluble medications, which must dissolve in water before they can pass through your cells. Water-soluble medications and vitamins include atenolol (Tenormin®), a common beta-blocker, and vitamins B6, 12, and C.
The size of a medication’s molecules also influences the speed of distribution. Many common medications have small molecules, which allow them to enter cell membranes more quickly. Insulin is an example of a medication composed of larger molecules, which is one reason it is administered by injection. Other injectable large-molecule medications include biologics, a type of specialty medication that treats complex conditions such as rheumatoid arthritis, psoriasis, and Crohn’s disease.
As a full-service pharmacy, Alto carries many specialty medications and can support you in managing a chronic condition.
Metabolism
In this stage, a medication becomes inactive so that it can exit the body. It typically happens in the liver, although some medications are metabolized by the kidneys. In either case, a medication travels to wherever it will eventually be metabolized during the process of distribution.
Individual metabolisms vary widely and are influenced by numerous factors. Since the liver is so instrumental to the process of metabolization, the function of this organ significantly affects metabolism. Cirrhosis, scarring of the liver, can prolong the process of metabolization and cause a medication to stay in the bloodstream for a longer duration of time. Due to aging-related changes in liver function, older adults often have slower metabolisms.
Genetics also play a role, with some people naturally metabolizing medications more quickly than others. Other physiological factors that can affect metabolism include body weight, percentage of body fat, hormonal make-up, and blood flow.
Certain foods can also affect the body’s ability to metabolize a medication. For example, grapefruit and grapefruit juice can block the enzymes your body needs to break down cholesterol-lowering statins. (The interference of food or beverages with a medication’s effects is referred to as a medication interaction. Asking your pharmacist or provider about the best way to take your medication can help you avoid common interactions.)
Excretion
This is the elimination of an inactive medication from your body. Many medications leave through your urine, and the kidneys are critical to this step. Medications that can’t be filtered through the kidneys exit the body through feces.
Relatedly, urine samples can help your care team understand your body’s response to certain medications. In some cases, measuring the amount of an active medication in a urine sample allows your provider to calculate how quickly you’re processing it and make any dosage adjustments, if necessary. (Narrow therapeutic index medications, which require extremely precise dosing and can cause adverse reactions at even slightly different blood concentrations, often require blood rather than urine samples during clinical monitoring.)
Food and medication absorption
As noted above, the physiological effects of eating food — such as increased blood flow and changes in gut acidity and motility — impact the absorption of different medications in different ways.
Some medications, including levothyroxine (Synthroid®) and the osteoporosis medications alendronate (Binosto®, Fosamax®) and ibandronate (Boniva®), are not absorbed as effectively with food. This is also the case with certain penicillins, which become less effective with prolonged exposure to acidic conditions. Food can also become a barrier to the wall of your gut, physically blocking certain medications from entering your bloodstream.
However, food can support absorption of other medications. For example, the antifungal itraconazole needs acidic conditions to be absorbed. Additionally, taking the antibiotics nitrofurantoin and cefpodoxime with food will help the medication enter your bloodstream in higher amounts.
There are other reasons that a medication should be taken with food or on an empty stomach, for example, to reduce side effects or prevent interactions. Consult with your pharmacist for specific instructions about your medication.
The pharmacy care you deserve
Our expert pharmacists can answer any questions you have about your medications right in the Alto app. We also offer fast and reliable delivery and medication management tools like reminders and auto refills to help you stay on track with treatment.
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This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or another qualified health provider with any questions you may have regarding a medical condition.
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