By David Joel Miller.
What is pharmacokinetics and why does it matter?
Drugs are everywhere in our society. Not just Street drugs, or the legal drugs such as tobacco and alcohol. Most of us are exposed to drugs all day, every day. Even the people who say they “don’t do drugs” should be concerned about drugs and pharmacokinetics. When we hear about drugs, most of us think illegal drugs. It’s easy to overlook the long-term effects of use and abuse of prescription medication, over-the-counter medication, and the vitamins and herbal remedies all around us every day.
Pharmacokinetics deals with how drugs enter the body, how they get absorbed, how they get transported and delivered throughout the body, and ultimately how are drugs eliminated from the body. In a past post, we talked about routes of administration; the way drugs get into the body.
How much of that drug did you take?
For most drugs the more you take, the stronger the effect. Let’s take a simple, common drug, alcohol to illustrate this principle. If someone drinks a twelve-ounce beer, they consume about half an ounce of pure alcohol. Drinking twelve ounces of whiskey will result in the consumption of about six ounces of alcohol. With whiskey, you drink the same amount of liquid, but because the whiskey is more concentrated, you received a much higher dose of Alcohol than the beer drinker does. Measurement of alcohol consumption requires the use of an idea called the standard drink.
Drug dose is computed based on body weight.
A three-hundred-pound man will need to take a higher dose of medicine than a twenty-pound child. Heavier people contain more volume of liquids, so any chemical they take into their system becomes more dilute. For most medications, your Doctor will want to know your body weight, so they know how much medication to give you.
When it comes to Street drugs or even alcohol, most people don’t consider the effect that body weight has on the drug using experience. Thin people will get higher blood concentrations of the drug even when they take the same amount. Recently we have seen many people who had weight loss surgery, lost a large amount of weight, and developed a significant problem when they consume alcohol or other drugs.
Drug absorption matters.
Some drugs are readily absorbed into the bloodstream. When you consume liquid drugs or very soluble ones, they readily pass through the stomach, into the intestine, and are absorbed into the bloodstream. Solid drugs vary a great deal in their bioavailability, which is the part of the drug that becomes absorbed into the bloodstream and reaches the site of action.
An example of the problem of bioavailability involves pregnant women. Calcium is often added to the diet of a pregnant woman to help the fetus develop strong bones. Limestone is high in calcium, but no matter how much you grind it up, most of the limestone will pass through the body undigested. How much of the calcium in your vitamin supplement will be absorbed into your bloodstream, it’s bioavailability, matters.
Drug distribution varies from drug to drug.
Drugs that are highly water-soluble travel readily throughout the body. Blood nourishes all the cells in the body, and the parts of the body that received the most blood also received the largest doses of drugs. Drugs tend to accumulate in the heart, brain, kidney, and liver. Parts of the body that get little blood flow, the muscles and fat, received little of the active drug. Can you see why taking an oral supplement to “melt away fat” is unlikely to work?
A few drugs, such as THC in marijuana, are fat soluble. These drugs will tend to accumulate in the parts of the body which have the largest fat content.
Drug elimination – how the drug leaves the body.
Eventually, any drugs that go into your body will get broken down and eliminated. Many drugs are metabolized by enzymes produced in the liver. These drugs are especially hard on the liver when taken in excessive quantities. This process is the reason heavy alcohol consumption increases the risk for four separate types of liver disease.
Some drugs are metabolized in the kidneys or the G.I. tract. Regardless of where the metabolism takes place, the majority of all drugs are removed from the body by the kidney. Some drugs, especially in large quantities, can be very hard on the kidneys. Drug abuse can result in impaired kidney function resulting in the need for kidney dialysis.
Drug metabolism is a sequential process.
Many drugs are broken down in stages. The first breakdown product is then metabolized into a second breakdown product and so on. These breakdown products or metabolic byproducts may also be psychoactive. When both cocaine and alcohol are present in the system, they and their metabolic byproducts can combine to produce Cocaethylene which is even longer lasting than the original cocaine and alcohol.
Staying connected with David Joel Miller
Two David Joel Miller Books are available now!
Bumps on the Road of Life. Whether you struggle with anxiety, depression, low motivation, or addiction, you can recover. Bumps on the Road of Life is the story of how people get off track and how to get your life out of the ditch.
Casino Robbery is a novel about a man with PTSD who must cope with his symptoms to solve a mystery and create a new life.
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For more about David Joel Miller and my work in the areas of mental health, substance abuse, and Co-occurring disorders see my Facebook author’s page, davidjoelmillerwriter. A list of books I have read and can recommend is over at Recommended Books. If you are in the Fresno California area, information about my private practice is at counselorfresno.com.