Hello everyone and welcome back. In our last sections we have been discussing aspects of the brain and the nerve cell. In this section we begin our discussion of how drugs enter, go through the system, and are eliminated from the system.

Let's begin by going to slide two. First of all, when we talk about the concept of getting drugs in and out of the system, what we are talking about is a term called neuropharmacology. Basically it is the scientific study of how drugs affect the nervous system. It is an all encompassing term and is applied to all drugs that influence the nervous system, including sensory, motor, cognitive functioning and other assorted other things.

In addition to that there are other terms that we need to know. The first of these terms and shown in slide three is psychopharmacology. Usually this is used to describe how drugs affect some kind of psychological parameter such as emotion and cognition. A second term is psychotropic. These are drugs that influence some kind of particular behavior. A third term and a major focus of this topic area is pharmacokinetics. Basically, this is the study of how drugs enter, are distributed into the system, are metabolized into the system, and then removed or excreted from the system. Finally, we have the term pharmacodynamics.  This is the study of what drugs do to various structures in the body, such as the nerve cells, the heart, or other structures.

So let's talk about pharmacokinetics on slide four. Basically what pharmacokinetics does is examine four different variables. How drugs enter the system, how drugs are distributed throughout the system, how they are metabolized in the system, and how they are eliminated from the system.

Let's talk about how drugs enter the system first. The way a drug enters the system will impact how fast a drug reaches its target organ, what structures the drug will influence, and also the risk of acquiring other types of diseases such as blood borne pathogens.

The first way one can get drugs into the system is shown on slide six. This is the oral method.  That is, you ingest it through the mouth. It has a slow onset of action. The advantage is that it is easy to take and it has low risk of blood borne pathogens.

Now there are other, faster routes of administration and these are shown in slide seven. Real fast types of administration include the respiratory system where you inhaling it through the nasal cavity or through the mouth by smoking it. Here two types of drugs people use are nicotine and cocaine. Another way to get drugs into the system relatively quickly is through the intravenous system. Basically, somebody is shooting up with drugs through a hypodermic needle.  Drugs used here include methamphetamines and opiates.

A third way to get drugs into the system rapidly is intra-arterial.  Again drugs used here include methamphetamines and opiates. The problem with intravenous and intra-arterial systems is the risk of blood borne pathogens such as hepatitis, HIV, and assorted other diseases. All of these faster routes take seconds to get the drug to the target site. So they are very, very quick once you get the drug into the system.

There are some slower routes as well; these take longer such as minutes. Classic examples of these include steroids which are injected into the muscle groups. Or, subcutaneous types of injections used with certain types of hallucinogens. And, finally, cutaneous methodologies which include dermal patches placed on the outside of the skin. Nerve agents, nicotine patches, and even some pain medications are taken this way today.

Now, there are also some additional scientific medical routes we use as well.  I am including them for thoroughness in this section. The first of these is intraperitoneal which is basically injecting substances into the abdominal cavity. Other methods include intracerebroventricular or intracerebral. These methods put material into the brain or the upper areas of the spinal cord. These methods of action can take minutes or seconds and can be quite dangerous if one is not trained in using them in correctly. There is basically minimal risk of blood borne pathogens with these types of techniques because of the sterile techniques used.

So, once we have drugs into the system how are drugs distributed throughout the system? The primary way is through the circulatory system. Basically, you have the heart which sends blood to the lungs which sends blood back to the heart and then to all the body structures via the arteries. The arteries then go to smaller blood vessels then the small blood vessels return to the heart via the veins and then you repeat the system.

Now, a concept (as we see in slide ten) that is very important is bioavailability. This concept is basically how much of a drug actually reaches a target. These effects or differences can depend on a wide variety of things including, gastrointestinal loading (you have a whole bunch of food in your stomach), liver metabolism (how well your liver is working in the first place), binding to plasma proteins that make the drug unavailable to the target (that is, some other protein is out there that is blocking it), plus some drugs cannot penetrate the blood-brain barrier or cannot penetrate some other kind of cell membrane. All of these variables are going to be very important if some drug is going to have an effect on the system.

Now, ultimately (as we see in slide eleven), all drugs bind to some kind of a receptor site and it does not matter where it is. Sometimes you have multiple sites and multiple receptors. Whatever the substance is, it has some type of effect on the target site.  This effect then creates some kind of behavioral effect (which we call the main effect). It also has a variety of unintended effects.  These are called side effects. Ultimately all of these aspects is related to a concept called pharmacodynamics.

Pharmocodynamics (as we see in slide twelve) is defined as the effect some particular drug has on the neurological system. However, it can also be associated with any type of system including the heart, the lungs, the liver, the endocrine system, etc. Lots of variables impact pharmocodynamics such as the amount of drug that is available, past use (tolerance), how stable a particular drug is (that is, how long the drug lasts in the body),, the drug consistency (that is, does it need to be metabolized or broken down before it can be used), etc.

Now, ultimately, once you have all these drugs in the body they need to be removed from the body in some way. As we see in slide thirteen, drugs can be removed in a wide variety of ways including breathing, through sweat, or through feces.  However, the primarily and major way most drugs are broken down or eliminated from the system is by liver metabolism. That is, you have specific enzymes in the liver that break down drugs to inactive compounds. This breakdown rate can be influenced however by liver disease, if other compounds are present (that is, you have multiple compounds), fluid levels that are in the body, or other kinds of health effect.

Now, once you have these drugs broken down, you then have to get them outside of the body (shown in slide fourteen). The primary way this removal occurs is through the kidneys. Basically, what the kidneys do is remove waste products from the blood.  However, removal can be influenced by fluid levels and other compounds such as salt within the system. The kidneys also also other drugs as well including birth control pills and other types of metabolites. These ultimately can cause problems in other organisms.

A final way products are removed (shown in slide fifteen) is through breathing, sweat, and feces. Usually, most drugs are not removed this way but small amounts of drugs are often eliminated through this process. As a result, you can develop techniques to analyze for those compounds.  The classic example and technique for examining alcohol levels is through using a breathalyzer.

So in general, as we see in slide sixteen, lots of variables can influence drugs in the body and it is important for the clinician to be aware of them. This is the reason psychopharmacology is so important. These are also the reasons to conduct medical exams on patients and are an important component for drug and alcohol treatment. Basically, you need to evaluate whether the person is even on the particular drugs.

In our next section we will continue on with this discussion and begin talking about some specific types of drugs. So until then, we hope you enjoy your day and we look forward to talking with you soon.

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