5 anxiety disorders

PHARMACOLOGY 23Only when we look at both pharmacodynamics and pharmacokinetics can wepredict the net effect that a medication will have. Appreciating these basic aspectsof pharmacology helps us not only to anticipate what symptoms or illnesses a medicationis likely to treat but also to recognize the side effects and potential interactionsthe medication is likely to have.2.4.2 PharmacokineticsBefore a medication can be of any help, it has to get to where it can act to produceits beneficial effects. For psychiatric medications, the action is, of course, in thebrain. The problem is that it is relatively difficult for medications to get there. Thisis no accident. Our bodies are designed to protect our most vital organs. Our ribcage surrounds our heart and lungs. The skull encloses the brain, and the brain isalso protected by the so-called blood–brain barrier from invaders that enter thebloodstream. In this section, we will describe the steps your medication takes to getto your brain and the hurdles it encounters along the way.Medication Transportation System. If the brain, the spinal cord, and thenerves make up the body’s communication system, then the heart, blood vessels,and blood are the body’s transportation system. Blood carries oxygen and nutrientsto the organs and then returns the wastes for disposal. Medications use this sameinternal highway system to travel throughout the body.There are three steps that a medication takes during its travel through the body.First, the medication must somehow travel from outside the body and enter thebloodstream. Second, the medication is escorted while it is circulating in the bloodstream.Third, the medication must exit the bloodstream. We’ll now describe eachof these three steps in a little more detail.1. Entering the Bloodstream. The way that a medication enters the bloodstreamdepends largely on how it is taken. There are many ways of ingesting medication,and those that are frequently used for psychiatric medications (or mind-alteringillicit drugs) are shown in Table 2.1. The route of administration dictates how muchof the medication reaches the bloodstream and how quickly it gets there.The most common way to take medications is by mouth (orally). This is theslowest and least efficient way to get medication into your system. When a tablet orcapsule is swallowed, much of it either passes through the gastrointestinal tractwithout ever being absorbed into the bloodstream or is inactivated by the liver beforeit has a chance to reach the rest of the body (more on this later). The fastest andmost efficient means to get medication into the bloodstream is to inject it directlyinto a vein (intravenously). If oral medication is so much slower and so much lessefficient, then why do we usually take our medications by mouth? We do so becauseit is easier, cheaper, safer, and painless to take medications orally.There is perhaps no better illustration of the impact of the route of administrationthan the sad story of cocaine. For centuries, coca leaves were chewed bythe indigenous peoples of South America for a boost of energy while working in