Practical Review of Pharm a c o l o g y C o n c e p t s Sue M. Janda Nancy L. Fagan he term p h a rm a c o l o g y Pharmacology concepts are used ro u t i n e ly in nu rsing practice.T h e s e is derived from the concepts may be as simple as drug names and side effe c t s , or as G reek words “phar- c o m p l ex as pharmacokinetics or pharmacody n a m i c s . All play major makon,” meaning dru g s , roles in drug efficacy and safe t y. A practical rev i ew of pharmacology, Tand “logos,” meaning science. i n cluding pharmacokinetic and pharmacodynamic concepts, will be P h a r macology dates back to p r e s e n t e d . ancient times when man used plants and roots to treat ailments. © 2010 Society of Urologic Nurses and Associates In more recent times, the United U rologic Nurs i n g, p p . 1 5 - 2 1 . States Congress has passed re g u- lations that re q u i re drug manu- f a c t u r ers to study and pro v e Key Wo rd s : Pharmacology, adverse effects, pharmacokinetics, d r ugs are safe and eff e c t i v e pharmacodynamics, therapeutic index. b e f o r e being approved, pre- scribed, and sold to the public. O b j e c t i v e s Even with these studies, no d r ugs are perfectly safe. 1. Explain the four phases of pharmacokinetics. Although all drugs produce dif- 2. Discuss the various ways a drug can be absorbed into the body. f e rent side effects, the objective 3. Describe pharmacodynamics. of drug therapy is to pro v i d e maximum benefits with minimal 4. Explain how patients can respond differently to drugs. h a r m. Pharmacology concepts a re used routinely in nursing practice (see Table 1). These con- cepts may be as simple as dru g names and side effects, or as will provide a practical review of administration can be divided complex as pharmacokinetics or p h a rma cokinetic and pharm a c o- into three categories: enteral, par- p h a rma codynamics. This art i c l e dynamic concepts. enteral, and other (non-enteral or p a r enteral) routes. The enteral P h a r m a c o k i n e t i c s route includes any route using the gastrointestinal tract – oral, Sue M. J a n d a , P h a r m D, FA S H P, is a Staff Pharmacokinetic concepts sublingual, buccal, and re c t a l . P h a rmacist, Alegent Health Immanu e l come into play once a drug enters The parenteral route entails intra- Medical Center, Omaha, NE, and an the body. They include the phases venous, intramuscular, and sub- A d j u n c t i ve Faculty Member, Department of of absorption, distribution, metab- C h e m i s t ry, Midland Lutheran College, cutaneous administrations. The Fremont, NE. olism, and excretion (Lilley, other route consists of inhalation, H a r rington, & Snyder, 2007). topical, transdermal, intranasal, N a n cy L. Fag a n , P h a r m D, is an Assistant intrathecal, intraventricular, and P r o fessor of Pharmacy Pra c t i c e, D e - Absorption ophthalmic (Lilley et al., 2007). p a r tment of Pharmacy Pra c t i c e, Creighton U n i ve r s i t y, Omaha, NE. Absorption is an import a n t The three most common phase of pharmacokinetics and methods of absorption are passive N o t e : The authors reported no actual or includes three aspects: 1) ro u t e s absorption, active absorption, potential conflict of interest in relation to this of administration, 2) methods of and pinocytosis. Passive absorp- c o n t i nuing nursing education art i c l e. absorption, and 3) factors that tion is also known as passive or N o t e : O b j e c t i ves and CNE Evaluation Fo rm a f fect the absorption pro c e s s simple diffusion. It is dependent appear on page 21. (Lilley et al., 2007). Routes of on a concentration gradient and is UROLOGIC NURSING / January-February 2010 / Volume 30 Number 1 15 Ta ble 1. Definitions of Pharmacology Concepts Te r m D e f i n i t i o n A b s o r p t i o n The uptake of substance by a tissue, such as nu t ri e n t s, though the wall of the gastrointestinal t ra c t . A g o n i s t A drug or other chemical that can combine with a receptor on a cell to produce a phy s i o l o g i c reaction typical of a naturally occurring substance. A n t a g o n i s t A drug that counteracts the effect of another dru g . B i o ava i l a b i l i t y The fraction of an administered dose that reaches the systemic circulation. C l e a ra n c e A measure of how well a patient can metabolize or eliminate a drug per unit time. Creatinine cleara n c e A measure of the kidney s ’ ability to eliminate creatinine from the body. E f fe c t i ve dose (ED50) The dose required to produce a specific therapeutic response in 50% of the patients. F i r s t - Pass D r ug removed from the blood or plasma fo l l owing absorption from the gastrointestinal tra c t b e fore reaching the systemic circulation. G l o m e rular filtra t i o n The volume of water filtered out of the plasma though glomerular capillary walls into Bow m a n ’s rate (GFR) capsules per unit of time. H a l f - l i fe The time required for the plasma concentration to be reduced to one-half of the original va l u e. Lethal dose (LD50) A dose that will produce a lethal toxicity in 50% of studied gr o u p. Data obtained from T D 5 0 . Pa r tial agonist A drug that produces a we a ker or less efficient response than an agonist. P h a rm a c o d y n a m i c s The study of the biochemical and physiological interactions of drugs at their sites of activity. P h a rm a c o k i n e t i c s The study of the absorption, distri bution, metabolism, and excretion of a drug, and its metabolites in the body. P h a rm a c o l o g y The science of dru g s, including their composition, uses, and effe c t s. P r o d ru g An inactive drug dosage fo rm that is conve r ted to an active metabolite by va rious biochemical reactions once it is inside the body. R e c e p t o r A molecular structure or site on the surface or interior of a cell that binds with substances, such as horm o n e s, antigens, dru g s, or neurotra n s m i t t e r s. Steady state Rate of drug administration is equal to the rate of drug elimination. Toxicity dose (TD50) A dose that will produce a given toxicity in 50% of the studied gr o u p. T h e rapeutic class A group of drugs with similar mechanism of actions that treat the same disease state. T h e rapeutic index The ratio of the dru g ’s LD50 to its ED50 and measures drug safety margins. Volume of distri bu t i o n The apparent volume required to account for all the drug in the body in the same concentra t i o n as in the sample from the plasma. S o u rc e s : D i c t i o n a ry.com, 2010a, 2010b, 2010c; W i n t e r, 2004. the most important mechanism m o re efficiently absorbed in the f rom an area of low concentra- for drug absorption. In simple stomach than in the intestine. In tion to an area of high concentra- d i ffusion, particles move from an contrast, the intestine is a basic tion. The third method is called a rea of high concentration to an e n v i ron ment and would favor pinocytosis. This process allows a rea of low concentration. There non-ionization of weak bases, cells to carry the drug acro s s is no energy expenditure during such as diazepam, which is more their membrane by engulfing the this process, and drugs must be e fficiently absorbed in the intes- d rug particles (Adams, Holland, small, lipid or fat soluble, and tine than in the stomach. The & Bostwick, 2008; Kee, Hayes, & non-ionized (no positive or nega- second method of absorption is McCuistion, 2009). tive charge) to cross the mem- active absorption, also known as Multiple factors affect absorp- branes. An acidic enviro n m e n t , active transport.