Pharmacology Made Easy- Introduction

by category, rather than each drug individually, because there are so many

• the drug providers most commonly describe in a drug category
• know these for each category

• generic drug name is interchangable with brand name
• generic and trade name drugs have the same chemical composition

address how various drug forms affect dissolution, absorption rate, and subsequently, a drug's onset of action

• enteric coated (EC): dissolve when the drug reaches the intestine
• Extended Release (ER), Extended Length (XL), Sustained Release (SR, XR) or Sustained Action (SA): all of these release a drug over a period of time

a form of drug that expedites release of the drug

• parenteral= injectable
• IV, IM or subQ

• IV: immediate and complete, drug acts right away
• IM/subQ: varies. if drug is highly water soluble and person has good circulatory blood flow it will be rapid absorption. absorption and action will be slower if less water soluble and/or poorer blood circulation

• applied directly to the skin
• can act directly on the skin: causing an immediate onset of action
• or can be absorbed through the skin: causing a delayed onset of action

describes the absorption, distribution, metabolism and excretion of drugs

• the movement of the drug from the site of administration to the various tissues of the body
• ie: oral drugs must absorb through the intestinal wall and enter the portal vein before passing through the liver and entering circulation

the liver

• since part of the drug may inactivate when it passes through the liver the actual amount available to the body can be less than what the patient ingested
• the first pass effect refers to this

the amount of drug available to the body after passing through the liver

• happens after absorption
• the movement of the drug by the circulatory system to its intended site of action
• areas of the body with a rich blood supply (liver kidneys and heart) receive the highest level of the drug
• lower areas such as bones or areas with barriers (ie blood brain barrier) wont receive as high a level

• The change that occurs in a drug into a more or less potent form, more soluble form of the drug or an inactive form of the drug
• the liver is responsible for this change most often

• the change that occurs in a drug's chemical nature during metabolism
• this change most often occurs in the liver

• the new or altered form of the drug after metabolism
• a by-product of metabolism

• the elimination of a drug or its metabolites by various parts of the body
• ie- kidneys eliminate many drugs in the blood in the urine
• or gi drugs eliminated in the feces, through the skin or out of the lungs

• the time it takes for the amount of a drug in the body to decrease by half
• this decrease reflects how quickly and effeciently a drug metabolizes and excretes
• short half-life drug administration could be several times per day while a long half-life drug is only needed once per day

a decrease in the functioning of the liver or kidneys increases the half life of a drug, since it wont be metabolized or excreted as quickly- so if you dont adjust the dosage and frequency of the drug these patients can experience toxicity

the amount of time it takes for the drug to demonstrate a therapeutic response

the time it takes a drug to demonstrate its full therapeutic effect

the time that a drug's therapeutic effect lasts

the point in time when a drug is at its lowest level in the body

• take samples of blood to measure the amount of drug in the patients blood
• some drugs (ie antibiotics) require you to maintain a constant therapeutic level in the blood in order for them to continue to have an effect

biochemical changes that occur in the body as a result of taking a drug

therapeutic effects are the intended effects of the drug while side or adverse effects are unintended effects

these occur after a change in either how cells function, the cellular environment or in the action of enzymes in the body

• changes in cellular function cause a greater or lesser response than what normally occurs
• drugs that do this are agonists and antagonists

drugs that bind a receptor on a cell and cause a greater than typical response

• drugs that bind on a receptor on cells and block/inhibit or lessen the typical response
• antagonists can exert their effect in a competitive or non competitive manner

antagonists that compete with an agonist for the same receptor site

• antagonists that block an agonist's access to receptor sites
• these bind non agonist receptor sites to inactivate the receptor

• changes in the cellular environment occur when drugs interfere with the structure of the cell, such as the cell wall, or one of the cells critical processes such as replication
• ie: penicillin abx inhibit cell wall synthesis resulting in destruction of certain bacteria

• includes selective interaction
• selective interaction: a process where a drug may change a target molecule's typical response (inhibit or enhance the action of an enzyme)
• drugs that inhibit an enzymes effects will create less metabolites than usual while drugs that enhance it will create more metabolites

• the action a drug exerts in the body
• a provider chooses drugs for a patients treatment plan based on the expected pharmacologic action of the drugs
• abx have the ability to kill bacteria so they are chosen for infections
• many drugs' pharmacological actions have more than one therapeutic use (ie diphenhydramine works for allergies, motion sickness or for parkinsons)

• both are unintended nontherapeutic effects of a drug that occur at a therapeutic dose
• side effects: unintended effects that commonly occur and are mild in nature
• adverse effects: unintended and unexpected effects that are more severe and can be life threatening

• allergic reaction- life threatening anaphylactic shock
• patients who get a mild reaction (ie rash) to a drug need to avoid taking it again due to the risk of anaphalaxis, more exposure increases sensitivity and may cause a more sever reaction next time

• an exaggerated response of the body's immune system to a drug that causes a massive release of histamine and other chemical mediators
• symptoms: swelling of eyes, face mouth, throat, difficulty breathing, wheezing, rapid heart rate, very low bp, cardiac arrest
• treatment: epinepherine to raise bp and dilate bronchi and diphenhydramine to block additional release of histamine. you want to reestablish airway and oxygen therapy

• drug tolerance
• cumulative effects
• drug toxicity

• the body's decreased response to a drug it receives over a period of time
• providers must increase the dosage to get a therapeutic effect
• tolerance to narcotic pain drugs can result after 10-14 days of therapy

• occur when the amount of drug a patient receives is greater than the rate its excreted
• common in- older adults with decreased cardiac and kidney function, those with kidney/liver disease
• for these people you need to decrease drug doses accordingly

• occurs when a patient receives excessive dosages of a drug
• can also happen when impaired excretion of a drug allows it to build up
• can also happen with a drug with a small margin of safety is given or when a drug given over a long period of time gradually builds up

• may be irreversable and life threatening
• ie vancomycin can cause permanent damage to cranial nerve #8, decreased hearing or deafness

• only use drugs that interact with certain medical conditions/ foods when necessary and when the benefits outweigh the risk
• take extra precaution with patients with medical conditions- ie a person put on blood thinners for stroke but also has peptic ulcers needs to be monitored to prevent stomach bleeding
• limit certain types of food that react with certain drugs

• drugs a provider should not prescribe because they have the potential to cause serious or life threatening effects
• some drugs are contraindicated for certain populations or in combination with certain foods

when one drug changes the way another drug affects the body

• when the combined effect of 2 drugs you give together is the same as each drug you give alone in similar doses
• ie when a patient takes 2 CNS depressents (alcohol +opioids) they add together
• 1+1= 2

• occur when the effect of one drug is greater if you give it with another drug. 
• 1+1 = greater than 2 
• ie when you give asprin with Warfarin (blood thinner) the effects of warfarin increase and severe bleeding can occur

• occur when the effect of one drug is decreased or blocked if you give it with another drug
• 1+1= less than 2
• ie give a drug for asthma to open airway and another drug for cardiovascular effect that has a side effect that constricts the airway it inhibits the other (This is 1+1=0 effect)

• a food changes the way a drug effects the body
• can result in increased levels of drug in the body, which occurs when food increases the amount of drug absorbed or the rate at which its metabolized
• can also result in decreased levels of the drug in the body, which occurs when food decreases the absorption amount or rate. the rate of metabolism then counteracts the action of the drug

grapefruit juice can cause sertraline to not be broken down as well by the liver leading to possible toxicity

• women who are pregnant
• women who are breastfeeding
• pharmacokinetic age variations
• dosage adjustments
• physiological changes with aging

• should only take prescribed drugs and only after determining the benefits outweigh the risks
• must avoid all teratogens 
• There are 5 categories of risk to pregnancy- the last 2 are D and X.

possible fetal risk, must weigh benefits against the risks before making a decision

positive fetal risk, should not be used during pregnancy unless absolutely necessary

• again, only take prescribed drugs from provider and only drugs where benefits outweigh risk
• drug levels in breast milk are lower than in blood but can still be transferred
• depending on the type of drug, transferring it to the infant could be dangerous- dependent on the infant size and amount of milk they consume

• in neonates (under 1 month), infants (1month to 1year) and children (1yr to 12 years) -absorption, distribution, metabolism and excretion of drugs is different than in adults
• gastric emptying is slower until 6 to 8 months
• gastric pH is higher until age 2 and until liver matures at 1 year
• less of a drug is metabolized by the liver in its first passthrough
• IM injections have delayed absorption in neonates
• IM injections in infants/children have higher rate of absorption

• the higher water and lower body fat content of these age groups affects distribution
• Infants have a less effective blood brain barrier which allows drugs to enter the brain easier
• fewer enzymes are produced by a neonate or infants liver until age 1, which affects drug metabolism

• fewer enzymes are produced by a neonates immature liver until 1 year of age which effects metabolism
• metabolism increases greatly between 1 and 2 years, it doesnt increase as fast after this but doesnt reach adult rate until 12 years

decreased perfusion of kidney, rate of filtration, tubular resorption

must be made in relation to age, weight and body surface areas to avoid toxicity and overdosage

• affect the absorption, distribution, metabolism and excretion of drugs
• Kidney: decreased blood flow to kidney, decreased glomerular filtration rate
• GI Tract: decreased gastric pH and decreased emptying, decreased intestinal absorption and peristalsis
• Liver: decreased blood flow to liver and lower enzyme production
• Circulatory system: decrease in cardiac output and Tissue perfusion
• you should determine liver and kidney function prior to surgery when considering amount of anesthetic and recovery time and analgesic prescription dose and frequency