Drug Actions PDF

Most successful treatments require a combination of any of the following: 1. Drug therapy/treatment using drugs 2. Diet therapy/diet restrictions 3. Physiotherapy - refers to treatment such as light, water and heat 4. Psychological therapy GENERAL PRINCIPLES OF D R U G ACTION About 8 0 % of d...

Most successful treatments require a combination of any of the following: 1. Drug therapy/treatment using drugs 2. Diet therapy/diet restrictions 3. Physiotherapy - refers to treatment such as light, water and heat 4. Psychological therapy GENERAL PRINCIPLES OF D R U G ACTION About 8 0 % of drugs are taken orally and undergo 4 phases, namely the: 1. Pharmaceutic phase or dissolution - refers to the reduction of drugs in solid form (e.g. tablets and capsules) into smaller particles and their dissolution into a liquid to facilitate absorption 2. Pharmacokinetic phase - refers to the process of drug movement, its absorption, distribution, metabolism and excretion. 3. Pharmacodynamics - is the mechanism of drug action and its effects on the body 4. Pharmacotherapeutic phase - includes the different approaches to treating diseases  Pharmaceutic Phase - A process where drugs in solid form (tablet or capsule) must disintegrate into small particles to dissolve into liquid. Pharmaceutic Phase  DISINTEGRATION – Breakdown of a tablet into smaller particles  DISSOLUTION – Dissolving of the smaller particles in the GI fluid before absorption Pharmacokinetic Phase - Process of drug movement to achieve drug action - This phase describes the time course and disposition of a drug in the body, based on its absorption, distribution, metabolism, and elimination. - 4 Process: ABSORPTION - DISTRIBUTION - METABOLISM - EXCRETION Kinetics = movement Deals with drug’s actions as it moves through the body. How the body acts on the drug How? → ABSORBED (taken into the body) → DISTRIBUTED (moved into various tissues) → METABOLIZED (change into a form that can be excreted) → EXCRETED (removed from the body) In clinical practice, pharmacokinetic considerations include the following: 1. the onset of drug action (how long it will take to see the beginning of the therapeutic effect) 2. drug half-life, timing of the peak effect (how long it will take to see the maximum effect of the drug) 3. duration of drug effects (how long the patient will experience the drug effects) 4. metabolism or biotransformation of the drug 5. and the site of excretion. LOADING DOSE Amount of drug to immediately provide a therapeutic effect or reach critical concentration  Absorption It refers to what happens to a drug from the time it is introduced to the body until it reaches the circulating fluids and tissues. A drug’s movement from its administration site into systemic circulation Can vary depending on factors such as: → Administration route → Patient’s age & condition → Drug’s solubility, interactions Drugs can be absorbed: → GI tract: Orally & Rectally → Mucous membranes → Skin → Lungs → Muscle and SQ How are drugs absorbed? → At cellular level: active transport or passive diffusion Passive transport ​(diffusion and facilitated diffusion) - DOESN’T require energy to move drugs across the membrane - occurs in two (2) processes: 1. Diffusion - drug moves across the cell membrane from an area of higher concentration to lower concentration. 2. Facilitated Diffusion - relies on a carrier protein to move the drug from an area of higher concentration to lower concentration. Active Transport ​(needs enzyme or protein) - Requires a CARRIER such as enzyme or a protein to move drugs against a concentration medium. - Energy is required for active absorption. 1. Drugs in liquid form are more rapidly absorbed than solid drugs. 2. Drugs given intramuscularly are absorbed faster in muscles that have increased blood flow like deltoid than those that DO NOT like gluteus maximus. 3. Drugs given rectally are absorbed slower than drug administered by mouth 4. Subcutaneous has decreased blood flow when compared with Intramuscular thus absorption rate is slower in subcutaneous than in IM.  Other factors that affect absorption:  Lipid/water solubility  Acidity of the stomach  Blood flow  pH  Presence/absence of food  Pain/stress Bioavailability percentage of the administered drug dose that reaches the systemic circulation. Factors affect include the drug form, route, GI mucosa, food and other drugs and changes in liver metabolism. FAST ACTING If only a few cells separate the active drug from systemic circulation, absorption occurs rapidly, and drug quickly reaches therapeutic level Sublingual, IV, Inhalation NOT SO FAST Oral, IM, SQ - slower rate of absorption Due to complex membrane systems of GI mucosal layers, muscle, and skin delay drug passage MORE BLOOD, MORE ABSORPTION Increased blood flow to an absorption site improves drug absorption More rapid absorption leads to quicker onset of drug action Pain and stress decrease absorption due to: a. change in blood flow b. reduced movement through GI High fat and solid foods - slow rate at which contents leave stomach and enter intestine Drug combination or with food – cause interactions that may increase or decrease absorption Distribution Refers to movement of a drug from the systemic circulation into tissues. As with absorption, factors that can affect distribution include the drug’s lipid solubility and ionization and the perfusion of the reactive tissue. Depends on several factors: a. Blood flow/Perfusion b. Lipid solubility c. Protein binding BLOOD FLOW Drug is quickly distributed to organs with large blood supply like heart, liver, kidneys Slower distribution rate (internal organs, skin, fats and muscle) LIPID SOLUBILITY Ability to cross cell membrane –depends whether it is water or lipid soluble Membrane crossing : lipid soluble easily cross thru cell membrane PROTEIN BINDING Drugs can remain free or bind to protein INACTIVE → Portion of drug that bind to protein → NO therapeutic effect ACTIVE → Free or unbound portion Most drugs are bound to some extent to proteins in the blood to be carried into circulation. The more bound to the protein, the more difficult it can be for the medication to be released and able to cross membranes to get to the tissue cells. Metabolism Also called Biotransformation Process by which body change a drug from its dosage form to a more water-soluble form that can be excreted The liver is the most important site of drug metabolism, or biotransformation, the process by which drugs are changed into new, less active chemicals. Everything that is absorbed from the GI tract first enters the liver to be “treated.” The liver detoxifies many chemicals and uses others to produce needed enzymes and structures. FIRST PASS EFFECT A mechanism wherein liver metabolizes much of the drug before it enters circulation FACTORS THAT AFFECT METABOLISM 1. Age. Infant and elderly have reduced ability to metabolize some drugs. 2. Nutrition. Liver enzymes involved in metabolism rely on adequate amounts of amino acids, lipids, vitamins and carbohydrates. 3. Insufficient amounts of major body hormones. HALF-LIFE Time it takes for the plasma concentration of a drug to fall to half of its original value Time it takes for one half of the drug to be eliminated by the body Example: Drug is 20 mg - half life 2 hours. 10 mg of the drug will remain after 2 hours from administration Factors that affect a drug’s half-life include its rate of absorption, metabolism, excretion Knowing how long a drug remains in the body helps determine how frequently a drug should be administered EXCRETION Elimination of drugs from circulation Kidneys through urine-major site Other exit points of drugs → liver, lungs, into breast milk, through saliva, tears & sweat Creatinine and blood urea nitrogen (BUN) are use to determine renal function It is important for nurses to know their patient’s kidney function to ensure correct dosage Factors that Affect Drug Excretion 1. Renal excretion. 2. Drugs can affect elimination of other drugs. 3. Blood concentration levels. ONSET OF ACTION Time from administration until therapeutic effect begins Rate of onset -varies depending on route of administration and other pharmacokinetic properties PEAK CONCENTRATION Maximum blood concentration level achieved through absorption DURATION OF ACTION Length of time the drug produces its therapeutic effect  Pharmacodynamic Phase How the drugs affect the body Study of drug mechanisms that produce biochemical or physiologic changes in the body. Science dealing with interactions between the chemical components of living systems and the foreign chemicals including drugs that enter those systems DRUG ACTION Interaction at the cellular level between a drug and cellular components DRUG EFFECTS Response resulting from this drug action MECHANISMS OF DRUG ACTIONS 1. To replace or act as substitutes for missing chemicals 2. To increase or stimulate certain cellular activities 3. To depress or slow cellular activities 4. To interfere with the functioning of foreign cells (microorganism or neoplasm) Dose-Response Relationship It is the body’s physiologic response to changes in drug concentration at the site of action Potency Amount of drug needed to elicit a specific physiologic response to a drug A drug with high potency produces significant therapeutic response at low concentration Low potency produces minimal therapeutic responses at a low concentrations Maximal Efficacy The point at which increasing the drug’s dosage no longer increases the desired therapeutic response Therapeutic Index Describes the relationship between the therapeutic dose of the drug (ED50) and the toxic dose of the drug (TD50) Difference between the toxic and therapeutic doses Therapeutic Dose (ED50) Is the dose of a drug that produces a therapeutic response in 50% of the population Toxic Dose (TD50) Is the dose of a drug that produces a toxic response in 50% of the population If therapeutic and toxic doses are close, the drug is said to have a narrow therapeutic index-require close monitoring to ensure patient safety  Onset, Peak and Duration of Action Onset The time it takes of a drug to reach the minimum effective concentration after administration Peak Drug reaches its highest concentration in blood Duration of Action length of time the drug exerts therapeutic effect  Related terms in Pharmacology Agonist -Drugs that activate receptors and produce a desired response Antagonist -Drugs that prevent receptor activation and block a response Nonspecific drug -Drug that affect multiple receptor sites Nonselective drug -Drug that affect multiple receptors  Drug toxicity -occurs when drug levels exceed the therapeutic range toxicity may occur secondary to overdose or drug accumulation Tolerance -A decrease responsiveness to a drug over the course of therapy Tachyphylaxis -Acute, rapid decrease in response to a drug. -Drug tolerance to a frequently repeated administration of a certain drug.  Drug interaction -Altered or modified action or effect of a drug as a result of interaction with one or multiple drugs. Drug nutrient interactions -food may increase, decrease or delay the body’s pharmacokinetic response to drugs. Additive drug effect -response is increased beyond what either could produce alone. Example: diuretic and antihypertensive  Synergist drug effect or potentiation -The clinical effect of the two drugs given together is substantially greater than that of either drug alone Example: Co-Amoxiclav Antagonistic drug effect One drug reduces or blocks the effect of the other Example: antidotes  Placebo effect -A drug response not attributed to the chemical properties of a drug. -Physiologic benefit from a compound that may not have the chemical structure of a drug effect. Ethnopharmacology -A subdivision of ethnomedicine and focuses on the use of herb, powder, teas and animal products as healing remedies