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Pharm Study Questions Test 1 Key Concepts
Module 1
What are the BON rules and regulations for prescriptive authority for the
advance practice nurse?
- Its determined by state law
- Schedule II meds cannot be prescribed by phone
Describe the pharmacokinetic processes of absorption, distribution,
metabolism and elimination and how differences in these areas affect drug
action.
- Absorption : drugs movement from site of administration to the blood o IV: drug must be water soluble to absorb o IM: rapid absorption with water soluble drugs, slow with poorly soluble drugs o Rate= how soon o Amounts=how intense o Chemically equivalent= same amount of identical compound o Equal bioavailability= absorbed at same rate to same extent o
- Distribution : drugs movement from the blood into interstitial space of tissues and from there into cells. o Properties affecting drugs crossing a membrane: ▪ Lipid/water solubility ▪ pH: affections ionization of drug ▪ protein binding ▪ size of molecule (smaller molecules are more able to diffuse) o Determined by: ▪ Blood flow to tissues: Good perfusion=good distribution. Bad blood flow in abscesses and tumors. Lip soluble drugs = high affinity for adipose tissue ▪ Ability of drug exit the vascular system: (once a drug is delivered to the organ or tissue by blood circulation, then it must exit the vasculature). leave through capillary cells, normally not impeded. Impeded in - BBB (blood brain barrier): (only lipid soluble and transport system can cross and PGP pumps drug out and back into blood) BBB not fully functional at birth. - Drugs can cross placenta , but those that are ionized, highly polar, or protein bound do not, and PGP can pump drugs out of placenta and back into mom. - Protein Binding: Albumin too large to leave bloodstream, so if drug binds to protein (albumin) then drug is stuck in bloodstream while
bound. Drug must be unbound to reach site of action or undergo metabolism (restricts distribution). If 2 drugs bind to proteins, then drug-drug interactions can occur because of albumin binding competition. One drug is displaced which = Tconcentration of displaced drug=T plasma drug level=T toxicity ▪ Ability of drug to enter cells: practically all must enter for metabolism and excretion. Determined by lipid solubility, presences of transport system or both
- Metabolism (AKA biotransformation): the enzymatically mediated alteration in drug structure o Hepatic-drug metabolizing enzymes-P450 system (cytochrome P450 (CYP families)): ▪ Induction of drug-metabolizing enzymes- P450 enzyme inducers ↑ rate of drug metabolism = ↓ drug plasma levels= need for higher dose to be effective ▪ Inhibition of drug-metabolizing enzymes- P450 enzyme inhibitors ↓ rate of drug metabolism = ↑ drug plasma levels= need for lower dosing and watch for toxicity ▪ Substrates are metabolized by P450 hepatic enzymes ▪ Therapeutic consequences of drug metabolism: 1. Accelerated renal excretion of drugs- The most important consequence of drug metabolism is renal drug excretion. Can’t excrete lipid soluble drugs, so metabolic conversion of lipid soluble drugs into water-soluble can accelerate renal excretion. 2. Drug inactivation- metabolism can convert active compounds to inactive forms. Common end results of drug metabolism 3. ↑ therapeutic action- metabolism can ↑ effectiveness of some drugs. Ex codeine -> morphine 4. Activation of prodrugs- a prodrug is inactive when administered but converted to be active through metabolism. Ex: BBB drugs lipid soluble then converted to active form once across the BBB 5. ↑ toxicity 6. ↓ toxicity o Special Considerations ▪ First pass effect- hepatic inactivation of certain oral drugs. Give IV ▪ Nutritional status- Metabolism compromised in malnourished pts ▪ Competition between drugs- Competition= one or both drugs metabolized slower= ↑ drug accumulation
- Excretion : where the drugs and their metabolites move out of the body (kidneys most important). Urine, bile, swear, saliva, breast milk, expired air o Steps: ▪ Glomerular Filtration - from blood into tubular urine. Large molecules not filtered. If bound to albumin, then drug stays in blood and not filtered. ▪ Passive tubular reabsorption- lipid soluble drugs are reabsorbed and go back into blood circulation through passive reabsorption. Non lipid soluble drugs (ions & polar compounds) are excreted in urine.
▪ ↓ Therapeutic= propranolol+albuterol= albuterol doesn’t work ▪ ↓ Adverse= morphine+naloxone= no more OD
➢ Unique response
▪ Alcohol + Antabuse= very unpleasant ❖ Pharmacokinetic:
➢ Altered absorption- ↑ gastric ph, laxatives, reduced peristalsis, vomiting, drugs that
reduce regional blood flow (epi with local anesthetic)
➢ Competition for protein binding- If both like to bind to albumin then the level of one or
both will build in the blood and be eliminated quickly unless pt has renal problems
➢ Alteration of extracellular pH
➢ Altered metabolism:
▪ Induction of CYP enzymes- will increase drug metabolism, might need to increase dose of drug being metabolized quicker. If patient stops taking inducer, remember to lower the dose of the other med ▪ Inhibition of CYP enzymes- Will decrease drug metabolism, so might need lower doses of other drug to prevent toxicity.
➢ Altered renal secretion- through filtration, reabsorption, and active secretion.
➢ Interactions that involve P-glycoprotein (PGP)- transports drugs out of cells. Drugs
that induce (increase) PGP, ↓absorption, ↓ fetal drug exposure, ↓brain drug exposure, and ↑ drug elimination ❖ Pharmacodynamic interactions:
➢ Interactions at same receptor- mostly inhibitory
➢ Interactions resulting from actions at different sites- can be potentiative or inhibitory
➢ Combined toxicity- both drugs toxic to same organ
❖ P450 substrates- are drugs that are metabolized b p450 hepatic enzymes. (CNS drugs, B- blockers, antidysrhythmic, antiviral/bacterial, opioids, statins, calcium channel blockers…) ❖ P450 inducers: ↑ rate of drug metabolism ❖ P450 Inhibitors: ↓ rate of drug metabolism
Identify medications with a narrow therapeutic index requiring drug level
monitoring.
➢ Therapeutic Index
▪ Safety = ratio of drug’s LD50/ED50 = ↑ (large) therapeutic index is goo d, ↓ (narrow) therapeutic index is bad ▪ Highest dose required to produce wanted effect should be much lower than lowest dose required to produce death
Discuss the effect of ionization and pH on absorption.
❖ Because ionization of drugs is pH dependent, when the pH and the fluid on one side of the membrane differs from the pH on the other side, the molecules tend to accumulate on the side where the pH most favors ionization
❖ Many drugs are either weak organic acids or weak organic bases, and this can exists in charged and uncharged forms, and whether a weak acid or base carries an electrical charge is determined by the pH that surrounds the medium ❖ Acids tend to ionize in basic media ➢ Acids: proton donor ➢ Weak acids are best absorbed in acidic environments (gastic acid) because they remain in non-ionized form ❖ Bases tend to ionize in acidic media ➢ Bases: proton acceptor ❖ Acidic drugs accumulate on the alkaline side, and basic drugs accumulate on the acidic side. This is what is known as pH partitioning or ion trapping
Discuss factors affecting drug distribution.
o Properties affecting drugs crossing a membrane: ▪ Lipid/water soluablility ▪ pH: affections ionization of drug ▪ protein binding ▪ size of molecule (smaller molecules are more able to diffuse) Discuss barriers affecting drug distribution—such as placental membrane, blood brain barrier and volume of distribution.
- Determined by: o Blood flow to tissues: Good perfusion=good distribution. Bad blood flow in abscesses and tumors. Lip soluble drugs = high affinity for adipose tissue o Ability of drug exit the vascular system: (once a drug is delivered to the organ or tissue by blood circulation, then it must exit the vasculature). leave through capillary cells, normally not impeded. Impeded in ▪ BBB (blood brain barrier): (only lipid soluble and transport system can cross and PGP pumps drug out and back into blood) BBB not fully functional at birth. ▪ Drugs can cross placenta , but those that are ionized, highly polar, or protein bound do not, and PGP can pump drugs out of placenta and back into mom. ▪ Protein Binding: Albumin too large to leave bloodstream, so if drug binds to protein (albumin) then drug is stuck in bloodstream while bound. Drug must be unbound to reach site of action or undergo metabolism (restricts distribution). If 2 drugs bind to proteins, then drug-drug interactions can occur because of albumin binding competition. One drug is displaced which = Tconcentration of displaced drug=T plasma drug level=T toxicity o Ability of drug to enter cells: practically all must enter for metabolism and excretion. Determined by lipid solubility, presences of transport system or both
compounds ❖ Non-renal routes of excretion: ➢ Breast Milk- lipid soluble drugs are easily passed through breast milk ➢ Bile- if drug doesn’t undergo enterohepatic recirculation then leaves this way ➢ Lungs- volatile anesthetics (alcohol) leave this way ❖ Factors that modify renal excretion: ➢ pH dependent ionization- can hasten drug’s elimination by altering urinary pH. Useful with poisons and toxic doses. ➢ Competition between drugs for active tubular transport- delays excretion= prolonged drug effects ➢ Patient age- Newborns and geriatrics have ↓ renal excretion
Discuss terms used to describe drug actions-agonist, partial agonist,
antagonist.
❖ Agonists: activate receptors and mimic body’s own response. Has affinity and high intrinsic
activity
❖ Antagonists: prevent (block) receptor activation. Has infinity, but no intrinsic activity. If
there is no agonist, then antagonists have no effect. ❖ Partial agonists: has moderate intrinsic activity. Can act as antagonist and agonists.
❖ Receptor sensitivity:
❖ Continuous exposure to agonis t =↓ responsive = desensitized/refractory/downregulation ❖ Continuous exposure to antagonist = hypersensitive/supersensitive.
Discuss the impact of food on drug absorption, drug metabolism and on drug
toxicity and action—as well as the timing of drug administration.
❖ Decreased absorption
➢ Can decrease rate and extent
➢ Ex: calcium and tetracycline antibiotics, high fiber and digoxin
❖ Increased absorption
➢ Ex: high calorie food ad invirase more than doubles drug absorption
❖ Food on drug metabolism: Grapefruit Juice
➢ Inhibits metabolism (CYP3A4), therefore raises drug levels. Can last about 3 days.
Doesn’t affect IV drugs.
❖ Food on drug toxicity
➢ Foods with Tyramine + monoamine oxidase inhibitors = high BP
➢ Theophylline (Asthma meds) + caffeine = CNS agitation
➢ Spironolactone + salt substitutes = ↑ K
➢ Antacids with aluminum + citrus drinks = ↑ aluminum
❖ Food on drug action
➢ Vitamin K + warfarin= warfarin doesn’t work
❖ Timing with meals
➢ Most drugs cause upset stomach if taken with no food, if safe then take with food
