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Absorpt + distrib
Drug Absorption and Distribution
| Question | Answer |
|---|---|
| Drug absorption | The movement of drug molecules across biological barriers (mostly layers of cells) from the site of administration to the blood stream. |
| Bioavailability | % dose that gets into body |
| Bioequivalence | Similarity between 2 formulations of same drug (active ingredient) |
| Speed of drug onset | How long it takes the drug to begin working |
| Dosing interval | How often the drug should be given |
| Site of action | Whether drug stays local or acts systemically |
| What factors affect drug absorption? | • Rate of release of drug from pharmaceutical preparation • Membrane permeability of drug • Surface area in contact with drug • Blood flow to site of absorption • Destruction of drug at or near site of absorption |
| What determines the rate of release of drug from pharmaceutical preparation? | Dosage form, additives, manufacturing parameters, delayed release preparation, sustained release preparations |
| Describe the rate of release for drugs prepared as: A) solutions, B) capsules and tablets, C) creams, ointments and suppositories | A) no delay, immediate release, B) delay (dissolution) followed by rapid release, C) NO DELAY but slow release |
| What additives (excipients) decrease the rate of dissolution? Increase rate? What factors increase rate of dissolution? What factos have variable effects on rate of dissolution? | Decrease: binders, lubricants, coating agents. Increase: disintegrants. Variable: diluents, coloring agents, flavoring agents |
| How does tablet compression affect rate of release of a drug? Shape? Size? | Compressed (hard) tablets dissolve more slowly; round tablets dissolve more slowly; large tablets dissolve more slowly |
| What is an enteric coating used for? | Coating that dissolves in intestines, NOT STOMACH (example: some aspirin formulations to avoid gastric bleeds) |
| How do reservoir diffusion products work? | Drug diffuses from pill core through membrane shell |
| How do matrix diffusion products work? | Drug diffuses through matrix in which it is embedded |
| How do matrix dissolution products work? | Drug release as matrix dissolves |
| How do osmotic tablets work? | Drug pumped out by osmotic forces |
| How do ion-exchange products work? | Drug bound to resin exchanges with endogenous ions |
| How does lipophilicity affect membrane permeability of drugs? | It increases it |
| What molecular groups enhance lipophilicity? Which ones decrease it? | Aliphatic and aromatic structures; polar groups |
| How does ionization affect membrane permeability? | Ionization DECREASES membrane permeability |
| Weak acids in intestines are mostly (ionized/nonionized); in stomach, they are mostly (ionized/nonionized). Which one of the two epithelia will it be able to pass through? | Ionized; nonionized; stomach (since ionized in intestine) |
| Weak bases in intestines are mostly (ionized/nonionized); in stomach, they are mostly (ionized/nonionized). Which one of the two epithelia will it be able to pass through? | Nonionized; ionized; intestine (since ionized in the stomach) |
| What is the pH of the stomach? | ranges from 1 to 2 |
| What is the pH of the intestines? | ranges from 6.6 to 7.5 |
| Which anatomical structures have low surface areas? Which structures have high surface areas? | Eyes, nasal cavity, buccal cavity, rectum, stomach, large intestines. Small intestines and lungs |
| What determines tissue blood flow? | Physiology and pharmacology (presence of vasoconstrictors or vasodilators in drug) |
| What structures have low blood flow (5)? | Eyes, stomach, large intestines, rectum, subcutaneous tissue |
| What structures have high blood flow (5)? | small intestines, lungs, muscle, buccal cavity, nasal cavity |
| Why are some painkillers administered with vasoconstrictors? | To limit the systemic spread (e.g. epinephrine administered with anesthetics in dental procedures to restrict blood flow from site of injection to rest of body) |
| How can biochemistry determine whether a drug is destroyed at or near site of administration (give body organs)? | Liver (hepatic enzymes)--("first pass effect"); microflora in colon; stomach digestive enzymes and acids |
| What does enteral mean? | Term used to describe administration of drug that involves absorption by the GI tract (e.g. oral, sublingual, and rectal) |
| What doe the following parenteral administration abbreviations stand for: IV, IA, SC, ID, IM, IP | intravenous, intra-arterial, subcutaneous, intradermal, intramuscular, intraperitoneal |
| Rank the safety profile of oral, SC, IM, and IV administrations from high to low | Oral>SC>IM>IV |
| Rank the convenience profile of oral, SC, IM, and IV administrations from high to low | Oral>SC>IM>IV |
| Rank the cost profile of oral, SC, IM, and IV administrations from high to low | IV>IM>SC>Oral |
| Rank the bio-availability profile of oral, SC, IM, and IV administrations from high (and reliable) to low (and unreliable) | IV>IM=SC>Oral |
| Rank the onset of action profile of oral, SC, IM, and IV administrations from immediate to delayed | IV>IM>SC>Oral |
| Rank the patient compliance profile of oral, SC, IM, and IV administrations from high to low | IV>IM>SC>Oral |
| Rank the interactions with food risk profile of oral, SC, IM, and IV administrations from high to low | Oral>IV=IM=SC=none (only Oral has risk) |
| Rank the commercial availability of dosage forms of oral, SC, IM, and IV administrations from high to low | Oral>IM=SC=IV |
| Rank the volume of drug profile of oral, SC, IM, and IV administrations from high to low (???) | Oral=IV>IM>SC |
| Rank the availability of sustained release dosage forms of oral, SC, IM, and IV administrations from high to low | IM>Oral>SC>IV |
| Rank the availability of possible vehicles for administering drug via oral, SC, IM, and IV administrations from high to low | Oral=IM=SC>IV |
| What are the advantages of administering drugs sublingually? | Rapid absorption that bypasses liver (e.g. nitroglycerine) |
| What are the advantages of administering drugs rectally? | Great for vomiting patient or one that cannot (will not) swallow medication; partially (50% bypasses liver) |
| What administration routes can be used to concentrate drugs in: lungs, skin, nose, eye, ear? | inhalation, topical, intranasal, opthalmic, otic |
| What is/are the purpose(s) of administering drugs at target site? | Increase efficacy, decrease toxicity (by limiting systemic absorption) |
| Drug distribution determines what? | Where drugs act |
| What antibiotic might be used to treat prostatitis? | Ciprofloxacin penetrates the prostate gland and is thus effective in bacterial prostatitis (most antibiotics don't enter prostate-->ineffective) |
| Why is fexofenadine considered a non-sedating antihistamine? | Excluded from Brain by BBB, therefore nonsedating; others freely enter the brain and cause marked drowsiness |
| How is penicillin removed from the body? | Actively transported into proximal tubules and rapidly excreted by kidneys |
| How are inhalation anesthetics distributed + eliminated? | Distribute into alveolar spaces-->eliminated by lungs |
| Drug distribution determines where drugs are ____. | eliminated |
| How is raloxifene eliminated? | Transported by liver into intestines-->reabsorbed (enterohepatic circulation)-->greatly increases time raloxifene lasts in body |
| What is raloxifene used for? | Treatment of osteoporosis in postmenapausal women |
| What (7) physiological factors affects drug distribution? | Organ blood flow, barriers to drug diffusion, adipose tissue, tissue protein binding, plasma protein binding, drug transport, ion trapping |
| Describe how blood flow affects drug distribution and effect (over time) | High blood flow: larger amounts delivered to them over time (high initial concentration and initial effect) but will diminish as it's redistributed throughout body to sites with lower blood flow |
| How does the endothelium affect drug diffusion? | Pores on capillary endothelium allow for rapid (paracellular) diffusion of most drugs into interstitial space; tight junctions close the pores->drug molecules must diffuse across (transcellular) |
| Which types of drugs diffuse freely across capillary beds with tight junctions? | Lipophilic drugs rapidly diffuse across capillary beds with tight junctions; hydrophilic drugs mostly excluded |
| What are the (3) main components of the Blood brain barrier (BBB)? | Tight junctions, capillaries in brain wrapped by pericapillary glial cells that enhance BBB, P-glycoprotein in brain capillaries pump out drugs of endothelial cells-->contributes to BBB |
| When can hydrophilic drugs enter the brain? | GENERALLY: BBB impermeable to hydrophilic drugs, but barrier is broken during ischemia and inflammation (allows antibiotics to perfuse through) |
| What is the effect of adiptose tissue on drug distribution? | Lipophilic drugs distribute into adipose tissue-->may need more initial drug bolus to achieve desired effect (more dose), though deposit in fat may increase ammount of time it remains in body; distribution may differ in thin vs obese patients |
| How does tissue protein binding affect drug distribution? | Some drugs highly bound to tissue protein; may necessitate larger inital bolus of drug to achieve desired effect; large depots of drugs may necessitate longer period of time for drug to exit body |
| What is the effect of plasma protein binding on drug distribution? | Some drugs highly bound to plasma proteins; binding of drugs by plasma proteins limits distribution of drugs out of vascular compartment-->more drug initially to achieve desired effect; delivery to elimination organs |
| What plasma protein do acidic drugs bind to? What about basic drugs? | Albumin; alpha1-acid glycoprotein |
| Describe the potential drug-drug interaction between two drugs that bind strongly to plasma proteins | Displacement of highly plasma protein bound drug by another drug may lead to rapid increase in the availability of "free" unbound drug (e.g. unconjugated bilirubin displaced from albumin by drugs, esp in newborns) |
| What is the effect of drug transport on drug distribution? | May increase or decrease distribution of drugs to certain tissues; most diuretics transported by proximal tubules into nephron, process that delivers diuretics to site of action |
| Describe a potential drug-drug interaction due to drug transport | Example: probenecid (gout medicine) blocks transport of diuretics into proximal tubule-->blunts effects of diuretics on salt and water excretion |
| What is ion trapping? Low pH compartments trap which type of drugs? What about high pH compartments? Why? | Weak bases trapped in low pH compartment (ionized-->can't pass membranes). Weak acids trapped in high pH compartments (same reason). Nonionized drug can pass freely through membrane |
| How would increase removal of aspirin in the case of an overdose? | Ion trapping can be used to distribute drugs into urinary compartment to increase excretion of poisons; systemic addition of Na2CO3 alkalinizes urine to treat overdoses of aspirin and phenobarbital (weak acids) |
| How would increase removal of amphetamine in the case of an overdose? | Systemic addition of ammonium chloride useful to treat amphetamine overdoses (acidifies urine-->ion trapping since amphetamines mildly basic) |
Created by:
karkis77
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