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Lecture 2
Pharmacokinetics I
| Question | Answer |
|---|---|
| Pharmacokinetic principles | once a drug is administered: Absorbed into bloodstream Distributed to site of action Permeate through each compartment Metabolized (liver) Eliminated (kidney) |
| Prodrug | inactive precursor chemical that is absorbed and then converted to active drug (clopidogrel for ex.) |
| Drug routes for enteral | PO, SL, buccal |
| Drug routes for parenteral | IV, IM, SC, ID |
| Advantages for parenteral | rapid onset of action; dosing control |
| Disadvantages for parenteral | local tissue damage/infections |
| IV | rapid effect and max control; bolus; infusion |
| IM | aqueous solutions; specialized depot preps; sustained dose over an extended interval |
| SC | simple diffusion; minimizes risks seen with IV injection; not recommended for drugs that cause tissue irritation |
| Oral | toxicities/overdoses treated with antidotes; disadvantages include pathways involved with drug absorption; enteric-coated preparations; extended-release preparations ER, XR, XL, SR |
| ID | used for diagnostic purposes, desensitization |
| Inhalation/nasal preps | effects almost as rapid as with IV bolus |
| Intrathecal/IV | directly into CSF; local rapid effects |
| Topical | used for local effect |
| Transdermal | systemic effects; rate of absorption varies, characteristics of skin at application site and lipid solubility of medication |
| Rectal | bypasses 50% of portal circulation, minimizing biotransformation of drugs by liver; bypasses GI, absorption erratic and incomplete |
| Absorption | administration site into bloodstream; administration routes (not IV) cause partial absorption/lower bioavailability |
| Absorption factors | where drug is absorbed; characteristics of drug; route of administration |
| Bioavailability | percent of medication that reaches circulation |
| Passive Diffusion | high to low concentration; no carrier; not saturable; lipid-soluble go through liid bilayer; water soluble - channel pore |
| Special Carriers ** | active transport and facilitated diffusion; ABC (ATP-binding cassette) family: p-glycoprotein, multi drug resistance, type 1 transporter |
| Special Carriers | selective, saturable, inhibitable |
| Facilitated Diffusion | transmembrane carrier proteins undergo conformational changes; large molecules; faster than passive diffusion; does not require energy; saturable; competition for carrier protein |
| Active Transport | carrier proteins span the membrane; energy dependent; across a concentration gradient; can be saturated; selective |
| Endo/Exocytosis | large size drugs; in/out of cell |
| Factors Influencing Absorption | expression of p-glycoprotein; contact time; total surface area; blood flow; pH |
| Weak Acids/Bases | acidic drugs release protons forming a charged anion; weak bases release a proton; uncharged drugs pass through; lower pKa of a drug --> more acidic |
| Weak Acids/Bases | uncharged form more lipid soluble; weak acids excreted faster in alkaline urine; weak bases excreted faster in acidic urine |
| P-glycoprotein | efflux; expression decreases absorption; associated with drug resistance |
| Bioavailability | IV drugs = 100%; converted to oral 50%; PO drugs = first pass metabolism |
| Bioavailability factors influencing | solubility of drug = hydrophilic drugs poorly absorbed --> not soluble in aqueous body fluids, cannot reach cells chemical instability = in stomach pH; GI tract enzymes Nature of drug formulation --> effects dissolution and rate of absorption |
| Capillary Permeability | slit junctions --> large protein bound; NOT BRAIN (undergo active transport) tight junctions prevents protein bound and hydrophilic --> form BBB lipid soluble drugs readily penetrate CNS |
| Protein Binding ** | plasma proteins: albumin = major drug binding protein --> keeps drug in blood |
| Protein Binding | tissue proteins: drugs in tissues and tissue reservoirs = source of drug |
| Volume of Distribution | fluid volume required to contain the entire drug in body at same concentration measured in plasma |
| "Apparent" volume of distribution | ratio of total amount in body vs. drug plasma concentration |
| High Vd | lots of drug in tissue; extravascular and lipophilic |
| Low Vd | lots of drug in blood; size MW, plasma, hydrophilic |
| Factors affecting Vd ** | 1) size (MW): high MW drugs remain in plasma, low VD 2) plasma protein; binding/extravascular --> plasma (same water) = low VD; extravascular = high vd 3) hydrophilic = low vd; lipophilic = high vd 4) capillary permeability |
Created by:
bluedolphin7
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