Module 1 Pharmacokinetics

Front 1

biopharmaceutics

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the study of the relationship between the nature and intensity of the drugs biological effect and various drug formulation or administration factors

Front 2

pharmacokinetics

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a study of the time course of drug of absorption, distribution, metabolism, and excretion

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Disposition

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what occurs after the drug is absorbed (distribution & elimination)

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Absorption

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process by which unchanged drug proceeds from side of administration to sight of measurement within the body; the penetration of free drug molecules through a biological membrane

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distribution

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process of delivering drugs into body tissues and fluids following absorption

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metabolism

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chemical alteration of the drug in the body to a different chemical species

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excretion

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removal of intact drug or metabolite from the body

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elimination

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irreversible removal of drug from the body by all routes of elimination; the combined effort of biotransformation and excretion

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absorption is dependent on

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solubility, molecular weight, permeability

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clinical pharmacokinetics

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the application of pharmacokinetic principles to the safe and effective therapeutic management of drugs and an individual patient

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objectives of clinical pharmacokinetics

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1. initial design of drug ghosting regiment 2. refinement of dosing regimen based on serum samples 3. pharmcokinetic work-up 4. research

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Pharmacodynamics

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relationship between the drug concentration at the site of the action and pharmacologic response ; what the drug does to the body

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therapeutic drug monitoring

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the utilization of plasma drug concentrations and clinical data to individualize and optimize a patient's drug therapy

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bioavailability

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the percentage or fraction of the administered dose which reaches the systemic circulation

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bioequivalence

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comparison of bioavailabilities of different formulations, drug products, or batches of the same drug product

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duration of action

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the time the plasma concentration is above the MEC

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lag time

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the time that it takes for drugs to begin being absorbed

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onset time

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the time it takes the plasma drug concentration to reach the MEC

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the intensity of the drug plasma concentration is proportional to

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the number of drug receptor sites occupied

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drug dosing regimen

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dose, route, interval, etc

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bioavailability (F) <1 because

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absorption incomplete, degradation in GI tract, first pass metabolism

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zero order

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the amount of drug decreases at a constant rate

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first order

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the amount of drug decreases at a rate that is proportional to the amount of drug

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nine routes of drug administration

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IV bolus, IV infusion, IM, SC, SL, PO, PR, transdermal, inhalation

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reasons to give drug intravenously

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controlled rate, rapid response, drug has absorption difficulties or stability problems

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reasons to give drugs orally

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avoid high early toxic levels, avoid rapid allergic reactions, easy to administer, drug problems with physical or chemical stability of formulation

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for a drug to be absorbed, it must first…

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be dissolved in fluid at the absorption site (cannot pass through membrane in particulate form)

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the most common rate limiting step in oral absorption

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dissolution (there is also disintegration & GI transfer)

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absorption of drug not complete

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chemical nature of drug (very polar), dosage form, physiology of the patient

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transcellular absorption

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passage of molecule through cell membrane

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paracellular absorption

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that passage of molecules through pores in membrane

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what form of the drug is absorbed better and why

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unionized form, can cross membranes much easier (more lipid soluble)

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the most common method for drug absorption

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passive diffusion

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passive diffusion

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drug goes from area of high concentration to the area of low concentration

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acidic drugs tend to be absorbed from

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the stomach (low pH) *HA

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basic drugs tend to be absorbed from

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the intestine (high pH) *B

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active transport

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specialized transport mechanism whereby drugs are moved against a concentration gradient, requires a carrier, requires energy

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drugs which utilize active transport are analogues of

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endogenous substances

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mechanisms of absorption

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passive diffusion, active transport, facilitated diffusion, ion pair formation

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facilitated diffusion

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carrier mediated, does not require energy, can be saturated and and inhibited, moves along concentration gradient

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ion pair formation

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ionized drug links up with oppositely chared ion, forming a neutral pair (cation drug + anion carrier)

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stomach pH

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1 to 3

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small intestine pH

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5 to 8

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large intestine pH

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6 to 7

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acidic drugs are soluble in the _____ and basic drugs are soluble in the ______

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stomach, intestine

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major area for absorption of drugs and nutrients

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small intestine (huge surface area)

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Gastic emptying rate

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the rate of movement of the GI mass from the stomach to the duodenum

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factors that alter gastric emptying rate

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food, drug coadministration, body position, physiological status of patient

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factors affecting drug distribution

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cardiac output, plasma protein binding, chemical structure of drug

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perfusion ratio

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blood flow /tissue mass

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highly perfused tissues

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spleen, kidney, gut, pancreas, brain, heart, and lungs

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__ of cardiac output is delivered to tissues that comprise less than __ of the body weight

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3/4, 1/10

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stronger acids --> _____ distribution

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narrower

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drug distribution patterns

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remains within the vascular compartment, uniformly distributed through body water, concentrated in a particular tissue, non uniform distribution

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drugs in the brain can only be eliminate by

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the blood

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drug penetration to the placenta is greater in

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the third trimester

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Ion trapping of _____ drugs occurs in the milk

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basic

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proteins involved in binding drug

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albumin, alpha1 glycoprotein, lipoproteins

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albumin

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responsible for maintaining osmotic pressure of the blood and for transport of endogenous substances

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binds to specific site on albumin

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acidic drugs

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extent to which a drug binds to albumin depends on

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a affinity of drug to albumin, number of binding sites on albumin for particular drug, concentration of drug, concentration of albumin

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alpha1 acid glycoprotein primarily binds

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basic drugs

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liver disease causes

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decrease albumin concentration due to decreased protein synthesis

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as free drug increases, drug distribution

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increases

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restrictive elimination

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process of elimination which occurs only to unbound drugs

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characteristics of restrictive elimination

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drug tightly bound to protein, small plasma clearance, small hepatic extraction ratio

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non restrictive elimination

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process of elimination which occurs to protein bound rugs

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characteristics of non restrictive elimination

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drug weakly bound to protein, high liver extraction

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major route for polar drug excretion

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renal

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mechanisms of renal secretion

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glomerular filtration, secretion, reabsorption

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glomerular filtration

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unidirectional process of filtration through porous capillaries of bowman's capsule

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secretion

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active transport of drug from blood into urine, occurs in proximal tubule

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reabsorption

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mechanism for reuptake of drug, offsets effect of filtration, occurs in distal part of tubule

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renal blood flow

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1200mL/min or 1730 L/day

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factors that affect renal excretion

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drug protein binding, partition coefficient, urine PH, molecular size, active secretion properties

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total body clearance

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the volume of fluid cleared of drug per unit time by the entire body

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organ clearance

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measure of an organ's ability to clear a substance

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renal clearance

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the volume of plasma that is cleared of drug per unit time through the kidney

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max renal clearance

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650mL/min

Front 80

if Clr is between 120-650mL/min

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filtration & secretion taking place

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if Clr is between 0-120mL/min

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filtration & reabsorption are taking place

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used to estimate renal function

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inulin, creatinine

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biliary excretion

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drugs can be excreted from the liver into the bile by active transport

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enterohepatic circulation

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cycle in which the drug is absorbed from GI, excreted into bile, & reabsorbed

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properties for biliary excretion

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MW >500, strong polar group, active transport

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three carriers for biliary excretion

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organic anions, organic cations, non-ionized

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biotransformation

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chemical modification of parent drugs resulting in loss of drug from body

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phase one reactions

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oxidative, reduction, hydrolysis

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oxidative reactions

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aromatic hydoxylation, side chain hydroxylation, N- O- S-dealkylation, deamination, sulfoxidation, N-oxidation, N-hydoxylation

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reduction reactions

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azoreduction, nitroreduction, alcohol dehydrogenase

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hydrolysis reactions

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ester hydolysis, amide hydrolysis

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phase two reactions

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glucuronide conjugation, peptide conjugation, methylation, acetylation, sulfate conjugation, glutatione conjugation

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glucuronide conjugation

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esther glucoronide, ester glucoronide, amide glucuronide

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major site of drug metabolism

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liver