Agonists, Antagonists, Receptors & Biopharmaceutics

PHARMACOKINETICS & PHARMACODYNAMCS Jessica Tagerman, PharmD, RPh PHARMACOKINETICS & PHARMACODYNAMICS Pharmacodynamics: What the drug does to the body Pharmacokinetics: What the body does to the drug P H ARM AC ODY N AM IC S What the drug does to the body

TO BEST UNDERSTAND HOW DRUGS WORK, WE ARE GOING TO COMPARE THEIR MECHANISM OF ACTION TO A LOCK AND KEY MODEL. UNLESS YOU HAVE THE

CORRECT KEY, THE LOCK WONT OPEN! Receptor agonis t AN ENDOGENOUS AGONIST IS A N AT U RA L S U BS TA N C E P R O D U C E D BY T H E BO DY. THE AGONIST BINDS TO A SPECIFIC R E C E P T O R , A N D C A U S E S S O M E S O RT O F

P H Y S I O LO G I C A L R E S P O N S E I N T H E BO DY. Agonist moves towards and then binds to the receptor S I M I L A R T O T H E LO C K A N D K E Y M O D E L , T H E AG O N I S T M U S T F I T P E R F E C T LY I N T O T H E R E C E P T O R T O C A U S E AC T I VAT I O N . Physiological Response Agoni

Agoni st st Receptor Molecule IF T H E M OL E C UL E D OE SN T F IT P E R FE C T LY IN T O TH E RE C E P T OR , TH E C E L L W ON T AC T IVAT E AN D A P H Y SIO LOGIC AL RE SP O N SE W IL L N O T OC C U R. (T H E RE F ORE , TH E M OL E C UL E ISN T

C ON S IDE RE D T O B E AN AGON IS T) Not a perfect fit, so this molecule will NOT activate the receptor Agoni st Receptor No Physiological Response

Agoni st IF TH E M OL E C UL E D OE SN T FIT P E RFE C T LY IN T O TH E RE C E P T O R, T H E C E L L W O N T AC TIVAT E AN D A P H Y SIOLOGIC AL RE S P ON SE W IL L N OT OC C UR. (T H E R E FO RE , TH E M OL E C UL E ISN T C ON SID E RE D TO B E AN AGON IST ) This molecule is only an agonist for

Agoni st THIS RECEPTOR! MEDICATIONS Now, lets talk about how medications relate to this model. Drugs can be exogenous agonists, in which they mimic the endogenous agonist, bind to the receptor, and produce the pathological response. Or, drugs can be antagonists, which block the receptor, and therefore prevent the endogenous agonist from binding and causing a physiological response (See next

slide) Agoni st A N TAG O N IS TS: B IN D T O TH E RE C E P T OR IN OR D E R T O B LOC K T H E E N D OGE N O US AGON IST F ROM B IN D IN G. TH E RE F ORE , N O P H YS IOLOGIC AL RE S P ON S E W ILL OC C UR. Agoni st

Receptor Agonist moves towards the receptor, but cant bind, because the antagonist is blocking the receptor Agoni st

No Physiological Response Agoni st Antagonist S U M M A RY Agonists BIND to the receptor, and ACTIVATE a cellular response Antagonists BIND to the receptor, but DO NOT activate a cellular response When you are studying the

medications, understanding the physiological processes behind the diseases will help you understand treatment options! SWITCHING GEARS P H A R MA C OKI N E T IC S What the body does to the drug PH A R M A C O K IN E T I C S

Absorptio n Distributi on Metabolis m Excretion ABSORPTION Absorption = Describes the process whereby a drug enters the

circulatory system Unless the drug is given via IV route, it needs to move from the site of administration into the bloodstream, so 100% of the drug may not be available as active medication (AKA, a drugs BIOAVAILABILITY) Oral Medications: esophagus stomach withstand stomach enzymes small bowel liver systemic circulation DISTRIBUTION Distribution = The movement of the drug throughout the bloodstream and delivery to the site of action Common sites of distribution: blood, muscles, fat tissue, organs You need to be sure the drug is being delivered to where your body

needs it! (Remember carbidopa/levodopa? We needed the dopamine to be delivered directly to the brain, otherwise the medication wouldnt work!) METABOLISM Metabolism = when the drug is broken down or changed by various enzyme systems Purpose of metabolism: mainly to begin elimination! Drugs that have been metabolized = metabolites, may be active or inactive Metabolites are formed with the help of enzymes Some drugs are inactive until they are metabolized to the active form that will cause the effect (These drugs AKA pro-drugs)

Some metabolites are responsible for the toxic side effects of medications. EXCRETION Excretion = how the drug and its metabolites are eliminated from the body Routes of excretion depend on physiochemical properties of drug and function of excreting organ Mainly excreted through urine and feces Can also exit the body through exhalation and sweating, but to a lesser extent Patient with kidney failure: adjust medication dose, otherwise concentration of drug may increase to a toxic range

HALF-LIFE Half-Life: Amount of time it takes for the blood concentration of a drug to decline to of the initial value Example: Medication with life of 3 hours Time Concentration At 3 hrs (max concentration) 60 mcg/mL At 6 hrs

30 mcg/mL At 9 hours 15 mcg/mL Five times the half-life is used to estimate how long it takes to essentially remove the drug from the body. This would be 5 times the half-life of 3 hours, or 15 hours in the example above. BLOOD CONCENTRATION-TIME PROFILES Minimum Toxic Concentration: Largest drug concentration beyond which

there are toxic/undesirable effects Minimum Effective Concentration: Smallest drug concentration needed for effect BIOEQUIVALENCE Bioequivalence = drug products with same bioavailability Pharmaceutical Equivalents

Same active ingredient (same salt form) Same amount of active ingredient Same dosage form Inactive ingredients can be different Pharmaceutical Alternatives

Same active ingredient (but different salt form) Amount of active ingredient can be different Dosage form can be different Inactive ingredients can be different Therapeutic Equivalents Pharmaceutical equivalents that produce the same effects in patients QUESTIONS ?

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