BIOL G200-Pharmacology Ch.4: Pharmacokinetics

What is pharmacokinetics?

movement of medicine; the study of how drugs move throughout the body & how the body deals with meds

What is target tissue?

the cells that are the focus of action by a chemical (hormone, medication, other molecules)

What are the 4 processes of pharmacokinetics?

1. Absorption

2. Distribution

3. Metabolism

4. Excretion

What is the Absorption process in pharmacokinetics?

movement of substance from site of administration, across body membrane into circulating fluids (i.e., bloodstream)

Most drugs (not all) must be _____ for their action.

absorbed

What is passive transport or active transport the most common method of med entry ? How?

passive transport via simple diffusion

Which type of diffusion is faster for medication absorption?

simple diffusion

How do high fat meals affect med absorption?

high fat meals = decreases stomach movement = delayed absorption

How does the combo of certain antibiotics + metallic cations (e.g., Ca2+, Fe2+, Mg2+, Al3+) affect med absorption?

decreases absorption; binds to form heavy insoluble complex that body cannot absorb

How do certain ingredients in dietary supplements that have laxative effects influence med absorption?

increases intestinal movement of ingested material = prevent/hinders intestinal absorption

Why do some drugs have the greatest effect with slower absorption & dissolution? Example?

some drugs are needed to act over a longer period of time before being expelled from the system (e.g., T3 & T4 for hyperthyroidism)

Why do some drugs have the greatest effect with fast absorption & dissolution? Example?

some are required for instant effect (e.g., famotidine= pepcid RP —> stomach acid inhibition)

What are some of the patient variability in liver metabolic activity?

1) Age effect

2) Pt’s w/ Severe Liver Damage (e.g., cirrhosis); decreased liver metabolic activity 

3) Individuals w/ natural genetic mutations or disorders that result in differential liver metabolism

What is the spectrum of liver metabolic activity & what do they implicate?

Poor (PM)→ Intermediate(IM) → Extensive (EM) → Ultra-Rapid (UM)

Poor metabolizer = loss of activity resulting in little to no metabolic activity

Intermediate metabolizer = expresses less than normal metabolic function

Extensive metabolizer = normal metabolic function (aka standard)

Ultra-rapid = above normal metabolic function; presence of duplicates of gene(s)

All drugs must be absorbed except for the ones through ____.

IV

Why do drugs have to eventually pass through the liver regardless of route of administration?

Meds have to eventually pass through the liver bc we have a closed circulatory system.

What should you do for pt’s who have ultrarapid metabolizers gene & why?

increase drug dosage; less bioavailability

What should you do for pt’s who have poor metabolizers gene & why?

decrease drug dosage; high toxicity bc of high bioavailability

What is excretion in pharmacokinetics?

The removal of drugs from the body.

What determines the drug blood concentration?

drug excretion rate determines drug blood concentration

What organ is the primary site for drug excretion?

kidneys are the primary site for drug excretion

What types of drugs can be reabsorbed and how?

lipophilic drugs via renal tubule back into circulation

What types of drugs are NOT reabsorbed & what happens to them instead?

hydrophilic drugs, they stay in renal filtrate to turn into urine for excretion

When should another dose be given during repeated dosing?

subsequent doses should be administered before drug-blood level drops below min. effective concentration

What is the relationship between half-life and repeated dosing?

they have an inverse relationship

What is the goal of repeated dosing?

to get input=output so that drug-blood concentration reaches therapeutic range and maintains constant over time

note: input rate (amount in system) = excretion rate (amount leaving system) AKA equilibrium

How many half-lives does it theoretically take to reach equilibrium?

4 half-lives to reach equilibrium

What is a dose?

amount input in pt’s body

What is a half-life?

the amount leaving pt’s body

What happens when drug absorption rate = excretion of drug?

Pt is in therapeutic range so steady therapeutic lvl distributed to tissues

Where does biotransformation of drugs occur in the body?

intestines, kidney, & liver (highest biotransformation)

*note: intestines & kidneys contain enzymes in cells that have same function as liver

If a pt has adverse effect to an acidic drug, what can be done to increase excretion rate?

give pt sodium bicarbonate (e.g., aspirin) to produce a basic environment in renal filtrate; acidic meds + alkaline environment = ionization → increased excretion

If a pt has adverse effect to an basic/alkaline drug, what can be done to increase excretion rate?

give pt citric acid or ammonium chloride (e.g., diazepam) to produce acidic environment in renal filtrate; basic meds + acidic environment = ionization → increased excretion

Why must therapeutic drug monitoring be done?

to ensure drug-blood lvl does NOT reach toxic concentration range; drugs have various therapeutic ranges (some have wide range, others have narrow range)

What technique of dosing reaches therapeutic range faster?

loading dose

What is loading dose ?

giving pt a higher amount of drug as a first dose to reach minimum effective concentration so that drug blood lvl can reach therapeutic range more quickly before initiating maintenance doses/normal doses

Which dose technique should be used in urgent situations when pt’s drug-blood lvl needs to be raised quickly?

loading dose

What is the only true difference between loading dose & repeated dose?

the time it requires to reach therapeutic range

Which dose technique is often used with drugs that have a higher half-life (t_1/2)?

loading dose

if pt requires 2-weeks of antibiotics what would the nurse do?

give CONTINUOUS I.V. infusion