1. Pharmacokinetics

2. Pharmacokinetics The study of drug movement throughout the body
Describes how the body deals with medications
Factors act on drug as travels to target cells
Derived from the root words pharmaco, which means “medicine” and kinetics, which means “movement of motion”
Medications are given to achieve a desirable effect. In order to do so, the drug much reach its target cells. Example topical agents for skin conditions, this is simple, I have a skin condition like acne, I will apply some proactive.
For other drugs, the process of reaching the target cell in sufficient quantities to produce a physiologic change may be challenging. Example, control BP, HR with medications especially in a patient who may have other medical problems, we call co-morbidities.
Drugs are exposed to different barriers and destructive processes after they enter the body, thus altering the desirable effect.

3. Pharmacokinetics
Allows nurses to better understand and predict the actions and side effects of medications in their patients.
and the many obstacles, such as membranes, barriers, fluids, and physiological processes, a drug faces to reach its target cells.
Drugs face numerous obstacles in reaching their target cells.
Many membranes that separate drugs from reaching target cell. Ex: taking medication by mouth, must be digested and broken down by mucosal cells of GI tract and capillary membranes to reach bloodstream. And then to leave blood stream again cross capillary cells, travel through interstitial fluid and may have to enter other target cells and cellular organelles such as the nucleus to enter target cell.
Penetrate several layers before produces a response.
When moving toward target cells and passing through various membranes, drugs subjected to numerous physiologic processes

4. Four Components of Pharmacokinetics

5. Absorption
Process involving movement of substance from site of administration, across body membranes, to circulating fluids
Absorbed across skin, mucous membranes (what/where are mucous membranes?), membranes that line the GI or respiratory tract.
Faster absorption in the case of medications administered in critical care designed to be absorbed in seconds or minutes via blood
Absorption is the primary pharmacokinetic factor determining the length of time it will take a drug to produce an effect. The more rapid the absorption, the faster the onset of drug action.
Ex: drugs in emergency department or critical care meant to be absorbed fast. Contraception as Mirena placed in uterus meant to be absorbed over time as provides protection for number of years before have to replace.
Elixir vs. tablet
IV vs. IM
Speed of digestion, motility, enzymes present
Other drug interactions include presence of food in stomach, herbal products, other drug interactions, etc.
What are some primary sites of how medications are administered?

6. Distribution Transport of pharmacologic agents throughout the body
Lipid vs. water soluble
Drug-protein complexes
Drug-drug and food-drug interactions
Simplest factor determining distribution is blood flow to body tissues.
Lower blood supply is more difficult to deliver high concentrations of drugs to these areas.
Most blood supply –heart , liver, kidneys, and brain
Lower blood supply –skin, bone, adipose tissue
Topical, Systemic
Accumulate and storen
Not all drug molecules will reach target cells because drugs bind reversibly to plasma proteins, particularly albumin to form drug-protein complexes. Too large to cross capillary membranes, thus not allowing drug to distribute to body tissues.
Drugs bound to proteins circulate in plasma until released or displaced from drug-protein complex.
Only unbound free drugs can reach target cells or be excreted by kidneys.

7. Distribution Blood-Brain Barrier and Fetal-Placental Barrier
Brain and placenta possess special anatomic barriers that prevent many chemicals and medications from entering.

8. Distribution
Blood-Brain Barrier
Fetal-Placental Barrier
Medications such as sedatives, antianxiety agents, and anticonvulsants readily cross blood-brain barrier to produce actions in the CNS
Most antitumor medications do not easily cross this barrier, making brain cancers difficulty to treat
Serves as important protective function, because prevents potentially harmful substances from passing mother’s bloodstream to fetus
Alcohol, cocaine, caffeine, and certain prescription medications easily cross placental barrier, potentially harming fetus
Some meds such as sedative, anti-anxiety agents, anti-convulsants readily cross the blood-brain barrier to produce it’s actions, where as most anti-tumor meds do not easily cross making it difficult to treat brain cancers/
Fetal placental serves as an important protective function to no harm fetus. Prevents from passing harmful substances from mothers blood to fetus. However there are substances that can pass through such as alcohol, caffeine, certain prescription drugs.
Always consult with healthcare provider.

9. Metabolism
Process of chemically converting a drug to a form that is usually more easily removed from the body
Primary site of drug metabolism is the liver, although kidney and cells of intestinal tract also have high metabolic rates
HEPATIC MICROSOMAL ENZYME P-450 SYSTEM
Complex biochemical pathway and reactions that will alter drugs, nutrients, vitamins, minerals.
Drugs become more water soluable in order to be more easily excreted by the kidneys.
HEPATIC MICROSOMAL ENZYME P-450 SYSTEM: PRIMARY ACTION IS TO INACTIVATE DRUGS AND ACCELERATE EXCRETION
Changes can produce chemical alteration of drug via either making more active than original form causing med to work more, or increase rate of metabolic activity in liver, resulting in need for higher dose of med…
either increase the rate of drug elimination (ultrametabolizers, leading to faster metabolic clearance potentially resulting in reduced effectiveness and need for higher doses) or decrease drug metabolism (poor metabolizers, which may increase the potential for drug interactions and adverse events).
Two populations where hepatic enzyme is reduced?

10. Metabolism
First-pass effect –drugs absorbed after oral administration cross directly into hepatic portal circulation, carrying blood to liver

11. Excretion Removal of drugs from the body
Primary site if excretion is the kidneys
Liver disease of renal failure interfere with natural excretion mechanism –dosing regimens must be carefully adjusted
Other sites
The rate medications are excreted determines their concentration in the bloodstream and tissues
respiratory, glandular
Glandular –saliva, sweat, breast milk

12. Drug’s Plasma Half-Life and Therapeutic Ranges
Length of time required for a medication to decrease concentration in the plasma by one- half after administration
Repeated doses of medication result in an accumulation of a drug in the bloodstream. A plateau is reached, level of drug in plasma is maintained continuously within therapeutic range
Greater the half-life the longer it takes for the drug to be excreted.
Determine how often to take med
Drugs with a half-life of 24 to 30 hours would be administered on a dose schedule of
Three times a day
Twice a day
Once a day
Every other day
Equilibrium occurs because the amount of drug administered = amount of drug eliminated, and there is a continuous therapeutic level of drug distributed to body tissues

13. Drug’s Plasma Half-Life and Therapeutic Ranges
DIGOXIN
Medication for atrial fibrillation
Half-Life: 36-48hrs
Normal Digoxin Level: ng/mL
COUMADIN
Also medication for a- fib, heart valve repair
Normal INR:
Recommended INR:
Drugs with a half-life of 24 to 30 hours would be administered on a dose schedule of
Three times a day
Twice a day
Once a day
Every other day

14. Loading and Maintenance Doses
Loading Dose
Maintenance Dose
Higher amount of drug given once or twice so the plateau is reached faster and the drug quickly produces a therapeutic response
Given to keep the plasma-drug concentration in the therapeutic range