L2. Pharmacokinetics

Question 1

What drug absorption route, while the safest and most convenient, has the slowest onset effect and is least predictable?

Answer 1

Oral (PO) route

Question 2

What is Gastric Emptying time? What is one way to speed this up?

Answer 2

Gastric emptying time is the time it takes for a drug to move from the stomach to the small intestine where most of the absorption takes place. This may be sped up by using the liquid form of a drug.

Question 3

How does lipid solubility affect drug absorption in the GI tract?

Answer 3

More lipid soluble drugs are able to move through gastrointestinal membranes into the bloodstream much more easily than polar drugs that require pores to squeeze through

Question 4

What is the affect of drug pH on absorption? Note: This affect is greater in the stomach than in the small intestine, why?

Answer 4

pH affects the polarity of drugs, which as we discussed earlier can greatly affect absorption. In the stomach where the pH is quite low, drugs that are weak bases pick up an H+ making them neutral and lipid soluble, while weak acids pick up an H+ making them polar. In the SI this affect is not as great b/c it is closer to neutral pH and there is more surface area allowing drugs to be absorbed against pH gradients.

Question 5

Why might it be difficult to get someone numb with lidocaine in an area of infection?

Answer 5

Inflammation resulting from an infection causes the surrounding areas pH to drop. This drop in pH charges the lidocaine molecules, which causes them not to be absorbed through the nerve membranes.

Question 6

Why can’t penicillin G and Insulin by taken orally?

Answer 6

B/c both are destroyed by stomach acids.

Question 7

Why does the First Pass Effect make dosing for drugs such as the opioid morphine difficult?

Answer 7

The first pass effect states that when drugs taken orally pass through the small intestine and the portal system (liver) that enzymes, located in these areas, can inactivate as much as 60-90% of a drug compared to when it is injected. This means that the final drug concentration absorbed is variable and that much more drug is required if administered orally rather than via injection

Question 8

Intravenous administration of drugs results in no issues with disintegration, food interactions, acid destroying the drug, or first pass effect. IV administration is the most dangerous route, however, why is this?

Answer 8

B/c once a drug is administered into the bloodstream there is no way to get it out in case of an overdose.

Question 9

While IV administration is dangerous, what is one way that overdoses are easily avoided during drug administration?

Answer 9

IV route is Titratable. This allows small incremental doses to be given and the effects can be observed as they start to take effect.

Question 10

What route are local anesthetics used in dentistry administered by?

Answer 10

Submucosal injections

Question 11

Why is the vasoconstrictor epinephrine added to local anesthetics?

Answer 11

Epinephrine is an adrenergic receptor agonist that constricts blood vessels in the area of surgery, decreasing blood loss and maintaining high concentrations of anesthetic at the local site while preventing high levels in the blood throughout the rest of the body.

Question 12

What is phentolamine mesylate (Oraverse) used for?

Answer 12

Oraverse is an alpha-blocker, which opposes the effects of epinephrine, causing vasodilation at the site of injection leading to a quick decrease in concentration of local anesthetic and thus a quicker recovery from the local.

Question 13

What is a Scopolamine Patch (Transderm Scop) used for? How is the drug administered? How long does it take to have an affect?

Answer 13

Scopolamine Patches are administered topically by placing patch behind ear. It is used to prevent motion sickness. Takes a couple of hours to work

Question 14

What is the mechanism by which Scopolamine patches work to prevent motion sickness?

Answer 14

The mechanism of action of a scopolamine patch is its anticholinergic (antimuscarinic) effect. This anticholinergic effect (muscarinic receptor antagonist) blocks the release of Acetylcholine by the stability receptors in the ear, which contributes positively to the vomiting center.

Question 15

Under the 3 compartment model, a drug is diluted in an approximate 40 Liters of total body water within what 3 compartments?

Answer 15

1. Blood - 3 L
2. Extracellular fluid - 9 L
3. Intracellular fluid - 28 L

Question 16

What does Vd stand for? What is the formula used to determine Vd?

Answer 16

Vd stands for the apparent Volume of distribution (how much fluid the drug is dissolved in) and is determined by the formula Vd=Q/Co; where Q = Amount of drug & Co = initial concentration

Question 17

What are two reasons why you should never prescribe ibuprofen to patients on warfarin (Coumadin)?

Answer 17

1. Protein bumping. 99% of warfarin is bound to proteins (albumin) in blood plasma, leaving only 1% of drug prescribed to exert the desired affect. When ibuprofen, another protein binding drug, is prescribed at the same time it knocks approximately 4% of warfarin into the blood stream, effectively quadrupling the drugs effect, which may lean to internal hemorrhaging.
2. Ibuprofen also has an anticoagulant effect which will exacerbate the blood thinning effect of warfarin.

Question 18

What is the effect of displacing the 90-99% protein bound drugs Tolbutamide, Chlorpropamide, & Glyburide?

Answer 18

These 3 drugs are taken for type II diabetes, and displacement can result in hypoglycemia.

Question 19

What does it mean when a drug has a Vd of 4,000 L?

Answer 19

That the drug is highly lipid soluble and is sequestered in cells like neurons and other lipophilic tissues. Thes drugs, like propofol (Diprivan), are generally ultrashort acting anesthetics