Ch 4-8 Flashcards
(178 cards)
Factors Affecting Drug Absorption
- The rate of drug dissolution
- The absorptive surface area
- Blood flow at the site of absorption
- Lipid solubility of the drug
- pH partitioning between the site of absorption and plasma
enteral drugs
Drugs administered by the oral route (per os, or PO)
parenteral
drugs administered outside the GI route
Capsule:
Drugs given by mouth pass through the stomach and are metabolized in the liver before reaching systemic circulation
Syringe:
Drugs administered by syringe immediately enter the circulatory system
Patch
Parenteral routes such as a transdermal patch release drugs directly into systemic circulation.
PO
oral or enteral
Bioavaliability
The percentage of a drug dose that actually reaches the systemic circulation chemically unchanged
IP
Intraparitoneal - up the ass
causes of low oral bioavalability
- The drug does not dissolve readily.
- Enzymes in the intestine may metabolize some of the drug before it is absorbed.
- The liver, metabolizes some of the drug on its first pass through the liver on the way to the systemic circulation.
advantages to IV route
- Has no membrane barriers; absorption is instantaneous and complete (100% bioavailability)
- Allows precise control of drug dose and duration
- Permits administration of poorly soluble drugs that must be dissolved in a large volume of fluid
- Allows irritating drugs to dilute rapidly in blood (e.g., cancer chemotherapeutic drugs would damage muscle if administered IM)
can enteric coated drugs be crushed and given through feeding tubes?
never because the protective coating will be lost. The crushed drug (now without the enteric coating) may be inactivated by the gastric acid or the drug may irritate the gastric mucosa.
can Sustained-release (XL, ER) medications be crushed and administered via feeding tubes?
Never. because crushing such formulations will cause a problem called dose dumping. Rather than a continuous delivery of medication to the site of absorption in the intestine, with dose dumping the entire dose is absorbed at once, and drug concentrations in the blood could reach toxic levels.
Can meds be desolved in hot water before being put in a feeding tube?
Never. Hot water may inactivate some drugs and precipitate others. The precipitate may accumulate on the side of the container or on the feeding tube itself and not be absorbed.
Disadvantages of IV administration of drugs
expensive, invasive, inconvenient
•Cannot remove the drug once it has been administered
•Risk for too high a drug concentration if injected too rapidly
•Risk for fluid volume overload
•Risk for infection
•Risk for embolism (from a clot, cellular debris, undissolved drug, or air)
•Risk for using wrong formulation (e.g., a concentrated solution designed for IM injection)
What if your IV solution looks dark?
Do not administer it! •IV solutions are dilute; IM solutions are concentrated and can be fatal if administered by IV.
Rate of absoorption after subcutaneous or IM injection is affected by…
- The ability of the drug to move through the fenestrations (gaps) in the capillary wall
- The solubility of the drug in water (plasma)
- Blood flow at the site of injection
disadvantages of IM and subcutaneous administration
- Bioavailability may be less than 100%.
- Non–water-soluble drugs may precipitate at the injection site.
- IM injections can cause local tissue injury and nerve damage if not administered properly.
- If a serious adverse reaction occurs (e.g., allergy), further absorption cannot be stopped.
Advantages of Transdermal adminstration
They provide for zero-order delivery, which means there is a constant plasma drug concentration with no peaks and troughs.
Peaks and Trophs
The highest and lowest drug levels in the plasma as measured over time
Characteristics needed in a drug for successful transdermal delivery
•A small molecular size
•Both hydrophilic and lipophilic properties
◦Lipophilicity is needed to penetrate the stratum corneum barrier.
◦Hydrophilicity is needed to diffuse into the extracellular fluid
The amount of drug delivered to the blood from transdermal patches
- The concentration of the drug in the patch or ointment
- The size of the application area
- The thinness of the stratum corneum and number of hair follicles (drug absorption from the chest > legs > arms > scalp > axillary > posterior ear > shin > palm)
when are Fluctuating drug levels in the blood (peaks and troughs) desirable?
antiinfectives, cancer chemotherapy
T or F: Drugs that can be absorbed through the skin are both lipid and water soluble.
True!