Absorption is the movement of a drug from the administration site into the bloodstream. The rate and amount of absorption determines when drug effects begin and how intense they are. Absorption is affected by factors like dissolution, surface area, blood flow, lipid solubility, and pH. Intravenous administration has no barriers to absorption and instant onset, while oral absorption is slow and variable due to passing through the GI tract. The degree and rate of absorption ultimately influence a drug's onset, peak level, duration, and bioavailability.
2. Why is absorption important?
⢠The RATE of absorption determines how soon
the drugâs effects will begin.
⢠The AMOUNT of absorption determines the
intensity of the effects.
⢠The RATE and AMOUNT of absorption vary
depending on several factors, many of them
dependant on administration site.
3. ABSORPTION FACTORS
⢠Rate of Dissolution
⢠Surface Area
⢠Blood Flow
⢠Lipid Solubility
⢠pH Partitioning
4. Intravenous
⢠No barriers to absorption
⢠Instantaneous
⢠Advantages:
â Rapid onset, control, large dosages, reduced
irritation
⢠Disadvantages:
â Irreversible, expensive, inconvenient, difficult,
high risk, drug-specific
5. Intramuscular / Subcutaneous
⢠Must pass the capillary wall
⢠Rapid or slow absorption
⢠Advantages:
â Use with poorly soluble drugs, use with depot
preparations
⢠Disadvantages:
â Discomfort, inconvenient, potential for injury
6. Oral
⢠Must pass the capillary wall and GI tract
⢠Slow and variable absorption
⢠Advantages:
â Easy and convenient, inexpensive, self-med,
potentially reversible
⢠Disadvantages:
â Variable, inactivation, gastrointestinal side
effects, patient adherence
9. Nursing Implications of Absorption
⢠The degree and rate of absorption are
important because they are ultimately going
to affect the drugâs:
â onset of activity
â peak level
â duration
â bioavailability (the percentage of drug absorbed
into the systemic circulation for activity)
10. References
Comerford, K. (2004). Fundamentals of nursing pharmacology. In Straight A's in
nursing pharmacology (pp. 1-15). Springhouse, PA: Lippincott Williams & Wilkins.
Drug absorption, distribution and elimination: Pharmacokinetics. (n.d.). In
Columbia.edu. Retrieved September 6, 2012, from
http://www.columbia.edu/itc/gsas/g9600/2004/GrazianoReadings/Drugabs.pdf
Kelly, j. (2001, Dec. 1). Minimising potential side-effects of medication at different
ages. Nursingtimes.net. Retrieved from http://www.nursingtimes.net/minimising-
potential-side-effects-of-medication-at-different-ages/197723.article
Lehne, R. (2013). Orientation to pharmacology. In Pharmacology for nursing care (8th
ed., pp. 1-4). St. Louis, MO: Elsevier Saunders.
Hinweis der Redaktion
Hi! My name is John and Iâm going to discuss the topic of Absorption. Absorption simply means the movement of a drug from the administration site into the blood.
So why is absorption important? Understanding the factors that influence the rate and amount of absorption will be important in understanding how the medications will affect the patient. The faster the rate of drug absorption, the faster the drug will begin working. And the more of a drug that is absorbed, the more of an effect that drug will have on the patient. Therefore you can see how having a good understanding of the factors that affect absorption will be critical.
There are 5 primary factors that affect drug absorption: Rate of Dissolution, Surface Area, Blood flow, Lipid Solubility, and pH partitioning. Each of the first three factors has a direct relationship with drug absorption. Therefore, a rapidly dissolving drug, a large surface area, and high rate of blood flow can each lead to a high rate of absorption. Drugs that have high lipid solubility are more rapidly absorbed. pH partitioning affects how a drug moves from the site of administration into the blood plasma. As nurses, we are mostly concerned with the first three factors as those are the factors we can have the greatest impact on. =================================================================================There are 5 key factors that affect absorption. For a drug to be absorbed it must be dissolved. Therefore the faster a drug dissolves the faster it can be absorbed. Surface area is a major factor in determining absorption rate. The greater the available surface area, the more rapid absorption will be. Blood flow is important because sites that have rapid blood flow will have a faster rate of absorption. Blood that has absorbed the drug will circulate quickly, allowing the drug to be absorbed by blood that is drug-free. Lipid Solubility is a factor because drugs coming from certain administration sites have to pass through cell membranes that are made up of a lipid bilayer. Drugs that are not lipid soluble cannot make it through these membranes. pH partitioning affects absorption, as the difference in the pH levels of the blood plasma and site of administration will have an effect on drug absorption.
However, those factors have very little to do with our first method of administration. When giving drugs intravenously there are no barriers to absorption! Intravenous drugs enter the blood stream immediately. This is the most efficient method of drug delivery and has several advantages like immediate onset and greater control of the medication administered. There are also many risks associated with this direct path into the blood stream so a nurse needs to be cautious and precise when giving IV drugs.=============================================================================Intravenous therapy refers to the infusion of substance directly into a vein. There are no barriers to absorption with IV medications and it occurs instantaneously. The advantages of IV therapy include rapid onset, precise control over the amount of drug entering the blood, suitability for use with large volumes of fluid, and suitability for irritant drugs. The disadvantages include that absorption is irreversible, expensive, and inconvenient, as well as the medications are poorly suited for self-administration, thee is a risk for fluid overload, infection, and embolism, and finally, the drugs administered must be water soluble.
Intramuscular and subcutaneous injections are also efficient ways of giving medication. However there are some barriers to absorption with this method. Absorption is affected by the water solubility of the drug and the blood flow to the site of injection. Drugs that are highly water soluble will be rapidly absorbed. If blood flow is high to the injection site then absorption will be rapid. An advantage to this method is that drugs that donât dissolve very well can be administered through an IM or SUBQ injection but cannot be given intravenously. Unlike IV therapy, intramuscular and subcutaneous medications must first pass through the capillary wall, which is fairly easy to pass. The rates of absorption are variable, which occurs rapidly for water soluble drugs and slowly with poor soluble drugs. The advantages for SQ/IM administration include the permitted use of poorly soluble drugs and the use of depot preparations. The disadvantages for this type of administration include possible discomfort, inconvenience, and the potential for injury.
Oral medications are typically the most commonly used and prescribed medications today. Medications administered orally must pass both the capillary wall and the GI tract. The absorption of oral medications is the slowest and most variable of all the methods. The advantages include ease and convenience, an inexpensive price tag, the results are potentially reversible, and finally, the medications are ideal for self-administration. The disadvantages include variability, inactivation, GI side effects, and patient adherence.
Topical medications are useful for treating external ailments. Applying medication directly to the site can enhance absorption. Rectal and vaginal suppositories allow for local treatment of problems. Topical medications and rectal suppositories are also alternate routes for absorption of medication into the blood stream. Inhalants are useful for treating conditions involving the lungs, and allow for rapid absorption of the drug. Some conditions require direct injection of the drug into sites like joints, the heart, and nerves.Some additional routes include; topical medications, rectal and vaginal suppositories, inhalants, and direct injection.
Drug absorption has special concerns when considering very young and very old patients. To start with neonates have prolonged and erratic gastric emptying. This means that drugs that are absorbed in the stomach have much more time to be absorbed increasing the dose that gets to the target. This can lead to increased risk of toxicity. Drugs that are absorbed in the intestine may be delayed and absorption cannot be predicted.IM injection absorption in neonates is also slow and erratic due to decreased blood flow to the muscles. However, infancy brings about a much more rapid absorption of IM drugs. Once again increasing the risk of toxicity.Infants also have a more rapid absorption of transdermal medications. This is due to thin skin and increased blood flow to the skin. Yet again increasing the risk of toxicity.Once the pediatric patient reaches childhood(age 1 and over), these routes of absorption start to level out to adult levels.
So how does absorption affect drug therapy? What factors do you need to know? Here are the main points. Factors that influence the degree and rate of absorption are the administration route, the patientâs age and physical condition, lipid or water solubility, and the drugâs mechanism of action.These factors will ultimately affect the drugâs onset of activity, peak level, duration, and bioavailability. ⌠each of which are directly related to the drug therapy desired.
