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29 Cards in this Set
- Front
- Back
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IM administration
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A solution, suspension, or emulsion may be injected into a muscle with a needle and syringe and the injected bolus forms a depot that releases drug over a period of time.
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Pros of IM administration
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Avoid high peak levels and increase patient compliance.
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Factors influencing IM drug absorption
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-Drug and dosage form factors
-Physiologic factors |
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Common IM sites
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-buttocks
-lateral thigh -quadriceps |
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Cons of IM/SC administration
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Some drugs may not be fully absorbed (insulin)
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Size of IM injection
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2 to 5 ml (0.25 ml for infants)
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Absorption of aqueous IM solution
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A first order process that usually takes about 30 minutes
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Blood flow range for IM sites
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0.02 to 0.07 ml/min depending on vascularity and muscle activity
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Factors contributing to variability in IM drug absorption
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-blood flow rate (exercise, disease)
-manner of injection -dispersal |
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Absorption rates from different sites
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(Goes from top to bottom)
-deltoid -shoulder (rapid) -vastus lateralis -side of thigh (intermediate) -gluteal muscle -butt (least rapid) |
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Subcutaneous (SC) administration
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small volume bolus injection under the skin
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Size of SC injection
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2 ml or less
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Onset and absorption of SC administration
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-blood flow is slower
-onset and absorption of SC administration is slower than IM and IV |
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Hyperdermoclysis
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Infusion of a LVP (large volume parenteral) fluid at a relatively slow rate for a few days to provide a continuous abundant supply of drug, e.g., antibiotics, for children
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Hyaluronidase
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An enzyme that temporarily lyses the normal interstitial barrier, is used to enhance fluid absorption of SC infusions
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Characteristics of hyperdermoclysis
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-Uses a solution of one third normal saline and two thirds 5% glucose
-Safe compared to IV administration |
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ka
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absorption rate constant
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Fastest to slowest absorption rate constants (ka)
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-aqueous solution (min to hrs)
-aqueous suspension -oil solution -oil-in-water emulsion -water-in-oil emulsion -oil suspension (weeks to months) -pellet, implant |
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Why does an aqueous solution have the fastest ka (absorption rate)?
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It only has to diffuse from the injection site to the capillary.
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Why is an aqueous suspension the second fastest ka (absorption rate)?
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There are particles at the injection site that must dissolve before they can diffuse from the injection site to the capillary.
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Why is an oil solution the third fastest ka (absorption rate)?
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The oil droplets must partition at the injection site before they can diffuse from the injection site to the capillary.
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Cosolvents
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The precipitation of a drug from a cosolvent formulation after IM injection can lead to incomplete drug absorption.
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High Ko/w
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Prolongs release by lowering rate
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What are some examples of drugs that sometimes precipitate from cosolvents?
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ACDP
-ampicillin -chlordiazepoxide -diazepam -phenytoin |
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Mechanism of clearance of oil solutions
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-absorption through capillaries
-lymphatic absorption -phagocytosis -metabolism at the site and absorption |
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Peanut oil and ethyl oleate
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-route and volume of injection have no effect on t1/2
-peanut oil has a longer t1/2 than ethyl oleate: about two weeks versus 10 days |
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Parenteral suspensions in water or oil
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-The major use of suspensions injected IM or SC is to provide a slow release prolonged effect with one dose.
-Ideally, want a depot that releases drug at a constant rate. -The most widely used approach utilizes a relatively insoluble drug so that its dissolution rate is rate limiting for absorption. -Regularly used IM or SC, but not IV (If injected IV, must have a size less than 0.5-1.0 micron and must be biodegradable) |
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Dissolution of injectable suspension in water
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Dissolution is controlled by diffusion across an unstirred layer of thickness, h.
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What equation governs injectable suspensions in water?
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Noyes-Whitney equation
dw/dt = DSa(Cs - Ct)/h w=amount diffusing t=time Sa=surface area D=diffusion coefficient |
