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ENDOCRINE > D. PARENTERAL DRUG DELIVERY > Flashcards

D. PARENTERAL DRUG DELIVERY Flashcards

1
Q

what is the difference between the parenteral and oral route

A
  • parenteral isn’t via the digestive system
  • parenteral is usually applied to injectable formulations only
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2
Q

what are the 4 main routes of injection

A

intravenous
intramuscular
intradermal
subcutaneous

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3
Q

what are the specialised needs of parenterals

A
  • sterility as they bypass infection barriers
  • isotonic and pH 7.4 as this is when proteins are active
  • small volumes
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4
Q

where is an intradermal drug injected

A

superficial layer of skin (extremely tilted)
0.1ml

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5
Q

where is an intravenous drug injected

A

the vein (in the dermis)
(very tilted)
>5mL

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6
Q

where is a subcutaneous drug injected

A

loose connective tissue (SC tissue)
(slightly tilted)
1.3ml

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7
Q

where is an intramuscular drug injected

A

muscle mass
(not tilted at all)
2ml

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8
Q

why use parenteral delivery

A
  • speed of action as IV drug enters plasma immediately and rapidly disperses to tissues
  • local/targeted effect ie: local anaesthetics, cytotoxics
  • 100% bioavailability as drug doesn’t have to cross absorption barriers in gut. Can administer drugs that are unabsorbed/degraded by oral route
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9
Q

issues and precautions with parenterals

A
  • air embolism: injection of air bubbles
  • bleeding: in haemophilia so don’t use here
  • cost of training and formulation
  • fever from pyrogens
  • infiltration/extravasation: local tissue damage so rotate injection spot
  • overdosage will be serious due to rapid onset
  • particulates can cause a pulmonary embolism
  • sepsis so need sterile practice
  • thrombosis (blood clot)
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10
Q

advantages of IV delivery

A
  • rapid onset
  • no issue with incomplete absorption
  • good for orally inactive drugs
  • suitable for unconscious, uncooperative or nauseous patients
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11
Q

disadvantages of IV delivery

A
  • extensive training (locate vein)
  • sterility needs to be maintained
  • dosage error = serious injury/death
  • complications (as stated with parenterals)
  • loss of sites in long-term treatment
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12
Q

pathway of IV injection

A
  1. drug injected into vein
  2. passes to heart
  3. through pulmonary circulation
  4. heart pumps it around tissues
  5. then to gut and then liver
  6. drug returns to heart through liver - metabolism begins (not first pass as goes to tissues first)
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13
Q

why is absorption efficient with IV

A

blood flow in tissues is slow
(trip takes 10-30 seconds)

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14
Q

IV bolus injection

A
  • rapid increase in drug concentration in blood plasma
  • after distribution, concentration falls (reversible transfer of drug)
  • drug concentration in plasma affected by dose and quantity of drug transferred into tissues
  • slower decrease in drug concentration due to irreversible excretion and metabolism
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15
Q

IV infusion

A
  • large volume of fluid at slow rate (antibiotics, nutrition etc)
  • ensures drug enters general circulation at constant rate
  • drug concentration in plasma rises and achieves steady state
  • stop infusion: elimination, follows first order kinetics
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16
Q

how can small volumes be administered by IV

A
  • directly: slowly if concentrated
  • admixed into large volume parenterals (eg - glucose)
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17
Q

how can large volumes be administered by IV

A
  • via central venous catheter emptying into subclavian vein
18
Q

how to give a continuous infusion

A
  • via a drip feed (poorly controlled)
  • by a metering pump which has a set amount (eg - for analgesia or chemotherapy)
19
Q

how is continuous out of hospital treatment administered

A
  • ambulatory and implantable pumps
  • for patient-controlled analgesia
20
Q

what do small volume (<100ml) parenterals require for formulation

A
  • sterile and particle free (unless delivering particles)
  • pH 3-9 as long as injection is slowly/rapidly diluted
  • pH > 9 = tissue necrosis
  • pH < 3 = pain and phlebitis in tissue
  • buffers: acetate, citrate, phosphate buffers
  • co-solvents: EtOH, propylene glycol
  • preservatives: benzyl alcohol, phenol
  • surfactants to aid solubility (eg. deoxycholate with amphotericin B)
21
Q

what do large volume (>100ml) parenterals require for formulation

A
  • used as electrolyte balance, parenteral nutrition, plasma replacement, acid-base balance, contrast agents etc
  • pH 6 to 8
  • large differences of pH from physiological conditions NOT tolerated as for small volume parenterals
  • usually made isotonic with glucose or NaCl
  • if hypotonic solution (lower osmotic pressure than blood plasma) fluid passes into blood cells by osmosis, blood cells swell and burst
  • if hypertonic solution (higher osmotic pressure than blood plasma) – red blood cells loose fluids and shrink
  • preservatives not permitted
22
Q

how is IM injection absorbed into muscle tissue

A
  • perfusion of muscle by blood (well supplied so rapid)
  • < rapid, but generally > lasting than IV
23
Q

what type of formulations can be injected intramuscularly

A
  • solutions, suspensions, depot implants
  • injections don’t need to be water-miscible
  • small-volume route (2 mL - deltoid of arm, 5 mL - gluteal region)
24
Q

what are the common IM injection sites for adults

A

Point of injection – as far as possible from major nerves or blood vessel to avoid
injuries
- upper outer quadrant of gluteus maximus
- deltoid - in shoulder (more painful)

25
Q

what are the common IM injection sites for infants and children

A
  • deltoid muscles of upper arm
  • mid-lateral muscles of thigh - injection at upper or lower portion of deltoid, well away from radial nerve

*gluteal area is small & composed primarily of fat - muscle poorly developed
- injection in this area too close to sciatic nerve (esp. if child is resisting injection)

26
Q

advantages of IM delivery

A
  • rapid absorption
  • can formulate sustained depot (days/months)
  • implanted devices may be removable
27
Q

disadvantages of IM delivery

A
  • local muscle damage
  • cannot be used in cardiac failure (no muscle perfusion)
  • must avoid blood vessels
28
Q

PKs of IM delivery

A
  • release of drug from formulation into intercellular fluid (ICF)
  • absorption from ICF into blood and lymphatics
  • transport from local blood volume to general circulation
  • metabolism
29
Q

what factors affect IM absorption rate

A
  • very hydrophobic drugs don’t dissolve in ICF
  • strongly ionised or water soluble drugs can’t cross capillary membrane
  • strongly protein-bound drugs slowly absorbed
  • some drugs in solution absorbed slowly if composition of formulation changes after injection
  • muscle movement and blood flow: moving increases absorption compared to rest after IM injection
30
Q

intradermal delivery

A
  • dermis has little fluid available and is poorly perfused by blood
  • drugs persist at site for long period of time
  • usual site is anterior forearm
  • volume for injection is small (0.1mL, up to 0.2mL)
  • eg: tuberculin & allergy testing
31
Q

subcutaneous delivery

A
  • SC tissues have significant volume of interstitial fluid in which the drug can diffuse
  • volume for injection is small (1.3 - 2 mL)
  • less well perfused (often adipose) than IM route, so slower absorption
  • cannot give irritating formulations
  • used for insulin, vaccines, some vitamins
32
Q

what type of formulations can be injected subcutaneously

A
  • injections are prepared as aqueous solutions or suspensions (no oils)
33
Q

common injection site for SC drugs

A
  • anterior abdomen (belly), upper arm, thigh & buttocks
    (if frequent SC injection given, alternate injection sites are used)
  • the injection site affects the absorption rate (e.g. insulin is more readily absorbed from the abdomen and deltoid region compared to thigh and buttocks)
34
Q

how is insulin delivered

A
  • subcutaneously
35
Q

how is insulin affected by liver and kidney

A
  • inactivated, 10% excreted in urine
36
Q

how are longer acting (basal) preparations made

A
  • precipitating insulin with protamine or zinc forms fine
    amorphous solid/insoluble crystals, injected as suspension from
    which insulin is slowly absorbed, e.g. isophane insulin
  • modifying insulin amino acid structure to create analogues (genetic engineering, rDNA tech) insulin forms a slow-dissolving precipitate once injected, e.g. insulin glargin

*analogues also created for rapid acting insulin, e.g. lispro

37
Q

ultra short acting insulin

A
  • clear solution
  • neutral pH with traces of Zn
  • Insulin Lispro (or aspart) absorbed rapidly
  • peaks at 1 hr and lasts < 3-4 hr
38
Q

short acting insulin

A
  • regular insulin
  • soluble crystalline Zn insulin
  • effect appears in 30mins
  • peaks 2 hrs, lasts 5-7 hrs
39
Q

intermediate acting insulin

A
  • suspension of Zn insulin crystalline, 2 µm particle size
  • peaks 4 – 8 hrs, lasts 16 hours max
  • onset delayed by combination of insulin and protamine
    e.g. NPH (Neutral Protamine Hagedorn)
40
Q

long acting insulin

A
  • suspension mixture of 30% Semilente (amorphous
    precipitate of insulin with Zn ions for rapid onset) and
  • 70% Ultralente (poorly soluble crystal of Zn insulin for delayed onset and prolonged duration) to give rapid absorption with sustained long action
  • eg: deter, glargine
  • 10 – 40 µm particle size
  • peaks at 8 – 12 hr

ENDOCRINE (17 decks)

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