Module 2 Absorption Flashcards
Absorption
- Movement of drug from administration site into blood
- Speed of drug effects
Affecting Factors of Absorption
- Rate of dissolution
- Surface area
- Blood flow
- Lipid solubility
- pH partitioning
- Activity of transport proteins
Rate of Dissolution
- Speed of dissolving in solution
- Determines speed of onset
Surface Area
- Larger area provides faster absorption
Blood Flow
- Concentration gradient drives absorption
- Exercise increases absorption
- High blood flow = fastest absorption
Lipid Solubility
- Ability to cross cell membrane
- Faster absorption
pH Partitioning
- pH gradient between site of administration & ionized in blood
Transport Protein Activity
- Uptake transporters increase absorption
- Efflux transporters decrease absorption
Routes of Administration
- Oral
- Sublingual
- Transdermal
- Rectal
- Intravenous (V)
- Subcutaneous (SC)
- Intramuscular (IM)
- Pulmonary
External Route
- GI Tract
External Route Examples
- Oral
- Rectal
Parenteral Route
- Everything EXCEPT GI tract
Parenteral Route Examples
- Intravenous
- Intramuscular
- Subcutaneous
Stomach Absorption Factors
- Small surface area
- Thick mucous layer
Small Intestine Absorption Factors
- Large surface area
Pharmaceutical Phase
- After tablet is swallowed
- Disintegration of tablet
- Dissolution of drug
Gastric Emptying
- Movement from stomach into intestine
Increase Gastric Emptying
- Empty stomach
- Cold water
- Lying on right side
- Tube feeding (high osmolality)
- Prokinetic drugs (increase motility)
Decrease Gastric Emptying
- High fat
- Heavy exercise
- Lying on left side
- Inhibiting vagus nerve (anticholinergic)
Enteric Coating
- Prevent dissolution in acidic conditions (stomach)
- Dissolves in alkaline duodenum
Bioavailability
- Fraction of dose reaching circulation unchanged
Affecting Factors of Bioavailability
- Drug formulation
- Route of administration
- Degree of metabolism
Sublingual Absorption
- Dissolve under tongue
- Absorbed across oral mucosa
- Venous drainage to superior vena cava
- Lipophilic & uncharged drugs only
Transdermal Absorption
- Dissolve in extracellular fluid
- Lipophilic to penetrate epidermis
- Hydrophilic to dissolve
Transdermal Considerations
- Patches, sprays, ointments
- Constant levels
- Drug free periods to avoid tolerance
Affecting Factors of Transdermal Absorption
- Thickness of skin
- Hydration
- Hair follicles
- Application area
- Skin barrier integrity
Skin Thickness
- Inversely proportional absorption
Hydration
- Increased absorption when well hydrated
Hair Follicles
- Bypass epidermis barrier
- More follicles = better absorption
Application Area
- Surface area increases absorption
Skin Barrier Integrity
- Damaged barrier increases absorption
Rectal Absorption
- Situations of vomiting/loss of consciousness
- Bypass liver
Disadvantages of Rectal Absorption
- Incomplete absorption
- Irritation of rectal mucosa
Intravenous (IV) Absorption
- Injection into peripheral vein
- Bolus or IV drip
IV Bolus
- Single dose
- Short time period
IV Drip
- Continuous infusion
- Long time period
- Diluted solution
Advantages of IV Absorption
- No barriers
- 100% bioavailability
- Control of dosage & duration
- Dilution increases solubility
- Irritants slowly injected
Disadvantages of IV Absorption
- Expensive
- Invasive
- No mechanism of removal
- Infection/fluid overload risk
- Risk of improper formula
Subcutaneous Absorption
- Subcutaneous tissue injection
- Capillary wall only barrier
Affecting Factors of Subcutaneous Absorption
- Blood flow
- Water solubility
- Irritant drugs cause adverse effects
Intramuscular (IM) Absorption
- Muscle tissue injection
- Pass fenestrations of capillary wall
Advantages of IM Absorption
- Useful for poorly soluble drugs
- Depot preparations (long time period)
Disadvantages of IM Absorption
- Pain/discomfort
- Tissue/nerve damage
Affecting Factors of IM
- Blood flow
- Exercise (increase flow & absorption)
- Heart failure/hypotension (decrease flow)
Pulmonary Absorption
- Gaseous & volatile drugs
- Inhaled & absorbed via pulmonary epithelium
- Rapid absorption (lung surface area)
- Delivered to site of action (asthma)
