Routes of Drug Administration in Pharmacology

Routes of drug administration include:

  • Enteral routes
    • Oral (PO)
    • sublingual
    • buccal
  • Parenteral routes
    • Intravenous (IV)
    • Intramuscular (IM)
    • Subcutaneous (SC)
    • Intradermal (ID)
  • Other routes
    • Topical
    • Inhalation
    • Intranasal
    • Rectal
    • Intrathecal/ Intraventricular
    • Transdermal

Oral routes (PO)

  • •Oral administration involves the most complicated absorption process because it goes through many different absorbing surfaces 
  • •Drugs go through the low ph of stomach (1.5) that inactivates a lot of drugs
  • •To solve this problem: wide range of oral preparations are available including:
    • •Immediate release preparations (which have enteric coating)
    • •extended release preparations: those have many layers and dissolve slowly leading to slower absorption and prolonged duration of action, better compliance and less toxicity compared to immediate release, e.g. morphine half life 2-4 hours 6 times daily, 2 times with extended release)
  • •Advantages
    • •easily self administered
    • •toxicities and overdose maybe overcome with antidotes like activated charcoal
    • •economical
  • •Disadvantages:
    • •limited absorption to some drugs
    • •food affect absorption
    • •patient compliance 
    • •first pass metabolism
  • •Example: amoxicillin tablet

Sublingual/ buccal routes

  • -Sublingual/ buccal: placement under tongue or between cheek and gum, drug absorbed to circulation.
  • •Advantages:
    • •rapid absorption
    • •bypass of harsh GI environment
    • •avoidance of first pass metabolism
  • •Disadvantages
    • •limited to certain types of drugs that doesn’t cause irritation
    • •limited to drugs that is taken in small doses
  • •Example: sublingual nitroglycerin 

Parenteral

  • •Parenteral introduces drugs directly into systemic circulation through injecting drugs directly into:
    • •Veins (IV)
    • •Subcutaneous (SC)
    • •Muscle (IM)
    • •Dermis (ID)
  • •Used for:
    • •Poorly absorbed Drugs from GI like heparin
    • •unstable in GI like insulin
    • •patients unable to take oral like unconscious
    • •in circumstances required rapid onset (acutely ill patients)
  • •Advantages include better control over dose
  • •Disadvantages
    • •Irreversibility
    • •Pain
    • •Fear
    • •Local damage
    • •Infections

Intravenous route (IV)

  • •Most common parenteral route, Drug goes directly into the bloodstream
  • •Advantages:
    • •Rapid effect and maximum control over the dose
    • •Ideal for large volumes
  • •Disadvantages:
    • •Unsuitable for oily substances,
    • •Bolus injection may result in adverse effects (e.g. acute heart failure)
    • •Most substances must be slowly injections (hypersensitivity),
    • •Strict aseptic techniques
    • •Risk of thrombosis and hemolysis
  • •Examples: vancomycin IV, heparin IV

Intramuscular route (IM)

  • •Parenteral
  • •Drug injected in the muscle, and then diffuse into systemic circulation
  • •Drugs administered IM can be in:
    • •aqueous solutions which absorbed rapidly
    • •specialized depot preps which absorbed slowly providing sustained dose over an extended interval
  • •Advantages: suitable for oily drugs, preferable if patient must self administer
  • •Disadvantages: can be painful, blood creatine kinase increased
  • •Example: benzathine penicillin

Subcutaneous route (SC)

  • •Parenteral
  • •Drug injected into subcutaneous fat and diffuse into blood after by simple diffusion, slower than IV route
  • •Advantages:
    • •Minimize risks of hemolysis or thrombosis associated with IV injection
    • •Provide constant , slow and sustained effects
  • •Disadvantages: if drug causes tissue irritation, this leads to severe pain and necrosis may occur, so this route not used with drugs causes tissue irritation
  • •Example:
    • •Insulin (SC)
    • •Heparin (SC)

Intradermal route (ID)

  • •Parenteral
  • •Injection into dermis (under epidermis), have the longest absorption time of the parenteral routes
  • •Used for
    • •allergy for a specific drug
    • •diagnostic testing such as tuberculin test to check for TB

Oral inhalational route

  • •Provide rapid delivery of the drug to lungs respiratory epithelium,
  • •suitable for drugs that are gases (example: some anesthetics like isoflurane) and those that can be dispersed in an aerosol
  • •Used for:
    • •Respiratory disorders like asthma, copd
    • •Anesthesia
  • •Advantages: 
    • •the drug action is as rapid as IV route
    • •minimal systemic effects
  • •Disadvantages:
    • •most addictive route (drug can go to brain quickly)
    • •difficult to use inhalers
  • •Examples: albuterol inhaler

Intranasal route

  • •Topical administration of drugs directly into the nose
  • •The drug put into and cross nasal mucosa and it either treat nasal mucosa or go to blood supply and act systemically
  • •Used to treat nose disorders like allergic rhinitis

Intrathecal/ Intraventricular route

  • •Drug is given directly to CSF fluid using these methods
  • Intrathecal: drug injected into CSF through spinal cord
  • Intraventricular: drug injected into CSF through brain ventricles
  • •Brain and spinal cord are protected by BBB which prevent most drugs from going to brain , so intrathecal route is very good in giving drugs to work on brain and spinal cord directly
  • •Used:
    • •When local and rapid effects of drugs are needed such as If patient has meningitis or encephalitis
    • •Used if the drug can’t cross the BBB such as high molecular weight antibiotics or anticancer chemotherapy

Intraarticular route

  • •Drug injected Into the joint space
  • •E.g. steroid injections given in arthritis to relive joint pain and inflammation 

Topical route

  • •Applied to skin or mucosa
  • •The action intended to work locally at the skin , eyes, intravaginal
  • •Disadvantages:
    • •some systemic absorption can occur,
    • •unsuitable for drugs with high molecular weight or poor lipid solubility
  • •Example:
    • •clotrimazole cream
    • •hydrocortisone cream

Transdermal

  • •Differentiate between intradermal , transdermal
  • •Applied to skin, crosses skin to systemic circulation
  • •The intention for the drug to cross the skin and enter systemic blood supply to treat disorder unrelated to the skin
  • •Advantages:
    • •Bypass first pass effect
    • •Convenient and painless
    • •Ideal for drugs that are quickly eliminated
  • •Disadvantages:
    • •Some pt. allergic to patches
    • •Limited drugs that can be taken in small daily doses
  • •Examples: nitroglycerin patch, nicotine patch

Rectal (PR)

  • •Absorbed into rectal mucosa which 50% of rectal region drainage bypasses portal circulation (where first pass metabolism occur) so it is minimized
  • •prevent destruction of drug in the GI
  • •Useful if:
    • •patient is vomiting
    • •drug can’t be taken orally 
    • •patient unconscious
  • •Disadvantages: drugs may irritate rectal mucosa
  • •Example: diazepam PR
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