Drug Application Routes: Local

• Routes of drug application are categorized into two groups, local and systemic, based on the drug's target and the condition of the application site
• For a drug to take effect in a specific area, it has to be present in an adequate amount known as MEK (minimum effective concentration)
• The dosage and application sites of the drug should ensure that the active substance attains MEK at the desired location

Local Application Routes

• Local application is when the drug's effect is intended for the body's surface
• Local Application Routes include:
  • Epidermal
  • Intracutaneous
  • Intrathecal
  • Intrapleural
  • Intraperitoneal
  • Intracardiac
  • Intraarticular
  • Intrauterine
  • Intravaginal
  • Into the rectum and colon
  • On the conjunctiva
  • Intranasal and buccal

Epidermal Route

• The epidermal route is suitable for localized and accessible lesions
• Drugs administered epidermally should have minimal or no absorption
• This route has no or minimal systemic side effects.

Intracutaneous Route

• Intracutaneous application involves injecting a drug into the dermis layer, located just below the epidermis
• Sterile solutions and test serums for allergy and bacteriology tests use the intracutaneous route

Conjunctiva Route

• The conjunctiva is used for various infections
• Ophthalmic preparations administered through the conjunctiva should always be sterile

Intranasal Route

• Intranasal applications treat diseases of the nasal mucosa and paranasal sinuses
• Anti-inflammatory, vasoconstrictor, and local anesthetic drug solutions are administered this way
• Systemic application is also possible via the intranasal route

Buccal (Intraoral) Route

• The buccal route is used for treating mouth and gum infections

External Ear Canal Route

• The external ear route treats some diseases of the external ear canal or eardrum

Intrathecal Route

• Intrathecal administration involves sterile antibiotic or local anesthetic solutions
• It is applied to create a local effect on the meninges or spinal nerve roots

Intracardiac Route

• The intracardiac route is for emergencies
• The intracardiac route is for cardiac resuscitation during surgery
• The intracardiac route is for stimulant drugs like adrenaline

Intraperitoneal Route

• Used for inflammation of the peritoneum, injections go into the abdominal cavity

Intraarticular Route

• The intraarticular route treats joint diseases
• The intraarticular route administers corticosteroids or antibacterial drugs into the joint

Rectal and Colonic Application

• Application involves suppository or enema form
• The rectal and colonic application is used for superficial lotions of the rectum, hemorrhoids and some diseases of the colon

Intrauterine Route

• The intrauterine administers oxytocic hormone into the myometrium
• The intrauterine action is to accelerate uterine contraction and reduce bleeding after cesarean sections

Intravaginal Route

• Medications are typically administered into the vagina using a pessary
• Spermicide drugs in foam and gel forms stop pregnancy

Systemic Application Routes

• Systemic drug application methods are:
  • Enteral (oral, sublingual, rectal)
  • Parenteral (intravenous, subcutaneous, intramuscular, into the bone marrow)
  • Transdermal
  • Inhalation

Enteral Route

• The enteral includes oral, sublingual, and rectal administrations

Parenteral Route

• The parenteral drugs are not absorbed or broken down in the gastrointestinal tract
• The parenteral route is the administration of drugs via a sterile syringe into veins or tissues for quick effect

Transdermal Route

• Transdermal is the application of a drug to the skin using a special pharmaceutical form
• The transdermal route allows the drug to be absorbed from the skin into the circulation

Inhalation Route

• The inhalation route is when lipophilic medications in gas or vapor formats pass through the alveolar membrane
• Inhaled medications make their way into the general blood circulation

Oral Route

• The oral route (per os) is the most common, practical, and economical
• Orally administered drugs must pass through the liver for absorption before entering the systemic cirulation
• Some oral routes result in drug inactivation and incomplete absorption

Sublingual Route

• Sublingual route is used when a drug's effect is desired to start rapidly
• Sublingual drugs dissolve quickly, create an effect with small amounts, and are highly soluble in fat
• Drugs in small tablets (nitroglycerin, nifedipine) use this route

Rectal Route

• Rectal drugs have either a local or systemic effect achieved by absorption through the rectal mucosa
• Rectal administration is common for patients who cannot take oral medication, like infants

Parenteral Administration is Required

• Drugs cannot be absorbed or broken down sufficiently in the gastrointestinal tract
• Drugs require a rapid onset of effect
• Patients are unconscious, can't swallow, are experiencing nausea, vomiting, or diarrhea

Disadvantages of Parenteral Administration

• Can cause vascular or tissue damage
• Psychological stress
• Is unable to be administered by the patient alone
• May be expensive

Intravenous Route

• Only water-soluble or water-mixable drugs can be administered intravenously
• Intravenous is best when rapid effect is desired
• Bioavailability is 100%
• Drug solutions up to 10 ml are injected intravenously in 1 to 2 minutes
• Intravenous infusion is a slow administration of large volumes of drugs (1 to 2 hours) into a vein

Disadvantages of Intravenous Route

• Only water-soluble drugs can be given intravenously
• Oily solutions and suspensions may cause embolism
• Drugs with low water solubility may precipitate in the vein
• Administered intravenously may have high risk of anaphylaxis
• Irritant drugs may cause tissue damage if extravasation occurs

Intramuscular Route

• Intramuscular involves injecting the drug into an appropriate muscle tissue
• The gluteal or deltoid muscle is usually preferred for intramuscular injection
• IM solution <= 5ml
• Absorption of the injected drug is affected by blood flow in the affected area
• Absorption can be increased by massage or exercise

Subcutaneous Route

• The subcutaneous (under the skin) is the outer surface of the humerus or femurregion
• A maximum of 2 ml of solution should be applied subcutaneously to prevent pain on the skin
• Irritant drugs should be applied intramuscularly instead
• The subcutaneous route places some drugs under the skin in the form of implants or pellets
• The subcutaneous route is for slow and regular drug release

Intraosseous Injection

• The intraosseous injection is used in infants and some adults if veins aren't found
• A drug is injected into bone marrow (sternum) that passes rapidly into the blood
• This method is very rare

Transdermal Route

• The transdermal route applies a drug to the skin to achieve systemic effect
• Drugs should be lipophilic and in small doses like nitroglycerin, scopolamine, clonidine, fentanyl, or testosterone
• This route makes use of patches

Inhalation Route

• This utilizes alveoli with a large surface area and a permeable membrane
• When inhaled, drugs pass into the bloodstream of the lungs
• Gaseous and vaporous drugs like sevoflurane have high fat solubility
• Asthma and COPD drugs are administered via inhalation

Local Areas of Drug Administration

• Epidermal — ointment, pomade, cream, lotion, powder, soap, solution, liniment, plaster, paste
• Intranasal — nasal drops and nasal spray
• Intravaginal — vaginal suppository, vaginal tablet, ointment, gel, foam
• Buccal (inside the mouth) — lozenge, solution, gargle
• Rectal — ointment, suppository, enema
• Colon — enema
• External ear — otic (ear) drops (solution, suspension)

Systemic Areas of Drug Administration

• Oral — solid or liquid forms
• Parenteral — solution or suspension
• Inhalation — gas, vapor or aerosol
• Transdermal — patch or ointment
• Others — nasal spray