Routes of Drug Application

• Drugs need to be present at a sufficient concentration to have an effect
• The concentration to be reached is the Minimum Effective Concentration (MEK)
• Application sites and amounts need to be determined to reach MEK

Routes of Application

• Routes of application are divided into two based on the condition of the area to affect and the target/purpose of the drug
• The choice of administration route depends on patient and drug factors

Local Application

• The place the drug is intended to affect is on the body surface
• Types of local application:
  • Epidermal
  • Intracutaneous
  • Intrathecal
  • Intrapleural
  • Intraperitoneal
  • Intracardiac
  • Intraarticular
  • Intrauterine
  • Intravaginal
  • Into the rectum and colon
  • On the conjunctiva
  • Intranasal and buccal

Epidermal Application

• Applied to localized lesions in accessible areas
• Used for drugs that have minimal to no absorption in those areas
• There are no or minimal systemic side effects or toxicity

Intracutaneous Application

• It is applied to the dermis layer, which is below the epidermis
• Sterile solutions and test serums for allergy and bacteriology tests are applied this way

Conjunctiva Application

• Used in various eye infections
• Ophthalmic preparations are called 'colir'
• Preparations must be sterile

Intranasal Application

• Used in diseases of the nasal mucosa and paranasal sinuses
• Anti-inflammatory, vasoconstrictor, and local anesthetic drug solutions can be applied this way
• Systemic application is also possible

Buccal (Intraoral) Application

• Used for mouth and gum infections

External Ear Canal Application

• Used in some diseases of the external ear canal or eardrum

Intrathecal Application

• Sterile antibiotic or local anesthetic solutions administered to create a local effect
• Affects the meninges or spinal nerve roots

Intracardiac Application

• Used in emergency situations or for cardiac resuscitation during cardiac surgery
• Stimulant drugs like adrenaline can be administered directly to the heart

Intraperitoneal Application

• Injections can be made into the abdominal cavity in cases of inflammation of the peritoneum

Intraarticular Application

• Corticosteroids or antibacterial drugs can be injected into the joint for joint diseases

Rectal and Colonic Application

• Suppository, enema, or ointment-shaped preparations used for superficial lotions of the rectum
• Treats hemorrhoids and some diseases of the colon

Intrauterine Application

• Oxytocic hormone is injected into the myometrium to accelerate uterine contraction after cesarean sections and reduce bleeding

Intravaginal Application

• Medications are administered into the vagina in the form of a pessary
• Spermicide drugs in foam and gel form are used to prevent pregnancy

Systemic Application

• Application methods include:
  • Enteral (oral, sublingual, rectal)
  • Parenteral (intravenous, subcutaneous, intramuscular, into the bone marrow)
  • Transdermal
  • Inhalation

Enteral (Oral, Per Os) Application

• Most common, practical, and economical route
• Drugs used orally must pass through the liver after absorption before entering the systemic circulation
• Some drugs may be inactivated, and absorption may not be complete

Sublingual Application

• Used in cases where a quick drug effect is desired
• Quick dissolving, able to create an effect with small amounts
• Highly soluble in fat
• Drugs in small tablets, such as nitroglycerin and nifedipine, are administered this way

Rectal Administration

• Achieves either a local or systemic effect through absorption from the rectal mucosa
• Drugs administered as suppositories or enemas
• Used in patients who cannot take oral medication and in infants

Parenteral Administration

• Used for drugs that cannot be absorbed or are broken down in sufficient amounts from the gastrointestinal tract when administered orally
• Used when drugs require a rapid onset of effect in emergency situations
• Also used when the patient is unconscious, unable to swallow, experiencing nausea, vomiting, or diarrhea

Parenteral Administration Disadvantages

• Can be painful
• Can cause vascular or tissue damage
• Creates psychological stress
• Cannot be administered by the patient alone
• The pharmaceutical form used can be expensive

Intravenous (IV) Administration

• Only water-soluble or water-mixable drugs can be administered this way
• Used when a rapid effect is desired, or if the patient is unconscious and cannot swallow the drug
• Bioavailability is usually 100%
• Drug solutions up to 10 ml are injected in 1-2 minutes
• Intravenous infusion is the slow administration of large volumes of drug solutions (over 1-2 hours) into a vein

Intravenous (IV) Disadvantages

• Only water-soluble drugs can be administered
• Oily solutions and suspensions cannot be administered intravenously due to the risk of embolism
• Drugs with low water solubility may precipitate in the vein if injected rapidly (diazepam, 5 mg/min)
• Administered drugs cannot be retrieved
• High risk of anaphylaxis
• Irritant drugs may cause tissue damage if extravasation occurs -Anaphylaxis is a severe allergic reaction

Intramuscular (IM) Administration

• Injecting the drug into the appropriate muscle tissue
• The gluteal or deltoid muscle is usually preferred
• The volume of solution administered should not exceed 5 ml
• Absorption of the injected drug is mostly affected by blood flow in that area
• Massage or exercise increases absorption

Subcutaneous Administration

• Administered under the skin, the outer surface of the humerus or femur region is often preferred
• A maximum of 2 ml of solution should be applied to prevent pain on the skin
• Irritant drugs should be applied intramuscularly rather than subcutaneously
• Some drugs are placed under the skin in the form of implants or pellets (such as compressed tablets), so that the drug is released slowly and regularly

Intraosseous Injection

• Used in infants and sometimes adults if veins cannot be found
• The drug is injected into a suitable bone marrow (sternum) and from there it passes rapidly into the blood
• This is a very rare method

Transdermal Application

• Application of the drug to the skin surface for systemic effect
• Highly lipophilic and small dose effective drugs (such as nitroglycerin, scopolamine, clonidine, fentanyl, testosterone) are applied this way
• Uses a transdermal therapeutic system (patch)

Inhalation Application

• Advantageous due to the alveoli having a very large surface area and a highly permeable membrane, and the blood flow rate in the lungs is also very high
• When inhaled, they quickly pass through the alveolar membrane in the lungs and enter the bloodstream
• Drugs that are gaseous and vaporous (sevoflurane) and have high fat solubility, such as general anesthetics (nitrous oxide), and asthma and COPD drugs are administered this way

Local Application Areas and Pharmaceutical Forms

• Epidermal (on the skin): 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 canal: Otic (ear) drops (solution, suspension)

Systemic Application Sites and Pharmaceutical Forms

• Oral:
  • Solid Forms: tablet, dragee, capsule, film-coated tablet, enteric tablet, chewable tablet, packet, effervescent tablet, cachet, pill
  • Liquid Forms: Syrup, elixir, solution, suspension, drop (concentrated solution), lotion, emulsion, extract
• Parenteral: Solution or suspension for injection, emulsion (ampoule, vial, powder for reconstitution), implantation pellet
• Inhalation: Gas, vapor, aerosol, inhaler, nebulizer
• Transdermal: Patch (TTS), ointment
• Others: Nasal spray