Routes of Drug Application

Application Places of Drugs

• Drugs must be present at a certain concentration to have an effect; this concentration is called MEK (minimum effective concentration)
• Drug amounts and application sites must be determined so the active substance reaches the place of effect in MEK

Routes of Application of Drugs

• Routes are divided into local and systemic, based on the drug's target and the condition of the place to be affected
• The choice of administration route depends on drug and patient factors

Local Application Routes

• Types of local application include:
  • Epidermal
  • Intracutaneous
  • Intrathecal
  • Intrapleural
  • Intraperitoneal
  • Intracardiac
  • Intraarticular
  • Intrauterine
  • Intravaginal
  • Into the rectum and colon
  • On the conjunctiva
  • Intranasal and buccal

Epidermal Application

• Indicated for localized lesions in accessible areas
• Used for drugs with minimal or no absorption
• Minimal or no systemic side effects or toxicity

Intracutaneous Application

• Applied to the dermis layer, just below the epidermis
• Used for sterile solutions and test serums for allergy and bacteriology tests

Conjunctiva Application

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

Intranasal Application

• Used for diseases of the nasal mucosa and paranasal sinuses
• Solutions include anti-inflammatories, vasoconstrictors, and local anesthetics
• Systemic application is also possible

Buccal (Intraoral) Application

• Used for mouth and gum infections

External Ear Canal Application

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

Intrathecal Application

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

Intracardiac Application

• Used in emergency situations or for cardiac resuscitation during cardiac surgery
• Stimulant drugs such as adrenaline may be administered

Intraperitoneal Application

• Injections are made into the abdominal cavity for some cases of inflammation of the peritoneum

Intraarticular Application

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

Rectal and Colonic Application

• Suppository or enema preparations are used for superficial lotions of the rectum, hemorrhoids, and some diseases of the colon

Intrauterine Application

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

Intravaginal Application

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

Systemic Drug Application Methods

• Enteral: oral, sublingual, rectal
• Parenteral: intravenous, subcutaneous, intramuscular, into the bone marrow
• Transdermal: application of drug to the skin for absorption into the circulation
• Inhalation: lipophilic drugs in gas or vapor form pass through the alveolar membrane and enter the general blood circulation

Oral Administration

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

Sublingual Administration

• Uses cases where a drug effect is desired to start quickly
• Involves drugs that are quickly dissolving and highly soluble in fat, in the form of small tablets
• Example drugs: nitroglycerin and nifedipine

Rectal Administration

• Local or systemic effect achieved by absorption from the rectal mucosa
• Drugs are administered in the form of suppositories or enemas
• More commonly used in patients unable to take oral medication and in infants

Parenteral Administration

• Used for drugs that cannot be absorbed or broken down sufficiently in the gastrointestinal tract
• Used for drugs that require rapid onset of effect in emergency situations
• Used for patients that are unconscious, unable to swallow, or experiencing nausea/vomiting/diarrhea

Disadvantages of Parenteral Route

• Can be painful
• Can cause vascular or tissue damage
• Creates psychological stress
• Cannot be administered by the patient alone
• 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

Disadvantages of Intravenous Administration

• Only water-soluble drugs can be administered
• Oily solutions and suspensions cannot be administered intravenously (embolism)
• Drugs with low water solubility may precipitate in the vein if injected rapidly
• The drug can't be retrieved
• High risk of anaphylaxis (severe allergic reaction)
• Irritant drugs may cause tissue damage if extravasation occurs

Intramuscular (IM) Administration

• Drug is injected into the appropriate muscle tissue
• Gluteal or deltoid muscle is usually preferred
• 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

• Outer surface of the humerus or femur region is often preferred
• 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 so the drug is released slowly and regularly

Intraosseous Injection

• In infants and sometimes adults, if veins cannot be found, the drug is injected into a suitable bone marrow (sternum) to pass rapidly into the blood
• A very rare method

Transdermal Administration

• Application of drug to the skin surface for systemic effect
• Highly lipophilic and small-dose drugs are used
• Involves transdermal therapeutic systems (patch)
• Applied to the skin surface for systemic effect
• Effective drugs are highly lipophilic and delivered in small doses such as nitroglycerin, scopolamine, clonidine, fentanyl, testosterone

Inhalation Application

• It is advantageous in that the alveoli have a very large surface area and a highly permeable membrane, and that the blood flow rate in the lungs is also very high
• The drug passes through the alveolar membrane and enters the bloodstream when inhaled
• Gaseous and vaporous drugs such as general anesthetics, sevoflurane, nitrous oxide and asthma and COPD drugs are administered in this way

Application areas and pharmaceutical forms - Local

• 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)

Application sites and pharmaceutical forms - Systemic

• Oral: Solid - tablet, dragee, capsule, film-coated tablet, enteric tablet, chewable tablet, packet, effervescent tablet, cachet, pill. Liquid - 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