Routes of Drug Application

• Routes of drug application are divided based on the target of the drug and the condition of the application site.
• The choice of administration route depends on both drug and patient factors.

Application Places of Drugs

• For a drug to be effective, it must reach a certain concentration at the site of action.
• This concentration is called MEK (minimum effective concentration).
• Drug dosages and application sites should ensure the active substance reaches the affected area at the MEK.

Local Application Routes

• Local application involves the drug affecting an area on the body surface.
• Routes include epidermal, intracutaneous, intrathecal, intrapleural, intraperitoneal, intracardiac, intraarticular, intrauterine and intravaginal.
• Other routes are into the rectum and colon; on the conjunctiva; and intranasal and buccal.

Epidermal

• Suitable for localized lesions in accessible areas.
• Best for drugs with minimal or no absorption.
• It results in minimal or no systemic side effects or toxicity.

Intracutaneous (into the skin)

• Applied to the dermis layer directly below the epidermis.
• Sterile solutions and test serums for allergy and bacteriology tests can be applied by this method.

On the Conjunctiva

• This method is used to treat various infections, as it is applied directly to the eye
• Ophthalmic preparations used here are sterile and known as 'colir' (eye drops).

Intranasal application

• Utilized for nasal mucosa and paranasal sinus diseases
• Anti-inflammatory, vasoconstrictor, and local anesthetic drugs are administered this way
• Systemic application is also possible via this route.

Buccal (intraoral)

• It is used for mouth and gum infections.

External Ear Canal

• This route is used to apply medication for external ear canal or eardrum diseases

Intrathecal

• Sterile antibiotic or local anesthetic solutions are given this way.
• It is done to create a local effect on the meninges or spinal nerve roots.

Intracardiac

• It is used in emergency situations for cardiac resuscitation during cardiac surgery.
• Stimulant drugs like adrenaline can be directly administered to the heart in this way.

Intraperitoneal

• Injections can be made into the abdominal cavity to treat inflammation of the peritoneum.

Intraarticular

• It involves injecting corticosteroids or antibacterial drugs directly into a joint for joint diseases

Rectal and Colonic Application

• It involves using suppositories, enemas, or ointment-shaped preparations for superficial conditions of the rectum.
• This route is used for hemorrhoids and some colon diseases.

Intrauterine

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

Intravaginal

• Medications, typically in pessary form, are administered into the vagina
• Spermicide drugs in foam and gel forms prevent pregnancy.

Systemic Drug Application Methods

• Systemic application affects the entire body.
• Routes include enteral, parenteral, transdermal, and inhalation.

Enteral Route

• Enteral routes include oral, sublingual, and rectal administration.

Parenteral Route

• Parenteral administration involves intravenous, subcutaneous, intramuscular, and intraosseous routes.
• It bypasses the gastrointestinal tract and avoids drug breakdown.
• Drugs are administered via sterile syringe directly into a vein or tissue for quick action.

Transdermal Route

• It involves applying a drug to the skin in a special pharmaceutical form for absorption into the circulation.

Inhalation Route

• Lipophilic drugs in gas or vapor form pass through the alveolar membrane.
• They then enter the general blood circulation through inhalation.

Oral Administration

• This is the most common, practical, and economical route.
• Orally administered drugs must pass through the liver after absorption.
• Some drugs may be inactivated, resulting in incomplete absorption.

Sublingual Administration

• It is utilized when rapid drug effect is desired.
• Drugs are administered in the form of small, quickly dissolving tablets.
• These tablets contain highly soluble drugs like nitroglycerin and nifedipine.

Rectal Administration

• Achieves either a local or systemic effect through absorption via the rectal mucosa.
• A drug is administered in the form of suppositories or enemas.
• Commonly used for patients who cannot take oral medication and in infants.

Parenteral Administration Uses

• It is used when drugs can't be absorbed or are broken down in the gastrointestinal tract.
• Used when drugs require a rapid onset of effect, especially in emergency situations.
• Administered when the patient is unconscious or unable to swallow, or is experiencing nausea, vomiting or diarrhea.

Disadvantages of Parenteral Administration

• It can be painful and cause vascular or tissue damage
• It creates psychological stress and needs to be administered by someone else.
• The pharmaceutical forms used can be expensive.

Intravenous (IV) Administration

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

Disadvantages of Intravenous (IV)

• Only water-soluble drugs can be administered.
• Oily solutions and suspensions cannot be administered this way (embolism risk).
• Drugs with low water solubility may precipitate if injected rapidly.
• Administered drugs cannot be retrieved, posing a high risk of anaphylaxis.
• Irritant drugs may cause tissue damage if extravasation occurs.

Intramuscular (IM) Injection

• Drug is injected into the appropriate muscle tissue, typically the gluteal or deltoid muscle.
• The volume of solution administered should not exceed 5 ml.
• Absorption is most affected by blood flow in the injected area.
• Massage or exercise increases absorption.

Subcutaneous (Under the Skin) Injection

• Typically administered on the outer surface of the humerus or femur region.
• 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).
• It allows the drug to be released slowly and regularly, which provides a long-lasting effect.

Intraosseous Injection

• It is used in infants and adults when veins cannot be found.
• The drug is injected into a suitable bone marrow (sternum).
• It passes rapidly into the blood, but it's a very rare method.

Transdermal Application

• It involves applying the drug to the skin surface for systemic effect.
• It requires highly lipophilic and small-dose effective drugs.
• Drugs like nitroglycerin, scopolamine, clonidine, fentanyl, and testosterone are applied this way.
• A transdermal therapeutic system (patch) is used.

Inhalation Application

• The alveoli provide a very large surface area and a highly permeable membrane.
• The blood flow rate in the lungs is also very high.
• Inhaled drugs pass quickly through the alveolar membrane and enter the bloodstream.
• Gaseous and vaporous drugs (e.g., sevoflurane), anesthetics (e.g., nitrous oxide).
• Asthma and COPD drugs are administered this way.

Local Application Areas and Pharmaceutical Forms

• Epidermal (on the skin): Ointments, pomades, creams, lotions, powders, soaps, solutions, liniments, plasters, pastes
• Intranasal: Nasal drops and nasal sprays
• Intravaginal: Vaginal suppositories, vaginal tablets, ointments, gels, foams
• Buccal: Lozenges, solutions, gargles
• Rectal: Ointments, suppositories, enemas
• Colon: Enemas
• Outer ear canal: Otic (ear) drops (solution, suspension)

Systemic Application Sites and Pharmaceutical Forms

• Oral: Solid Forms – tablets, dragees, capsules, film-coated tablets, enteric tablets, chewable tablets, packets, effervescent tablets, cachets, pills; Liquid Forms – syrups, elixirs, solutions, suspensions, drops, concentrated solutions, lotions, emulsions, extracts
• Parenteral: Solutions or suspensions for injection, emulsions (ampoules, vials, powders for reconstitution), implantation pellets
• Inhalation: Gases, vapors, aerosols, inhalers, nebulizers
• Transdermal: Patches (TTS), ointments
• Others: Nasal sprays