Pharmacology: Dosage Forms and Routes

Study Notes

Dosage Forms and Routes of Administration

Various dosage forms exist for drugs, each with distinct characteristics and delivery methods.
Routes of administration include enteral, parenteral, inhalation, and topical.

Enteral Route

This route involves administering drugs through the gastrointestinal tract.
Liquid forms include suspensions and solutions.
Solid forms include tablets, capsules, and powders.

Parenteral Route

Drugs are administered directly into the bloodstream or other tissues bypassing the digestive tract.
Liquid forms include injections.
Types of injections:
- Ampoules (single use)
- Vials (single or multiple use)
- Bottles (or IV bags)
- Prefilled syringes
Subtypes of injections include Intravenous (IV), Intramuscular (IM), Subcutaneous (SC), and Intradermal (ID).

Inhalation Route

Drugs are delivered directly into the lungs via inhalation.
This method allows for rapid absorption into the bloodstream.

Topical Route

Drugs are applied to the surface of the skin or mucous membranes.
Forms include creams, ointments, lotions, and transdermal patches.
Creams are oil-in-water emulsions
Ointments are typically vaseline or oil-based.
Lotions are aqueous solutions, which are useful for wet lesions.

Parenteral Dosage Forms & Routes

Injections are classified as liquid formulations.
Common formats include ampoules (single use), vials (single or multi-dose), bottles/IV bags (for large volumes), and prefilled syringes.

Parenteral Dosage Forms (Liquid)

Drugs are administered employing ampoules, vials, and bottles (or IV bags), as well as prefilled syringes.
- Ampoules: Single-use containers for sterile solutions or suspensions.
- Vials: Single or multi-dose containers often used for solutions or suspensions requiring larger volumes which are sterile.
- Bottles/IV bags: Used for large-volume administration, typically for intravenous fluids or medications.
- Prefilled syringes: Convenient pre-measured doses in a syringe with a needle.

Solid (S.C. implantation)

Solid implants, such as contraceptive pellets, are inserted beneath the skin.

Types of Injections

Intravenous (IV):
- Administration site: Superficial veins in the dorsum of the hand and forearm; Subclavian, common internal or external jugular vein for extended administration.
- Volume: From less than 1 ml to liters (suitable for large volumes)
- Requirements: Requires trained personnel, aqueous solutions, slow administration with patient monitoring.
- Precautions: Accurate dose calculation, strict aseptic conditions, slow administration, excluding air, ensuring insertion into a vein.
- Advantages: Immediate onset (emergency situations), 100% bioavailability, suitable for irritant drugs & large volumes.
- Indications: Emergency conditions (shock, convulsions), fluid therapy (saline, blood), anesthesia.
- Disadvantages: Risk of disease transmission (hepatitis, AIDS), allergic reactions, phlebitis/thrombophlebitis (if irritants), extravasation, air embolism, irreversible injection, unsuitable for oily preparations (fat embolism). Infection of IV catheter/thrombi on tip, skilled personnel.
Intramuscular (IM):
- Volume: <5 ml
- Sites: Deltoid muscle (lateral aspect of arm), preferred in children; vastus lateralis (lateral aspect of thigh); ventrogluteal/dorsogluteal muscles (buttocks).
- Precautions: Avoid major blood vessels and nerves; Rotate injection sites.
- Advantages: Rapid absorption; Suitable for depot or oily preparations.
- Disadvantages: Unsuitable for large volumes (or irritants), painful, abscess, IV or nerve injury.
Subcutaneous (SC):
- Volume: <2 ml
- Sites: Lateral aspect of upper arm, thigh, and abdomen, avoiding nerves and major vessels; Rotate injection sites.
Intradermal (ID):
- Volume: <0.5 ml
- Site: Ventral forearm
- Use: For sensitivity tests.

Injection Technique

Intramuscular injections: 90-degree angle
Subcutaneous injections: 45-degree angle
Intravenous injections: 25-degree angle
Intradermal injections: ~10-15-degree angle

External (Topical) Dosage Routes

External application to the skin or mucous membranes.

Topical Skin Forms

Lotion: Aqueous solution
Cream: Oil-in-water
Ointment: Vaseline/oil-based
Solid: Powder (e.g., antifungal)

Ointments, creams, and lotions

These are topical applications.
Ointments are for dry lesions; creams for semi-wet; lotions for wet lesions

Transdermal Patches

Consist of clear backing, drug reservoir, drug-release membrane, and contact adhesive.
Advantages: No first-pass metabolism, gradual onset, long duration, no GI tract irritation, not affected by GI enzymes.
Disadvantages: Variable absorption rate, local allergies.

Other Routes

Intranasal (for systemic and local effects).
Intrathecal.
Intraarterial.

Intraarterial chemotherapy

Infusion of anticancer drugs (or embolization particles) into arteries via catheter for direct treatment of cancerous masses within the blood vessels.