JNTU B.Pharmacy III PHARMACOLOGY-I Previous Question Paper (March-2021 - R17)

Routes of drug administration are broadly classified into two main categories: Enteral (involving the gastrointestinal tract) and Parenteral (administered via routes other than the GI tract).

1. Enteral Routes

These include oral, sublingual, and rectal administration.

• Oral: The most common route. Advantages: Convenient, safe, economical, and does not require sterile conditions. Disadvantages: Slow onset of action, potential for first-pass metabolism, gastric irritation, and unsuitability for unconscious patients or drugs destroyed by digestive enzymes.
• Sublingual: Drug is placed under the tongue. Advantages: Rapid absorption, bypasses first-pass metabolism, and avoids gastric acid. Disadvantages: Limited to lipid-soluble drugs and can cause local irritation.
• Rectal: Advantages: Useful for vomiting or unconscious patients and reduces first-pass metabolism. Disadvantages: Inconvenient, erratic absorption, and potential for rectal mucosal irritation.

2. Parenteral Routes

These include injections (intravenous, intramuscular, subcutaneous) and inhalation.

• Intravenous (IV): Advantages: Immediate onset, 100% bioavailability, suitable for large volumes and irritating drugs. Disadvantages: Risk of infection, embolism, anaphylaxis, and requires skilled personnel.
• Intramuscular (IM): Advantages: Rapid absorption of aqueous solutions, suitable for moderate volumes and oily vehicles. Disadvantages: Painful, risk of nerve damage, and limited volume.
• Subcutaneous (SC): Advantages: Suitable for self-administration (e.g., insulin) and slow, sustained absorption. Disadvantages: Cannot be used for large volumes or irritating drugs.
• Inhalation: Advantages: Rapid absorption due to large surface area of alveoli, local effect for respiratory conditions. Disadvantages: Requires specialized equipment and patient coordination.

3. Topical Routes

Includes transdermal, ophthalmic, and intranasal. Advantages: Provides localized effect with minimal systemic side effects. Disadvantages: Limited to lipid-soluble drugs and potential for contact dermatitis.

The transport of drugs across biological membranes is essential for absorption, distribution, metabolism, and excretion. Drugs cross these lipid bilayers primarily through the following mechanisms:

1. Passive Diffusion: The most common mechanism where drugs move from an area of high concentration to low concentration. It is non-saturable, non-selective, and does not require energy. Lipid-soluble, non-ionized drugs diffuse readily across the membrane.
2. Facilitated Diffusion: Involves carrier proteins that transport drugs down their concentration gradient. This process is saturable and selective but does not require ATP.
3. Active Transport: Requires energy (ATP) to move drugs against their concentration gradient. It is highly selective, saturable, and can be inhibited by competitive molecules. Examples include the transport of levodopa and certain ions.
4. Filtration: Drugs with low molecular weight and water solubility pass through aqueous pores or channels in the membrane driven by hydrostatic or osmotic pressure.
5. Endocytosis and Exocytosis: Used for large, complex, or lipid-insoluble molecules. In endocytosis, the membrane engulfs the drug to form a vesicle (pinocytosis), while exocytosis involves the expulsion of substances from the cell.
6. Ion-Pair Transport: Highly ionized drugs can form neutral ion pairs with endogenous substances (like mucin), allowing the neutral complex to cross the lipid membrane via passive diffusion.