JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Pharmacy II Year PHARMACOLOGY - I Previous Question Paper (November/December-2020 - R17)

Routes of drug administration are the paths by which a drug is brought into contact with the body. They are broadly classified into enteral, parenteral, and topical routes.

1. Enteral Routes

These involve the gastrointestinal tract.

• Oral: Most common, convenient, and economical. Advantages: Safe, non-invasive, self-administered. Disadvantages: Slow onset, risk of first-pass metabolism, potential gastric irritation, and poor absorption of certain drugs.
• Sublingual/Buccal: Drug is placed under the tongue or in the cheek pouch. Advantages: Rapid absorption, bypasses first-pass metabolism. Disadvantages: Limited to lipid-soluble drugs, unpleasant taste, potential for mucosal irritation.
• Rectal: Used when oral is not possible (e.g., vomiting). Advantages: Useful in unconscious patients or children, bypasses partial first-pass metabolism. Disadvantages: Inconvenient, erratic absorption, potential for rectal inflammation.

2. Parenteral Route

Parenteral administration refers to drugs given by injection, bypassing the gastrointestinal tract. This route ensures rapid, predictable, and complete bioavailability.

• Intravenous (IV): Injected directly into the vein. Advantages: Immediate onset, allows titration of dose, suitable for large volumes. Disadvantages: Irreversible, risk of infection, requires trained personnel.
• Intramuscular (IM): Injected into skeletal muscle. Advantages: Faster absorption than oral, suitable for depot preparations. Disadvantages: Painful, risk of nerve damage, limited volume.
• Subcutaneous (SC): Injected into the loose connective tissue under the skin. Advantages: Suitable for self-administration (e.g., insulin), slow and constant absorption. Disadvantages: Limited to non-irritant drugs, slow onset compared to IV.
• Intradermal (ID): Injected into the dermis. Primarily used for diagnostic tests (e.g., Mantoux test) and vaccines.

3. Topical Routes

Application to body surfaces like skin, eyes, or mucous membranes. Advantages: Localized effect, minimal systemic side effects. Disadvantages: Poor absorption through intact skin, risk of systemic toxicity if applied over large areas.

Note on Parenteral Route: The parenteral route is essential in emergency medicine and for drugs that are poorly absorbed, unstable in gastric acid, or subject to extensive first-pass metabolism. It requires strict aseptic techniques to prevent infection and embolism. While it provides the highest bioavailability, it carries higher risks of anaphylaxis and tissue injury compared to enteral routes.

Pharmacokinetics is the study of the time course of drug absorption, distribution, metabolism, and excretion (ADME). It describes what the body does to the drug, focusing on the relationship between the dose administered and the concentration of the drug in the plasma over time.

Drug metabolism (biotransformation) is the chemical alteration of drugs by the body, primarily occurring in the liver, to convert lipid-soluble drugs into water-soluble metabolites for easier excretion. Several factors influence the rate and extent of drug metabolism:

• Physiological factors: Age significantly affects metabolism; neonates have immature hepatic enzyme systems, while the elderly often exhibit reduced hepatic blood flow and enzyme activity. Gender can also influence metabolism due to hormonal differences affecting specific cytochrome P450 enzymes.
• Genetic factors: Pharmacogenetic variations, such as polymorphisms in CYP450 enzymes, lead to inter-individual differences in metabolism. Patients may be classified as poor, intermediate, extensive, or ultra-rapid metabolizers based on their genetic profile.
• Enzyme induction and inhibition: Certain drugs can induce (increase) the synthesis of metabolizing enzymes (e.g., rifampicin, phenobarbital), leading to decreased plasma concentrations of co-administered drugs. Conversely, enzyme inhibitors (e.g., ketoconazole, erythromycin) decrease the rate of metabolism, potentially leading to drug toxicity.
• Pathological factors: Liver diseases such as cirrhosis, hepatitis, or obstructive jaundice impair the functional capacity of hepatocytes, significantly reducing the metabolic clearance of drugs.
• Nutritional status: Malnutrition or protein deficiency can reduce the availability of amino acids and cofactors required for phase II conjugation reactions, thereby slowing down drug metabolism.
• Environmental and dietary factors: Exposure to environmental pollutants or dietary components can affect enzyme activity. For example, polycyclic aromatic hydrocarbons in cigarette smoke induce CYP1A2, while grapefruit juice inhibits intestinal CYP3A4.