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General Pharmacological Principles - Chapter 1 Answer Key

LONG/ESSAY ANSWER QUESTIONS (10 Marks)

Q1. Classify routes of drug administration. Discuss advantages, disadvantages, and examples of oral and parenteral routes.

Classification of Routes

Routes of drug administration are broadly classified into three categories (Lippincott Pharmacology):

Enteral - drug enters via GI tract (oral, sublingual, buccal, rectal)
Parenteral - drug introduced directly into systemic circulation, bypassing GI tract (IV, IM, SC, intradermal)
Topical/Other - local application (transdermal, inhalation, intranasal, ocular)

A. Oral Route

Advantages:

Most common, convenient, and economical
Self-administered easily by patients
Wide variety of formulations available (tablets, capsules, enteric-coated, extended-release)
Overdose can be managed with antidotes (e.g., activated charcoal)
Non-invasive; no risk of infection at injection site

Disadvantages:

Most complicated absorption pathway
Low gastric pH inactivates some drugs (e.g., penicillin G)
Subject to significant first-pass hepatic metabolism (e.g., nitroglycerin, lidocaine)
Cannot be used in unconscious patients
Onset of action is slow (not suitable for emergencies)
Some drugs are destroyed by GI enzymes (e.g., insulin)
Drug absorption is unpredictable if patient has vomiting or diarrhea

Examples: Paracetamol, metformin, amoxicillin, omeprazole (enteric-coated)

Special oral formulations:

Enteric-coated: Protects acid-labile drugs (e.g., omeprazole, aspirin enteric-coated) - coating dissolves in the small intestine, not the stomach
Extended-release (ER/SR/CR/XL): Controls drug release for slower absorption, prolonged action, improved compliance. Example: morphine SR is given twice daily instead of six times; diclofenac SR for osteoarthritis

B. Parenteral Routes

The parenteral route introduces drugs directly into the systemic circulation, bypassing the GI tract. Used when drugs are poorly absorbed orally (heparin), unstable in GI tract (insulin), in unconscious patients, or when rapid onset is needed.

Common parenteral routes:

Route	Onset	Volume	Special features
Intravenous (IV)	Fastest	Large	100% bioavailability; irreversible
Intramuscular (IM)	Minutes	Up to 5 mL	Good for oily or depot preparations
Subcutaneous (SC)	Slower	Small	Used for insulin, vaccines
Intradermal	Slowest	Tiny	Used for allergy testing, BCG vaccine

Advantages of parenteral routes:

Bypasses first-pass metabolism - full bioavailability
Reliable absorption regardless of GI state
Used when oral route is impossible (unconscious, NPO)
Precise dose control
Rapid onset (IV = immediate)
Can deliver large volumes (IV infusion)

Disadvantages:

Painful; risk of fear and non-compliance
Requires trained personnel and sterile conditions
Risk of infection, phlebitis, tissue damage
IV administration is irreversible - no antidote if overdose given
More expensive

Examples:

IV: heparin, morphine in acute pain, adenosine in arrhythmia
IM: benzathine penicillin, depot antipsychotics, vaccines
SC: insulin, low-molecular-weight heparin
Intradermal: Mantoux test, BCG

Q2. Explain first-pass metabolism with examples. How does the route of administration affect it?

First-pass (presystemic) metabolism refers to the biotransformation of a drug during its initial passage from the GI tract through the intestinal wall and liver via the portal circulation, before reaching the systemic circulation. This significantly reduces the amount of active drug available.

Mechanism:

After oral absorption, drug enters the portal vein and passes through the liver
Liver enzymes (primarily CYP450) metabolize a fraction of the drug
Only the remaining unchanged drug enters the systemic circulation
This reduces bioavailability

Classic example - Nitroglycerin:

More than 90% of nitroglycerin is cleared during first-pass metabolism. Hence, it is primarily administered via the sublingual, transdermal, or intravenous route. - Lippincott Pharmacology

Other examples of high first-pass metabolism drugs:

Morphine, propranolol, lidocaine, verapamil, salbutamol, testosterone, progesterone

How route of administration affects first-pass metabolism:

Route	First-pass effect?	Reason
Oral	YES (maximum)	Drug absorbed via portal vein → passes through liver before systemic circulation
Sublingual/buccal	NO	Absorbed into superior vena cava; bypasses portal system entirely
Rectal (lower rectum)	Partial bypass	Inferior rectal veins drain to systemic, not portal circulation
Intravenous	NO	Directly enters systemic circulation
Intramuscular / SC	NO	Absorbed into systemic capillaries
Transdermal	NO	Absorbed via skin capillaries into systemic circulation
Inhalation	NO (mostly)	Lungs bypass hepatic first pass; some pulmonary metabolism may occur

Clinical significance:

Drugs with high first-pass metabolism need higher oral doses than parenteral doses (e.g., morphine oral:IV ratio is ~3:1)
Such drugs are better given sublingually or transdermally (e.g., nitroglycerin, buprenorphine)
First-pass metabolism can be saturated at high doses, causing non-linear pharmacokinetics (e.g., propranolol)

SHORT ESSAY/SHORT ANSWER QUESTIONS (3-5 Marks)

Q1. Factors influencing choice of route of administration

Patient condition - unconscious patients need IV/IM; vomiting patients cannot take oral drugs
Drug properties - lipid solubility (affects absorption), stability in GI tract (insulin destroyed → must be SC), first-pass metabolism (nitroglycerin → sublingual)
Desired speed of onset - emergencies require IV for immediate effect
Site of action - local effect (topical) vs. systemic effect
Age of patient - infants/elderly may prefer liquid oral or rectal formulations
Duration of action required - depot IM injections for long-acting effect
Dose required - large volumes only possible IV

Q2. Situations where oral route cannot be used

Unconscious or uncooperative patient (e.g., coma, seizure)
Severe vomiting (e.g., chemotherapy-induced nausea)
Patient kept nil by mouth (pre-operative, bowel obstruction)
Drug is destroyed in GI tract (e.g., insulin, heparin, streptokinase)
Drug undergoes excessive first-pass metabolism (e.g., nitroglycerin, GTN)
Emergency requiring immediate drug action (e.g., IV adrenaline in anaphylaxis)
Drug poorly absorbed orally (e.g., gentamicin - not absorbed because it is a large polar molecule)
Malabsorption states

Q3. Systemic vs. Local Routes

Feature	Systemic Route	Local Route
Intent	Drug reaches bloodstream and acts throughout the body	Drug acts at the site of application
Examples	Oral, IV, IM, SC	Topical cream, eye drops, ear drops, inhalers (partly)
Adverse effects	More systemic side effects	Fewer systemic effects
Example drug	Paracetamol oral for fever	Betamethasone cream for eczema

Q4. Short Notes

a. Orphan Drugs Drugs developed for rare diseases (affecting <200,000 people in the US, or fewer than 1 in 2000 in EU). Because market is small, pharmaceutical companies may not invest in development without government incentives (tax credits, extended market exclusivity, fast-track approval). Example: enzyme replacement therapy for Gaucher's disease (imiglucerase).

b. Essential Drugs Defined by the WHO as drugs that satisfy the healthcare needs of the majority of the population. They should be available at all times in adequate amounts at affordable prices. India maintains a National List of Essential Medicines (NLEM). Examples: aspirin, paracetamol, amoxicillin, metformin, atenolol.

c. Over-The-Counter (OTC) Drugs Drugs that can be purchased without a prescription. They are generally safe with low abuse potential, self-treatable conditions, and clear labeling. Examples: paracetamol, antacids, antihistamines (loratadine), ORS. In India, these are regulated as drugs sold without a Schedule H requirement.

d. Sublingual Route Drug placed under the tongue. Absorbed into rich sublingual venous plexus → directly into superior vena cava → systemic circulation. Key advantages:

Rapid onset (nitroglycerin acts in 1-2 minutes)
Bypasses first-pass metabolism completely
Avoids harsh GI environment
Can be used when swallowing is difficult Examples: nitroglycerin (angina), buprenorphine, isosorbide dinitrate

e. Rectal Route Drug administered via suppository or enema. About 50% bypasses portal circulation (inferior rectal veins → systemic) while 50% enters portal circulation. Used when:

Patient is vomiting or unconscious
Drug irritates GI tract
Local treatment (hemorrhoids, inflammatory bowel disease)
Pediatric patients who refuse oral medication Examples: diazepam rectal for febrile convulsions, diclofenac suppository, glycerin suppository

f. Parenteral Route Refers to any route that bypasses the GI tract. Includes IV, IM, SC, intradermal. Main features:

Direct entry into systemic circulation (or tissues)
No first-pass metabolism
Used for emergency, unconscious patients, poorly absorbed drugs
Requires sterile technique

g. Transdermal Therapeutic System (TTS) A drug-delivery patch applied to skin for systemic absorption through the dermis into capillaries.

Drug reservoir in patch; rate of release controlled by membrane
Provides near zero-order release (constant, steady plasma levels - no peaks and troughs)
No first-pass metabolism
Convenient (once-daily or multi-day patches)
Milder adverse effects due to steady levels
Suitable for lipid-soluble drugs Examples: nitroglycerin patch, fentanyl TTS (72-hour patch for chronic pain), estradiol, nicotine patch, rivastigmine patch

SCENARIO-BASED QUESTIONS (5-10 Marks)

Scenario 1. A 60-year-old diabetic man brought in unconscious after massive hypoglycemic episode. Doctor considers 50% dextrose.

a. Most appropriate route - Intravenous (IV), and why: The patient is unconscious and cannot take anything by mouth. IV is the only safe, effective route. It provides immediate, direct entry of dextrose into the bloodstream, rapidly correcting hypoglycemia. Oral/sublingual is impossible (risk of aspiration). IM/SC absorption would be too slow in this emergency.

b. Advantages and limitations of IV route:

Advantages:

Fastest onset (immediate) - critical in hypoglycemic emergency
100% bioavailability
Precise dose control
Useful for unconscious patients
Allows large fluid volumes (50% dextrose can be given as slow IV push)

Limitations:

Irreversible - overdose cannot be recalled
Requires venous access and trained personnel
Risks: phlebitis (50% dextrose is hypertonic and irritating to veins), extravasation causing tissue necrosis, infection
Cannot be self-administered by patient

c. Routes of drug administration with one clinical example each:

Route	Example
Oral	Metformin for diabetes
Sublingual	Nitroglycerin for angina
Rectal	Diazepam suppository for febrile convulsions
IV	50% dextrose for hypoglycemia
IM	Adrenaline for anaphylaxis
SC	Insulin for diabetes
Transdermal	Fentanyl TTS patch for chronic cancer pain
Inhalation	Salbutamol nebulizer for asthma
Topical	Betamethasone cream for dermatitis

Scenario 2. 25-year-old man with opioid (morphine) overdose - drowsy, pinpoint pupils, shallow breathing.

a. Drug schedule for morphine under Indian regulations: Morphine falls under Schedule X (and is also classified as a narcotic analgesic under the NDPS Act - Narcotic Drugs and Psychotropic Substances Act, 1985). Schedule X drugs in India require:

A valid prescription retained by the pharmacist for 2 years
Strict record-keeping
Licensed premises

b. Important provisions of Schedule H and Schedule X drugs:

Schedule H:

Prescription-only medicines (POM)
Cannot be sold without a valid prescription from a registered medical practitioner
Label must bear "Schedule H Drug - Warning: To be sold by retail on the prescription of a Registered Medical Practitioner only"
Includes antibiotics, antiepileptics, hypnotics
Prescription to be kept for 2 years

Schedule X:

High-risk drugs including psychotropic substances and certain habit-forming drugs
Even stricter controls than Schedule H
Prescription to be kept for 2 years
License required to stock/sell
Includes morphine, codeine-containing combinations, benzodiazepines (some), barbiturates
Maximum supply quantity limits apply
Red-label "Schedule X" warning on packaging

c. Why strict regulation is important:

High addiction potential - opioids cause physical and psychological dependence
Risk of misuse and diversion to non-medical use (as in this case - unauthorized source)
Narrow therapeutic index - small excess dose can cause respiratory depression and death (as seen in this patient with shallow breathing)
Prevents self-medication of dangerous drugs
Reduces drug trafficking and illicit supply
Ensures accountability in the supply chain
Protects public health and prevents epidemic of substance abuse

Scenario 3. 50-year-old woman with osteoarthritis prescribed sustained-release diclofenac.

a. Rationale for sustained-release formulations: Regular (immediate-release) diclofenac has a short half-life and gives sharp peaks (causing GI side effects, toxicity) and troughs (loss of analgesic effect). A sustained-release (SR) formulation releases the drug slowly and continuously, maintaining therapeutic plasma levels throughout the day for long-term pain control. This is ideal for a chronic condition like osteoarthritis.

Per Lippincott Pharmacology: "ER formulations may maintain concentrations within the therapeutic range over a longer duration, as opposed to immediate-release dosage forms, which may result in larger peaks and troughs in plasma concentration."

b. SR vs. conventional formulation - compliance and plasma concentration:

Feature	Conventional (Immediate Release)	Sustained Release
Dosing frequency	3 times daily (TDS)	Once or twice daily
Plasma profile	Peaks and troughs; may go above toxic or below therapeutic	Relatively flat; stays within therapeutic window
Compliance	Lower (frequent dosing)	Higher (less frequent dosing)
GI side effects	More (higher peak levels)	Less (lower, steadier peak)

c. Two advantages and two disadvantages of SR formulations:

Advantages:

Reduced dosing frequency → better patient compliance
Steadier plasma levels within therapeutic range → more consistent pain relief and fewer side effects

Disadvantages:

If an adverse reaction occurs, drug cannot be quickly removed - sustained effect continues
If the patient crushes/chews the tablet, the dose-dumping effect releases the entire dose at once, causing toxicity
More expensive than conventional formulations

d. Other clinical examples where SR preparations are used:

Morphine SR (MS Contin) - twice-daily dosing for chronic cancer pain (vs. 6x/day for immediate release)
Metformin SR - once-daily for type 2 diabetes with better GI tolerability
Nifedipine SR - for hypertension/angina (once-daily vs. three times daily for immediate release)
Venlafaxine XR - once-daily for depression/anxiety

REASONING TYPE QUESTIONS (Give Reason Why)

1. Drugs with high first-pass metabolism are given sublingually. Sublingual absorption occurs via the sublingual venous plexus directly into the superior vena cava, bypassing the portal circulation and hepatic first-pass metabolism entirely. So drugs like nitroglycerin (>90% cleared on first pass orally) achieve adequate plasma levels only when given sublingually. (Lippincott Pharmacology, p. 41)

2. Gentamicin is not used orally for systemic effect. Gentamicin is an aminoglycoside antibiotic that is highly polar (positively charged) and water-soluble. It cannot cross the lipid bilayer of the GI epithelium and is therefore not absorbed from the gut when given orally. It must be given parenterally (IV or IM) to achieve systemic levels. (It is sometimes used orally for GI tract decontamination specifically because it stays in the gut.)

3. Insulin and penicillin G are not given orally.

Insulin is a protein (polypeptide) that is degraded by proteolytic enzymes (trypsin, chymotrypsin) in the GI tract. It does not survive oral administration.
Penicillin G is acid-labile and rapidly destroyed by gastric acid. Only acid-stable penicillins (e.g., penicillin V, amoxicillin) can be given orally.

4. Pressurized metered-dose inhalers achieve quick action with milder adverse effects. Inhalers deliver the drug directly to bronchial smooth muscle (site of action in asthma). This means:

Very small doses needed (microgram range) vs. systemic doses (milligram range) → fewer systemic side effects
Drug bypasses systemic absorption for local effect → rapid bronchodilation within minutes
Lower systemic bioavailability → reduced side effects (e.g., tachycardia, tremor from salbutamol are much less with inhaled vs. oral route)

5. Controlled-release tablets provide near zero-order release. The specialized coating/matrix of controlled-release tablets releases drug at a constant rate that is independent of the drug concentration remaining in the tablet. This mimics zero-order kinetics - a fixed amount of drug is released per unit time, not a fraction. The result is steady, predictable plasma levels that remain within the therapeutic window for an extended period, avoiding peaks (toxicity) and troughs (loss of efficacy).

Sources: Lippincott Illustrated Reviews: Pharmacology (Lippincott); Goodman & Gilman's The Pharmacological Basis of Therapeutics; Katzung's Basic and Clinical Pharmacology, 16th Edition; Miller's Anesthesia, 10e

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