NRCMA Pharmacology Basics 2 — Questions and Answers

Question 1: The 'therapeutic index' of a drug refers to:

The time it takes for a drug to reach peak plasma concentration
The ratio between the toxic dose and the effective dose (Correct answer)
The route of administration with the fastest onset
The drug's half-life in the body

Correct answer: The ratio between the toxic dose and the effective dose

The therapeutic index (TI) is the ratio of the toxic dose to the effective dose. A narrow TI means the toxic dose is close to the effective dose, requiring careful monitoring.

Drugs with narrow therapeutic indices — digoxin, warfarin, lithium, phenytoin, vancomycin — require regular blood level monitoring. A high TI indicates a wide safety margin (e.g., penicillin). The therapeutic window defines the concentration range between minimum effective and minimum toxic concentration.

Question 2: Which schedule of controlled substances has the highest potential for abuse and NO accepted medical use in the US?

Schedule II
Schedule III
Schedule IV
Schedule I (Correct answer)

Correct answer: Schedule I

Schedule I substances (e.g., heroin, LSD) have no accepted medical use and the highest abuse potential, making them illegal for any clinical prescribing.

DEA Controlled Substance Schedules: Schedule I (no medical use, highest abuse — heroin, LSD), Schedule II (high abuse, accepted use — opioids, amphetamines), Schedule III (moderate abuse — ketamine, buprenorphine), Schedule IV (lower abuse — benzodiazepines, zolpidem), Schedule V (lowest — cough preparations with small amounts of codeine).

Question 3: An antagonist drug works by:

Mimicking the effect of a natural body chemical at a receptor
Blocking a receptor and preventing a response (Correct answer)
Increasing enzyme production
Stimulating hormone release

Correct answer: Blocking a receptor and preventing a response

An antagonist binds to a receptor without activating it, blocking agonists from binding and producing a response.

Agonists bind and activate receptors, producing a biological response. Antagonists competitively or non-competitively bind and block agonist effects. Examples: naloxone (opioid antagonist), atropine (muscarinic antagonist), beta-blockers (beta-adrenergic antagonists). Understanding agonist/antagonist relationships is essential for understanding antidotes.

Question 4: Enteral routes of drug administration include:

Intravenous, intramuscular, and subcutaneous
Oral, sublingual, and rectal (Correct answer)
Intradermal, topical, and transdermal
Inhalation and intrathecal

Correct answer: Oral, sublingual, and rectal

Enteral routes involve the gastrointestinal tract: oral (swallowed), sublingual (under tongue), and rectal (via rectum).

Routes: Enteral (GI tract) = oral, sublingual, buccal, rectal. Parenteral (bypassing GI) = IV, IM, subcutaneous, intradermal. Topical = skin surface. Transdermal = systemic absorption through skin patch. Oral is most convenient but has variable absorption due to first-pass metabolism. IV has fastest onset but highest risk of adverse reactions.

Question 5: Penicillin is an example of which drug category?

Antifungal
Antibiotic (beta-lactam) (Correct answer)
Antiviral
Antipyretic

Correct answer: Antibiotic (beta-lactam)

Penicillin is a beta-lactam antibiotic that inhibits bacterial cell wall synthesis, used primarily against gram-positive bacteria.

Beta-lactam antibiotics include penicillins, cephalosporins, carbapenems, and monobactams. They inhibit transpeptidase enzymes needed for bacterial cell wall synthesis. Penicillin allergy is the most common drug allergy. Antifungals include fluconazole. Antivirals include acyclovir. Antipyretics (acetaminophen, ibuprofen) reduce fever.

Question 6: The 'first-pass effect' affects drugs taken by which route?

Intravenous
Intramuscular
Oral (Correct answer)
Sublingual

Correct answer: Oral

Orally administered drugs absorbed from the GI tract pass through the liver via portal circulation before reaching systemic circulation, where hepatic metabolism can significantly reduce bioavailability.

First-pass metabolism occurs when drugs absorbed in the intestines travel through the portal vein to the liver where CYP450 enzymes metabolize a portion before systemic distribution. Sublingual and rectal routes partially bypass first-pass metabolism. IV, IM, and subcutaneous routes completely bypass it. Drugs with high first-pass metabolism require higher oral doses or alternative routes.

NRCMA Pharmacology Basics 2

The 'therapeutic index' of a drug refers to: