Download PDF โ RRB PH UT09 – Pharmacology Practice Test 1: General Pharmacology & Pharmacokinetics
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RRB PH UT09 – Pharmacology Practice Test 1: General Pharmacology & Pharmacokinetics
Q1. According to the pH-partition hypothesis, what physicochemical form of a weakly acidic drug (such as Aspirin, pKa 3.5) preferentially diffuses across gastric mucosal lipid bilayers?
Biological membranes are primarily lipid bilayers permeable to non-ionized, lipid-soluble molecules. For a weak acid (pKa = 3.5) in the acidic gastric lumen (pH ~1.5), the Henderson-Hasselbalch equation indicates that over 99% of the drug molecules remain in the non-ionized, lipophilic state, facilitating passive transcellular diffusion across gastric mucosal barriers.
Q2. How is absolute oral bioavailability (F) quantitatively determined from plasma concentration-time curves following oral and intravenous administration?
A) F = (AUC_oral / AUC_iv) ร 100 without dose adjustment
B) F = (AUC_iv ร Dose_oral) / (AUC_oral ร Dose_iv)
C) F = (Cmax_oral ร Dose_iv) / (Cmax_iv ร Dose_oral)
D) F = (AUC_oral ร Dose_iv) / (AUC_iv ร Dose_oral)
A) F = (AUCoral / AUCiv) ร 100, dose adjustment เคเฅ เคฌเคฟเคจเคพ
B) F = (AUCiv ร Doseoral) / (AUCoral ร Doseiv)
C) F = (Cmaxoral ร Doseiv) / (Cmaxiv ร Doseoral)
D) F = (AUCoral ร Doseiv) / (AUCiv ร Doseoral)
Answer: (D)
Absolute bioavailability (F) compares the systemic exposure of an extravascular (oral) dose to an equivalent intravenous reference dose where absorption is 100% (F = 1.0). It is calculated as: F = [AUC_oral ร Dose_iv] / [AUC_iv ร Dose_oral], where AUC represents the area under the plasma concentration-time curve from time zero to infinity.
Q3. A drug exhibits an Apparent Volume of Distribution (Vd) of 350 Liters in an adult weighing 70 kg. What does this value indicate regarding its tissue distribution?
A) The drug is strictly confined to systemic intravascular plasma water
B) The drug is extensively sequestered in peripheral tissues and intracellular compartments
C) The drug is distributed uniformly throughout total extracellular fluid
D) The drug cannot cross capillary endothelia due to high molecular weight
In a 70 kg adult, plasma volume is about 3 L and total body water about 42 L. An apparent Vd of 350 L (5 L/kg) greatly exceeds anatomical body-fluid volumes, indicating extensive distribution or binding outside plasma, such as tissue binding or intracellular sequestration. Vd alone does not prove low plasma-protein binding or a single specific mechanism.
Q4. Which Cytochrome P450 isoenzyme is among the most abundant in human adult hepatocytes and is commonly cited as metabolizing about half of clinically used drugs?
CYP3A4 is one of the most abundant CYP isoenzymes in human liver and contributes to the Phase I oxidative metabolism of many drugs. It is often cited as being involved in the metabolism of about half of clinically used drugs; the exact proportion depends on the source and how drugs are counted.
Q5. Which classic Phase II metabolic conjugation pathway involves the transfer of an endogenous glucuronic acid moiety from UDPGA catalyzed by UDP-glucuronosyltransferases?
Glucuronidation is the most prevalent Phase II conjugation reaction. Microsomal UDP-glucuronosyltransferases (UGTs) transfer glucuronic acid from uridine diphosphate-glucuronic acid (UDPGA) to drug functional groups (-OH, -COOH, -NH2, -SH). This introduces multiple polar hydroxyl groups and an ionizable carboxyl group, rendering the conjugate highly water-soluble for rapid biliary or renal excretion.
Q6. In G-protein-coupled receptor (GPCR) signal transduction, what immediate biochemical event occurs upon agonist binding to a Gs-protein-coupled receptor?
A) The cytoplasmic tail phosphorylates nuclear transcription factors directly
B) Galpha-i subunit activates Phospholipase C-beta to generate IP3 and DAG
C) Galpha-q subunit opens inward-rectifier potassium channels directly
D) Galpha-s subunit exchanges bound GDP for GTP and activates Adenylyl Cyclase
Ligand binding to a Gs-coupled receptor induces a conformational shift that catalyzes the exchange of GDP for GTP on the Galpha-s subunit. The active GTP-bound Galpha-s subunit dissociates from the Gbeta-gamma dimer and binds to the catalytic domain of membrane-bound Adenylyl Cyclase, stimulating the conversion of cellular ATP into cyclic adenosine monophosphate (cAMP).
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