Concours de fin de PACES — Pharmacie (Université d'Antananarivo)

According to the Brønsted-Lowry acid-base theory, how is an acid defined, and what is the conjugate base of the bicarbonate ion (HCO3-) in an aqueous pharmaceutical solution?

• AA proton (H+) donor; its conjugate base is CO3(2-)
• BA proton (H+) acceptor; its conjugate base is H2CO3
• CAn electron-pair acceptor; its conjugate base is CO2
• DA hydroxide (OH-) donor; its conjugate base is H2O

What is the pH of an aqueous solution of acetic acid (CH3COOH) at a concentration of 0.010 M, given that the acid dissociation constant pKa of acetic acid is 4.76 at 25 °C (assuming [H+] << [CH3COOH])?

• A2.38
• B3.38
• C4.76
• D5.24

A pharmaceutical buffer solution is prepared by mixing 0.050 M sodium acetate and 0.100 M acetic acid (pKa = 4.76). What is the resulting pH of this buffer at 25 °C (given log 2 ≈ 0.301)?

• A4.46
• B4.76
• C5.06
• D3.76

Under what condition is the buffer capacity (beta) of a monoprotic weak acid/base buffer system maximal, and what is its theoretical value in terms of total buffer concentration C (according to Van Slyke)?

• AAt pH = pKa + 1.0; beta_max = 2.303 * C
• BAt pH = 7.00; beta_max = C / 2
• CAt pH = pKa; beta_max = 0.576 * C
• DAt pH = pKa - 1.0; beta_max = 0.250 * C

The solubility product constant (Ksp) of silver chloride (AgCl) in water at 25 °C is 1.8 × 10^-10. What is the molar solubility (s) of AgCl in a 0.010 M aqueous solution of sodium chloride (NaCl), accounting for the common ion effect?

• A1.34 × 10^-5 M
• B1.8 × 10^-8 M
• C1.8 × 10^-10 M
• D9.0 × 10^-9 M

In electrochemistry and pharmaceutical redox systems, how does the standard reduction potential (E°) relate to the spontaneity of an oxidation-reduction reaction under standard conditions?

• AA reaction is spontaneous when the overall cell potential E°cell is positive, correspondi…
• BA reaction is spontaneous when the overall cell potential E°cell is negative, correspondi…
• CSpontaneity requires both half-cells to have negative standard reduction potentials E° < 0
• DStandard reduction potential indicates reaction velocity but provides no thermodynamic in…

A 0.90% (w/v) sodium chloride solution (normal saline, Mw = 58.44 g/mol) is isotonic with blood plasma. Given the cryoscopic constant of water Kf = 1.86 °C·kg/mol and a van 't Hoff factor i = 1.86 for NaCl at this concentration, what is the expected freezing point of this solution?

• A-0.53 °C
• B-0.28 °C
• C-1.06 °C
• D0.00 °C

Which of the following characteristics is uniquely associated with a bimolecular nucleophilic substitution (SN2) reaction mechanism?

• AFormation of a carbocation intermediate with complete loss of optical stereospecificity
• BA concerted single-step mechanism with Walden inversion of stereochemical configuration a…
• CA two-step pathway favored by bulky tertiary alkyl halides and polar protic solvents
• DA rate law that is strictly first-order with respect to the substrate and independent of…

In electrophilic aromatic substitution (EAS), which of the following substituents acts as a strongly deactivating, meta-directing group on a benzene ring?

• AHydroxyl group (-OH)
• BAmino group (-NH2)
• CNitro group (-NO2)
• DMethyl group (-CH3)

Why are ester prodrugs (such as oseltamivir or enalapril) typically hydrolyzed significantly faster in systemic circulation than corresponding amide prodrugs?

• AEsters have much greater resonance stabilization of the carbonyl group than amides
• BAmides have substantial C-N double bond character from resonance donation, making the car…
• CCarboxylesterases in plasma and liver cannot bind amide bonds under any circumstances
• DEsters are non-polar covalent bonds whereas amides are completely ionic at physiological…

Which of the following molecules has the lowest pKa (i.e., is the strongest Brønsted acid) among the listed organic compounds?

• AEthanol (CH3CH2OH)
• BPhenol (C6H5OH)
• C4-Nitrophenol (4-NO2-C6H4OH)
• D4-Methoxyphenol (4-CH3O-C6H4OH)

What functional group is formed by the nucleophilic addition of a primary amine (R-NH2) to an aldehyde or ketone in the presence of a trace acid catalyst?

• AAn imine (Schiff base)
• BAn enamine
• CAn acetal
• DAn amide

Which reagent selectively oxidizes a secondary alcohol to a ketone without causing over-oxidation or carbon-carbon bond cleavage?

• ASodium borohydride (NaBH4)
• BPyridinium chlorochromate (PCC) in anhydrous dichloromethane
• CLithium aluminium hydride (LiAlH4)
• DConcentrated sulfuric acid at 180 °C

What is the correct ranking of carboxylic acid derivatives in order of decreasing reactivity toward nucleophilic acyl substitution (from most reactive to least reactive)?

• AAcyl chloride > Acid anhydride > Ester > Amide
• BAmide > Ester > Acid anhydride > Acyl chloride
• CAcyl chloride > Amide > Ester > Acid anhydride
• DEster > Acyl chloride > Acid anhydride > Amide

How many stereocenters (asymmetric chiral carbons) are present in an aldohexose molecule in its linear Fischer projection (e.g., D-glucose)?

• A2
• B3
• C4
• D5

Using the Cahn-Ingold-Prelog (CIP) priority rules, what is the priority order of the following substituents attached to a chiral carbon: -OH, -CH2OH, -COOH, -CH3?

• A-OH > -COOH > -CH2OH > -CH3
• B-COOH > -OH > -CH2OH > -CH3
• C-OH > -CH2OH > -COOH > -CH3
• D-CH3 > -CH2OH > -COOH > -OH

Which of the following statements correctly differentiates enantiomers from diastereomers?

• AEnantiomers have identical melting points, boiling points, and solubility in achiral medi…
• BEnantiomers rotate plane-polarized light in the same direction, whereas diastereomers rot…
• CDiastereomers are non-superimposable mirror images of each other, whereas enantiomers are…
• DEnantiomers can always be easily separated by simple fractional distillation in the absen…

A solution of an active pharmaceutical ingredient is prepared at a concentration of 4.0 g per 100 mL (0.040 g/mL). When placed in a 20.0 cm polarimeter tube at 20 °C with sodium D-line light, it produces an observed optical rotation of +4.80°. What is the specific optical rotation [alpha]D^20 of the substance?

• A+60.0°·mL/(dm·g)
• B+24.0°·mL/(dm·g)
• C+12.0°·mL/(dm·g)
• D+120.0°·mL/(dm·g)

In the Michaelis-Menten kinetic model of enzyme action, what does the Michaelis constant (Km) represent physically?

• AThe maximum rate of reaction achieved when all enzyme active sites are fully saturated
• BThe substrate concentration at which the initial reaction velocity is exactly half of Vmax
• CThe turnover number (kcat) representing catalytic cycles per active site per second
• DThe equilibrium association constant for enzyme-inhibitor complex formation

An enzyme catalyzing the phosphorylation of a drug displays Michaelis-Menten kinetics with Vmax = 120 μmol/(min·mg) and Km = 3.0 mM. What is the initial reaction velocity (v0) when the substrate concentration [S] is 6.0 mM?

• A40 μmol/(min·mg)
• B60 μmol/(min·mg)
• C80 μmol/(min·mg)
• D90 μmol/(min·mg)

In a Lineweaver-Burk double reciprocal plot (1/v versus 1/[S]), how does the presence of a classical competitive enzyme inhibitor alter the graph?

• AThe slope increases and the x-intercept shifts closer to zero, while the y-intercept rema…
• BThe y-intercept increases while the slope and x-intercept remain completely unchanged
• CBoth the x-intercept and y-intercept shift upward by an identical factor, producing a par…
• DThe slope decreases while the y-intercept shifts downward toward the origin

How does an uncompetitive enzyme inhibitor interact with an enzyme, and how does it affect the kinetic parameters Km and Vmax?

• AIt binds only to the free enzyme (E); it increases Km and has no effect on Vmax
• BIt binds equally to free enzyme (E) and enzyme-substrate complex (ES); it decreases Vmax…
• CIt binds exclusively to the enzyme-substrate complex (ES); it decreases both apparent Km…
• DIt covalently destroys the catalytic residues; it reduces Vmax to zero irreversibly witho…

For a metabolic isomerization reaction A ⇄ B, the standard biochemical free energy change ΔG°' is +7.50 kJ/mol at 298 K (R = 8.314 J/(mol·K)). At what product-to-substrate concentration ratio [B]/[A] will the reaction become thermodynamically spontaneous in the forward direction (ΔG < 0)?

• A[B]/[A] < 0.048
• B[B]/[A] > 1.00
• C[B]/[A] > 20.7
• D[B]/[A] = 1.00

What is the standard free energy of hydrolysis of ATP to ADP and inorganic phosphate (Pi) under standard biochemical conditions (pH 7.0, 25 °C, 1 mM Mg2+), and why is this reaction so exergonic?

• AΔG°' ≈ -30.5 kJ/mol (-7.3 kcal/mol); due to relief of electrostatic repulsion among negat…
• BΔG°' ≈ -14.2 kJ/mol (-3.4 kcal/mol); due to the breaking of the strong covalent carbon-ca…
• CΔG°' ≈ +30.5 kJ/mol (+7.3 kcal/mol); due to the formation of high-energy phosphoanhydride…
• DΔG°' ≈ -61.0 kJ/mol (-14.6 kcal/mol); due exclusively to the ionization of adenine at phy…

According to the Singer-Nicolson fluid mosaic model, what is the primary structural characteristic of the mammalian plasma membrane that governs passive drug permeation?

• AA rigid, continuous monolayer of carbohydrates anchored by covalent bonds to cytoskeletal…
• BAn amphipathic phospholipid bilayer with hydrophobic fatty acyl tails oriented inward and…
• CA dense sheet of peptidoglycan cross-linked by transpeptidase enzymes
• DA completely impermeable lipid matrix devoid of protein channels or fluid movement

According to Fick's first law of passive diffusion (dM/dt = (D * A * K / h) * (C1 - C2)), how is the rate of drug transfer affected if the surface area (A) of the absorbing membrane is doubled while its thickness (h) is halved?

• AIt remains unchanged
• BIt increases by a factor of 2
• CIt increases by a factor of 4
• DIt decreases by a factor of 4

How does facilitated diffusion across a cellular membrane differ from simple passive diffusion?

• AFacilitated diffusion transports solutes against their electrochemical gradient using ATP…
• BFacilitated diffusion requires specific transmembrane carrier or channel proteins and exh…
• CFacilitated diffusion occurs exclusively for non-polar gases like oxygen and carbon dioxi…
• DFacilitated diffusion rate increases infinitely in direct linear proportion to extracellu…

What is the primary physiological and pharmacological function of P-glycoprotein (P-gp / ABCB1) located on the apical membrane of intestinal enterocytes and brain capillary endothelial cells?

• AFacilitating the intracellular influx and systemic absorption of hydrophobic peptide drugs
• BAn ATP-dependent active efflux pump that expels xenobiotics and lipophilic drugs out of c…
• CSynthesizing cholesterol and sphingomyelin to maintain blood-brain barrier tight junction…
• DHydrolyzing prodrugs into active pharmaceutical metabolites in the intestinal lumen

What is the stoichiometry and electrogenic nature of the sodium-potassium pump (Na+/K+-ATPase) per cycle of ATP hydrolysis in animal cells?

• APumps 3 Na+ ions out of the cell and 2 K+ ions into the cell, generating a net negative i…
• BPumps 2 Na+ ions out of the cell and 3 K+ ions into the cell, generating a net positive i…
• CPumps 3 Na+ ions into the cell and 3 K+ ions out of the cell, maintaining electrical neut…
• DPumps 1 Na+ ion and 1 Ca2+ ion out of the cell in exchange for 2 K+ ions

Which chemical feature fundamentally distinguishes ribonucleic acid (RNA) from deoxyribonucleic acid (DNA) at the pentose sugar level?

• ARNA contains a hydroxyl group (-OH) at the C-2' position of the ribose ring, whereas DNA…
• BRNA contains a deoxyribose sugar lacking an oxygen at C-3', whereas DNA has a full ribose…
• CRNA pentose is a six-membered pyranose ring, whereas DNA contains a five-membered furanos…
• DRNA contains beta-D-fructose instead of beta-D-ribose

Bacterial 70S ribosomes differ from eukaryotic 80S cytosolic ribosomes in subunit composition. Which ribosomal subunit is specifically targeted by aminoglycosides and tetracyclines to inhibit bacterial protein synthesis?

• AThe 30S small bacterial ribosomal subunit
• BThe 50S large bacterial ribosomal subunit
• CThe 40S small eukaryotic ribosomal subunit
• DThe 60S large eukaryotic ribosomal subunit

Which eukaryotic RNA polymerase is responsible for transcribing protein-coding genes into precursor messenger RNA (pre-mRNA)?

• ARNA Polymerase I
• BRNA Polymerase II
• CRNA Polymerase III
• DDNA Polymerase alpha

In a diagnostic quantitative Polymerase Chain Reaction (qPCR) assay, starting with an initial quantity of 200 double-stranded DNA template copies, what is the theoretical number of amplicon copies generated after 20 complete cycles, assuming 100% amplification efficiency (E = 1.0)?

• A4,000 copies
• B2.097 × 10^8 copies
• C1.048 × 10^6 copies
• D4.194 × 10^10 copies

Why are therapeutic monoclonal antibodies (such as rituximab or trastuzumab) produced in mammalian expression systems (e.g., CHO cells) rather than bacterial hosts like Escherichia coli?

• ABacteria cannot transcribe DNA sequences that contain thymine bases
• BBacteria lack the endomembrane machinery for essential human-like post-translational modi…
• CMammalian cells produce recombinant proteins without needing any culture medium or asepti…
• DAntibodies produced in E. coli are composed entirely of D-amino acids that are immediatel…

What is the physical distinction between osmolarity and osmolality in pharmaceutical solution physics?

• AOsmolarity is expressed in osmoles per liter of solution and is temperature-dependent; os…
• BOsmolarity applies only to non-electrolytes, whereas osmolality applies exclusively to di…
• COsmolality changes when the solution expands thermally, while osmolarity remains constant
• DOsmolarity measures hydrostatic pressure, whereas osmolality measures colloidal oncotic p…

What is the theoretical osmolarity of an aqueous 5.0% (w/v) anhydrous D-glucose (dextrose, molecular weight = 180 g/mol) infusion solution?

• A139 mOsm/L
• B278 mOsm/L
• C556 mOsm/L
• D308 mOsm/L

What physical phenomenon occurs when the concentration of an amphiphilic surfactant in an aqueous solution exceeds its Critical Micelle Concentration (CMC)?

• ASurfactant molecules precipitate out as an insoluble crystalline sediment
• BSurface tension continues to drop linearly toward zero indefinitely
• CSurfactant monomers spontaneously aggregate into thermodynamically stable colloidal struc…
• DThe solution immediately separates into two macroscopic immiscible phases without any agg…

According to the Beer-Lambert law (A = epsilon * b * c), if a 2.0 × 10^-5 M solution of a drug exhibits an absorbance (A) of 0.500 in a standard quartz cuvette with path length b = 1.0 cm at 260 nm, what is the molar absorptivity (molar extinction coefficient, epsilon) of the drug at this wavelength?

• A25,000 L·mol^-1·cm^-1
• B10,000 L·mol^-1·cm^-1
• C50,000 L·mol^-1·cm^-1
• D2,500 L·mol^-1·cm^-1

In biostatistics and clinical trial analysis, what is the exact definition of the p-value obtained from a statistical hypothesis test?

• AThe probability that the alternative hypothesis (H1) is entirely false
• BThe probability that the drug will successfully cure at least 95% of patients in the targ…
• CThe probability of obtaining a test statistic at least as extreme as the observed value,…
• DThe probability that a Type II error (beta) was committed during sample selection

In a phase III randomized clinical trial comparing a new antimalarial drug to standard therapy, what does committing a Type I error (alpha) mean?

• AFailing to reject the null hypothesis when the new drug is genuinely superior in reality
• BRejecting the null hypothesis and concluding that the new drug is superior when, in reali…
• CSelecting an inadequate sample size that reduces the statistical power below 80%
• DEnrolling non-compliant patients which leads to post-randomization attrition bias

A diagnostic screening test for a rare tropical disease has 90% sensitivity and 90% specificity. If the disease prevalence in the screened population is 1.0% (10 cases per 1,000 individuals), what is the Positive Predictive Value (PPV) of the test?

• A90.0%
• B50.0%
• C8.3%
• D1.0%

Which epidemiological measure of association is appropriate for a retrospective case-control study where disease incidence cannot be directly measured?

• ARelative Risk (Risk Ratio, RR)
• BOdds Ratio (OR)
• CAttributable Risk (Risk Difference, RD)
• DIncidence Rate Ratio (IRR)

When comparing the distributions of plasma concentrations between two independent patient groups with small samples (n = 12 each) and a strongly violated normality assumption, which rank-based test is appropriate?

• ATwo-sample Student's t-test
• BMann-Whitney U test (Wilcoxon rank-sum test)
• COne-way ANOVA with Tukey's post-hoc test
• DPearson correlation coefficient test

Which pharmacokinetic acronym describes the four sequential physiological processes that govern the time course of drug concentrations in the human body?

• AADME (Absorption, Distribution, Metabolism, Excretion)
• BDISH (Dissolution, Ionization, Solubilization, Hydrolysis)
• CBANC (Bioavailability, Affinity, Neutralization, Clearance)
• DPASS (Permeation, Association, Secretion, Saturation)

A clinical pharmacokinetic study yields an Area Under the Curve (AUC) of 60.0 mg·h/L following a 200 mg oral dose of an antibiotic. In the same volunteer, an intravenous bolus of 100 mg yields an AUC of 50.0 mg·h/L. What is the absolute oral bioavailability (F) of this antibiotic formulation?

• A60%
• B30%
• C83%
• D120%

A patient receives a single 500 mg intravenous bolus of a hydrophilic antimicrobial agent. Immediate extrapolation of the plasma concentration-time curve back to time zero yields C0 = 25.0 mg/L. What is the apparent volume of distribution (Vd) of this drug?

• A20.0 L
• B12.5 L
• C50.0 L
• D5.0 L

Which fraction of a drug in the systemic circulation is pharmacologically active and capable of crossing endothelial barriers to reach tissue receptors and undergo glomerular filtration?

• AThe unbound (free) drug fraction (fu)
• BThe fraction bound to human serum albumin
• CThe fraction bound to alpha-1-acid glycoprotein
• DThe fraction conjugated with glucuronic acid