Medicinal Chemistry MCQs for Pharmacist License & Loksewa Exam

Are you preparing for the Pharmacist License Exam or the Loksewa Pharmacy Exam in Nepal? One of the most crucial and high-yield subjects you need to master is Medicinal Chemistry. Understanding drug structures, SAR (Structure-Activity Relationships), metabolism, and mechanisms of action is essential to score well and build a strong pharmaceutical foundation.

In this blog, we present carefully crafted Medicinal Chemistry Multiple Choice Questions (MCQs) tailored to match the syllabus and exam pattern. These questions are designed to challenge your concepts and help you prepare effectively.

1. Which of the following statements about lipophilicity is TRUE?

A. Lipophilicity decreases drug permeability across cell membranes
B. High lipophilicity always ensures high oral bioavailability
C. Lipophilicity enhances blood-brain barrier penetration
D. Lipophilic drugs are eliminated faster by the kidneys

Explanation: Lipophilic drugs cross lipid-rich barriers like the BBB more easily than hydrophilic drugs.

2. The partition coefficient (log P) is an important parameter in drug design because it:

A. Measures the drug’s ability to bind to plasma proteins
B. Indicates the drug’s lipophilicity and ability to cross biological membranes
C. Reflects the drug’s aqueous solubility
D. Predicts the drug’s metabolism by cytochrome P450 enzymes

Explanation: Log P is the ratio of concentrations of a compound in octanol and water, showing lipophilicity.

3. What is the effect of masking the phenolic 3-OH group of morphine with a methyl group (forming codeine)?

A. Increases potency
B. Increases lipophilicity and reduces receptor binding
C. Enhances binding to µ-opioid receptors
D. Converts it into an antagonist

Explanation: The 3-OH is crucial for receptor binding; masking it with -OCH₃ reduces binding but improves lipophilicity.

4. Which N-substitution in morphine derivatives converts an agonist into an antagonist?

A. N-Methyl
B. N-Allyl (as in Naloxone)
C. N-Phenylethyl
D. N-Hydroxyethyl

Explanation: N-allyl substitution leads to antagonistic activity, used in opioid overdose reversal.

5. What is the essential feature for antibacterial activity in penicillins?

A. Thiazolidine ring
B. Free carboxylic acid
C. Intact β-lactam ring
D. Phenyl ring in side chain

Explanation: The β-lactam ring is critical for inhibiting bacterial transpeptidase enzymes.

6. Adding bulky groups to the side chain of penicillin increases:

A. Acid stability
B. Water solubility
C. Resistance to β-lactamase
D. CNS penetration

Explanation: Bulky side chains prevent enzymatic degradation by hindering β-lactamase access.

7. Which substitution on the benzodiazepine ring enhances activity?

A. Hydrogen at position-7
B. Electron-withdrawing group at position-7 (e.g., Cl or NO₂)
C. Electron-donating group at position-7
D. Substitution at position-3 only

Explanation: EWG at position-7 enhances binding to GABA-A receptor, increasing activity.

8. Which structural feature is essential for the activity of classical benzodiazepines?

A. 6-membered non-aromatic A ring
B. Free amine at position-1
C. 1,4-Benzodiazepine fused ring system
D. Pyridine ring substitution

Explanation: The 1,4-benzodiazepine ring is the pharmacophore for BZD action.

9. Why is lipophilicity important in the design of CNS-active drugs?

A. It increases renal excretion
B. It promotes penetration through the blood-brain barrier
C. It decreases distribution volume
D. It enhances plasma protein binding only

Explanation: High lipophilicity helps CNS drugs cross the BBB efficiently.

10. A drug with very high partition coefficient (log P > 5) may show:

A. Enhanced solubility in GI fluids
B. Improved active transport
C. Poor aqueous solubility and limited oral absorption
D. Increased renal excretion

Explanation: Extremely high lipophilicity can reduce solubility in aqueous environments like the GI tract, limiting absorption.

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