NEET-PG 2019 — Pharmacology
40 Previous Year Questions with Answers & Explanations
Which of the following statements is true regarding a fixed-dose combination of drugs?
Carbapenem with the maximum seizure risk is:
Which of the following best demonstrates the variability in drug responsiveness among individuals?
What is the drug of choice (DOC) for a scorpion sting bite?
Which fluoroquinolone has the maximum bioavailability?
Which of the following drugs is used in SIADH?
Variation in sensitivity of response to different doses of a drug in different individuals is obtained from?
Carbapenem which has a tendency to cause maximum seizures?
Which among the following is most probable reason for preference of Cisatracurium over atracurium?
Imipenem, a newer antibiotic with a broad antibacterial spectrum, is co-administered with cilastatin. What is the primary reason for this combination?
NEET-PG 2019 - Pharmacology NEET-PG Practice Questions and MCQs
Question 1: Which of the following statements is true regarding a fixed-dose combination of drugs?
- A. The adverse effect of one drug may be mitigated by the other drug. (Correct Answer)
- B. The dose of one drug can be adjusted independently.
- C. Adverse effects can be attributed solely to one drug.
- D. Combining two drugs with different pharmacokinetics is straightforward.
Explanation: ***The adverse effect of one drug may be mitigated by the other drug.*** - Fixed-dose combinations are often designed such that the **therapeutic effect of one drug is enhanced**, or its **adverse effects are counteracted** by the other drug(s) in the combination. For example, a drug that causes gastrointestinal upset might be combined with one that reduces such side effects. - This synergistic or mitigating effect is a key rationale for developing certain fixed-dose combinations, aiming to improve **tolerability** and **patient adherence**. *The dose of one drug can be adjusted independently.* - In a **fixed-dose combination**, the doses of all drugs are predetermined and cannot be individually altered by the prescriber or patient. - This inflexibility is a major limitation, necessitating a separate prescription if **dose titration** for a single component is required. *Adverse effects can be attributed solely to one drug.* - When adverse effects occur with a fixed-dose combination, it is often challenging to definitively attribute them to a **single component**, as the pharmacodynamic and pharmacokinetic interactions between the drugs can be complex. - This makes managing side effects difficult, as stopping or reducing one drug is not possible without affecting the others. *Combining two drugs with different pharmacokinetics is straightforward.* - Combining drugs with **dissimilar pharmacokinetic profiles** (e.g., different absorption rates, half-lives, or metabolic pathways) can complicate fixed-dose formulations. - Achieving **optimal therapeutic windows** for both drugs concurrently can be challenging, potentially leading to suboptimal drug levels for one or both at various times.
Question 2: Carbapenem with the maximum seizure risk is:
- A. Imipenem (Correct Answer)
- B. Meropenem
- C. Doripenem
- D. Ertapenem
Explanation: ***Imipenem*** - **Imipenem** is primarily associated with a higher risk of seizures due to its ability to inhibit **GABAergic neurotransmission** in the central nervous system. - This effect is dose-dependent and more pronounced in patients with **renal impairment** or pre-existing CNS disorders, where drug accumulation occurs. *Meropenem* - While meropenem can also cause seizures, its **GABA antagonistic effect** is less potent than imipenem, resulting in a lower incidence of this adverse event. - It is generally considered safer than imipenem for patients at risk of seizures. *Ertapenem* - Ertapenem has an even lower propensity for causing seizures compared to imipenem and meropenem. - It is often preferred in outpatient settings due to its **once-daily dosing** and favorable safety profile regarding CNS adverse effects. *Doripenem* - Doripenem also has a **low seizure potential**, similar to meropenem and ertapenem. - Its **pharmacokinetic profile** and CNS penetration differ, but it is not associated with the same high risk as imipenem.
Question 3: Which of the following best demonstrates the variability in drug responsiveness among individuals?
- A. Potency
- B. Quantal Dose Response Curve (Correct Answer)
- C. Efficacy
- D. Graded Dose Response Curve
Explanation: ***Quantal Dose Response Curve*** - A **quantal dose-response curve** plots the percentage of individuals exhibiting a discrete, all-or-none effect against the log dose of a drug. - This curve directly illustrates the **variability in drug responsiveness** within a population by showing the range of doses required to produce a specific effect in different individuals. *Efficacy* - **Efficacy** refers to the maximum effect a drug can produce, regardless of the dose. - While efficacy is an important pharmacological parameter, it describes the drug's overall therapeutic potential, not the **individual variability** in response. *Potency* - **Potency** is a measure of the amount of drug needed to produce an effect of given intensity. - It relates to the absolute dose required for a particular effect but does not directly demonstrate the **inter-individual differences** in biological response. *Graded Dose Response Curve* - A **graded dose-response curve** depicts the relationship between the dose of a drug and the **magnitude of the effect** in a **single biological unit** (e.g., an individual, a tissue, or a cell). - This curve reflects the relationship between drug concentration and effect intensity, but not the **variability in response among different individuals** in a population.
Question 4: What is the drug of choice (DOC) for a scorpion sting bite?
- A. EDTA
- B. Neostigmine
- C. N-acetylcysteine
- D. Prazosin (Correct Answer)
Explanation: ***Prazosin*** - **Prazosin** is an **alpha-1 adrenergic antagonist** that effectively counteracts the symptoms of scorpion envenomation, particularly **autonomic hyperactivity** like hypertension and tachycardia. - It works by blocking the effects of norepinephrine released by the scorpion venom, helping to stabilize vital signs and reduce cardiovascular complications. *EDTA* - **EDTA (ethylenediaminetetraacetic acid)** is a **chelating agent** primarily used to treat **heavy metal poisoning**, such as lead or mercury. - It binds to metal ions, forming a stable complex that can then be excreted from the body; it has no role in scorpion envenomation. *Neostigmine* - **Neostigmine** is an **acetylcholinesterase inhibitor** used to treat conditions like myasthenia gravis or to reverse the effects of neuromuscular blocking agents. - It increases acetylcholine levels at the neuromuscular junction; it is not indicated for the management of scorpion stings. *N-acetylcysteine* - **N-acetylcysteine (NAC)** is primarily used as an **antidote for acetaminophen overdose** and as a mucolytic agent in respiratory conditions. - It replenishes glutathione stores, helping to detoxify harmful metabolites; it has no direct role in treating scorpion venom effects.
Question 5: Which fluoroquinolone has the maximum bioavailability?
- A. Gatifloxacin
- B. Ciprofloxacin
- C. Moxifloxacin
- D. Levofloxacin (Correct Answer)
Explanation: ***Levofloxacin*** - **Levofloxacin** exhibits high oral bioavailability, approximately 99%, meaning nearly all of the administered dose reaches systemic circulation [1]. - This high bioavailability allows for seamless transition from intravenous to oral administration without significant changes in drug exposure [1]. *Moxifloxacin* - **Moxifloxacin** has a high bioavailability of approximately 90%, which is slightly lower than levofloxacin's almost complete absorption [1]. - While excellent, it is not the absolute highest among fluoroquinolones. *Gatifloxacin* - **Gatifloxacin** has good oral bioavailability, around 96%, but it is still generally considered slightly less than that of levofloxacin [1]. - This difference, though small, makes levofloxacin the one with the highest overall bioavailability. *Ciprofloxacin* - **Ciprofloxacin** has the lowest oral bioavailability among the listed fluoroquinolones, ranging from 70% to 80% [1]. - Its absorption can be significantly impaired by co-administration with multivalent cations, leading to reduced systemic concentrations.
Question 6: Which of the following drugs is used in SIADH?
- A. Desmopressin
- B. Terlipressin
- C. Tolvaptan (Correct Answer)
- D. Von Willebrand factor
Explanation: ***Tolvaptan*** - **Tolvaptan** is a **vasopressin receptor antagonist** that blocks the action of **antidiuretic hormone (ADH)** at the **V2 receptors** in the kidneys [1]. - This action promotes **water excretion (aquaresis)** without significantly affecting electrolyte balance, thereby increasing serum sodium levels in patients with **SIADH** [1]. *Desmopressin* - **Desmopressin** is a synthetic analog of **ADH** that primarily acts on **V2 receptors**, promoting water reabsorption [3], [4]. - It is used in conditions like **diabetes insipidus** [3], [4] or **hemophilia** [2] to increase ADH activity or clotting factors, which is contrary to the goal in SIADH. *Von Willebrand factor* - **Von Willebrand factor** is a **glycoprotein** involved in **hemostasis**, promoting platelet adhesion and carrying **factor VIII**. - It plays no role in the direct management of **SIADH** or fluid balance disorders. *Terlipressin* - **Terlipressin** is an analog of **vasopressin** that primarily acts on **V1 receptors**, causing vasoconstriction [5]. - It is used in conditions like **hepatorenal syndrome** or **esophageal variceal bleeding**, not for treating **SIADH**.
Question 7: Variation in sensitivity of response to different doses of a drug in different individuals is obtained from?
- A. Dose-response relationship (Correct Answer)
- B. Therapeutic index
- C. Bioavailability
- D. Phase 1 clinical trials
Explanation: ***Dose-response relationship*** - The **dose-response relationship** (particularly the **graded dose-response curve**) describes how the magnitude of a drug's effect changes with different doses. - When plotted for different individuals or populations, these curves reveal **variation in sensitivity** through differences in potency (horizontal shift) and efficacy (maximum response). - This relationship helps characterize inter-individual variability in drug response and is the fundamental concept for understanding differential sensitivity. *Therapeutic index* - The **therapeutic index** is a measure of drug safety, representing the ratio between the toxic dose and the effective dose (TD50/ED50 or LD50/ED50). - It does not directly explain the variation in sensitivity to different doses among individuals, but rather provides information about the drug's overall safety margin. *Bioavailability* - **Bioavailability** refers to the fraction of an administered drug that reaches the systemic circulation unchanged. - While it influences the drug concentration at the site of action, it doesn't directly measure the variability in physiological response to that concentration among individuals. *Phase 1 clinical trials* - **Phase 1 clinical trials** are the first stage of testing a new drug in humans, primarily focusing on safety, dosage range, and pharmacokinetics in a small group of healthy volunteers. - While variability in response may be observed during these trials, they are not the *pharmacological concept* that describes this variation; rather, dose-response relationships are used to interpret findings from these trials.
Question 8: Carbapenem which has a tendency to cause maximum seizures?
- A. Imipenem (Correct Answer)
- B. Ertapenem
- C. Doripenem
- D. Meropenem
Explanation: ***Imipenem*** - **Imipenem** is associated with the highest risk of **seizures** among the carbapenems, particularly in patients with **renal impairment**, pre-existing **CNS disorders**, or high doses. - Its high affinity for **GABA-A receptors** in the central nervous system is thought to contribute to its proconvulsant effects. *Ertapenem* - While all carbapenems carry some risk of seizures, **ertapenem** has a **lower incidence** compared to imipenem. - It is often favored in patients without CNS infections or severe renal dysfunction due to its once-daily dosing. *Doripenem* - **Doripenem** also has a relatively **low risk of seizures** compared to imipenem. - It is generally well-tolerated, with side effects similar to other carbapenems but at a reduced frequency for CNS events. *Meropenem* - **Meropenem** is known to have a **lower seizure potential** than imipenem, making it a preferred choice for patients with a history of seizures or those with CNS infections. - Its **reduced affinity** for GABA-A receptors contributes to its better CNS tolerability.
Question 9: Which among the following is most probable reason for preference of Cisatracurium over atracurium?
- A. Decreased histamine release (Correct Answer)
- B. Increased histamine release
- C. Decreased CNS toxicity
- D. Due to elimination by non-specific plasma esterases
Explanation: ***Decreased histamine release*** - **Cisatracurium** is preferred over atracurium primarily due to its significantly **lower potential for histamine release**, which can cause undesirable side effects like **hypotension**, **tachycardia**, and **bronchospasm**. - This reduced histamine release contributes to a **more stable hemodynamic profile** and **fewer allergic-type reactions**, especially in critically ill or hemodynamically unstable patients. *Increased histamine release* - This is incorrect because **atracurium** is known to cause **more histamine release** compared to cisatracurium, which is why cisatracurium is often preferred. - Increased histamine release is an **undesirable effect** that can lead to adverse cardiovascular and respiratory reactions. *Decreased CNS toxicity* - While both drugs are **quaternary ammonium compounds** and do not readily cross the blood-brain barrier, **CNS toxicity** is not a primary concern or differentiating factor between atracurium and cisatracurium in clinical practice. - The potential for CNS effects from their metabolites (like **laudanosine**) is generally low with standard dosing, and **cisatracurium produces less laudanosine**. *Due to elimination by non-specific plasma esterases* - Both cisatracurium and atracurium are eliminated primarily by **Hofmann elimination** and **non-specific plasma esterases**. This is a shared characteristic, not a reason for cisatracurium's preference over atracurium. - **Hofmann elimination** is a non-enzymatic chemical degradation process that occurs at physiological pH and temperature, making their elimination **independent of renal or hepatic function**.
Question 10: Imipenem, a newer antibiotic with a broad antibacterial spectrum, is co-administered with cilastatin. What is the primary reason for this combination?
- A. Cilastatin enhances the gastrointestinal absorption of imipenem.
- B. Cilastatin inhibits the beta-lactamase enzyme that degrades imipenem.
- C. Cilastatin prevents the degradation of imipenem by inhibiting an enzyme in the kidneys. (Correct Answer)
- D. The combination of antibiotics is synergistic against Pseudomonas species.
Explanation: ***Cilastatin prevents the degradation of imipenem by inhibiting an enzyme in the kidneys.*** - **Imipenem** is susceptible to degradation by **dehydropeptidase-1 (DHP-1)**, an enzyme found in the renal tubules, leading to inactivation and the production of potentially nephrotoxic metabolites. - **Cilastatin** is a **DHP-1 inhibitor** that prevents the inactivation of imipenem in the kidneys, thereby increasing its urinary concentration and reducing the risk of renal toxicity. *Cilastatin enhances the gastrointestinal absorption of imipenem.* - **Imipenem** is administered parenterally (intravenously) because it has **poor oral bioavailability** and is extensively metabolized in the gastrointestinal tract. - Cilastatin’s primary role is not to enhance GI absorption, as the drug is not intended for oral administration. *Cilastatin inhibits the beta-lactamase enzyme that degrades imipenem.* - **Imipenem** itself is highly resistant to most bacterial **beta-lactamase enzymes** due to its unique carbapenem structure. - Cilastatin does not have significant beta-lactamase inhibitory activity; its main function is renal enzyme inhibition. *The combination of antibiotics is synergistic against Pseudomonas species.* - While both imipenem and cilastatin together are effective due to preservation of imipenem, the combination itself is not a synergistic pair of antibiotics in the traditional sense against *Pseudomonas*. - Synergy typically refers to two different antibiotics working together, whereas cilastatin is an enzyme inhibitor, not an antibiotic.