What would happen to the half-life and plasma concentration of a drug which follows first-order kinetics, if the dose is doubled?
A patient is on phenytoin for a seizure disorder. He was prescribed sucralfate 4 times a day for peptic ulcers. What should be the minimum duration of time between consumption of these drugs?
What is the mechanism of action of cyclosporine?
Which of the following is the most effective drug in smoking cessation?
Which of the following is a centrally acting non-opioid antitussive?
INI-CET 2021 - Pharmacology INI-CET Practice Questions and MCQs
Question 11: What would happen to the half-life and plasma concentration of a drug which follows first-order kinetics, if the dose is doubled?
- A. Half - life and plasma concentration remains the same
- B. Half - life doubles and plasma concentration remains the same
- C. Half - life remains the same and plasma concentration doubles (Correct Answer)
- D. Half - life and plasma concentration doubles
Explanation: ***Half - life remains the same and plasma concentration doubles*** - In **first-order kinetics**, drug elimination is proportional to the **plasma concentration**, meaning a constant *fraction* of the drug is eliminated per unit of time. - Doubling the dose will **double the initial plasma concentration**, but the **half-life** (time taken for plasma concentration to halve) remains constant because the *rate of elimination proportionally increases* with concentration. *Half - life and plasma concentration remains the same* - This would only be true if the dose was not changed, or if the drug followed **zero-order kinetics** and the elimination system was already saturated, which is not the case here. - If the plasma concentration remained the same after doubling the dose, it would imply either no absorption or extremely rapid elimination, contradicting typical first-order drug behavior. *Half - life doubles and plasma concentration remains the same* - For **half-life to double**, there would need to be a **decrease in drug clearance** or an *increase in volume of distribution*, not simply a dose increase. - If plasma concentration remained the same despite a doubled dose, it would suggest a **major increase in clearance** or volume of distribution, which is not stated. *Half life and plasma concentration doubles* - While plasma concentration doubles with a doubled dose in **first-order kinetics**, the **half-life remains constant**. - Half-life is an **intrinsic pharmacokinetic parameter** determined by clearance and volume of distribution, not by the administered dose in first-order kinetics.
Question 12: A patient is on phenytoin for a seizure disorder. He was prescribed sucralfate 4 times a day for peptic ulcers. What should be the minimum duration of time between consumption of these drugs?
- A. 90 minutes
- B. 60 minutes
- C. 120 minutes (Correct Answer)
- D. 30 minutes
Explanation: **_120 minutes_** - **Sucralfate** forms a protective barrier in the stomach and can **adsorb other medications**, significantly reducing their absorption. - A minimum separation of **2 hours (120 minutes)** is recommended between sucralfate and other oral medications to prevent drug interactions. *90 minutes* - While a longer interval is beneficial, **90 minutes** may not be sufficient to completely avoid the significant reduction in **phenytoin absorption** caused by sucralfate. - Given the narrow therapeutic index of phenytoin, a more conservative approach with a longer separation is preferred. *60 minutes* - A **60-minute interval** is generally considered too short to prevent the **adsorption of phenytoin** by sucralfate. - This short duration increases the risk of **subtherapeutic phenytoin levels** and potential seizure recurrence. *30 minutes* - A **30-minute interval** is entirely inadequate and would almost certainly lead to a significant **reduction in phenytoin absorption**. - This would place the patient at high risk of **seizure recurrence** due to insufficient drug levels.
Question 13: What is the mechanism of action of cyclosporine?
- A. Inhibition of calcineurin (Correct Answer)
- B. Dihydro-orotate dehydrogenase inhibition
- C. AMP kinase stimulation
- D. IMP dehydrogenase inhibition
Explanation: ***Inhibition of calcineurin*** - Cyclosporine forms a complex with **cyclophilin**, which then inhibits the phosphatase activity of **calcineurin**. - This inhibition prevents the dephosphorylation and subsequent nuclear translocation of **NFAT (nuclear factor of activated T-cells)**, thereby blocking the transcription of **IL-2** and other cytokines essential for T-cell activation. *Dihydro-orotate dehydrogenase inhibition* - This is the mechanism of action of **leflunomide**, another immunosuppressant, which works by inhibiting *de novo* pyrimidine synthesis. - Leflunomide primarily affects rapidly proliferating cells, such as T-lymphocytes, by depriving them of essential pyrimidine nucleotides. *AMP kinase stimulation* - **AMP-activated protein kinase (AMPK)** is a cellular energy sensor that plays a role in metabolism and cellular growth. - While AMPK activation has various cellular effects, it is not the primary mechanism of action for cyclosporine or other calcineurin inhibitors. *IMP dehydrogenase inhibition* - This is the mechanism of action of **mycophenolate mofetil**, an immunosuppressant that selectively inhibits *de novo* guanosine nucleotide synthesis. - By depleting guanosine nucleotides, mycophenolate specifically inhibits the proliferation of T and B lymphocytes.
Question 14: Which of the following is the most effective drug in smoking cessation?
- A. Nicotine gum
- B. Buspirone
- C. Varenicline (Correct Answer)
- D. Rimonabant
Explanation: ***Varenicline*** - **Varenicline** is a **partial agonist** of the **nicotinic acetylcholine receptor (nAChR)**, reducing cravings and withdrawal symptoms while blocking the pleasurable effects of nicotine. - It has been shown to be more effective than other pharmacological interventions, including bupropion and nicotine replacement therapies, in achieving **long-term abstinence**. *Nicotine gum* - **Nicotine gum** is a form of **Nicotine Replacement Therapy (NRT)** that provides nicotine to reduce withdrawal symptoms. - While effective, NRTs (including gum) are generally less effective than varenicline in achieving sustained smoking cessation. *Buspirone* - **Buspirone** is an anxiolytic drug primarily used to treat generalized anxiety disorder. - It does not have a primary indication or significant evidence of effectiveness for smoking cessation. *Rimonabant* - **Rimonabant** is a **cannabinoid receptor 1 (CB1) antagonist** that was once explored for smoking cessation and weight loss. - It was withdrawn from the market due to significant psychiatric side effects, including depression and suicidal ideation, and is not used for smoking cessation.
Question 15: Which of the following is a centrally acting non-opioid antitussive?
- A. Ambroxol
- B. Guaifenesin
- C. Diphenhydramine
- D. Dextromethorphan (Correct Answer)
Explanation: ***Dextromethorphan*** - **Dextromethorphan** is a **centrally acting non-opioid antitussive** that suppresses the cough reflex by acting on the cough center in the medulla oblongata [1], [2]. - It is an **NMDA receptor antagonist** and a **sigma-1 receptor agonist**, which are the primary mechanisms responsible for its antitussive effects [2]. - Unlike opioid antitussives (codeine, hydrocodone), it does **not bind significantly to opioid receptors** at therapeutic doses and therefore lacks addiction potential, respiratory depression, and other opioid side effects [1], [3]. - It is a synthetic morphine analog (dextro-isomer) but is pharmacologically distinct from opioids [1]. *Ambroxol* - **Ambroxol** is a **mucolytic agent** that helps to thin and clear mucus from the respiratory tract. - It works by stimulating serous gland secretion and breaking down mucopolysaccharide fibers, which is different from suppressing the cough reflex centrally. *Guaifenesin* - **Guaifenesin** is an **expectorant** that increases the volume and reduces the viscosity of respiratory tract secretions. - This action helps to make coughs more productive, rather than directly suppressing the cough reflex. *Diphenhydramine* - **Diphenhydramine** is a first-generation **antihistamine** with significant sedative and anticholinergic properties. - While it has some antitussive effects, these are primarily due to its anticholinergic actions causing drying of respiratory secretions and its sedative properties, rather than direct central action on the cough center.