Diphenoxylate hydrochloride MCQs With Answer

Diphenoxylate hydrochloride MCQs With Answer is an essential revision resource for B. Pharm students preparing for pharmacology and clinical pharmacy exams. This concise introduction covers diphenoxylate hydrochloride’s mechanism as an opioid antidiarrheal, common formulations (usually combined with atropine), pharmacodynamic effects, typical adverse reactions, contraindications and key drug interactions. Emphasis is placed on clinical use, abuse potential, and safe prescribing considerations including dose adjustments and overdose management. These focused MCQs will deepen understanding of pharmacology, ADME, safety monitoring and therapeutic choices relevant to antidiarrheal therapy. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which receptor is primarily responsible for the antidiarrheal action of diphenoxylate hydrochloride?

• Alpha-1 adrenergic receptor
• Mu-opioid receptor
• GABA-A receptor
• Histamine H1 receptor

Correct Answer: Mu-opioid receptor

Q2. Why is atropine commonly combined with diphenoxylate in formulations like Lomotil?

• To enhance antidiarrheal potency by synergistic intestinal effects
• To prevent opioid-induced constipation
• To deter abuse by producing unpleasant anticholinergic effects at high doses
• To increase absorption of diphenoxylate from the gut

Correct Answer: To deter abuse by producing unpleasant anticholinergic effects at high doses

Q3. What is the primary clinical indication for diphenoxylate hydrochloride?

• Chronic constipation management
• Treatment of inflammatory bowel disease flares
• Symptomatic control of acute non-infectious diarrhea
• Opioid dependence maintenance therapy

Correct Answer: Symptomatic control of acute non-infectious diarrhea

Q4. Which of the following is a major contraindication for diphenoxylate therapy?

• Diarrhea caused by Clostridioides difficile or other invasive organisms
• Diarrhea due to dietary intolerance
• Traveler’s diarrhea of viral origin
• Mild functional diarrhea without systemic signs

Correct Answer: Diarrhea caused by Clostridioides difficile or other invasive organisms

Q5. What common adverse effect should students expect with therapeutic doses of diphenoxylate?

• Hypoglycemia
• Constipation
• Hepatotoxicity as the primary effect
• Hyperreflexia

Correct Answer: Constipation

Q6. How does diphenoxylate reduce intestinal motility?

• By blocking chloride channels in enterocytes
• By stimulating enteric serotonin receptors
• By activating opioid receptors on enteric neurons to decrease peristalsis
• By increasing local prostaglandin synthesis

Correct Answer: By activating opioid receptors on enteric neurons to decrease peristalsis

Q7. Which statement correctly contrasts diphenoxylate with loperamide?

• Diphenoxylate has greater peripheral selectivity than loperamide
• Loperamide readily crosses the blood–brain barrier causing central effects; diphenoxylate does not
• Diphenoxylate can produce central opioid effects at high doses, whereas loperamide has minimal CNS penetration
• Both drugs have identical abuse potential and CNS penetration

Correct Answer: Diphenoxylate can produce central opioid effects at high doses, whereas loperamide has minimal CNS penetration

Q8. Which pharmacokinetic property is most relevant to diphenoxylate’s systemic effects?

• Wide renal excretion of unchanged drug
• Extensive hepatic metabolism leading to active metabolites
• Exclusive biliary excretion without metabolism
• Complete oral bioavailability without first-pass effect

Correct Answer: Extensive hepatic metabolism leading to active metabolites

Q9. In overdose of diphenoxylate, which antidote is appropriate to reverse respiratory depression?

• Flumazenil
• Naloxone
• Atropine
• Activated charcoal only

Correct Answer: Naloxone

Q10. Which monitoring parameter is most important when a patient is on diphenoxylate?

• Blood glucose levels daily
• Frequency and consistency of bowel movements
• ECG monitoring for QT prolongation daily
• Serum potassium every 6 hours

Correct Answer: Frequency and consistency of bowel movements

Q11. Which patient population requires extra caution or avoidance of diphenoxylate?

• Healthy adults with short-term functional diarrhea
• Patients with severe hepatic impairment
• Adults with controlled hypertension only
• Individuals on topical antibiotics

Correct Answer: Patients with severe hepatic impairment

Q12. Which drug interaction is clinically significant with diphenoxylate?

• Concurrent use of anticholinergics increasing anticholinergic side effects
• Concurrent use with beta-blockers enhancing antihypertensive effect
• Combination with metformin increasing hypoglycemia risk
• Concurrent inhaled corticosteroids causing systemic steroid toxicity

Correct Answer: Concurrent use of anticholinergics increasing anticholinergic side effects

Q13. The purpose of adding a subtherapeutic amount of atropine to diphenoxylate formulations is primarily:

• To potentiate analgesic effects
• To reduce peripheral opioid activity
• To discourage deliberate overdose and abuse
• To treat concurrent allergic reactions

Correct Answer: To discourage deliberate overdose and abuse

Q14. Which of these signs would most suggest central opioid toxicity from diphenoxylate misuse?

• Increased bowel sounds and diarrhea
• Respiratory depression and miosis
• Hypertension and diaphoresis
• Ataxia with hyperreflexia

Correct Answer: Respiratory depression and miosis

Q15. Which formulation is most commonly used clinically for diphenoxylate administration?

• Intravenous diphenoxylate solution
• Oral tablet or combination with atropine
• Topical ointment
• Rectal suppositories only

Correct Answer: Oral tablet or combination with atropine

Q16. For a B. Pharm student, which concept best explains why diphenoxylate can cause constipation?

• It stimulates chloride secretion into the intestinal lumen
• It inhibits enteric neuronal activity, decreasing peristalsis and transit time
• It increases intestinal fluid secretion
• It breaks down mucosal glycoproteins increasing stool water

Correct Answer: It inhibits enteric neuronal activity, decreasing peristalsis and transit time

Q17. Which clinical scenario is an appropriate indication to avoid diphenoxylate?

• Traveler’s diarrhea without blood or fever
• Diarrhea with high fever and bloody stools suggesting invasive bacterial infection
• Non-specific chronic diarrhea due to IBS after other measures
• Acute watery diarrhea due to dietary indiscretion

Correct Answer: Diarrhea with high fever and bloody stools suggesting invasive bacterial infection

Q18. Which adverse effect may result from the atropine component rather than diphenoxylate itself?

• Bronchospasm
• Excessive salivation
• Dry mouth and blurred vision
• Increased bowel sounds

Correct Answer: Dry mouth and blurred vision

Q19. Which laboratory test should be considered if diphenoxylate toxicity with respiratory depression is suspected?

• Serum acetaminophen level
• Arterial blood gas (ABG) to assess respiratory status
• Fasting lipid profile
• Urine pregnancy test only

Correct Answer: Arterial blood gas (ABG) to assess respiratory status

Q20. What is the primary mechanism by which diphenoxylate reduces fluid secretion in the gut?

• Blocking enteric nicotinic receptors to increase secretion
• Decreasing intestinal motility thereby increasing absorption time
• Stimulating chloride channels to excrete water
• Increasing gastrointestinal endocrine secretions

Correct Answer: Decreasing intestinal motility thereby increasing absorption time

Q21. Which pharmacological classification best fits diphenoxylate?

• Antimuscarinic agent
• Opioid derivative (antidiarrheal opioid)
• 5-HT3 antagonist
• Laxative

Correct Answer: Opioid derivative (antidiarrheal opioid)

Q22. When counseling a patient on diphenoxylate therapy, which advice is most appropriate?

• Use continuously until bowel movements stop permanently
• Avoid driving if you experience dizziness or drowsiness
• Take with large meals to improve absorption
• Increase fluid intake to prevent constipation without monitoring

Correct Answer: Avoid driving if you experience dizziness or drowsiness

Q23. Which of the following best explains why diphenoxylate may be less suitable for infectious diarrhea?

• It enhances immune response against pathogens
• It increases intestinal motility, spreading infection
• It slows transit and may prolong retention of pathogens and toxins
• It neutralizes stool toxins causing rapid healing

Correct Answer: It slows transit and may prolong retention of pathogens and toxins

Q24. In terms of abuse potential, which statement is correct about diphenoxylate?

• It has no abuse potential because it lacks opioid activity
• It can be abused for opioid effects at high doses and is combined with atropine to reduce this risk
• It is only abused when given intravenously as it is inactive orally
• At therapeutic doses it causes euphoria in most patients

Correct Answer: It can be abused for opioid effects at high doses and is combined with atropine to reduce this risk

Q25. Which adverse effect is particularly concerning in elderly patients taking diphenoxylate–atropine?

• Improved cognition
• Urinary retention and confusion due to anticholinergic effects
• Increased appetite
• Enhanced renal clearance

Correct Answer: Urinary retention and confusion due to anticholinergic effects

Q26. Which statement about diphenoxylate metabolism is most accurate?

• It is primarily excreted unchanged via the lungs
• It undergoes hepatic metabolism with metabolites contributing to activity
• It is entirely metabolized by intestinal flora only
• It is not metabolized and is excreted unchanged in bile

Correct Answer: It undergoes hepatic metabolism with metabolites contributing to activity

Q27. Which of the following is a serious gastrointestinal complication associated with opioid antidiarrheals like diphenoxylate?

• Acute pancreatitis
• Paralytic ileus or toxic megacolon in susceptible patients
• Peptic ulcer perforation as a direct effect
• Esophageal varices formation

Correct Answer: Paralytic ileus or toxic megacolon in susceptible patients

Q28. Which clinical intervention is recommended if a patient taking diphenoxylate develops severe constipation and abdominal distension?

• Increase diphenoxylate dose
• Discontinue diphenoxylate and evaluate for obstruction or ileus
• Administer additional atropine
• Recommend high-dose opioids for pain

Correct Answer: Discontinue diphenoxylate and evaluate for obstruction or ileus

Q29. Which of these drug classes, when combined with diphenoxylate, may increase risk of CNS depression?

• Selective serotonin reuptake inhibitors only
• Benzodiazepines or other CNS depressants
• Topical antihistamines
• Proton pump inhibitors

Correct Answer: Benzodiazepines or other CNS depressants

Q30. In designing a question for exams, which pharmacodynamic property of diphenoxylate is most educational to test?

• Its role as a calcium channel blocker in the heart
• Its selective activation of intestinal opioid receptors decreasing secretions and motility
• Its function as a diuretic
• Its mechanism as an antibiotic

Correct Answer: Its selective activation of intestinal opioid receptors decreasing secretions and motility

Q31. Which of the following best describes the onset of action for oral diphenoxylate in treating diarrhea?

• Immediate effect within seconds
• Typically within 1 hour as intestinal motility slows
• Delayed onset after several days only
• No onset because it acts systemically only

Correct Answer: Typically within 1 hour as intestinal motility slows

Q32. For B. Pharm students, which laboratory finding might be expected in severe diphenoxylate–atropine overdose?

• Marked hypokalemia due to renal wasting
• Hyperthermia, dilated pupils and dry skin from anticholinergic toxicity
• Eosinophilia as a specific sign
• Elevated pancreatic enzymes exclusively

Correct Answer: Hyperthermia, dilated pupils and dry skin from anticholinergic toxicity

Q33. Which statement is correct regarding pediatric use of diphenoxylate?

• It is the first-line agent for all pediatric diarrhea
• It should be used cautiously and generally avoided in very young children due to risk of respiratory depression and anticholinergic effects
• It is safe in neonates
• Pediatric dosing is identical to adult dosing

Correct Answer: It should be used cautiously and generally avoided in very young children due to risk of respiratory depression and anticholinergic effects

Q34. Which of the following is an appropriate classroom question to assess knowledge of diphenoxylate’s adverse effect profile?

• Which antibiotic is diphenoxylate chemically related to?
• Which symptoms indicate anticholinergic toxicity when diphenoxylate–atropine is overdosed?
• What is the color of diphenoxylate tablets?
• How many manufacturers produce diphenoxylate worldwide?

Correct Answer: Which symptoms indicate anticholinergic toxicity when diphenoxylate–atropine is overdosed?

Q35. Which clinical advice is most appropriate for a patient taking diphenoxylate–atropine while breastfeeding?

• It is safe without any monitoring
• Advise caution: potential infant sedation and consult prescriber before use
• Increase dose to ensure effectiveness
• Double doses if maternal fever occurs

Correct Answer: Advise caution: potential infant sedation and consult prescriber before use

Q36. In pharmacology, which drug effect differentiates diphenoxylate’s peripheral vs central opioid actions?

• Peripheral effects include CNS euphoria
• Central actions include analgesia and respiratory depression at high doses
• Peripheral actions always produce sedation
• There is no difference; all effects are central only

Correct Answer: Central actions include analgesia and respiratory depression at high doses

Q37. Which teaching point about diphenoxylate–atropine is important for patients with glaucoma?

• It is safe without restrictions
• Use with caution because atropine may precipitate acute angle-closure glaucoma
• It treats glaucoma symptoms effectively
• It reduces intraocular pressure

Correct Answer: Use with caution because atropine may precipitate acute angle-closure glaucoma

Q38. Which feature of diphenoxylate pharmacology is important when considering drug design for antidiarrheals?

• Ability to increase CNS penetration to enhance efficacy
• Peripheral selectivity to reduce central opioid adverse effects
• Requirement for parenteral administration
• Strong prokinetic effects to promote motility

Correct Answer: Peripheral selectivity to reduce central opioid adverse effects

Q39. Which of the following is a reasonable MCQ topic comparing diphenoxylate to other antidiarrheals?

• Comparison of abuse potential and BBB penetration between diphenoxylate and loperamide
• Which has the brighter tablet color
• Which is more expensive per dose in a specific country
• Which has the longest brand name

Correct Answer: Comparison of abuse potential and BBB penetration between diphenoxylate and loperamide

Q40. What role does first-pass metabolism play in diphenoxylate’s clinical profile?

• It eliminates all pharmacologic activity so drug is inactive
• First-pass hepatic metabolism contributes to formation of active metabolites influencing duration and systemic effects
• There is no first-pass effect because drug is administered intravenously
• It solely reduces anticholinergic effects

Correct Answer: First-pass hepatic metabolism contributes to formation of active metabolites influencing duration and systemic effects

Q41. Which condition could be worsened by diphenoxylate due to reduced gut motility?

• Irritable bowel syndrome with constipation exclusively
• Acute infectious colitis or toxic megacolon risk
• Simple flatulence without systemic symptoms
• Asymptomatic lactose intolerance

Correct Answer: Acute infectious colitis or toxic megacolon risk

Q42. For exam prep, which pharmacovigilance concern is most relevant to diphenoxylate?

• Monitoring for allergic skin rash only
• Reporting cases of misuse, dependence or severe anticholinergic reactions
• Frequent monitoring of serum cholesterol
• Mandatory ECG monitoring in all patients

Correct Answer: Reporting cases of misuse, dependence or severe anticholinergic reactions

Q43. Which symptom would suggest a paradoxical reaction to diphenoxylate in a patient?

• Resolution of diarrhea within 30 minutes
• Increased abdominal cramping and hyperactive bowel sounds
• Gradual improvement of stool consistency
• Dry mouth and constipation only

Correct Answer: Increased abdominal cramping and hyperactive bowel sounds

Q44. Which of the following is a rational MCQ about dose adjustments for diphenoxylate?

• How to increase dose in renal failure without monitoring
• Need for caution and potential dose adjustment in hepatic impairment due to metabolism
• Always double the dose in elderly for efficacy
• No adjustments needed in any comorbidity

Correct Answer: Need for caution and potential dose adjustment in hepatic impairment due to metabolism

Q45. In the context of drug discovery, why might chemists modify diphenoxylate structure?

• To increase central opioid effects to produce euphoria
• To reduce BBB penetration and abuse potential while retaining peripheral antidiarrheal action
• To make it phototoxic
• To transform it into an antibiotic

Correct Answer: To reduce BBB penetration and abuse potential while retaining peripheral antidiarrheal action

Q46. Which teaching point addresses safe discontinuation of diphenoxylate therapy?

• Stop abruptly after a single dose always
• Discontinue when diarrhea resolves and monitor for constipation or recurrence; tapering generally not required for short courses
• Continue indefinitely to prevent recurrence
• Switch immediately to another opioid to avoid withdrawal

Correct Answer: Discontinue when diarrhea resolves and monitor for constipation or recurrence; tapering generally not required for short courses

Q47. Which of the following is true about diphenoxylate’s impact on electrolyte balance?

• It directly causes hypocalcemia in all patients
• By reducing diarrhea, it can help prevent fluid and electrolyte losses but may worsen constipation-related issues
• It directly increases serum sodium consistently
• It causes immediate hyperkalemia

Correct Answer: By reducing diarrhea, it can help prevent fluid and electrolyte losses but may worsen constipation-related issues

Q48. Which clinical pearl is important when selecting an antidiarrheal for a patient with suspected opioid dependence?

• Diphenoxylate is always preferred because it reverses dependence
• Avoid diphenoxylate because it may precipitate withdrawal or be misused; consider alternatives and addiction history
• Use diphenoxylate at very high doses to treat dependence
• Prescribe diphenoxylate without counseling

Correct Answer: Avoid diphenoxylate because it may precipitate withdrawal or be misused; consider alternatives and addiction history

Q49. Which is an appropriate laboratory assay consideration for diphenoxylate in forensic or therapeutic drug monitoring?

• Diphenoxylate cannot be detected in biological fluids
• Assays must distinguish parent drug from active metabolites to interpret exposure and possible misuse
• Only urine pH is required to interpret levels
• Serum cholesterol measurement is required for detection

Correct Answer: Assays must distinguish parent drug from active metabolites to interpret exposure and possible misuse

Q50. For a pharmacology exam, which question best integrates clinical pharmacokinetics and safety of diphenoxylate?

• How does diphenoxylate color affect absorption?
• What are the implications of hepatic metabolism on dosing and risk of central effects in liver disease?
• Which brand name is most commonly used globally?
• How many tablets can be safely taken with alcohol for synergy?

Correct Answer: What are the implications of hepatic metabolism on dosing and risk of central effects in liver disease?

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com