B. Pharm students must understand biological rhythms and cycles because they profoundly influence drug pharmacokinetics, pharmacodynamics, dosing time, and chronotherapy. This concise guide covers circadian, ultradian, and infradian rhythms; central and peripheral clocks; molecular clock genes (CLOCK, BMAL1, PER, CRY); zeitgebers like light; and key outcomes such as melatonin and cortisol patterns. Emphasis is on chronopharmacology, drug metabolism variability, timing of administration, and implications for hypertension, asthma, cancer therapy, and shift work. Grasping these concepts supports optimized dosing, reduced toxicity, and improved therapeutic outcomes. Practical tips, clinical examples, and exam-focused points aid revision. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What best defines a circadian rhythm?
- Endogenous ~24-hour physiological cycle
- Hourly fluctuation driven by meals
- Monthly hormonal variation
- Random environmental responses
Correct Answer: Endogenous ~24-hour physiological cycle
Q2. Where is the primary mammalian central pacemaker located?
- Suprachiasmatic nucleus (SCN) in the hypothalamus
- Pineal gland
- Medulla oblongata
- Thalamus
Correct Answer: Suprachiasmatic nucleus (SCN) in the hypothalamus
Q3. Which of the following is the principal zeitgeber for human circadian rhythms?
- Light-dark cycle (light)
- Ambient noise
- Physical exercise
- Social interaction
Correct Answer: Light-dark cycle (light)
Q4. Which transcription factors form the primary positive limb of the molecular clock?
- CLOCK and BMAL1 transcription factors
- PER and CRY proteins
- SIRT1 and REV-ERBα
- PPARα and PGC-1α
Correct Answer: CLOCK and BMAL1 transcription factors
Q5. In the core molecular clock feedback loop, which proteins provide negative feedback?
- PER and CRY proteins inhibit CLOCK:BMAL1
- CLOCK and BMAL1 inhibit PER:CRY
- SIRT1 and REV-ERB activate CLOCK
- PPARs inhibit BMAL1
Correct Answer: PER and CRY proteins inhibit CLOCK:BMAL1
Q6. How do ultradian and infradian rhythms differ from circadian rhythms?
- Ultradian are <24 hours; infradian are >24 hours
- Ultradian are >24 hours; infradian are <24 hours
- Both are exactly 24 hours
- They refer only to seasonal changes
Correct Answer: Ultradian are <24 hours; infradian are >24 hours
Q7. Which gland secretes melatonin and when is secretion maximal?
- Pineal gland secretes melatonin at night
- Thyroid gland secretes melatonin in morning
- Adrenal gland secretes melatonin at noon
- Pituitary secretes melatonin intermittently
Correct Answer: Pineal gland secretes melatonin at night
Q8. When does cortisol typically reach its daily peak in healthy individuals?
- Early morning around waking
- Midnight during sleep
- Early afternoon after lunch
- Late evening before sleep
Correct Answer: Early morning around waking
Q9. What is chronopharmacology?
- Study of how biological rhythms affect drug action and disposition
- Analysis of drug chemistry and synthesis
- Study of drug interactions only
- Pharmacovigilance reporting system
Correct Answer: Study of how biological rhythms affect drug action and disposition
Q10. What does chronotherapy aim to achieve?
- Timing medication to biological rhythms to improve efficacy and reduce toxicity
- Increasing drug dose irrespective of time
- Randomizing dosing schedules
- Only reducing pill counts
Correct Answer: Timing medication to biological rhythms to improve efficacy and reduce toxicity
Q11. Do hepatic CYP enzyme activities exhibit circadian variation?
- Hepatic CYP enzyme activity varies with circadian rhythms
- No, CYP enzymes are constant across the day
- Only extrahepatic CYPs vary
- CYP activity changes only with diet
Correct Answer: Hepatic CYP enzyme activity varies with circadian rhythms
Q12. Why are short-acting statins often recommended at night?
- Short-acting statins are often taken at night because cholesterol synthesis peaks during sleep
- They cause insomnia if taken in the morning
- Night dosing enhances gastrointestinal absorption
- They are inactivated by daytime light
Correct Answer: Short-acting statins are often taken at night because cholesterol synthesis peaks during sleep
Q13. What is the normal nocturnal pattern of blood pressure?
- Blood pressure normally dips at night (nocturnal dipping)
- Blood pressure peaks at night in all individuals
- Blood pressure remains constant over 24 hours
- Blood pressure is lowest in the late afternoon
Correct Answer: Blood pressure normally dips at night (nocturnal dipping)
Q14. What is a common effect of chronic night shift work on circadian rhythms?
- Causes circadian desynchronization that affects metabolism and drug response
- Strengthens alignment of SCN and peripheral clocks
- Eliminates all ultradian rhythms
- Only affects mood without metabolic consequences
Correct Answer: Causes circadian desynchronization that affects metabolism and drug response
Q15. Jet lag primarily results from which problem?
- Mismatch between the internal clock and local light-dark cycle after rapid time-zone travel
- Permanent loss of SCN neurons
- Overexposure to dietary sodium
- Chronic sleep deprivation unrelated to travel
Correct Answer: Mismatch between the internal clock and local light-dark cycle after rapid time-zone travel
Q16. Which neural pathway conveys photic information from the retina to the SCN?
- Retinohypothalamic tract conveying light information to the SCN
- Optic radiation to the visual cortex
- Dorsal longitudinal fasciculus
- Corticospinal tract
Correct Answer: Retinohypothalamic tract conveying light information to the SCN
Q17. Which organ shows pronounced circadian variation in drug metabolism?
- Liver (major site of circadian drug metabolism)
- Bone marrow
- Adipose tissue only
- Cartilage
Correct Answer: Liver (major site of circadian drug metabolism)
Q18. Which agent is commonly used as a chronobiotic to shift circadian phase?
- Melatonin (chronobiotic agent that shifts circadian phase)
- Caffeine as a sleep promoter
- Insulin for clock resetting
- Atropine for melatonin release
Correct Answer: Melatonin (chronobiotic agent that shifts circadian phase)
Q19. Which pharmacokinetic parameter is often strongly influenced by circadian rhythms?
- Clearance (metabolism/excretion) shows strong circadian variation
- Volume of distribution never changes
- Bioavailability is constant across 24 hours
- Half-life is unaffected by time of day
Correct Answer: Clearance (metabolism/excretion) shows strong circadian variation
Q20. To blunt the morning blood pressure surge, when is antihypertensive dosing often recommended?
- Take antihypertensives at night to blunt the morning blood pressure surge
- Always take only in the late morning
- Dosing time is irrelevant for blood pressure control
- Only take when symptomatic
Correct Answer: Take antihypertensives at night to blunt the morning blood pressure surge
Q21. How does drug half-life influence sensitivity to dosing time?
- Drugs with short half-lives show greater sensitivity to dosing time
- Long half-life drugs are always more time-sensitive
- Half-life has no relation to chronotherapy
- Only depot formulations matter
Correct Answer: Drugs with short half-lives show greater sensitivity to dosing time
Q22. In the molecular clock, PER proteins primarily act to:
- Inhibit CLOCK:BMAL1 transcriptional activity
- Activate BMAL1 transcription
- Phosphorylate CLOCK proteins
- Promote immediate gene expression
Correct Answer: Inhibit CLOCK:BMAL1 transcriptional activity
Q23. When does core body temperature typically reach its minimum (nadir)?
- Lowest in early morning around the sleep nadir (~04:00)
- Highest at midnight
- Lowest in the late afternoon
- Constant across the day
Correct Answer: Lowest in early morning around the sleep nadir (~04:00)
Q24. Which chronotherapeutic strategy is commonly used for nocturnal asthma symptoms?
- Schedule medications in the evening to reduce nocturnal asthma symptoms
- Avoid any nighttime dosing
- Use only oral antibiotics at night
- Administer bronchodilators only in the morning
Correct Answer: Schedule medications in the evening to reduce nocturnal asthma symptoms
Q25. What is the principle of chronomodulated chemotherapy?
- Times drug delivery to reduce toxicity and improve efficacy
- Administers maximum tolerated dose continuously
- Delivers drugs randomly to prevent resistance
- Avoids consideration of patient circadian rhythms
Correct Answer: Times drug delivery to reduce toxicity and improve efficacy
Q26. What does the term “chronotype” describe?
- An individual’s preferred timing of sleep-wake cycle (morningness/eveningness)
- A drug’s half-life pattern
- Only seasonal affective tendencies
- Enzyme activity unrelated to behavior
Correct Answer: An individual’s preferred timing of sleep-wake cycle (morningness/eveningness)
Q27. What is “masking” in chronobiology?
- Direct effect of an external stimulus on a rhythm without changing the underlying pacemaker (entrainment resets pacemaker)
- Permanently abolishing the SCN rhythm
- Synchronizing peripheral clocks to the SCN
- Only a laboratory artifact with no physiological relevance
Correct Answer: Direct effect of an external stimulus on a rhythm without changing the underlying pacemaker (entrainment resets pacemaker)
Q28. Do peripheral tissues contain autonomous circadian clocks?
- Most peripheral tissues (liver, heart, kidney) have autonomous circadian clocks
- Only the brain contains circadian clocks
- Peripheral tissues depend solely on hormones
- Circadian clocks are absent in adult tissues
Correct Answer: Most peripheral tissues (liver, heart, kidney) have autonomous circadian clocks
Q29. Which measurement is commonly used to assess individual circadian phase in clinical research?
- Dim light melatonin onset (DLMO) measurement
- Blood glucose at noon
- 24-hour urine sodium only
- EEG during REM only
Correct Answer: Dim light melatonin onset (DLMO) measurement
Q30. Which practical strategy helps adapt quickly to a new time zone?
- Use timed bright light exposure, and shift sleep and meal times to the local schedule
- Avoid all sunlight and stay in a dark room for 48 hours
- Take high-dose sedatives at arrival without timing
- Maintain home time-zone schedule regardless of destination
Correct Answer: Use timed bright light exposure, and shift sleep and meal times to the local schedule
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