Barbiturate anticonvulsants – Phenobarbitone MCQs With Answer

Barbiturate anticonvulsants – Phenobarbitone MCQs With Answer

Barbiturate anticonvulsants such as phenobarbitone are foundational drugs in antiepileptic pharmacology and crucial for B. Pharm students to master. This concise introduction highlights mechanism of action, pharmacokinetics, dosing strategies, therapeutic drug monitoring, enzyme induction, adverse effects, neonatal and pregnancy considerations, and overdose management. Emphasis is placed on GABA-A receptor modulation, long half-life, interactions with CYP450 enzymes, and clinical uses including status epilepticus and neonatal seizures. These topic areas build clinical reasoning for safe dispensing and monitoring in hospital and community settings. Key topics include therapeutic index, GABA-A receptor modulation, CYP450 interactions, therapeutic drug monitoring, IV/oral formulations and dosing in hepatic or renal impairment. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which of the following best describes the primary mechanism of action of phenobarbitone?

• Competitive antagonist at NMDA receptors
• Positive allosteric modulation of GABA-A receptor, increasing duration of chloride channel opening
• Inhibition of voltage-gated sodium channels exclusively
• Selective inhibition of monoamine oxidase

Correct Answer: Positive allosteric modulation of GABA-A receptor, increasing duration of chloride channel opening

Q2. Phenobarbitone is classified as which type of barbiturate based on duration of action?

• Ultra-short acting
• Short acting
• Intermediate acting
• Long acting

Correct Answer: Long acting

Q3. The usual therapeutic plasma concentration range for phenobarbitone in seizure control is closest to which of the following?

• 1–5 µg/mL
• 5–15 µg/mL
• 15–40 µg/mL
• 50–100 µg/mL

Correct Answer: 15–40 µg/mL

Q4. Which clinical indication is phenobarbitone commonly used for in neonates?

• Neonatal sepsis
• Neonatal seizures
• Neonatal hypoglycemia
• Neonatal hyperbilirubinemia

Correct Answer: Neonatal seizures

Q5. Phenobarbitone’s effect on hepatic drug-metabolizing enzymes is best described as:

• Potent CYP450 inhibitor
• Neutral — no effect on hepatic enzymes
• Potent inducer of hepatic microsomal enzymes (CYP450)
• Inducer of renal drug-metabolizing enzymes only

Correct Answer: Potent inducer of hepatic microsomal enzymes (CYP450)

Q6. Which adverse effect is most characteristic of therapeutic doses of phenobarbitone?

• Severe hypertension
• Marked sedation and cognitive impairment
• Profound hyperreflexia
• Excessive lacrimation

Correct Answer: Marked sedation and cognitive impairment

Q7. Phenobarbitone is contraindicated or used with extreme caution in which of the following conditions?

• Acute intermittent porphyria
• Hyperthyroidism
• Essential hypertension
• Iron deficiency anemia

Correct Answer: Acute intermittent porphyria

Q8. Which statement about phenobarbitone pharmacokinetics is correct?

• It has a very short half-life (<6 hours)
• It is excreted unchanged only and not metabolized
• It has a long elimination half-life and undergoes hepatic metabolism
• It is eliminated exclusively by biliary excretion

Correct Answer: It has a long elimination half-life and undergoes hepatic metabolism

Q9. A standard intravenous loading dose of phenobarbitone for status epilepticus is approximately:

• 1–2 mg/kg
• 5 mg/kg
• 15–20 mg/kg
• 50 mg/kg

Correct Answer: 15–20 mg/kg

Q10. Which drug’s plasma concentration is most likely to decrease when co-administered with phenobarbitone due to enzyme induction?

• Propranolol
• Warfarin (leading to reduced anticoagulant effect)
• Insulin (subcutaneous)
• Heparin (IV)

Correct Answer: Warfarin (leading to reduced anticoagulant effect)

Q11. Which monitoring parameter is most important when a patient is on long-term phenobarbitone therapy?

• Serum sodium concentrations weekly
• Therapeutic drug monitoring of plasma phenobarbitone levels
• Urine glucose every visit
• Serum amylase monthly

Correct Answer: Therapeutic drug monitoring of plasma phenobarbitone levels

Q12. Phenobarbitone commonly causes enzyme induction. Which clinical consequence may result from this property?

• Increased effect of oral contraceptives leading to irregular bleeding
• Decreased metabolism of co-administered drugs causing toxicity
• Decreased plasma levels of co-administered drugs, reducing their efficacy
• Immediate hypersensitivity reactions to all co-administered drugs

Correct Answer: Decreased plasma levels of co-administered drugs, reducing their efficacy

Q13. Which of the following is a serious withdrawal symptom after abrupt discontinuation of chronic phenobarbitone therapy?

• Mild pruritus
• Seizure recurrence or withdrawal seizures
• Hyperpigmentation
• Improved sleep quality

Correct Answer: Seizure recurrence or withdrawal seizures

Q14. Regarding protein binding, phenobarbitone is best described as:

• Highly protein bound (>95%)
• Moderately protein bound (approximately 40–60%)
• Completely unbound in plasma
• Irreversibly bound to erythrocytes only

Correct Answer: Moderately protein bound (approximately 40–60%)

Q15. Which of the following signs is most suggestive of phenobarbitone overdose?

• Severe hypertension and tachycardia
• Progressive CNS depression and respiratory depression
• Isolated severe abdominal pain without CNS effects
• Isolated dermatological rash with no systemic signs

Correct Answer: Progressive CNS depression and respiratory depression

Q16. In phenobarbitone toxicity, which of the following interventions can enhance elimination?

• Urinary alkalinization to increase renal excretion
• Administering activated charcoal is contraindicated
• Giving intravenous lipid emulsion is the first-line measure
• Inducing metabolic acidosis to trap the drug in plasma

Correct Answer: Urinary alkalinization to increase renal excretion

Q17. Which property makes phenobarbitone a useful anticonvulsant for generalized tonic-clonic and partial seizures?

• Short half-life allowing rapid clearance
• Potent NMDA antagonism
• Broad-spectrum potentiation of GABAergic inhibition and long duration of action
• Selective dopamine receptor antagonism

Correct Answer: Broad-spectrum potentiation of GABAergic inhibition and long duration of action

Q18. Which of the following is a recognized teratogenic concern with phenobarbitone use during pregnancy?

• No known fetal risks; safe in all trimesters
• Increased risk of congenital malformations and neonatal bleeding disorders
• Guaranteed fetal kidney agenesis
• Pregnancy causes immediate drug inactivation

Correct Answer: Increased risk of congenital malformations and neonatal bleeding disorders

Q19. Which enzyme system is primarily induced by phenobarbitone leading to drug interactions?

• CYP450 hepatic microsomal enzymes
• Cytosolic aldehyde oxidase
• Monoamine oxidase
• Renal brush-border hydrolases

Correct Answer: CYP450 hepatic microsomal enzymes

Q20. Which benzodiazepine-compatible statement is true when used with phenobarbitone?

• Combined use eliminates need for dose adjustment of either drug
• Phenobarbitone antagonizes benzodiazepine effects
• Combined sedation and respiratory depression risk is increased
• Benzodiazepines always reduce phenobarbitone plasma levels

Correct Answer: Combined sedation and respiratory depression risk is increased

Q21. For therapeutic drug monitoring of phenobarbitone, trough levels are preferred because:

• Trough levels reflect steady-state clearance and risk of toxicity better
• Peak levels are always undetectable
• Trough levels are easier to assay due to metabolism
• Only trough levels correlate with hepatic enzyme induction

Correct Answer: Trough levels reflect steady-state clearance and risk of toxicity better

Q22. Which metabolic pathway contributes to phenobarbitone biotransformation?

• Glucuronidation and hepatic oxidation
• Direct renal filtration without metabolism
• Deamination by plasma cholinesterases
• Complete acetylation in the gut

Correct Answer: Glucuronidation and hepatic oxidation

Q23. Phenobarbitone is often preferred in resource-limited settings for seizures because:

• It is very expensive but widely available
• It has a long duration, low cost, and parenteral forms for acute use
• It requires no monitoring and has no side effects
• It cures epilepsy permanently

Correct Answer: It has a long duration, low cost, and parenteral forms for acute use

Q24. Which of the following best describes the effect of phenobarbitone on oral contraceptives?

• Increases contraceptive efficacy by inhibiting metabolism
• No interaction with oral contraceptives
• Reduces contraceptive efficacy by inducing metabolism of steroid hormones
• Causes permanent infertility in all women

Correct Answer: Reduces contraceptive efficacy by inducing metabolism of steroid hormones

Q25. In patients with hepatic impairment, phenobarbitone dosing should generally be:

• Unchanged because hepatic function does not affect its kinetics
• Increased due to rapid clearance
• Reduced or used with caution due to impaired metabolism and accumulation
• Switched to an oral contraceptive-based regimen

Correct Answer: Reduced or used with caution due to impaired metabolism and accumulation

Q26. Which laboratory test may be affected clinically by chronic phenobarbitone therapy due to enzyme induction?

• Serum lipid panel becomes invalid
• Prothrombin time/INR may decrease in patients on warfarin
• Serum creatinine is directly increased by phenobarbitone
• Serum potassium is always elevated

Correct Answer: Prothrombin time/INR may decrease in patients on warfarin

Q27. Which statement is true regarding phenobarbitone use in breastfeeding mothers?

• Phenobarbitone is not excreted in breast milk
• It is excreted in breast milk and may cause neonatal sedation
• It enhances milk production and is recommended
• It is destroyed in the infant’s stomach and poses no risk

Correct Answer: It is excreted in breast milk and may cause neonatal sedation

Q28. A common pediatric adverse reaction to phenobarbitone is which paradoxical effect?

• Excessive sedation only in all children
• Paradoxical hyperactivity and irritability in some children
• Permanent improvement of attention span
• Marked eosinophilia in all cases

Correct Answer: Paradoxical hyperactivity and irritability in some children

Q29. Which of the following best explains why phenobarbitone can reduce the efficacy of many co-administered drugs?

• It binds irreversibly to plasma proteins, displacing other drugs
• It induces hepatic enzymes, increasing metabolism of other drugs
• It alkalinizes urine and traps co-administered drugs in renal tubules
• It inhibits intestinal absorption of all oral drugs

Correct Answer: It induces hepatic enzymes, increasing metabolism of other drugs

Q30. Which clinical use of phenobarbitone is supported by its ability to produce long-lasting anticonvulsant effects?

• Short-term treatment for acute migraines
• Maintenance therapy for certain generalized and partial epilepsies
• Primary therapy for Parkinson’s disease
• First-line treatment for acute ischemic stroke

Correct Answer: Maintenance therapy for certain generalized and partial epilepsies

Q31. Which of the following drugs is most likely to have increased clearance when co-administered with phenobarbitone?

• Phenytoin
• Carbamazepine
• Oral contraceptives (ethinylestradiol)
• Levetiracetam (which is minimally metabolized)

Correct Answer: Oral contraceptives (ethinylestradiol)

Q32. Which property of phenobarbitone contributes to its usefulness in status epilepticus when benzodiazepines fail?

• Rapid GABA replacement therapy
• Ability to produce sustained CNS depression and interrupt seizure activity due to long action
• Immediate reversal of neuronal damage
• Stimulation of excitatory neurotransmission to reset circuits

Correct Answer: Ability to produce sustained CNS depression and interrupt seizure activity due to long action

Q33. In therapeutic drug monitoring, a rising phenobarbitone level with new sedation suggests:

• Therapeutic effect and no need for change
• Possible toxic accumulation and need to reduce dose or investigate interactions
• Lab error only, never drug-related
• Immediate need to add another enzyme inducer

Correct Answer: Possible toxic accumulation and need to reduce dose or investigate interactions

Q34. Which of the following is an appropriate immediate management step for a conscious patient with acute oral phenobarbitone overdose presenting within 1 hour?

• Wait and observe without intervention
• Administer activated charcoal to limit absorption
• Give oral phenothiazine as antidote
• Perform immediate hemodialysis without other measures

Correct Answer: Administer activated charcoal to limit absorption

Q35. Phenobarbitone’s oral bioavailability is best described as:

• Very low and unpredictable
• High and reliable, suitable for oral maintenance therapy
• Zero — only effective parenterally
• Dependent on gastric pH to a degree that prevents oral use

Correct Answer: High and reliable, suitable for oral maintenance therapy

Q36. Which group of patients requires particular caution or dose adjustment when using phenobarbitone?

• Patients with renal and hepatic impairment, and the elderly
• Young healthy adults only
• Patients with controlled asthma only
• Patients on daily multivitamins exclusively

Correct Answer: Patients with renal and hepatic impairment, and the elderly

Q37. Which adverse hematologic effect has been reported, though uncommon, with phenobarbitone therapy?

• Aplastic anemia and blood dyscrasias
• Immediate polycythemia in all patients
• Absolute eosinopenia always
• Thrombocytosis in every case

Correct Answer: Aplastic anemia and blood dyscrasias

Q38. Which of the following best explains why phenobarbitone may be preferred over some newer antiepileptics in low-resource settings?

• Lack of any adverse effects
• Low cost, oral and IV formulations, and well-established dosing and monitoring protocols
• It requires no training to dispense
• Guaranteed cure of epilepsy

Correct Answer: Low cost, oral and IV formulations, and well-established dosing and monitoring protocols

Q39. Which organ system monitoring is particularly important during chronic phenobarbitone therapy due to enzyme induction?

• Frequent ocular exams only
• Periodic liver function tests and clinical assessment of hepatic function
• No monitoring is needed
• Weekly brain MRI scans

Correct Answer: Periodic liver function tests and clinical assessment of hepatic function

Q40. Which statement about phenobarbitone interaction with alcohol is correct?

• Concomitant alcohol reduces phenobarbitone sedation
• Alcohol and phenobarbitone are synergistic and increase CNS and respiratory depression risk
• Alcohol prevents phenobarbitone absorption entirely
• Alcohol reverses phenobarbitone’s anticonvulsant effect

Correct Answer: Alcohol and phenobarbitone are synergistic and increase CNS and respiratory depression risk

Q41. Phenobarbitone’s molecular targets primarily include which neurotransmitter system?

• Serotonergic system only
• GABAergic inhibitory system
• Dopaminergic excitatory system
• Cholinergic neuromuscular junction exclusively

Correct Answer: GABAergic inhibitory system

Q42. Which of the following is TRUE regarding phenobarbitone and CYP-mediated drug interactions?

• Phenobarbitone inhibits CYP3A4 and increases levels of many drugs
• Phenobarbitone induces CYP enzymes and can decrease plasma levels of co-administered drugs
• Phenobarbitone has no effect on drug-metabolizing enzymes
• Phenobarbitone causes irreversible inhibition of hepatic metabolism

Correct Answer: Phenobarbitone induces CYP enzymes and can decrease plasma levels of co-administered drugs

Q43. Which of the following describes a pharmacological difference between phenobarbitone and ultra-short-acting barbiturates like thiopental?

• Phenobarbitone has faster onset and shorter duration than thiopental
• Phenobarbitone has longer duration of action and is used for maintenance, while thiopental is used for induction of anesthesia
• Both have identical clinical uses
• Thiopental is used for long-term seizure control

Correct Answer: Phenobarbitone has longer duration of action and is used for maintenance, while thiopental is used for induction of anesthesia

Q44. Which of the following is a common CNS adverse effect that may limit phenobarbitone use in learning-age B. Pharm students?

• Improved memory consolidation
• Impaired cognition, learning and attention
• Heightened alertness and insomnia
• Enhanced visual acuity

Correct Answer: Impaired cognition, learning and attention

Q45. Why is phenobarbitone sometimes used as a first-line emergency anticonvulsant in neonatal units?

• It is ineffective in neonates but used for tradition
• Availability, IV formulation, proven neonatal efficacy and clinician familiarity
• It has no respiratory depressant effects in neonates
• Neonates metabolize it extremely rapidly eliminating toxicity

Correct Answer: Availability, IV formulation, proven neonatal efficacy and clinician familiarity

Q46. Which monitoring is particularly useful after initiating phenobarbitone in an epileptic patient already on anticoagulation?

• Monitor blood glucose only
• Monitor INR or prothrombin time due to interaction with warfarin
• Stop monitoring because phenobarbitone prevents bleeding
• Monitor urine ketones hourly

Correct Answer: Monitor INR or prothrombin time due to interaction with warfarin

Q47. Chronic phenobarbitone therapy may cause tolerance. Which mechanism underlies tolerance development?

• Permanent receptor deletion
• Enzyme induction and receptor adaptations reducing drug effect over time
• Immediate renal elimination acceleration only
• Increasing intestinal absorption with time

Correct Answer: Enzyme induction and receptor adaptations reducing drug effect over time

Q48. Which of the following is true about phenobarbitone formulation for intravenous use?

• It is always acidic and incompatible with all IV fluids
• The sodium salt is commonly used for IV injection and must be administered slowly to avoid respiratory depression
• It is administered IM only and never IV
• It is available as an oral suspension only

Correct Answer: The sodium salt is commonly used for IV injection and must be administered slowly to avoid respiratory depression

Q49. Which of the following is the most appropriate counseling point for a patient starting phenobarbitone?

• There are no common drug interactions, so no precautions needed
• Avoid alcohol and inform prescribers about phenobarbitone due to many drug interactions and sedation risk
• Use double doses if a dose is missed
• Stop the drug abruptly if you feel sleepy

Correct Answer: Avoid alcohol and inform prescribers about phenobarbitone due to many drug interactions and sedation risk

Q50. Which of the following statements about long-term outcomes with phenobarbitone is most accurate?

• Phenobarbitone always cures epilepsy permanently without adverse effects
• Long-term use can control seizures in many patients but may be limited by cognitive side effects, interactions, and teratogenic risk
• It has no impact on quality of life
• It is never indicated beyond a single dose

Correct Answer: Long-term use can control seizures in many patients but may be limited by cognitive side effects, interactions, and teratogenic risk

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