Primidone is a key drug among miscellaneous anticonvulsants often taught in B.Pharm pharmacology. This introduction focuses on primidone’s mechanism, metabolism to phenobarbital and PEMA, pharmacokinetics, adverse effects, therapeutic uses (generalized tonic-clonic seizures, essential tremor), drug interactions, monitoring and dosing considerations. B.Pharm students should grasp enzyme induction, toxicity signs, contraindications (porphyria, pregnancy cautions), and management of overdose. Understanding primidone’s clinical role and differences from phenobarbital sharpens seizure management knowledge and safe dispensing practice. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which statement best describes the primary mechanism of action of primidone?
- Selective inhibition of NMDA receptors
- Enhancement of GABA-A receptor-mediated chloride influx and reduction of neuronal excitability
- Blockade of dopamine D2 receptors
- Activation of opioid receptors
Correct Answer: Enhancement of GABA-A receptor-mediated chloride influx and reduction of neuronal excitability
Q2. Primidone is primarily bioactivated to which active metabolite that contributes significantly to its anticonvulsant effects?
- Phenylbutazone
- Phenobarbital
- Phenytoin
- Valproic acid
Correct Answer: Phenobarbital
Q3. Besides phenobarbital, which other metabolite is formed from primidone metabolism?
- Phenylethylmalonamide (PEMA)
- Phenacetin
- Primidolactone
- Phenylalanine
Correct Answer: Phenylethylmalonamide (PEMA)
Q4. Which pharmacokinetic property is true for primidone and its metabolite phenobarbital?
- Both are exclusively renally excreted unchanged
- Primidone has a short half-life while phenobarbital has a much longer half-life
- Neither drug crosses the blood–brain barrier
- Both are not protein bound and are easily dialyzable
Correct Answer: Primidone has a short half-life while phenobarbital has a much longer half-life
Q5. Which clinical indication is primidone particularly used for besides epilepsy?
- Parkinsonian rigidity
- Essential tremor
- Migraine prophylaxis
- Alzheimer’s disease
Correct Answer: Essential tremor
Q6. What is a common central nervous system adverse effect of primidone therapy?
- Visual hallucinations exclusively in elderly patients
- Profound euphoria with high doses
- Sedation, ataxia and cognitive impairment
- Hypertensive crisis
Correct Answer: Sedation, ataxia and cognitive impairment
Q7. Which laboratory monitoring is most relevant during chronic primidone therapy?
- Serum phenobarbital concentrations and liver function tests
- Serum amylase only
- Fasting blood glucose weekly
- Thyroid stimulating hormone monthly
Correct Answer: Serum phenobarbital concentrations and liver function tests
Q8. Which drug interaction is a clinical concern with primidone due to enzyme induction?
- Reduced metabolism of warfarin leading to bleeding
- Increased effectiveness of oral contraceptives
- Accelerated metabolism of oral anticoagulants and oral contraceptives reducing their efficacy
- No significant interactions with other CNS drugs
Correct Answer: Accelerated metabolism of oral anticoagulants and oral contraceptives reducing their efficacy
Q9. Primidone is contraindicated or used with caution in which condition?
- Acute intermittent porphyria
- Essential tremor
- Generalized tonic-clonic seizures
- Hypothyroidism
Correct Answer: Acute intermittent porphyria
Q10. Which statement about primidone dosing initiation is most appropriate?
- Start with a large single loading dose to rapidly achieve levels
- Initiate with a low dose and titrate slowly to reduce sedation and adverse effects
- Give only at bedtime to avoid daytime benefit
- Dosing is irrelevant because primidone has no side effects
Correct Answer: Initiate with a low dose and titrate slowly to reduce sedation and adverse effects
Q11. In which population is primidone use especially cautious due to increased sensitivity to CNS depression?
- Young healthy adults
- Elderly patients
- Patients with hyperactivity disorders
- Professional athletes
Correct Answer: Elderly patients
Q12. The primary route of elimination for primidone and phenobarbital is:
- Hepatic metabolism with renal excretion of metabolites
- Exhalation unchanged via lungs
- Biliary excretion unchanged only
- Sweat and sebaceous gland excretion
Correct Answer: Hepatic metabolism with renal excretion of metabolites
Q13. Which effect on laboratory coagulation tests may occur due to primidone-induced enzyme induction?
- Prolonged bleeding time independent of warfarin
- Reduced INR in patients on warfarin due to increased warfarin metabolism
- Direct platelet inhibition causing thrombocytopenia
- Immediate hypercoagulability due to increased clotting factors
Correct Answer: Reduced INR in patients on warfarin due to increased warfarin metabolism
Q14. Which is a potential hematologic adverse effect associated with barbiturate therapy like primidone?
- Aplastic anemia and blood dyscrasias (rare)
- Marked polycythemia vera
- Isolated neutrophilia only
- Immediate hemolysis in all patients
Correct Answer: Aplastic anemia and blood dyscrasias (rare)
Q15. During pregnancy primidone use is categorized as which risk consideration?
- Absolutely safe with no fetal risk
- Associated with teratogenic risk and neonatal withdrawal; use only if benefits outweigh risks
- Guaranteed to prevent neonatal seizures
- Contraindicated because it causes spontaneous abortion in all cases
Correct Answer: Associated with teratogenic risk and neonatal withdrawal; use only if benefits outweigh risks
Q16. Which best describes primidone’s role in status epilepticus?
- First-line intravenous therapy for immediate seizure control
- Not typically used acutely in status epilepticus; benzodiazepines and phenytoin/phenobarbital are preferred
- Useful as a rapid intranasal agent in emergencies
- Only useful after surgical decompression
Correct Answer: Not typically used acutely in status epilepticus; benzodiazepines and phenytoin/phenobarbital are preferred
Q17. Which monitoring parameter is most useful to assess steady-state drug exposure in primidone-treated patients?
- Serum primidone concentration alone
- Serum phenobarbital concentration as reflective of active metabolite levels
- Daily urine color
- Blood pressure trend
Correct Answer: Serum phenobarbital concentration as reflective of active metabolite levels
Q18. Which statement about primidone’s protein binding is correct?
- Primidone is highly protein bound and can be displaced by other highly protein-bound drugs
- Primidone is completely unbound and freely filtered by kidneys
- Protein binding is irrelevant for primidone pharmacology
- Primidone only binds to muscle proteins
Correct Answer: Primidone is highly protein bound and can be displaced by other highly protein-bound drugs
Q19. A patient on primidone presents with nystagmus, ataxia and confusion—these signs most likely indicate:
- Therapeutic benefit of primidone
- Mild expected side effects that require no action
- Possible drug toxicity from excessive plasma concentration
- Allergic reaction requiring immediate epinephrine
Correct Answer: Possible drug toxicity from excessive plasma concentration
Q20. Which statement accurately reflects primidone’s classification?
- Primidone is a benzodiazepine derivative
- Primidone is a barbiturate derivative classified among miscellaneous anticonvulsants
- Primidone is a GABA reuptake inhibitor like tiagabine
- Primidone is a carbonic anhydrase inhibitor
Correct Answer: Primidone is a barbiturate derivative classified among miscellaneous anticonvulsants
Q21. Which organ impairment requires dose adjustment and careful monitoring when prescribing primidone?
- Severe hepatic impairment
- Broken bone in the arm
- Minor skin abrasion
- Corrected near vision
Correct Answer: Severe hepatic impairment
Q22. Which of the following best explains why primidone can reduce plasma concentration of co-administered drugs?
- Primidone blocks renal transporters increasing excretion of other drugs
- Primidone induces hepatic cytochrome P450 enzymes enhancing metabolism of other drugs
- Primidone chelates other drugs in the gut preventing absorption
- Primidone converts other drugs into inactive glucuronides instantly
Correct Answer: Primidone induces hepatic cytochrome P450 enzymes enhancing metabolism of other drugs
Q23. Which adverse effect would most likely require discontinuation of primidone therapy?
- Mild transient headache for 24 hours
- Severe skin rash with blistering suggestive of Stevens–Johnson syndrome
- Slight drowsiness controllable by dosing at night
- Transient mild nausea resolving in two days
Correct Answer: Severe skin rash with blistering suggestive of Stevens–Johnson syndrome
Q24. Which dosing consideration is important when converting a patient from phenobarbital to primidone?
- No adjustment is needed because they are identical drugs
- Titrate carefully because primidone is metabolized to phenobarbital and total barbiturate exposure must be considered
- Give primidone only once weekly
- Switch abruptly to avoid withdrawal
Correct Answer: Titrate carefully because primidone is metabolized to phenobarbital and total barbiturate exposure must be considered
Q25. Which symptom suggests a hypersensitivity reaction to primidone?
- Progressive fatigue over months without other signs
- Fever, lymphadenopathy, and rash after starting therapy
- Improvement in tremor severity
- Transient mild dizziness only after exercise
Correct Answer: Fever, lymphadenopathy, and rash after starting therapy
Q26. Which statement about primidone’s effect on mood and behavior is most accurate?
- Primidone consistently improves mood and prevents depression
- Primidone may cause irritability, depression, or behavioral changes in some patients
- Primidone only affects motor symptoms and never influences mood
- Primidone causes euphoria and increased sociability in all patients
Correct Answer: Primidone may cause irritability, depression, or behavioral changes in some patients
Q27. In the event of acute primidone overdose, which immediate management step is appropriate?
- Administer activated charcoal if within the appropriate time window and provide supportive care
- Give high-dose aspirin to neutralize the drug
- Induce vomiting with syrup of ipecac routinely
- There is no need for any intervention as primidone is harmless in overdose
Correct Answer: Administer activated charcoal if within the appropriate time window and provide supportive care
Q28. Which monitoring is important for women of childbearing potential on primidone?
- No monitoring is necessary as primidone does not affect contraceptives
- Counsel about reduced efficacy of oral contraceptives and consider alternative or higher-dose methods
- Recommend stopping contraception because primidone prevents pregnancy complications
- Only monitor blood glucose levels monthly
Correct Answer: Counsel about reduced efficacy of oral contraceptives and consider alternative or higher-dose methods
Q29. Which of the following is a pharmacodynamic effect shared by primidone and phenobarbital?
- Potentiation of GABAergic inhibition through GABA-A receptor modulation
- Specific blockade of calcium channels only in the heart
- Selective serotonin reuptake inhibition
- Antagonism at nicotinic acetylcholine receptors
Correct Answer: Potentiation of GABAergic inhibition through GABA-A receptor modulation
Q30. What is a clinical advantage of using primidone over phenobarbital in some patients?
- Primidone has no sedative effects compared to phenobarbital
- Primidone can be effective at lower plasma phenobarbital-equivalent exposures in some patients and may be better tolerated
- Primidone is a selective anticonvulsant with no interactions
- Primidone is a newer drug with extensive safety data that phenobarbital lacks
Correct Answer: Primidone can be effective at lower plasma phenobarbital-equivalent exposures in some patients and may be better tolerated
Q31. Which statement about primidone formulation and routes of administration is correct?
- Primidone is available only as an intravenous formulation
- Primidone is commonly available in oral tablet form for chronic therapy
- Primidone is administered subcutaneously for long-term use
- Primidone is delivered transdermally in patches
Correct Answer: Primidone is commonly available in oral tablet form for chronic therapy
Q32. Which pharmacological property explains the slow onset of full therapeutic effect with primidone?
- Rapid renal excretion prevents accumulation
- Prodrug conversion to phenobarbital and gradual attainment of steady-state concentrations
- Immediate receptor insensitivity that recovers over time
- Primidone does not cross membranes so accumulates slowly in fat
Correct Answer: Prodrug conversion to phenobarbital and gradual attainment of steady-state concentrations
Q33. Which enzyme family is primarily induced by primidone leading to drug interactions?
- Monoamine oxidases (MAO)
- Cytochrome P450 enzymes (CYP), especially CYP3A and CYP2C subfamilies
- DNA polymerases
- Lipoxygenases
Correct Answer: Cytochrome P450 enzymes (CYP), especially CYP3A and CYP2C subfamilies
Q34. When counseling patients about driving while on primidone, what advice is appropriate?
- Driving is always safe while on primidone
- Avoid driving or operating machinery until you know how primidone affects you due to sedation risk
- Primidone improves reaction time so driving is safer
- Only avoid driving on weekends
Correct Answer: Avoid driving or operating machinery until you know how primidone affects you due to sedation risk
Q35. Which metabolic pathway primarily converts primidone to phenobarbital?
- Oxidative hepatic metabolism (hepatic microsomal enzymes)
- Renal glucuronidation exclusively
- Gut flora conversion only
- Spontaneous non-enzymatic hydrolysis in plasma
Correct Answer: Oxidative hepatic metabolism (hepatic microsomal enzymes)
Q36. Which clinical sign in a neonate born to a mother on long-term primidone indicates neonatal withdrawal?
- Hyporeflexia and prolonged sleeping only
- Jitteriness, irritability, and possible seizures after birth
- Complete immunity to seizures
- High birth weight with no complications
Correct Answer: Jitteriness, irritability, and possible seizures after birth
Q37. In selecting antiseizure therapy, why might a clinician avoid primidone in a patient with severe depression?
- Primidone has no CNS effects on mood
- Primidone can exacerbate depression and suicidal ideation in susceptible individuals
- Primidone cures depression making concurrent antidepressants unnecessary
- Primidone causes euphoria and treats depression effectively
Correct Answer: Primidone can exacerbate depression and suicidal ideation in susceptible individuals
Q38. Which adverse endocrine effect might occur with chronic primidone use?
- Hyperprolactinemia is universal
- Increased vitamin D metabolism leading to lower bone density over time
- Immediate adrenal failure
- Complete pancreatic function suppression
Correct Answer: Increased vitamin D metabolism leading to lower bone density over time
Q39. Which statement about primidone use in pediatric patients is true?
- Pediatrics never require dose adjustments
- Use with caution; children may require different dosing and monitoring due to metabolic differences and sedation risk
- Primidone is a first-line agent for absence seizures in children
- It is safe to give adult doses to children based on weight alone without monitoring
Correct Answer: Use with caution; children may require different dosing and monitoring due to metabolic differences and sedation risk
Q40. Which adverse respiratory effect occurs in severe primidone overdose?
- Bronchospasm exclusively
- Respiratory depression potentially leading to hypoventilation and hypoxia
- Increased respiratory drive and hyperventilation
- Immediate resolution of asthma symptoms
Correct Answer: Respiratory depression potentially leading to hypoventilation and hypoxia
Q41. Which statement best summarizes primidone’s role in modern epilepsy treatment?
- Primidone is first-line for all seizure types due to superior safety
- Primidone remains useful for generalized tonic-clonic seizures and essential tremor but is less commonly used due to side effects and interaction profile
- Primidone has been completely replaced and has no role
- Primidone is only used as an intravenous emergency drug
Correct Answer: Primidone remains useful for generalized tonic-clonic seizures and essential tremor but is less commonly used due to side effects and interaction profile
Q42. Which counseling point is important for a patient starting primidone therapy?
- Expect immediate seizure freedom within hours
- Avoid alcohol and CNS depressants because combined sedation and respiratory depression risk increases
- There is no need to tell other healthcare providers about primidone use
- Increase vitamin K intake to mitigate interactions
Correct Answer: Avoid alcohol and CNS depressants because combined sedation and respiratory depression risk increases
Q43. Which monitoring is recommended during long-term primidone therapy to assess bone health?
- No monitoring required for bone health
- Periodic assessment of bone mineral density and vitamin D levels due to enzyme induction effects
- Frequent CT scans of the skeleton
- Only monitoring of serum sodium is relevant
Correct Answer: Periodic assessment of bone mineral density and vitamin D levels due to enzyme induction effects
Q44. Which adverse effect pattern differentiates primidone from many newer anticonvulsants?
- Primidone has fewer drug interactions than new agents
- Primidone commonly causes sedation and enzyme induction, whereas many newer agents have more favorable cognitive and interaction profiles
- Primidone causes selective renal toxicity not seen with others
- Primidone never causes cognitive side effects
Correct Answer: Primidone commonly causes sedation and enzyme induction, whereas many newer agents have more favorable cognitive and interaction profiles
Q45. Which adverse dermatologic condition is a known rare but serious risk with anticonvulsants including primidone?
- Acne vulgaris
- Stevens–Johnson syndrome and toxic epidermal necrolysis
- Common warts
- Psoriasis improvement
Correct Answer: Stevens–Johnson syndrome and toxic epidermal necrolysis
Q46. When assessing therapeutic efficacy of primidone in essential tremor, clinicians typically look for:
- Complete elimination of all tremor within minutes
- Reduction in tremor amplitude and improved function after dose titration
- Changes in hair color as an efficacy marker
- Only EEG changes without clinical improvement
Correct Answer: Reduction in tremor amplitude and improved function after dose titration
Q47. What is the impact of hepatic enzyme inducers on primidone plasma levels?
- They increase primidone plasma levels dramatically
- They may reduce primidone and phenobarbital levels by increasing metabolism
- Enzyme inducers have no effect on primidone metabolism
- They convert primidone into inactive inhaled gases
Correct Answer: They may reduce primidone and phenobarbital levels by increasing metabolism
Q48. Which statement regarding primidone and breastfeeding is most appropriate?
- Primidone is safe and requires no monitoring in nursing infants
- Primidone and metabolites are excreted in breast milk; breastfeeding requires risk–benefit discussion and monitoring of the infant
- Primidone eliminates all benefits of breast milk and should always stop breastfeeding
- Primidone enhances milk production and is recommended postpartum
Correct Answer: Primidone and metabolites are excreted in breast milk; breastfeeding requires risk–benefit discussion and monitoring of the infant
Q49. Which pharmacotherapeutic principle applies when combining primidone with other CNS depressants?
- No interaction; combinations are always safe
- Combined CNS depression is additive, so lower doses or avoidance is often necessary
- Primidone antagonizes other CNS depressants, making them ineffective
- Combining reduces primidone’s half-life to minutes
Correct Answer: Combined CNS depression is additive, so lower doses or avoidance is often necessary
Q50. Which clinical test might help distinguish primidone-induced toxicity from other causes of sedation?
- Serum phenobarbital (and primidone) levels correlated with clinical signs
- ECG alone without labs
- Complete blood count only without drug levels
- Urinalysis for glucose only
Correct Answer: Serum phenobarbital (and primidone) levels correlated with clinical signs
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.
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