Phenytoin sodium MCQs With Answer

Phenytoin sodium MCQs With Answer

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Phenytoin sodium MCQs With Answer provides B.Pharm students a focused, exam-ready review of phenytoin — a classic antiepileptic drug. This concise introduction and question set covers mechanism of action, pharmacokinetics (absorption, distribution, metabolism, zero-order kinetics), therapeutic drug monitoring, adverse effects (gingival hyperplasia, hirsutism, ataxia), drug interactions (CYP induction/inhibition), dosing strategies, formulations and clinical uses including status epilepticus. Emphasis is on clinically relevant pharmacy concepts, dosing calculations, and counseling points to build practical competence. Ideal for quick revision, practice tests, and internal assessment preparation. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which of the following best describes phenytoin’s primary mechanism of anticonvulsant action?

  • Enhancement of GABA-A receptor activity
  • Blockade of voltage-gated sodium channels
  • Inhibition of glutamate NMDA receptors
  • Activation of T-type calcium channels

Correct Answer: Blockade of voltage-gated sodium channels

Q2. Phenytoin exhibits which type of pharmacokinetics at therapeutic-to-high concentrations?

  • First-order kinetics throughout
  • Zero-order kinetics at therapeutic concentrations
  • Michaelis-Menten (saturable) kinetics leading to apparent zero-order at high doses
  • Linear kinetics with renal clearance dependent on GFR

Correct Answer: Michaelis-Menten (saturable) kinetics leading to apparent zero-order at high doses

Q3. Which enzyme system primarily metabolizes phenytoin?

  • CYP3A4
  • CYP2C9 and CYP2C19
  • MAO-A
  • UGT1A1

Correct Answer: CYP2C9 and CYP2C19

Q4. The most appropriate monitoring parameter to guide phenytoin dosing is:

  • Peak serum creatinine
  • Total serum phenytoin concentration and clinical response
  • Liver enzyme ALT only

Correct Answer: Total serum phenytoin concentration and clinical response

Q5. Which adverse effect is most characteristically associated with chronic phenytoin therapy?

  • Gingival hyperplasia
  • Nephrolithiasis
  • Pulmonary fibrosis
  • Hypothyroidism

Correct Answer: Gingival hyperplasia

Q6. A loading dose of intravenous phenytoin is used in status epilepticus to rapidly achieve therapeutic levels. Which formulation concern is important for IV phenytoin?

  • Contains propylene glycol which can cause hypotension and arrhythmias if infused too rapidly
  • Always given as a bolus push to minimize infusion time
  • Comes as an oil-based vehicle safe for peripheral infusion
  • Is incompatible with D5W and must be given with normal saline only

Correct Answer: Contains propylene glycol which can cause hypotension and arrhythmias if infused too rapidly

Q7. Which statement about oral phenytoin absorption is correct?

  • It is completely unaffected by food and should always be taken with meals
  • Phenytoin sodium suspension is absorbed faster than enteric-coated formulations
  • Enteral absorption is poor and mainly via rectal route
  • Bioavailability is zero due to extensive first-pass metabolism

Correct Answer: Phenytoin sodium suspension is absorbed faster than enteric-coated formulations

Q8. Which population requires careful dose adjustment of phenytoin due to altered protein binding?

  • Young healthy adults with high albumin
  • Patients with hypoalbuminemia (e.g., cirrhosis, nephrotic syndrome)
  • Patients with hyperlipidemia only
  • Those taking high-dose vitamin C

Correct Answer: Patients with hypoalbuminemia (e.g., cirrhosis, nephrotic syndrome)

Q9. Which drug interaction can decrease phenytoin plasma levels due to enzyme induction?

  • Cimetidine
  • Rifampicin
  • Sulfamethoxazole-trimethoprim
  • Fluconazole

Correct Answer: Rifampicin

Q10. Phenytoin is contraindicated or used with extreme caution in which situation?

  • Pregnancy due to risk of fetal hydantoin syndrome
  • Short-term migraine prophylaxis
  • Acute bacterial meningitis as first-line therapy
  • Uncomplicated tension headache

Correct Answer: Pregnancy due to risk of fetal hydantoin syndrome

Q11. Which lab finding is commonly monitored because phenytoin induces hepatic enzymes?

  • Serum creatine kinase only
  • Liver function tests (ALT, AST)
  • Serum troponin
  • Serum amylase only

Correct Answer: Liver function tests (ALT, AST)

Q12. Which side effect is dose-related and often reversible with dose reduction of phenytoin?

  • Gingival hyperplasia
  • Ataxia and nystagmus
  • Fetal hydantoin syndrome
  • Megablastic anemia

Correct Answer: Ataxia and nystagmus

Q13. Therapeutic total serum phenytoin concentrations typically range between:

  • 0.5–1.0 µg/mL
  • 10–20 µg/mL
  • 50–100 µg/mL
  • 100–200 µg/mL

Correct Answer: 10–20 µg/mL

Q14. Which pharmacogenetic consideration is relevant to phenytoin therapy?

  • CYP2C9 polymorphisms can alter phenytoin clearance and toxicity risk
  • UGT1A1*28 predicts phenytoin hypersensitivity
  • CYP3A5 genotype determines absorption rate
  • TPMT deficiency increases phenytoin activation

Correct Answer: CYP2C9 polymorphisms can alter phenytoin clearance and toxicity risk

Q15. Phenytoin can reduce the efficacy of hormonal contraceptives primarily by:

  • Increasing estrogen receptor sensitivity
  • Inducing hepatic enzymes that increase steroid metabolism
  • Directly inhibiting progesterone synthesis
  • Altering gastric pH to reduce absorption

Correct Answer: Inducing hepatic enzymes that increase steroid metabolism

Q16. Which adverse effect is associated with long-term phenytoin therapy and bone health?

  • Osteomalacia due to vitamin D metabolism induction
  • Increased bone density
  • Hypercalcemia and bone overgrowth
  • Acute gout flares

Correct Answer: Osteomalacia due to vitamin D metabolism induction

Q17. Which formulation of phenytoin is preferable for rapid IV administration in emergency settings to avoid propylene glycol toxicity?

  • Oral chewable tablets
  • Fosphenytoin (water-soluble prodrug)
  • Phenytoin suspension administered orally
  • Rectal suppository formulation

Correct Answer: Fosphenytoin (water-soluble prodrug)

Q18. A patient on chronic phenytoin therapy presents with rash and fever. The most concerning possibility to rule out is:

  • Drug-induced lupus
  • Stevens-Johnson syndrome or hypersensitivity reaction
  • Benign viral exanthem
  • Urticaria from food allergy

Correct Answer: Stevens-Johnson syndrome or hypersensitivity reaction

Q19. How does hypoalbuminemia affect interpretation of total phenytoin concentration?

  • Total concentration underestimates free (active) drug, so free level measurement or correction is needed
  • Total concentration overestimates free drug so dose should be increased
  • It has no effect because phenytoin is not protein bound
  • It only affects renal clearance, not serum concentration

Correct Answer: Total concentration underestimates free (active) drug, so free level measurement or correction is needed

Q20. Which clinical scenario is phenytoin especially indicated for?

  • Absence seizures (petit mal)
  • Generalized tonic-clonic seizures and partial seizures
  • Migraine prophylaxis as first-line
  • Acute ischemic stroke neuroprotection

Correct Answer: Generalized tonic-clonic seizures and partial seizures

Q21. Which counseling point is important for patients starting phenytoin?

  • Brush teeth and see a dentist regularly to monitor for gingival changes
  • Skip doses occasionally to prevent tolerance
  • Phenytoin causes immediate weight loss and appetite suppression
  • No need to warn about drug interactions

Correct Answer: Brush teeth and see a dentist regularly to monitor for gingival changes

Q22. An important cardiovascular risk of rapid IV phenytoin administration is:

  • Hypertension crisis
  • Severe hypotension and cardiac arrhythmias
  • Deep vein thrombosis
  • Bradycardia due to vagal stimulation only

Correct Answer: Severe hypotension and cardiac arrhythmias

Q23. Which laboratory test directly measures the pharmacologically active fraction of phenytoin?

  • Total phenytoin concentration in serum
  • Free (unbound) phenytoin concentration
  • Serum albumin only
  • Urinary phenytoin metabolites

Correct Answer: Free (unbound) phenytoin concentration

Q24. Which of the following drugs can have increased toxicity when co-administered with phenytoin due to displacement from protein binding or enzyme inhibition?

  • Warfarin with increased clearance and reduced effect only
  • Carbamazepine with no interaction
  • Valproic acid, which may increase free phenytoin concentrations and toxicity
  • Metformin causing lactic acidosis

Correct Answer: Valproic acid, which may increase free phenytoin concentrations and toxicity

Q25. In elderly patients, phenytoin dosing often requires adjustment because:

  • The elderly always metabolize drugs faster requiring higher doses
  • They have altered protein binding, reduced hepatic clearance, and increased sensitivity to CNS effects
  • Renal excretion is the main elimination route and is increased
  • They have increased gastric emptying accelerating absorption

Correct Answer: They have altered protein binding, reduced hepatic clearance, and increased sensitivity to CNS effects

Q26. Which is a classic dermatologic adverse effect associated with long-term phenytoin use?

  • Photosensitivity with blistering erythema
  • Hirsutism and coarse facial hair
  • Alopecia universalis
  • Pigmented purpuric dermatosis

Correct Answer: Hirsutism and coarse facial hair

Q27. Fosphenytoin differs from phenytoin mainly because it:

  • Is the oral sustained-release form of phenytoin
  • Is a prodrug that is water-soluble and can be infused faster with less vascular irritation
  • Has no anticonvulsant activity
  • Is contraindicated in status epilepticus

Correct Answer: Is a prodrug that is water-soluble and can be infused faster with less vascular irritation

Q28. Which monitoring frequency is appropriate after a major dose change of phenytoin?

  • No monitoring is needed after dose changes
  • Check levels after steady state is reached, typically 7–14 days for phenytoin
  • Check daily for one year only
  • Monitor only symptoms, never serum levels

Correct Answer: Check levels after steady state is reached, typically 7–14 days for phenytoin

Q29. Which laboratory abnormality may be seen with chronic phenytoin therapy and indicates hematologic toxicity?

  • Leukopenia, megaloblastic anemia, or thrombocytopenia
  • Isolated hyperglycemia
  • Marked eosinophilia only
  • Polycythemia vera

Correct Answer: Leukopenia, megaloblastic anemia, or thrombocytopenia

Q30. When converting a patient from oral to IV phenytoin, which consideration is essential?

  • IV phenytoin has identical formulation and can be given undiluted as a bolus
  • Adjust infusion rate to avoid cardiovascular toxicity; calculate equivalent dose and monitor levels
  • Oral doses are always doubled for IV administration
  • No monitoring is required after route change

Correct Answer: Adjust infusion rate to avoid cardiovascular toxicity; calculate equivalent dose and monitor levels

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