Miscellaneous anesthetics – Phenacaine MCQs With Answer

Miscellaneous anesthetics – Phenacaine is a topic B. Pharm students must master for safe topical anesthesia in ophthalmic practice. This concise introduction covers Phenacaine’s classification as an ester-type local anesthetic, its mechanism of action (sodium channel blockade), rapid onset and short duration, ester metabolism by plasma/tissue esterases to PABA derivatives, and common adverse effects such as corneal epithelial toxicity and allergic reactions. Understanding formulation, stability, contraindications, drug interactions, and clinical applications (tonometry, foreign body removal) is essential for pharmacists advising clinicians or patients. Clear knowledge of these points aids in rational use, monitoring, and management of complications. ‘Now let’s test your knowledge with 30 MCQs on this topic.’

Q1. What chemical classification best describes Phenacaine?

• Ester-type local anesthetic
• Amide-type local anesthetic
• Opioid analgesic
• General inhalational anesthetic

Correct Answer: Ester-type local anesthetic

Q2. What is the primary clinical use of Phenacaine?

• Topical ocular anesthesia for diagnostic and minor procedures
• Epidural anesthesia for labor
• Intravenous regional anesthesia
• Long-term topical skin analgesia

Correct Answer: Topical ocular anesthesia for diagnostic and minor procedures

Q3. What is the primary mechanism of action of Phenacaine?

• Blockade of voltage-gated sodium channels in nerves
• Activation of opioid receptors in the CNS
• Stimulation of GABA receptors
• Inhibition of cyclooxygenase enzymes

Correct Answer: Blockade of voltage-gated sodium channels in nerves

Q4. How quickly does Phenacaine typically produce anesthetic effect when applied topically to the cornea?

• Within seconds (very rapid onset)
• After 30–60 minutes (delayed onset)
• After several hours (prolonged onset)
• No measurable onset; systemic action required

Correct Answer: Within seconds (very rapid onset)

Q5. What is the usual duration of topical anesthesia provided by Phenacaine?

• Short duration, typically around 10–20 minutes
• Several hours (long duration)
• Less than 5 seconds
• Indefinite until metabolized systemically

Correct Answer: Short duration, typically around 10–20 minutes

Q6. Which enzyme system primarily metabolizes Phenacaine?

• Esterases (plasma and tissue esterases)
• CYP450 hepatic microsomal enzymes
• Monoamine oxidase
• Glutathione-S-transferase

Correct Answer: Esterases (plasma and tissue esterases)

Q7. Which metabolite-related issue is commonly associated with ester local anesthetics like Phenacaine?

• Formation of para-aminobenzoic acid (PABA) derivatives causing allergic reactions
• Formation of active amide metabolites causing prolonged effect
• Direct conversion to opioids producing sedation
• Generation of formaldehyde leading to systemic toxicity

Correct Answer: Formation of para-aminobenzoic acid (PABA) derivatives causing allergic reactions

Q8. What ocular adverse effect is most associated with repeated or prolonged use of topical Phenacaine?

• Corneal epithelial toxicity and delayed wound healing
• Retinal detachment
• Posterior uveitis
• Chronic conjunctival hyperplasia

Correct Answer: Corneal epithelial toxicity and delayed wound healing

Q9. Which patient condition is a clear contraindication to using Phenacaine?

• Known hypersensitivity to ester-type local anesthetics
• Controlled hypertension without ocular disease
• Minor allergic rhinitis unrelated to anesthetics
• Age over 65 years alone

Correct Answer: Known hypersensitivity to ester-type local anesthetics

Q10. Systemic toxicity after topical ocular Phenacaine is:

• Possible but uncommon; more likely with excessive systemic absorption
• Impossible because it is not absorbed systemically
• Universal after a single drop
• Only occurs with co-administration of opioids

Correct Answer: Possible but uncommon; more likely with excessive systemic absorption

Q11. How does the pKa of a local anesthetic influence onset, and which statement applies to Phenacaine?

• A pKa close to physiological pH favors a rapid onset; Phenacaine’s pKa is near physiological pH
• A very high pKa ensures immediate onset; Phenacaine has extremely high pKa
• pKa has no influence on onset of action
• Lower pKa always prolongs duration; Phenacaine has very low pKa

Correct Answer: A pKa close to physiological pH favors a rapid onset; Phenacaine’s pKa is near physiological pH

Q12. Which physicochemical property most influences potency and duration of local anesthetics like Phenacaine?

• Lipid solubility (higher lipid solubility increases potency and duration)
• Color of the solution
• Manufacturer’s logo
• Presence of sugar in the formulation

Correct Answer: Lipid solubility (higher lipid solubility increases potency and duration)

Q13. Protein binding influences the duration of local anesthetics. Which is true?

• Higher protein binding generally prolongs duration of action
• Lower protein binding prolongs duration
• Protein binding only affects potency, not duration
• Protein binding is irrelevant for topical agents

Correct Answer: Higher protein binding generally prolongs duration of action

Q14. If a patient is allergic to an ester anesthetic, what is the likelihood they will react to an amide anesthetic?

• Low cross-reactivity; amides are usually tolerated
• High cross-reactivity; avoid all local anesthetics
• Guaranteed cross-reaction in all cases
• Amides are always more allergenic than esters

Correct Answer: Low cross-reactivity; amides are usually tolerated

Q15. What is the recommended immediate management for severe systemic local anesthetic toxicity?

• Intravenous lipid emulsion therapy (and resuscitation measures)
• Give oral activated charcoal
• Topical antibiotic application to the eye
• No treatment; it resolves spontaneously

Correct Answer: Intravenous lipid emulsion therapy (and resuscitation measures)

Q16. Early central nervous system signs of systemic local anesthetic toxicity include:

• CNS excitation with tinnitus, metallic taste, agitation, and possible seizures
• Immediate profound hypotension without CNS symptoms
• Isolated skin rash and pruritus only
• Delayed paralysis of peripheral nerves only

Correct Answer: CNS excitation with tinnitus, metallic taste, agitation, and possible seizures

Q17. Adding a vasoconstrictor to a local anesthetic formulation typically:

• Reduces systemic absorption and prolongs local duration
• Always causes immediate systemic toxicity
• Makes the drug ineffective on mucous membranes
• Converts the ester to an amide

Correct Answer: Reduces systemic absorption and prolongs local duration

Q18. Regarding chemical stability, ester local anesthetics like Phenacaine are generally:

• Less stable in aqueous solutions and prone to hydrolysis
• Extremely stable and never degrade
• Stable only when exposed to light
• Stable at any pH

Correct Answer: Less stable in aqueous solutions and prone to hydrolysis

Q19. Which metabolite commonly formed from ester anesthetics is implicated in allergic reactions?

• Para-aminobenzoic acid (PABA) derivatives
• Benzoic acid glucuronide
• Sulfate conjugates of morphine
• Acetylsalicylic acid

Correct Answer: Para-aminobenzoic acid (PABA) derivatives

Q20. Typical ophthalmic procedures where Phenacaine is useful include:

• Tonometry, foreign body removal, and corneal scraping
• Cataract extraction under general anesthesia
• Deep posterior segment surgery without general anesthesia
• Prophylactic systemic analgesia for migraines

Correct Answer: Tonometry, foreign body removal, and corneal scraping

Q21. Which practice increases the risk of corneal toxicity with topical Phenacaine?

• Frequent or prolonged self-administration at high frequency
• Single supervised application in clinic
• Using once before tonometry
• Applying a single drop immediately before contact lens insertion

Correct Answer: Frequent or prolonged self-administration at high frequency

Q22. Interaction with cholinesterase inhibitors would likely have what effect on Phenacaine?

• Prolonged duration due to reduced metabolic breakdown
• Immediate neutralization rendering it inactive
• No interaction because Phenacaine is not metabolized by esterases
• Conversion to an amide resulting in allergy

Correct Answer: Prolonged duration due to reduced metabolic breakdown

Q23. Repeated topical dosing of Phenacaine to the cornea can lead to which histological change?

• Loss or disruption of corneal epithelial cells
• Hyperplasia of retinal ganglion cells
• Calcification of the lens capsule
• Thickening of the optic nerve

Correct Answer: Loss or disruption of corneal epithelial cells

Q24. Is Phenacaine recommended for use as an injectable infiltration anesthetic?

• No — it is intended for topical ocular use, not infiltration
• Yes — it is ideal for dental infiltration anesthesia
• Yes — used for spinal anesthesia
• No — it is an oral analgesic only

Correct Answer: No — it is intended for topical ocular use, not infiltration

Q25. What is the usual pharmaceutical presentation of Phenacaine for clinical use?

• Aqueous ophthalmic solution (eye drops)
• Oral tablets
• Transdermal patches
• Intravenous vials for infusion

Correct Answer: Aqueous ophthalmic solution (eye drops)

Q26. A commonly used alternative topical ocular anesthetic to Phenacaine is:

• Proparacaine (or tetracaine) eye drops
• Lidocaine oral syrup
• Intramuscular morphine
• Benzoyl peroxide cream

Correct Answer: Proparacaine (or tetracaine) eye drops

Q27. At the molecular level, how does Phenacaine prevent nerve conduction?

• By stabilizing neuronal membranes and decreasing sodium ion permeability
• By enhancing potassium efflux to hyperpolarize the nerve
• By blocking G-protein coupled receptors exclusively
• By inhibiting acetylcholinesterase at the neuromuscular junction

Correct Answer: By stabilizing neuronal membranes and decreasing sodium ion permeability

Q28. For which of the following is Phenacaine NOT appropriate?

• As sole anesthesia for intraocular surgery requiring akinesia and deep anesthesia
• Topical anesthesia for corneal foreign body removal
• Short diagnostic procedures like applanation tonometry
• Superficial corneal scraping in clinic

Correct Answer: As sole anesthesia for intraocular surgery requiring akinesia and deep anesthesia

Q29. How does increasing the pH of a local anesthetic solution influence onset of action?

• Alkalinization increases non-ionized fraction and speeds onset
• Alkalinization always prevents drug action
• Lowering pH increases the non-ionized fraction and speeds onset
• pH changes have no effect on onset

Correct Answer: Alkalinization increases non-ionized fraction and speeds onset

Q30. After applying Phenacaine eye drops, which patient instruction is most appropriate?

• Avoid contact lens use and manipulation until normal corneal sensation returns
• Drive immediately as vision is unaffected
• Use topical corticosteroids concurrently to prevent toxicity
• Take oral antibiotics to counteract local anesthetic effects

Correct Answer: Avoid contact lens use and manipulation until normal corneal sensation returns

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