INBDE practice questions: FK8 — Pharmacology

Answer D: Give a regional block at a site away from the acutely inflamed tissue

Local anesthetics block voltage-gated sodium channels from inside the nerve, and only the uncharged base crosses the nerve membrane; pKa relative to tissue pH governs how much exists in that form. In infected, acidic tissue more drug is trapped as the charged species, less crosses, and the block fails — the commonest clinical failure. The remedy is a regional block away from the inflamed field rather than more solution into it. A does precisely what the mechanism predicts will fail, while adding dose and injection-rate risk. B misattributes the failure to drug class: esters and amides differ in metabolism and allergy, not in their dependence on tissue pH. C converts a predictable pH failure into an allergy; true amide allergy is rare, and it presents as a reaction, not a failed block.

Common trap: Answering a failed block with more solution into the inflamed site.

Source: Malamed, Handbook of Local Anesthesia

Answer A: Two cartridges, since a third would exceed his 96.8 mg weight-based limit

A percentage is grams per 100 mL, so 2% lidocaine is 20 mg/mL and the cartridge volume printed on the carton converts that into milligrams: 1.7 mL delivers 34 mg. The conservative dental maximum of 4.4 mg/kg gives 96.8 mg for a 22 kg child, so two cartridges supply 68 mg while a third would reach 102 mg and breach the limit; sequence the appointment to the dose rather than the dose to the appointment. B applies an adult ceiling to a child, which is the commonest route to a paediatric overdose. C halves the conversion — per cent times ten is mg/mL, so 2% is 20 mg/mL. D invents an exemption: the conservative limit includes lidocaine with epinephrine, and the vasoconstrictor is counted separately against its own cap.

Common trap: Applying the adult milligram ceiling to a child instead of the weight-based limit.

Source: AAPD local-anesthesia best practice

Answer C: An amide such as lidocaine is appropriate; ester allergy reflects PABA metabolites

The class split predicts both metabolism and allergy. Esters — procaine, benzocaine and tetracaine — are hydrolysed by plasma esterases to PABA, the classic cause of true local-anesthetic allergy, while most amides such as lidocaine, mepivacaine, prilocaine and bupivacaine are metabolised mainly in the liver and true allergy to them is rare. A withholds an entire pharmacological class on the strength of a single-class reaction. B misses that benzocaine is itself an ester, and topical exposure is still exposure; benzocaine also carries a methemoglobinemia risk and may not be used orally in children under 2 years. D inverts the chemistry it invokes: articaine is the exception among the amides, carrying an ester side chain hydrolysed predominantly by plasma esterases.

Common trap: Treating a topical agent as exempt from the class that caused the allergy.

Source: FDA oral benzocaine safety action

Answer B: About 0.04 mg, roughly two cartridges, with aspiration and slow injection

Concentration is written as a ratio: 1:100,000 is 0.01 mg/mL, so a 1.7 mL cartridge carries 0.017 mg of epinephrine. The commonly cited ceiling is about 0.2 mg per appointment for a healthy adult and about 0.04 mg — roughly two cartridges — for a patient with significant but stable cardiovascular disease, which two 1.7 mL cartridges meet at 0.034 mg. A applies the healthy-adult figure to a cardiac patient. C is the over-correction the literature warns against: withholding vasoconstrictor produces shallow anesthesia, pain, and a surge of the patient's own epinephrine that cannot be dosed or stopped. D counts only the anesthetic, when the vasoconstrictor is a separate drug in the same cartridge with its own limit. Whether elective care suits him at all is decided first.

Common trap: Counting the milligrams of anesthetic and forgetting the vasoconstrictor's separate cap.

Source: Malamed, Handbook of Local Anesthesia

Answer A: Ibuprofen 400 mg with acetaminophen 500–1000 mg, at the lowest effective dose

The ADA's 2024 acute dental pain guideline places NSAID alone, or NSAID plus acetaminophen, first-line for most adults, keeping opioids for the uncommon case where non-opioids fail or are contraindicated; ibuprofen 400 mg with acetaminophen 500–1000 mg matches or beats typical opioid combinations with fewer harms, and NSAIDs act on exactly the prostaglandin mechanism that generates inflammatory dental pain. B selects on the invasiveness of the procedure rather than the evidence. C makes an opioid the base analgesic and discards the drug whose mechanism fits the pain. D is the "just-in-case" delayed prescription the guideline's good-practice statements advise against. Count every acetaminophen source, including combination products, and keep the total within the adult ceiling.

Common trap: Letting the invasiveness of the procedure, not the evidence, pick the analgesic.

Source: ADA 2024 Clinical Practice Guideline — Acute Dental Pain Management (adolescents, adults and older adults)

Answer D: Acetaminophen for pain, avoiding NSAIDs from about 20 weeks unless specifically advised

Definitive dental treatment is the real analgesic here, and the drug question is settled by FDA pregnancy advice: avoid NSAIDs from about 20 weeks onward unless specifically advised, use the lowest effective dose for the shortest time if they are necessary between 20 and 30 weeks, and avoid them after 30 weeks. At 24 weeks with no obstetric instruction, acetaminophen is the reasonable choice. A treats the second trimester as a safe window that the advice does not grant. B quotes a letter category that no longer exists: the Pregnancy and Lactation Labeling Rule removed A/B/C/D/X in 2015 in favour of narrative sections. C leaves severe pain and untreated pulpitis in place, which is neither analgesia nor safety.

Common trap: Trusting a remembered pregnancy letter category instead of current labeling.

Source: FDA NSAID pregnancy safety communication

Answer C: The letter categories were removed in 2015 and replaced by narrative sections

The FDA's Pregnancy and Lactation Labeling Rule, effective June 30, 2015, removed the A/B/C/D/X pregnancy letter categories and replaced them with narrative Pregnancy, Lactation, and Females and Males of Reproductive Potential subsections that must be read rather than looked up. A treats a deliberate regulatory change as a printing omission and sends the student to a manufacturer for something no longer produced. B invents a split between prescription and over-the-counter labeling that the rule does not create. D relocates the letters rather than retiring them. Quoting a remembered category is a recognised trap precisely because the single letter compressed away the nuance the narrative sections now set out, which is the information a prescribing decision in pregnancy actually needs.

Common trap: Hunting for a letter category that has not appeared on labeling for a decade.

Source: FDA Pregnancy and Lactation Labeling Rule (PLLR)

Answer B: Definitive dental treatment with analgesia now; antibiotics follow a systemic indication

For an immunocompetent adult with pulpal or periapical pain and localised swelling, the treatment is definitive dental treatment — pulpectomy, extraction or drainage — plus analgesia; systemic antibiotics are decided by systemic involvement or another clinical indication, not by pain and swelling alone. This patient has no fever, trismus, lymphadenopathy or spreading cellulitis. A is the "antibiotics to calm it down before the root canal" prescription the guideline was written to eliminate, and it postpones the only step that removes the source. C compounds the same error with a second drug, treating the word abscess as its own indication when antibiotics do not drain. D withholds the definitive treatment too, leaving an untreated source and uncontrolled pain.

Common trap: Reading a localised swelling as an antibiotic indication in a systemically well adult.

Source: ADA antibiotic guideline for urgent pulpal/periapical pain and swelling

Answer D: Whether he has taken sildenafil, tadalafil, vardenafil or avanafil

Nitroglycerin is contraindicated with the PDE-5 inhibitors sildenafil, tadalafil, vardenafil and avanafil, because the combination can cause severe hypotension, syncope or myocardial ischaemia; the question is asked before reaching for the bottle. The rest of the response is to stop, position, give oxygen, activate emergency services, then one tablet sublingually at the first sign of the attack, repeated every 5 minutes to no more than three tablets in 15 minutes. A is irrelevant to a sublingual route that bypasses the gut and its first-pass loss entirely. B inverts standard first aid: chewed aspirin belongs alongside oxygen and emergency activation in suspected myocardial infarction, not on a contraindication list. C invents a blood-pressure threshold that nitroglycerin labeling does not set for an anginal attack.

Common trap: Reaching for the emergency drug before asking the one question that bars it.

Source: Nitroglycerin sublingual tablets FDA labeling

Answer A: Azithromycin or clarithromycin 500 mg, or doxycycline 100 mg, before the extraction

Prophylaxis requires a highest-risk cardiac condition and a procedure that manipulates gingival tissue or the periapical region or perforates oral mucosa; her prosthetic valve and the extraction satisfy both, while the prosthetic knee is generally not an indication. With anaphylaxis to amoxicillin the permitted alternatives are azithromycin or clarithromycin 500 mg, or doxycycline 100 mg. B fails the operational rule that survives the unsettled cross-reactivity debate: no cephalosporin after anaphylaxis, angiedema or urticaria to penicillin or ampicillin. C offers the agent the 2021 statement removed, and credits the joint for an indication it does not create. D abandons an indicated regimen when non-beta-lactam options exist.

Common trap: Letting the joint, or a remembered clindamycin alternative, drive the prophylaxis decision.

Source: 2021 AHA Scientific Statement + current AHA wallet card