MJDF Pharmacology and Therapeutics 2

Question 1

What is the pharmacological basis for combining paracetamol and ibuprofen for post-operative dental pain?

Accepted Answer

They have different mechanisms of action (paracetamol: central COX inhibition and possible serotoninergic pathways; ibuprofen: peripheral COX-1 and COX-2 inhibition) providing additive or synergistic analgesia with fewer side effects than increasing the dose of either drug alone

Answer

Paracetamol and ibuprofen act through different mechanisms: paracetamol primarily acts centrally (inhibiting COX in the CNS, possibly involving the endocannabinoid system and serotoninergic pathways), while ibuprofen acts peripherally (inhibiting COX-1 and COX-2 at the site of tissue damage, reducing prostaglandin-mediated inflammation and pain). Combining them provides additive analgesia — studies show paracetamol 1000 mg + ibuprofen 400 mg is more effective than either alone and comparable to some weak opioid combinations, without the opioid side effects. They can be taken simultaneously or alternated, within recommended dose limits for each.

Question 2

A patient taking the oral contraceptive pill is prescribed a course of antibiotics for a dental infection. What is the current guidance regarding potential interaction?

Accepted Answer

Current UK guidance (FSRH and BNF) states that non-enzyme-inducing antibiotics (amoxicillin, metronidazole, clarithromycin) do NOT reduce the efficacy of combined hormonal contraception; additional contraception is NOT required. Only enzyme-inducing drugs (rifampicin, rifabutin) significantly reduce contraceptive efficacy

Answer

Previous advice to use additional contraception with broad-spectrum antibiotics has been superseded. The Faculty of Sexual and Reproductive Healthcare (FSRH) and the BNF now state that non-enzyme-inducing antibiotics (including amoxicillin, metronidazole, erythromycin, clarithromycin, tetracyclines) do NOT reduce the efficacy of combined hormonal contraceptives. The earlier concern about disruption of enterohepatic recirculation of ethinylestradiol has not been supported by pharmacokinetic studies. Only enzyme-inducing drugs (rifampicin, rifabutin, some anticonvulsants, some antiretrovirals) significantly affect contraceptive efficacy. Additional contraception is only needed with these specific drugs.

Question 3

What are the signs and symptoms of local anaesthetic toxicity and how should it be managed in the dental surgery?

Accepted Answer

Early signs include perioral tingling, metallic taste, tinnitus, light-headedness, and visual disturbance, progressing to tremors, seizures, respiratory depression, and cardiovascular collapse; management includes stopping injection, positioning supine, maintaining airway, administering oxygen, treating seizures with IV midazolam, and calling 999 — IV lipid emulsion (Intralipid 20%) is the specific antidote for severe cardiovascular toxicity

Answer

LA toxicity occurs from excessive plasma levels (overdose, inadvertent IV injection, or impaired metabolism). The progression follows CNS then CVS depression: CNS — perioral tingling, metallic taste, tinnitus, visual disturbance, light-headedness → slurred speech, drowsiness → muscle twitching → generalised seizures → unconsciousness. CVS — hypotension → bradycardia → arrhythmias → cardiac arrest. Management: stop administration, call for help, maintain airway (head tilt-chin lift), high-flow oxygen, treat seizures (midazolam 0.1-0.2 mg/kg IV or buccal), IV fluids, call 999. For cardiac arrest refractory to standard ALS: IV lipid emulsion (Intralipid 20%) 1.5 mL/kg bolus followed by infusion — this acts as a 'lipid sink' extracting lipophilic LA from cardiac tissue.

Question 4

What is the mechanism of action of metronidazole and why is alcohol consumption contraindicated during its use?

Accepted Answer

Metronidazole enters anaerobic bacteria where it is reduced to form cytotoxic intermediates that damage bacterial DNA; alcohol is contraindicated because metronidazole inhibits aldehyde dehydrogenase, causing accumulation of acetaldehyde leading to a disulfiram-like reaction (nausea, vomiting, flushing, headache, tachycardia)

Answer

Metronidazole is a nitroimidazole antibiotic that is selectively toxic to anaerobic organisms. Inside anaerobic bacteria, the nitro group is reduced by ferredoxin (electron transport protein) to form cytotoxic intermediates (nitroso free radicals) that damage DNA strands, causing cell death. It is bactericidal against obligate anaerobes but has no activity against aerobes. The alcohol interaction occurs because metronidazole inhibits aldehyde dehydrogenase, the enzyme that metabolises acetaldehyde (a toxic metabolite of alcohol). Accumulation of acetaldehyde causes a disulfiram-like reaction with nausea, vomiting, flushing, abdominal cramps, and headache. Patients should avoid alcohol during treatment and for 48 hours after completion.

Question 5

What are the key considerations when prescribing analgesics for a pregnant patient experiencing dental pain?

Accepted Answer

Paracetamol is the first-line analgesic throughout pregnancy; NSAIDs (ibuprofen) should be avoided after 28 weeks (risk of premature closure of the ductus arteriosus) and used with caution before this; codeine should be used at the lowest effective dose for the shortest duration; aspirin is contraindicated in the third trimester

Answer

Prescribing in pregnancy follows the principle of minimum effective dose for the shortest time. Paracetamol (all trimesters) is first-line — extensive safety data, no teratogenic effects at therapeutic doses. Ibuprofen: relatively safe in the first and second trimesters but CONTRAINDICATED after 28 weeks as it may cause premature closure of the fetal ductus arteriosus, reduced fetal renal function, and oligohydramnios. Codeine: use cautiously — maternal use near delivery can cause neonatal respiratory depression and withdrawal; ultrarapid CYP2D6 metabolisers convert codeine to morphine rapidly. Aspirin: avoid in third trimester (bleeding risk, ductus arteriosus closure). Always consider whether treatment can be deferred until after delivery.

MJDF Part 1 Practice Test

MJDF Part 1 Practice Test

MJDF Pharmacology and Therapeutics 2