A 40-year-old man on methadone maintenance took several extra doses. He is brought in drowsy with a respiratory rate of 6/min. IV naloxone wakes him within 2 minutes and he asks to go home. Ninety minutes later he is again drowsy with a respiratory rate of 7/min. What explains this?

Naloxone acts for a shorter time than methadone

Naloxone has caused acute opioid withdrawal

Methadone has formed a more toxic metabolite

Naloxone is only a partial agonist at mu receptors

A 70-year-old man with prostate cancer, bone metastases and CKD stage 5 not on dialysis has taken regular oral morphine for pain. Over a week he has become drowsy, with myoclonic jerks, pinpoint pupils and a respiratory rate of 10/min. Liver tests are normal. What explains his toxicity?

Accumulation of active glucuronide metabolites

Higher free morphine from low serum albumin

Tolerance developing to its analgesic effect

Reduced hepatic glucuronidation of morphine

Opioids, general and local anaesthetics

11 NEET-PG practice questions on Opioids, general and local anaesthetics, part of Pharmacology. The first 11 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 60-kg man in casualty needs a long scalp laceration sutured. The casualty medical officer uses 2% lignocaine with adrenaline and takes its maximum safe dose as 7 mg/kg. What is the largest volume of this solution he may inject?
1. A21 mL
2. B13.5 mL
3. C2.1 mL
4. D42 mL
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Answer: A · 21 mL
The maximum dose is 7 mg/kg x 60 kg = 420 mg. A 2% solution contains 2 g per 100 mL, that is 20 mg/mL, so 420 mg is in 420 / 20 = 21 mL. Adrenaline slows absorption from the site, which allows a higher dose than plain lignocaine and prolongs the block. Larger wounds need a more dilute solution or a regional block to stay within the limit.
- B: 13.5 mL uses the plain lignocaine limit of 4.5 mg/kg, not the limit with adrenaline.
- C: 2.1 mL treats 2% as 200 mg/mL, a tenfold unit error.
- D: 42 mL treats 2% as 10 mg/mL, double-counting the volume.
Question 2 · Medium
A 40-year-old man on methadone maintenance took several extra doses. He is brought in drowsy with a respiratory rate of 6/min. IV naloxone wakes him within 2 minutes and he asks to go home. Ninety minutes later he is again drowsy with a respiratory rate of 7/min. What explains this?
1. ANaloxone has caused acute opioid withdrawal
2. BMethadone has formed a more toxic metabolite
3. CNaloxone acts for a shorter time than methadone
4. DNaloxone is only a partial agonist at mu receptors
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Answer: C · Naloxone acts for a shorter time than methadone
Naloxone's effect lasts about 30-90 minutes, but methadone has a long and variable half-life of a day or more. Once naloxone wears off, the methadone still in his body again depresses breathing (re-narcotisation). Patients who took long-acting opioids need prolonged observation, with repeated naloxone doses or an infusion titrated to breathing. He should not be allowed to leave just because he woke up.
- A: Withdrawal causes agitation and arousal, not recurrent sedation.
- B: Methadone's effect is from the parent drug, not a toxic metabolite.
- D: Naloxone is a pure antagonist, not a partial agonist.
Question 3 · Easy
An 8-year-old boy is having squint surgery under general anaesthesia induced with sevoflurane, with suxamethonium for intubation. Soon after, his jaw is rigid, end-tidal CO2 climbs from 35 to 75 mmHg despite increased ventilation, pulse is 160/min and temperature is rising quickly. Which drug is specific for this condition?
1. ADantrolene
2. BCyproheptadine
3. CNeostigmine
4. DBromocriptine
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Answer: A · Dantrolene
Masseter rigidity, a rapid rise in end-tidal CO2, tachycardia and rising temperature after a volatile agent and suxamethonium are malignant hyperthermia. In susceptible people, usually with an RYR1 mutation, these triggers cause uncontrolled calcium release from the sarcoplasmic reticulum and a hypermetabolic state. The volatile agent is stopped, the patient hyperventilated with 100% oxygen and dantrolene given IV; dantrolene blocks calcium release through the ryanodine receptor. Potassium, CK and myoglobinuria are monitored, and the family is referred for susceptibility testing.
- B: Cyproheptadine is used for serotonin syndrome.
- C: Neostigmine reverses non-depolarising block and does nothing for the hypermetabolic state.
- D: Bromocriptine is used for neuroleptic malignant syndrome, not malignant hyperthermia.
Question 4 · Medium
A 70-year-old man with prostate cancer, bone metastases and CKD stage 5 not on dialysis has taken regular oral morphine for pain. Over a week he has become drowsy, with myoclonic jerks, pinpoint pupils and a respiratory rate of 10/min. Liver tests are normal. What explains his toxicity?
1. AHigher free morphine from low serum albumin
2. BAccumulation of active glucuronide metabolites
3. CTolerance developing to its analgesic effect
4. DReduced hepatic glucuronidation of morphine
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Answer: B · Accumulation of active glucuronide metabolites
Morphine is conjugated in the liver to morphine-6-glucuronide, which is a more potent opioid, and morphine-3-glucuronide, which is neuroexcitatory. Both are excreted by the kidneys and build up in renal failure, causing sedation, respiratory depression and myoclonus. In severe CKD, fentanyl or buprenorphine, which have no active renally cleared metabolites, are preferred, or doses are reduced and spaced out. Naloxone in small titrated doses reverses dangerous respiratory depression without losing all analgesia.
- A: Morphine is only weakly protein-bound, so low albumin matters little.
- C: Tolerance would reduce, not increase, the opioid effects.
- D: Hepatic conjugation is preserved; his liver tests are normal.
Question 5 · Medium
A 24-year-old man needs an elective inguinal hernia repair. His elder brother died of high fever and rigidity during general anaesthesia, and his father had a positive caffeine-halothane contracture test. The anaesthetist plans: 1. Give oral dantrolene for 3 days before surgery as routine. 2. Avoid all volatile anaesthetics and suxamethonium. 3. Total intravenous anaesthesia with propofol, an opioid and a non-depolarising relaxant is suitable. 4. Keep dantrolene available in theatre. Which parts of the plan are correct?
1. A1 and 2 only
2. B1, 2, 3 and 4
3. C2, 3 and 4 only
4. D2 and 4 only
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Answer: C · 2, 3 and 4 only
Statements 2, 3 and 4 are correct for a patient presumed susceptible to malignant hyperthermia. Volatile agents and suxamethonium are the triggers, so the vaporisers are removed and the machine flushed or fitted with charcoal filters, and anaesthesia is given with non-triggering drugs such as propofol, opioids and non-depolarising relaxants (or a regional technique). Dantrolene must be immediately available in theatre. Routine oral dantrolene pretreatment is not recommended, because it does not reliably prevent a crisis and causes weakness.
- A: Includes routine dantrolene pretreatment and omits keeping dantrolene ready.
- B: Includes routine oral dantrolene pretreatment, which is not recommended.
- D: Omits propofol-based anaesthesia, the suitable non-triggering technique.
Question 6 · Hard
A 65-year-old woman with normal kidney and liver function has a hip fracture fixed under spinal anaesthesia with intrathecal bupivacaine and morphine. She is comfortable and alert in recovery. Ten hours later on the ward she is drowsy, with pinpoint pupils and a respiratory rate of 7/min; she has received no other opioid. Which property of morphine explains this delayed effect?
1. AHigh lipid solubility, so it enters the brain rapidly
2. BLow lipid solubility, so it spreads up in the CSF
3. CSlow absorption from the spinal fat into the blood
4. DBuild-up of its active metabolite morphine-6-glucuronide
Answer and explanation in LearnFree account
Question 7 · Medium
A 55-kg woman is having a supraclavicular brachial plexus block with 25 mL of 0.5% bupivacaine. Near the end of injection she reports ringing in the ears, a metallic taste and numbness around the mouth, then has a seizure followed by broad-complex ventricular tachycardia. The airway is secured, the seizure is controlled with midazolam and CPR is started. Which specific treatment should be given?
1. AIntravenous sodium bicarbonate
2. BIntravenous 20% lipid emulsion
3. CIntravenous lignocaine for the VT
4. DIntravenous dantrolene
Answer and explanation in LearnFree account
Question 8 · Medium
A 4-year-old girl has a cream containing lignocaine and prilocaine applied thickly under an occlusive dressing over a large area before laser treatment of a birthmark. Two hours later she looks grey-blue. SpO2 is 85% on 100% oxygen while arterial PO2 is 260 mmHg, and the blood is chocolate-brown. Which is the treatment?
1. ASodium nitrite
2. BHyperbaric oxygen
3. CIntravenous lipid emulsion
4. DMethylene blue
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Question 9 · Easy
A 45-year-old woman on the surgical ward has received several extra IV morphine doses for pain on the night after a laparotomy. At 2 am the nurse finds her hard to rouse, with a respiratory rate of 6/min, SpO2 84% and pinpoint pupils. Oxygen and airway support are started. Which drug should be given?
1. AAtropine
2. BNaloxone
3. CFlumazenil
4. DPhysostigmine
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Question 10 · Medium
A 28-year-old man dependent on heroin is admitted to a de-addiction centre in Punjab. He last used heroin 3 hours ago. Thirty minutes after his first sublingual dose of buprenorphine he develops yawning, watering eyes, runny nose, gooseflesh, abdominal cramps and dilated pupils. What explains this?
1. AThe naloxone in the tablet was absorbed
2. BBuprenorphine is a pure mu receptor antagonist
3. CThe sublingual dose was too low to act
4. DBuprenorphine displaces heroin as a partial agonist
Answer and explanation in LearnFree account
Question 11 · Medium
A 30-year-old man is brought to casualty after a road traffic accident with a ruptured spleen. BP is 80/50 mmHg and pulse 130/min despite rapid fluid infusion. He needs rapid sequence induction for an emergency laparotomy. Which induction agent best preserves his blood pressure?
1. AKetamine
2. BPropofol
3. CMidazolam
4. DThiopentone sodium
Answer and explanation in LearnFree account

Opioids, general and local anaesthetics

A 60-kg man in casualty needs a long scalp laceration sutured. The casualty medical officer uses 2% lignocaine with adrenaline and takes its maximum safe dose as 7 mg/kg. What is the largest volume of this solution he may inject?

A 40-year-old man on methadone maintenance took several extra doses. He is brought in drowsy with a respiratory rate of 6/min. IV naloxone wakes him within 2 minutes and he asks to go home. Ninety minutes later he is again drowsy with a respiratory rate of 7/min. What explains this?

A 70-year-old man with prostate cancer, bone metastases and CKD stage 5 not on dialysis has taken regular oral morphine for pain. Over a week he has become drowsy, with myoclonic jerks, pinpoint pupils and a respiratory rate of 10/min. Liver tests are normal. What explains his toxicity?

A 28-year-old man dependent on heroin is admitted to a de-addiction centre in Punjab. He last used heroin 3 hours ago. Thirty minutes after his first sublingual dose of buprenorphine he develops yawning, watering eyes, runny nose, gooseflesh, abdominal cramps and dilated pupils. What explains this?

A 30-year-old man is brought to casualty after a road traffic accident with a ruptured spleen. BP is 80/50 mmHg and pulse 130/min despite rapid fluid infusion. He needs rapid sequence induction for an emergency laparotomy. Which induction agent best preserves his blood pressure?