Synthetic Opioids MCQs

Although fentanyl is now the predominant analgesic in the phenylpiperidine class, meperidine continues to be used. This older opioid has significant antimuscarinic effects, which may be a contraindication if tachycardia would be a problem. Meperidine is also reported to have a negative inotropic action on the heart. In addition, it has the potential for producing seizures secondary to accumulation of its metabolite, normeperidine, in patients receiving high doses or with concurrent renal failure. Given this undesirable profile, use of meperidine as a first-line analgesic is becoming increasingly rare. Reference: LANG’ Basic & clinical pharmacology by Bertram G. Katzung, Susen B. Masters and Anthony J. Trevor 12 th edition. Chapter 31- Opioid Analgesics & Antagonists by Dr. Mark A. Schumacher,PhD,MD, Dr. Alan I. Basbaum,PhD,& Dr. Walter L. Way,MD. Page no. 557

These opioids differ mainly in their potency and biodisposition. Sufentanil is five to seven times more potent than fentanyl. Alfentanil is considerably less potent than fentanyl, but acts more rapidly and has a markedly shorter duration of action. Remifentanil is metabolized very rapidly by blood and nonspecific tissue esterases, making its pharmacokinetic and pharmacodynamic half-lives extremely short. Such properties are useful when these compounds are used in anesthesia practice. Reference: LANG’ Basic & clinical pharmacology by Bertram G. Katzung, Susen B. Masters and Anthony J. Trevor 12 th edition. Chapter 31- Opioid Analgesics & Antagonists by Dr. Mark A. Schumacher,PhD,MD, Dr. Alan I. Basbaum,PhD,& Dr. Walter L. Way,MD. Page no. 557

Propoxyphene is chemically related to methadone but has extremely low analgesic activity. Its low efficacy makes it unsuitable, even in combination with aspirin, for severe pain. The increasing incidence of deaths associated with its use and misuse caused it to be withdrawn in the United States. Reference: LANG’ Basic & clinical pharmacology by Bertram G. Katzung, Susen B. Masters and Anthony J. Trevor 12 th edition. Chapter 31- Opioid Analgesics & Antagonists by Dr. Mark A. Schumacher,PhD,MD, Dr. Alan I. Basbaum,PhD,& Dr. Walter L. Way,MD. Page no. 558

Explanation: Active Metabolite Matching: Morphine: Active metabolite is Morphine 6 glucuronide. Diamorphine: Active metabolites are 6 monoacetylmorphine and morphine. Pethidine: Active metabolite is Norpethidine. Codeine: Active metabolites are Norcodeine and Morphine. Tramadol: Active metabolite is O desmethyltramadol known as the M1 metabolite. Paracetamol: Incorrectly matched with Poro paracetamol because its primary active metabolite is N acetyl p benzoquinone imine also known as NAPQI. (Option B) Key Takeaways: Paracetamol is incorrectly paired with Poro paracetamol since its true active metabolite is NAPQI. Correct knowledge of opioid metabolites is essential for safe analgesic use and monitoring toxicity.

Fentanyl is administered clinically in a wide range of doses Low doses of fentanyl -> 1 to 2 mg/kg IV , are injected to provide -> analgesia Fentanyl -> 2 to 20 mg/kg IV , may be administered as -> an adjuvant to inhaled anaesthetics to blunt circulatory responses to: (a) direct laryngoscopy for intubation of the trachea (b) sudden changes in the level of surgical stimulation Large doses of fentanyl -> 50 to 150 mg/kg IV , have been used alone -> to produce surgical anaesthesia Analgesia produced by neuraxial opioids, in contrast to regional anaesthesia with local anaesthetics, is not associated with sympathectomy, sensory block, or motor weakness Reference : Stoelting's pharmacology and physiology in anaesthetic practice 5th edition

Except for remifentanil , all opioids depend primarily on the liver for biotransformation and are metabolized by the cytochrome P (CYP) system , conjugated in the liver, or both The ester structure of remifentanil makes it susceptible to hydrolysis (in a manner like esmolol) by nonspecific esterase in red blood cells and tissues Reference : Stoelting's pharmacology and physiology in anaesthetic practice 5th edition