Thiopentone produces unconsciousness at a lower total body dose in elderly patients due to pharmacokinetic changes. The primary reason for this altered dose requirement is:
- A Reduced plasma protein binding increasing free drug fraction
- B Increased hepatic CYP450 activity accelerating brain equilibration
- C Decreased initial volume of distribution increasing peak brain concentration ✓
- D Increased renal elimination reducing redistribution clearance
Explanation
Thiopentone's rapid offset after bolus dosing depends on redistribution from brain to muscle and fat. In the elderly, decreased cardiac output and reduced lean body mass means a smaller initial volume of distribution, so a given dose achieves a higher peak brain concentration. Additionally, slower circulatory transit time prolongs brain exposure. Hepatic metabolism of thiopentone is a minor determinant of effect duration (redistribution matters most); hepatic CYP450 is not increased in the elderly. Protein binding decreases slightly but this is less important than the redistribution pharmacokinetics.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.