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Table 33-1

DrugBolus AdministrationMultiple Boluses or InfusionComments
Propofol20–60% reduction
Dose on lean body mass (1 mg/kg in very old patients)
50% reduction
Infusions beyond 50 min progressively increase the time required to decrease the blood level by 50% (but effect site levels may decrease faster in elderly patients)
Possible increased brain sensitivity
Decreased Vcen
Slowed redistribution
Thiopental20% reduction20% reductionDecreased Vcen
Etomidate25–50% reductionSlowed redistribution
MidazolamCompared to age 20, modest reduction at age 60, 75% reduction at age 90 yearsSimilar to bolusIncreased brain sensitivity
MorphineProbably 50% reduction
Peak morphine effect is 90 min (half of peak effect at 5 min)
Long effect site equilibration time translates into a very slow reduction in the effect on termination of the infusion (4 h for 50% reduction)Metabolite morphine-6 glucuronide buildup requires prolonged morphine use, but its renal excretion makes it very long lasting
Fentanyl50% reduction50% reductionIncreased brain sensitivity
Minimal change in pharmacokinetics
Delayed absorption from fentanyl patch
Alfentanil50% reduction50% reductionProbably increased brain sensitivity
Sufentanil50% reduction50% reductionMinimal changes in pharmacokinetics
Remifentanil50% reduction50% reductionSlower blood–brain equilibration, suggesting slower onset and offset
Modest decreased Vcen
MeperidineUsed only for postoperative shiveringDo not useToxic metabolite normeperidine whose renal excretion decreases with age
VecuroniumSlower onsetSlower recoverySlightly greater liver metabolism than renal metabolism
Older age
nearly doubles metabolic half-time
CisatracuriumSlower onsetNo significant changes with ageMostly Hoffmann elimination
Modest prolongation of metabolic half-time
RocuroniumMinimally slower onsetLiver metabolism slightly greater than renal metabolism
Modest increase in metabolic half-time
SuccinylcholineSlower onsetDecreased Vcen
EdrophoniumSimilar dosing and onsetPrimarily renal elimination
Modest increase in metabolic half-time
NeostigmineDespite pharmacokinetic changes, some studies indicate the need for an increased dose with ageDecreased Vcen
Hepatic elimination
Modest increase in metabolic half-time

Vcen = central volume of distribution or initial volume of distribution; a smaller Vcen increases initial plasma levels and enhances transfer of drug in the target organ (brain, muscle).