Pharmacokinetic-pharmacodynamic modeling of atracurium in intensive care patients

Pharmacodynamic models: parameterizing the hill equation, Michaelis-Menten, the logistic curve, and relationships among these models

The Hill equation is often used in dose-response or exposure-response modeling. Aliases for the Hill model include the Emax model, and the Michaelis-Menten model. There is confusion about the appropriate parameterization, how to interpret the parameters, what the meaning is of the various parameterizations found in the literature, and which parameterization best approximates the statistical inferences produced when fitting the Hill equation to data. In this paper, we present several equivalent versions of the Hill model; show that they are equivalent in terms of yielding the same prediction for a given dose, and are equivalent to the four-parameter logistic model in this same sense; and deduce which parameterization is optimal in the sense of having the least statistical curvature and preferable multicollinearity.

Clinical manifestations and neurodevelopmental outcome following an event of accidental intramuscular injection of atracurium in newborns

Pediatric populations are at risk for medication errors that may be associated with mortality and disability. The purpose of this study was to describe the clinical manifestations of seven newborns following an event of accidental intramuscular injection of atracurium and to assess the impact on neurodevelopmental outcome. This study enrolled seven newborns who were accidentally administered 10 mg of atracurium, equivalent to 2.6-3.3 mg/kg, in a local perinatal clinic. Accident reports and hospital records were reviewed to obtain the history and medical data for the event. The survivors were prospectively examined for their growth, health and neurodevelopment until 24 months of age. All newborns showed immediate apnea and cyanosis requiring resuscitation after atracurium injection and presented with respiratory failure and flaccid paralysis on arrival for emergency medical services. One newborn was asystolic despite resuscitation and died of multiple organ failure. Of the five survivors available for follow-up, all achieved favorable growth outcomes. However, four showed mild to significant delay in development; and two manifested mild hypomyelination of cerebral white matter on the brain magnetic resonance imaging.

CONCLUSION

Newborns accidentally injected with high doses of atracurium are at risk of death and neurodevelopmental delay. The serious clinical manifestations, developmental delay and cerebral hypomyelination were most likely due to insufficient immediate respiratory assistance following atracurium injection.

Neuromuscular blocking properties of atracurium during sevoflurane or propofol anaesthesia in dogs

OBJECTIVE

To quantify the neuromuscular blockade (NMB) produced by atracurium in either sevoflurane or propofol-anaesthetized dogs.

ANIMALS

Twelve healthy, female adult mixed-breed dogs weighing 13 +/- 3 kg (range 10-22 kg).

MATERIALS AND METHODS

Three doses of atracurium (0.1, 0.2 and 0.3 mg kg(-1)) were tested at 1-week intervals. Anaesthesia was induced with inhaled sevoflurane or intravenous propofol and maintained with end-tidal sevoflurane concentrations of 1.95% (1.25 x MAC) or propofol 0.6 mg kg(-1) minute(-1) respectively. Acceleromyography and train-of-four stimulation of the fibular nerve were used for the assessment of NMB. The percentage depression of the first twitch (T1) and the fourth to the first twitch ratio (T4/T1), the maximum degree of neuromuscular block achieved and surgical muscle relaxation were recorded. Before and during neuro muscular blockade (at 10 minute intervals) body temperature, ECG, arterial blood pressure, inspired and expired CO2 concentrations and SpO2 were recorded.

RESULTS

Atracurium produced a dose-dependent duration of NMB in both propofol and sevoflurane-anaesthetized dogs. Duration of block was longer in dogs anaesthetized with sevoflurane. All studied doses of atracurium caused twitch depression > or =95% with little or no cardiovascular changes.

CONCLUSIONS

Sevoflurane produces a clinically relevant potentiation of atracurium-induced NMB in dogs compared with propofol.

CLINICAL RELEVANCE

Significant differences in the potentiation of NMB drugs are encountered with commonly used anaesthetics in the dog.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.