One potential consideration with the use of pethidine is its metabolite norpethidine. Norpethidine is an excitatory neurotoxin that has been shown to cause seizures in animals. It is renally excreted, and hence may accumulate in patients with renal failure. There are case reports of patients experiencing seizures during the use of PCA pethidine.19 20 21 In each of these cases the patients had received high doses, long-term therapy, or both. The average reported dose administered in the 24 hours prior to the seizure was 1900 mg. By contrast, the mean 24-hour dose in the Woodhouse study18 was 410 mg, and none of the 135 patients in those studies18 17 exhibited any excitatory side effects.