Reactions 718 - 12 Sep 1998

SChlorzoxazone overdose

Coma: case reportComa occurred in a 57-year-old man on 2 separate

occasions after he took overdoses of chlorzoxazone [‘ParafonForte’].

The man’s medications included disulfiram, oxazepam,phenobarbital and chlorzoxazone. On the first occasion, hewas found in a somnolent state with slurred speech. On arrivalat an emergency department, he became comatose for 12hours and required intubation and mechanical ventilation. Hewas extubated after 24 hours and recovered uneventfully. Onadmission, his phenobarbital concentration was sub-therapeutic and his nordiazepam concentration was low. Hereported taking 7 chlorzoxazone tablets (3.5g) over a 2-hourperiod for back spasms.

On the second occasion, the man was found in a somnolent,confused state and, when paramedics arrived, he wascomatose. Treatment with naloxone was unsuccessful.Following treatment with IV flumazenil, he awoke in aconfused state, and then became comatose again. Following asecond dose of the agent, he awoke, and was conversant. Hereported taking a ‘handful’ of chlorzoxazone pillsapproximately 4 hours before admission; his chlorzoxazoneconcentration was 39 µg/ml.

Author comment: Despite the possibility of synergisticdepressant effects from the other drugs involved, thesubtherapeutic phenobarbital and low-therapeuticbenzodiazepine concentrations at the first admission suggestthat chlorzoxazone was the major depressive agent.Chlorzoxazone should not be given with concomitantdisulfiram because inhibition of the specific metabolic catalystfor chlorzoxazone can lead to increased serum levels andtoxicity. ‘Flumazenil may be a useful antidote for CZX[chlorzoxazone] toxicity, but further experience will berequired to more clearly delineate its ultimate role.’Roberge RJ, et al. Two chlorzoxazone (Parafon Forte) overdoses and coma in onepatient: reveral with flumazenil. American Journal of Emergency Medicine 16:393-395, Jul 1998 - USA 800693457

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Reactions 12 Sep 1998 No. 7180114-9954/10/0718-0001/$14.95 Adis © 2010 Springer International Publishing AG. All rights reserved