Intrathecal morphine overdose in a dog.
METHODS
A healthy 6-year-old 28.5-kg (62.7-lb) spayed female Boxer undergoing surgical repair of a ruptured cranial cruciate ligament was inadvertently administered an overdose of morphine (1.3 mg/kg [0.59 mg/lb]) via subarachnoid injection.


RESULTS
50 minutes after administration of the overdose, mild multifocal myoclonic contractions became apparent at the level of the tail; the contractions migrated cranially and progressively increased in intensity and frequency during completion of the surgery.


RESULTS
The myoclonic contractions were refractory to treatment with midazolam, naloxone, phenobarbital, and pentobarbital; only atracurium (0.1 mg/kg [0.045 mg/lb], IV) was effective in controlling the movements. The dog developed hypertension, dysphoria, hyperthermia, and hypercapnia. The dog remained anesthetized and ventilated mechanically; treatments included continuous rate IV infusions of propofol (1 mg/kg/h [0.45 mg/lb/h]), diazepam (0.25 mg/kg/h [0.11 mg/lb/h]), atracurium (0.1 to 0.3 mg/kg/h [0.045 to 0.14 mg/lb/h]), and naloxone (0.02 mg/kg/h [0.009 mg/lb/h]). Twenty-two hours after the overdose, the myoclonus was no longer present, and the dog was able to ventilate without mechanical assistance. The dog remained sedated until 60 hours after the overdose, at which time its mentation improved, including recognition of caregivers and response to voice commands. No neurologic abnormalities were detectable at discharge (approx 68 hours after the overdose) or at a recheck evaluation 1 week later.


CONCLUSIONS
Although intrathecal administration of an overdose of morphine can be associated with major and potentially fatal complications, it is possible that affected dogs can completely recover with immediate treatment and extensive supportive care.
da Cunha
Anderson F
AF
Department of Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Carter
Jennifer E
JE
Grafinger
Michael
M
Montgomery
Heather
H
Marks
Steven L
SL
Posner
Lysa P
LP
Burns
Patrick
P
D000818:Animals; D001279:Atracurium / Q000627:therapeutic use; D003975:Diazepam / Q000627:therapeutic use; D004283:Dog Diseases / Q000139:chemically induced* / Q000188:drug therapy; D004285:Dogs; D062787:Drug Overdose / Q000662:veterinary*; D004831:Epilepsies, Myoclonic / Q000139:chemically induced / Q000188:drug therapy / Q000662:veterinary*; D005260:Female; D007262:Infusions, Intravenous / Q000662:veterinary; D009020:Morphine / Q000008:administration & dosage / Q000009:adverse effects*; D009270:Naloxone / Q000627:therapeutic use; D015742:Propofol / Q000627:therapeutic use; D016896:Treatment Outcome
D001279:Atracurium; D009270:Naloxone; D009020:Morphine; D003975:Diazepam; D015742:Propofol