The fatal dose of co-proxamol may be as little as 10-20 tablets for an adult, especially when CNS depressants such as alcohol, sedatives and tranquillisers have also been taken.
Early features are due to the dextropropoxyphene (opioid) content and include coma, severe respiratory depression, convulsions, and cardiac arrest. These may occur within 30 minutes of ingestion, particularly if alcohol has also been ingested.
Cardiac arrhythmias including ventricular tachycardia may occur up to 12 hours after ingestion, particularly if features of CNS depression are also present.
In less severe cases, pallor, nausea and vomiting may persist for about 24 hours.
Psychotic reactions may occur.
Later features are due to the paracetamol content. After 1-3 days features of hepatic necrosis may appear with persistent nausea and vomiting, right subcostal pain and tenderness followed by jaundice. Loin pain, haematuria and proteinuria after the first 24 hours strongly suggest the development of renal tubular necrosis and the risk of acute renal failure.
Abnormalities of glucose metabolism and metabolic acidosis may occur. In severe poisoning, hepatic failure may progress to encephalopathy, coma and death. Pancreatitis has been reported.
This should include general symptomatic and supportive measures. Naloxone will reduce the respiratory depression and should be given intravenously if coma or respiratory depression is present. Consider activated charcoal if the patient presents within one hour of ingestion of a potentially toxic amount. Consider gastric lavage in adults within one hour of a potentially life-threatening overdose.
The ECG should be monitored and hypoxia, electrolyte abnormalities and acid base disturbance should be corrected.
The need for N-acetylcysteine as treatment for paracetamol intoxication should be determined by measuring the plasma paracetamol concentration at least four hours after ingestion. N-acetylcysteine should be started immediately if it is thought that more than 150 mg/kg body weight or 12 g in an adult (whichever is the smaller) has been ingested more than eight hours earlier. If risk of liver damage is confirmed by measurement of plasma paracetamol concentration, continue administration of the antidote.
Liver and renal failure should be managed conventionally.