Lack of respiratory depression in paracetamol-codeine combination overdoses

Codeine containing analgesics are commonly taken in overdose, but the frequency of respiratory depression is unknown. We investigated whether paracetamol-codeine combination overdoses caused respiratory depression more than paracetamol alone.

We reviewed deliberate self-poisoning admissions with paracetamol (>2 g) and paracetamol-codeine combinations presenting to a tertiary toxicology unit (1987-2013). Demographic information, clinical effects, treatment (naloxone, length of stay [LOS], mechanical ventilation) were extracted from a prospective database. Primary outcome was naloxone requirement or ventilation for respiratory depression.

From 4488 presentations, 1376 admissions were included with paracetamol alone (929), paracetamol-codeine combinations (346) or paracetamol-codeine-doxylamine combinations (101) without co-ingestants. Median age was 23 years (12-89 years); 1002 (73%) were female. Median dose was 12 g (interquartile range [IQR]: 7.5-20 g). Median LOS was 16 h (IQR: 6.5-27 h) and 564 (41%) were given acetylcysteine. Significantly larger paracetamol doses were ingested and more acetylcysteine given in paracetamol alone versus paracetamol combination overdoses. Seven out of 1376 patients were intubated or received naloxone (0.5%; 95% CI: 0.2-1.1%), three intubated, three given naloxone and one both. Three out of 929 patients ingesting paracetamol alone (0.3%; 95% CI: 0.1-1%) required intubation or naloxone, compared to two out of 346 ingesting paracetamol-codeine combinations (0.6%; 95% CI: 0.1-2.3%; absolute difference, 0.26%; 95% CI: -0.7-1.2%; P = 0.62). Two out of 101 patients ingesting paracetamol-codeine-doxylamine combinations (2%; 95% CI: 0.3-8%) required intubation or naloxone. Four patients were intubated for reasons other than respiratory depression: hepatotoxicity (2), retrieval (1), no data (1). Two out of 929 (0.2%) paracetamol alone overdoses had a Glasgow coma score < 9 compared to three out of 346 (0.9%) in the paracetamol-codeine group.

Paracetamol-codeine combination overdoses are rarely associated with severe respiratory depression, with only two given naloxone and none intubated for respiratory depression.