Adult clonidine overdose: prolonged bradycardia and central nervous system depression, but not severe toxicity

There are limited reports of adult clonidine overdose. We aimed to describe the clinical effects and treatment of clonidine overdose in adults.

This was a retrospective review of a prospective cohort of poisoned patients who took clonidine overdoses (>200 μg). Demographic information, clinical effects, treatment, complications (central nervous system and cardiovascular effects) and length of stay (LOS) were extracted from a clinical database or medical records.

From 133 admissions for clonidine poisoning (1988-2015), no medical record was available in 14 and 11 took staggered ingestions. Of 108 acute clonidine overdoses (median age 27 years; 14-65 years; 68 females), 40 were clonidine alone ingestions and 68 were clonidine with co-ingestants. Median dose taken was 2100 μg (interquartile range [IQR]: 400-15,000 μg). Median LOS was 21h (IQR: 14-35 h) and there were no deaths. Glasgow coma score [GCS] <15 occurred in 73/108 (68%), and more patients taking co-ingestants (8/68; 12%) had coma (GCS <9) compared to clonidine alone (2/40; 5%). Miosis occurred in 31/108 (29%) cases. Median minimum HR was 48 bpm (IQR: 40-57 bpm), similar between clonidine alone and co-ingestant overdoses. There was a significant association between dose and minimum HR for clonidine alone overdoses (p = 0.02). 82/108 (76%) had bradycardia, median onset 2.5 h post-ingestion (IQR: 1.7-5.5 h) and median duration 20 h (2.5-83 h), similar for clonidine alone and co-ingestant overdoses. There were no arrhythmias. Three patients ingesting 8000-12,000 μg developed early hypertension. Median minimum systolic BP was 96 mmHg (IQR: 90-105 mmHg) and hypotension occurred in 26/108 (24%). 12/108 patients were intubated, but only 2 were clonidine alone cases. Treatments included activated charcoal (24), atropine (8) and naloxone (23). The median total naloxone dose was 2 mg (IQR: 1.2-2.4 mg), but only one patient given naloxone was documented to respond with partial improvement in GCS.

Clonidine causes persistent but not life-threatening clinical effects. Most patients develop mild central nervous system depression and bradycardia. Naloxone was not associated with improved outcomes.