CPCS Specialist Guideline
BARBITURATES
I. Mechanism of Toxicity
· Central acting CNS depressants. May cause respiratory depression or myocardial depression.
· Concomitant use of benzodiazepines, ethanol, inhaled anesthetics or other sedatives may potentiate toxicity.
II. Toxic Dose
· Toxic dose is variable. Chronic use can lead to tolerance.
· Potentially lethal dose phenobarbital 6-10 g.
· Potentially lethal dose of amobarbital, secobarbital and pentobarbital 2-3 g.
|
Drug |
Normal Elimination Half-Life (Hr) |
Usual Duration of Effect (Hr) |
Usual Hypnotic Dose (Adult) |
Minimum Toxic Level (mg/L) |
Ultra Short Acting |
|
|
|
|
|
Methohexital |
1-2 |
<0.5 |
50-120mg |
>5 |
|
Thiopental |
6-46 |
<0.5 |
50-75mg |
>5 |
Short Acting |
|
|
|
|
|
Pentobarbital |
15-48 |
>3-4 |
100-200mg |
>10 |
|
Secobarbital |
15-40 |
>3-4 |
100-200mg |
>10 |
Intermediate Acting |
|
|
|
|
|
Amobarbital |
8-42 |
>4-6 |
65-200mg |
>10 |
|
Aprobarbital |
14-34 |
>4-6 |
40-160mg |
>10 |
|
Butabarital |
34-42 |
>4-6 |
50-100mg |
>10 |
Long-acting |
|
|
|
|
|
Mephobarbital |
11-67 |
>6-12 |
50-100mg |
>30 |
|
Phenobarbital |
80-120 |
>6-12 |
100-320mg |
>30 |
|
Primidone |
10-12 metabolized to phenobarbital |
>6-12 |
50-250mg |
>10; check phenobarbital level |
III. Clinical Presentation
IV. Diagnosis
|
|
Therapeutic level |
Toxic level |
Potentially lethal level |
Ultra Short Acting |
|
|
|
|
Methohexital |
|
|
|
|
Thiopental |
1-5mcg/ml |
coma 30-100mcg/ml |
|
Short Acting |
|
|
|
|
Pentobarbital |
1-5mcg/ml |
coma 10-50mcg/ml |
|
|
Secobarbital |
1-2mcg/ml |
>5 |
|
Intermediate Acting |
|
|
|
|
Amobarbital |
1-5mcg/ml |
>10mcg/ml |
>50mcg/ml |
|
Aprobarbital |
|
|
|
|
Butabarbital |
|
28-73mcg/ml |
|
Long-acting |
|
|
|
|
Mephobarbital |
15-40mcg/ml |
|
|
|
Phenobarbital |
15-40mcg/ml |
nystagmus &ataxia 35-80mcg/ml |
coma w/ reflex 65-117mcg/ml coma w/o reflexes>100mcg/ml |
|
Primidone |
5-12mcg/ml |
>15mcg/ml |
|
Recommended laboratory tests:
· Serum phenobarbital levels.
· In significantly symptomatic patients, consider ABG, chemistries and renal function tests.
V. Treatment:
Decontamination
· Activated charcoal.
· Multiple dose activated charcoal (MDAC) has been shown to increase clearance of phenobarbital, but has not at this time been shown to improve outcome.
·
· Phenobarbital can be removed by hemodialysis or hemoperfusion in severe cases.
· Although urinary alkalinization may increase phenobarbital elimination, this therapy has not been shown to improve outcome.
Consider referral to HCF if:
· Patient is symptomatic.
· Self-harm gesture.
Mode of transport:
Private auto:
· Patient is mildly symptomatic. A second adult is recommended to accompany the driver if transported by private auto to assist victim if needed.
Consider paramedic transport:
· Patient has significant altered mentation.
· Prolonged (greater than 1 hour) transport time.
· Self-harm gesture.
When to Consider Backup Consultation
· Patients who may need hemodialysis or hemoperfusion.
· Patients with refractory hypotension.
VI. Follow-up calls
Home-managed cases:
· Follow up in 1-2 hours to identify any symptoms if indicated.
· Follow up in 4-6 hours post exposure at SPI discretion.
HCF managed cases:
·
· Once every 8 hours while symptomatic in the ED or ICU.
· Once daily until medically cleared.
· Minimal recommended information to obtain at follow up:
1. Brief clinical status: e.g., awake, oriented, vital signs.
2. Phenobarbital or other levels as appropriate and obtainable.
3. Other labs if available.
Approved: December 1998
Revised: August 2005