Sivilotti et al developed a nomogram for evaluating a patient treated with N-acetylcysteine following an acetaminophen overdose. This can help identify a patient at significant risk for hepatotoxicity. The authors are from Queen's University in Kingston, Regional Poison Information Centre Toronto, University of Calgary, University of Toronto and Banner Good Samaritan Medical Center in Phoenix.
Assumptions:
(1) The patient is not an alcoholic.
(2) The patient did not co-ingest alcohol.
Endpoint: probability of developing a peak aminotransferase >= 1,000 IU/L
The nomogram of Rumack-Matthew can be approximated by (see above):
serum or plasma acetaminophen concentration for serious toxicity, µg/mL =
= 10^ ((-0.075 * (hours since ingestion)) + 2.6)
The probability curves in the new nomogram are:
|
Curve |
Probability |
|---|---|
|
A |
1% |
|
B |
2% |
|
C |
5% |
|
D |
10% |
|
E |
20% |
|
F |
50% |
Procedure:
(1) Measure the initial serum level of acetaminophen in µg/mL on admission and determine the time since ingestion in hours. There is no need to measure further acetaminophen levels.
(2) Determine the LOG10 for the initial serum acetaminophen level.
(3) Determine the time that N-acetylcysteine was administered in hours after ingestion.
If N-acetylcysteine therapy is started within 6 hours of ingestion then the risk of serious hepatotoxicity is < 1%.
A calculated value is determined by drawing a line from the initial level with the same slope (parallel to) the line from the Rumack-Matthew nomogram (slope is -0.075).
Since the slope of this line = -0.075 =
= (LOG10(calculated value) - LOG10(initial acetaminophen value)) / ((hours after ingestion to N-acetylcysteine) - (hours after ingestion that acetaminophen measured))
LOG10(calculated value)=
= ((slope) * ((hours after ingestion to N-acetylcysteine) - (hours after ingestion acetaminophen measured))) + LOG10(initial value) =
= ((-0.075) * ((hours after ingestion to N-acetylcysteine) - (hours after ingestion acetaminophen measured))) + LOG10(initial value)
calculated value when N-acetylcysteine given in µg/mL =
= 10^(equation above)
The probability of serious liver injury depends on where this point is relative to the 6 probability curves.
value for each probability curve =
= 10^(equation below for time interval)
|
Curve |
Hours |
Equation |
|---|---|---|
|
NA |
< 6.1 |
< 1% |
|
A |
6.1 - 7 |
(1.428 * ((hours)^2)) - (19.58 * (hours)) + 69.21 |
|
A |
7 - 10 |
(0.0325 * ((hours)^2)) - (0.6875 * (hours)) + 5.327 |
|
A |
10 - 21 |
(-0.07576 * (hours)) + 2.446 |
|
B |
6.1 - 7 |
(0.8389 * ((hours)^2)) - (11.75 * (hours)) + 43.41 |
|
B |
7 - 10 |
(0.035 * ((hours)^2)) - (0.751 * (hours)) + 5.5771 |
|
B |
10 - 21 |
(-0.07609 * (hours)) + 2.516 |
|
C |
6.23 - 7 |
(0.63689 * ((hours)^2)) - (9.157 * (hours)) + 35.33 |
|
C |
7 - 11 |
(0.02929 * ((hours)^2)) - (0.6861 * (hours)) + 5.795 |
|
C |
11 - 21 |
(-0.07473 * (hours)) + 2.595 |
|
D |
6.4 - 7 |
(0.7599 * ((hours)^2)) - (10.75 * (hours)) + 40.66 |
|
D |
7 - 11 |
(0.02857 * ((hours)^2)) - (0.6943 * (hours)) + 6.089 |
|
D |
11 - 21 |
(-0.07601 * (hours)) + 2.724 |
|
E |
6.7 - 7 |
(0.333* (hours)) + 5.231 |
|
E |
7 - 12 |
(0.02625 * ((hours)^2)) - (0.6725 * (hours)) + 6.303 |
|
E |
12 - 21 |
(-0.07736 * (hours)) + 2.907 |
|
F |
8 - 13 |
(0.01339 * ((hours)^2)) - (0.4233 * (hours)) + 5.564 |
|
F |
13 - 21 |
(-0.08248 * (hours)) + 3.37 |
Purpose: To determine the probability of serious hepatotoxicity in a patient who has taken an overdose of acetaminophen using the nomogram of Sivilotti et al.
Specialty: Toxicology, Emergency Medicine, Critical Care
Objective: risk factors, adverse effects
ICD-10: T39.1,
