NOMOGRAM FOR N-ACETYLCYSTEINE TREATMENT


SI units (micromol/L)

Hours post dose
UK/Australia
USA
Risk factors
4
1300
1000
650
4.5
1192
917
596
5
1093
841
547
5.5
1002
771
501
6
919
707
460
6.5
843
648
421
7
773
595
386
7.5
709
545
354
8
650
500
325
8.5
596
459
298
9
547
420
273
9.5
501
386
251
10
460
354
230
10.5
421
324
211
11
386
297
193
11.5
354
273
177
12
325
250
162
12.5
298
229
149
13
273
210
137
13.5
251
193
125
14
230
177
115
14.5
211
162
105
15
193
149
97
15.5
177
136
89
16
162
125
81
16.5
149
115
75
17
137
105
68
17.5
125
96
63
18
115
88
57
18.5
105
81
53
19
97
74
48
19.5
89
68
44
20
81
62
41
20.5
75
57
37
21
68
53
34
21.5
63
48
31
22
57
44
29
22.5
53
41
26
23
48
37
24
23.5
44
34
22
24
41
31
20

The 3 columns reflect the 3 most commonly used nomogram lines. Although the lines are commonly extrapolated to 24 hours, they have not been validated beyond 16 hours.

Column one reflects Prescott's original data and is widely used in the United Kingdom, Australia and Europe.

Column two reflects the original USA study protocol and is the standard of care in USA.

Column three is not based on any good data, see high risk groups (below).

Either of the UK or USA columns is reasonable to assess risk and need for therapy for most patients, the US line is more aggressive .

Units of measure

Paracetamol (acetaminophen) concentrations are commonly reported in either SI units (micromol/L or mmol/L) or in mass units (mg/L). This can sometimes lead to confusion when interpreting results to assess the risk of hepatotoxicity. Be sure that you know which units your laboratory uses.

High Risk groups

Theoretically toxicity is more likely if the P450 enzymes are induced by chronic alcohol ingestion, anticonvulsants or barbiturates (i.e. more toxic metabolite). Inhibition of P450 enzymes at the time of the overdose may reduce the production of toxic metabolites. This most commonly occurs with acute alcohol ingestion (4-6 drinks) & may also occur with co-ingestions or chronic medication with drugs that inhibit these enzymes (e.g. cimetidine). Patients with depleted glutathione may be at increased risk of toxicity e.g. chronic ingestion of paracetamol, malnutrition & eating disorders.

The nomogram represented by the risk column has been suggested to be used for these patients.