The implementation of per-se limits for driving under the influence of benzodiazepines and related drugs: No increased risk for arrest during therapeutic use in Norway

Figures & data

Table 1. Legislative limits, maximum allowed daily doses, and finding of benzodiazepines (BZDs) and z-drugs in samples of whole blood from suspected drug-impaired drivers in Norway from 2013 to 2015.

	Alprazolam	Diazepam	Clonazepam	Nitrazepam	Oxazepam	Zolpidem	Zopiclone	Total
Legislative limit (ng/mL)	3	57	1.3	17	172	31	12	–
Maximum allowed daily dose (mg)	1 mg × 2	5 mg × 2	0.5 mg × 2	7.5 mg	10 mg × 3	10 mg	7.5 mg	–
Expected maximum therapeutic concentration (ng/mL)	27.8	213.6	11.1	101.3	974.9	64.6	27.2	–
Number of drivers testing positive for BZDs or z-drugs (n)	1073	2852	4656	566	471	204	426	10248
Single drug findings ≥ legislative limits^a, % (n)	2.4 (26)	2.0 (57)	3.6 (168)	1.4 (8)	4.9 (23)	27.0 (55)	12.4 (53)	3.8 (390)
Single drug findings ≥ maximum therapeutic concentrations^a, % (n)	1.8 (19)	0.7 (19)	2.2 (102)	0.7 (4)	1.1 (5)	26.0 (53)	7.7 (33)	2.3 (235)
Single drug concentrations above legislative limits but below maximum therapeutic concentrations, % (n)	0.7 (7)	1.3 (38)	1.4 (66)	0.7 (4)	3.8 (18)	1.0 (2)	4.7 (20)	1.5 (155)
Single drug concentrations below legislative limits	0.2 (2)	0.8 (24)	0.1 (4)	0.7 (4)	2.1 (10)	3.9 (8)	5.9 (25)	0.8 (77)
Females, %^b (n)	11.1 (1)	22.6 (14)	21.4 (15)	25.0 (2)	39.3 (11)	60.0 (6)	57.8 (26)	32.3 (75)
Age > 40 years, %^b (n)	33.3 (3)	48.4 (30)	42.9 (30)	75.0 (6)	50.0 (14)	70.0 (7)	91.1 (41)	56.5 (131)

^a An analytical safety margin of 34% was deducted from quantified drug concentrations in whole blood.

^bPercent of drivers with single drug concentrations below the expected maximum concentration when taking maximum allowed drug doses.