Impairment related to blood amphetamine and/or methamphetamine concentrations in suspected drugged drivers

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Abstract

Experimental studies have investigated effects of low oral doses of amphetamine and methamphetamine on psychomotor functions, while less work has been done on effects of high doses taken by abusers in real-life settings. There are indications that intake of high doses may impair traffic related skills, and that abuse of amphetamines may cause hypersomnolence at the end-of-binge. The present study aimed at investigating the concentration–effect relationship between blood amphetamines concentrations and impairment in a population of real-life users. Eight hundred and seventy-eight cases with amphetamine or methamphetamine as the only drugs present in the blood samples were selected from the impaired driver registry at The Norwegian Institute of Public Health. In each case the police physician had concluded on whether the driver was impaired or not. 27% of the drivers were judged as not impaired, while 73% were judged as impaired. There was a positive relationship between blood amphetamines concentrations and impairment. The relationship reached a ceiling at blood amphetamines concentrations of 0.27–0.53 mg/l. Younger drivers were more often judged impaired than older drivers at similar concentrations. Despite the performance enhancing qualities of amphetamines demonstrated in some low dose laboratory experiments; this study revealed a positive relationship between blood amphetamines concentration and traffic related impairment.

Introduction

Amphetamine and methamphetamine are among the most commonly used illegal drugs in the world (Ahmad, 2003, Anglin et al., 2000, Logan, 2001, Melbye et al., 2002, Skurtveit et al., 1999, Ujike and Sato, 2004). Chronic abuse often involves high doses (50–300 mg) administered intravenously. Amphetamine is prescribed as a medicinal drug in single doses usually of 5–10 mg, and not exceeding 30 mg (Baselt, 2001, Logan, 2002).

Human laboratory studies on amphetamine and methamphetamine (in this paper referred to as amphetamines) have mostly used small doses (5–40 mg). One study has demonstrated decreased simulated driving performance after intake of approximately 30 mg of dexamphetamine (Silber et al., 2005a), but most studies have concluded that amphetamines improve psychomotor skills (Kelly et al., 2004, Koelega, 1993, Mills et al., 2001), or at least restore performance to baseline level in fatigued subjects (Caldwell et al., 2003, Logan, 2002, Newhouse et al., 1989). Some authors have, however, pointed out that different effects are caused by low single doses, which may enhance performance, and high dose, often chronic abuse (Logan, 2002, Mørland, 2000). Clinical effects following use of elevated doses are difficult to investigate in controlled experimental studies due to ethical reasons. High doses may decrease traffic related performance by for instance irrational behaviour (Logan, 1996). Chronic abuse of amphetamines often consists of intense drug abuse periods lasting several days with escalating intravenous doses. Such binge abuse may be followed by fatigue and hypersomnolence. Paranoid thought disturbances may occur after intake of high doses or at the end of the binge or after withdrawal (Anggård et al., 1970, Griffith et al., 1972, Logan, 1996).

Some culpability studies related to traffic accidents have included investigation of amphetamines (Drummer, 1994, Drummer et al., 2004, Longo et al., 2000, Terhune et al., 1992). These studies do not unequivocally establish that use of amphetamines causes adverse driving events. It has been difficult to reach a clear conclusion regarding an increased culpability rate regarding amphetamines, probably due to small sample sizes and because amphetamines may cause diverse effects related to pattern of use and doses taken.

The Norwegian system for enforcement on laws against drugged driving ensures the apprehension of a relatively large group of drivers that have taken illegal drugs. Drivers suspected of driving under the influence of non-alcoholic drugs are tested on a clinical test for impairment (CTI) by a police physician and have a blood sample drawn simultaneously. The aim of the present study was to investigate the relationship between impairment as assessed by the CTI and blood amphetamines concentrations in a population of suspected drugged drivers.

Section snippets

Materials and methods

All the present data were taken from the impaired driver registry at The Norwegian Institute of Public Health, Division of Forensic Toxicology and Drug Abuse. The registry contains information on all drivers apprehended and suspected of driving under the influence of non-alcohol drugs in Norway. The researchers handled the data anonymously.

The institute analyses approximately 4000–5000 blood samples each year from drivers suspected driving under the influence of non-alcohol drugs. All blood

Results

The material consisted of 878 suspected drivers from 17 to 60 years-of-age with mean age 31.2 years (S.D. 7.6 years). 786 (89.5%) were male. The male drivers were on average older than the female drivers (31.5 years (S.D. 7.7 years) versus 29.5 years (S.D. 7.2 years), Student's T-test, p < 0.05).

691 (78.7%) of the cases contained amphetamine alone and 31 (3.5%) of the cases contained methamphetamine alone. The remaining 156 cases (17.8%) contained both amphetamine and methamphetamine. The median

Discussion

This study demonstrated a modest, but significant relationship between blood amphetamines concentration and impairment. A ceiling effect was observed above the blood amphetamines concentration of 0.27–0.53 mg/l. Younger drivers were more often judged impaired than older drivers at similar blood amphetamines concentrations.

The effects of amphetamines have most often been studied with single intake of oral doses, rarely exceeding 40 mg. Such doses give rise to a Cmax about 0.10–0.15 mg/l (Silber et

Acknowledgements

This work has been done solely by the funding of internal resources. None of the authors have any conflicts of interest that might inflict upon the present work.

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