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Movement disorders
Published in Henry J. Woodford, Essential Geriatrics, 2022
Apomorphine is a DA that is taken by a parenteral route. It mainly activates D1 and D2 receptors. When given subcutaneously it has an onset of action after 5–15 minutes.59 The initial concomitant use of domperidone limits (but may not remove) the associated nausea, vomiting and postural hypotension. It may be appropriate for some people with advanced PD plus motor fluctuations. It is usually given as either a continuous subcutaneous infusion, via a portable infusion pump, or as intermittent subcutaneous injections that are self-administered. To select people who are likely to benefit an ‘apomorphine test' may be performed. This involves increasing bolus doses of apomorphine at 90-minute intervals, with careful monitoring, until either an anti-parkinsonian effect or unacceptable adverse effects occur.59 The threshold dose that leads to benefit is recorded and is used to calculate the starting dose for individual patients. It may be possible to slowly reduce, and occasionally withdraw, levodopa therapy once a continuous infusion is established.60
Radiation Safety
Published in Debbie Peet, Emma Chung, Practical Medical Physics, 2021
Debbie Peet, Elizabeth Davies, Richard Raynor, Alimul Chowdhury
The second category of non-stochastic (deterministic) effects only occur above a certain threshold dose. Above this threshold, the severity of direct tissue damage, or other effects, increases linearly with dose. Non-stochastic effects are important in radiotherapy, and some forms of interventional radiology, where erythema (skin reddening similar to a burn) can be a consequence of exposure. Indeed in radiotherapy, specific doses of radiation are administered with the intention of damaging tumour cells, and Chapter 6 describes this and many techniques to minimise e×posure to healthy tissues.
Mock examination
Published in Damian Tolan, Rachel Hyland, Christopher Taylor, Arnold Cowen, Get Through, 2020
Damian Tolan, Rachel Hyland, Christopher Taylor, Arnold Cowen
True – although rare, some deterministic skin effects have occurred following interventional procedures.False – deterministic effects do not occur in properly conducted examinations.False – deterministic effects occur over a fairly well defined range of doses – hence the term ‘deterministic’. Since there is a range of dose below a threshold, where the probability is zero, the variation cannot be linear.True – the threshold dose is around 2 Gy.True – the threshold dose is between 0.2 and 2 Gy, depending on age, sex, dose fractionation and whether temporary or permanent impairment is considered.
Approaches for the setting of occupational exposure limits (OELs) for carcinogens
Published in Critical Reviews in Toxicology, 2023
From a biological and mechanistic point of view, there is most likely a threshold at very low doses, even for directly DNA-reactive carcinogens. However, for most such substances there are not sufficient data to confirm that there is a threshold and even less data to determine the threshold dose and the shape of the dose–response curve. Considering the precautionary principle, LNT extrapolation (i.e. simply drawing a straight line from the PoD down to dose zero) remains the best option in these cases. One of the advantages of the LNT approach is that it most likely does not underestimate the risk at low, workplace-relevant, exposure levels. Also, the use of LNT conveys the message that an administrative policy is followed, and that the quantitative assessment is not based on exact biological knowledge. The exposure levels corresponding to predefined risk levels (or the cancer risk estimates at relevant exposure levels) should be clearly described, along with a description of the underlying exposure–response data.
Dose-dependent long-term effects of a single radiation event on behaviour and glial cells
Published in International Journal of Radiation Biology, 2021
Marie-Claire Ung, Lillian Garrett, Claudia Dalke, Valentin Leitner, Daniel Dragosa, Daniela Hladik, Frauke Neff, Florian Wagner, Horst Zitzelsberger, Gregor Miller, Martin Hrabĕ de Angelis, Ute Rößler, Daniela Vogt Weisenhorn, Wolfgang Wurst, Jochen Graw, Sabine M. Hölter
Ionizing radiation (particles, X-rays or gamma rays) is not only present in the environment and cosmic ray exposure during aeroplane travel, but used also for medical diagnostic and therapeutic purposes. This application has increased over the past two decades in both the United States and Europe. In Germany, for example, it represents half of the total average public radiation exposure (Abbott 2015). This exposure has potential health risks. Besides tumour formation consecutive to direct DNA damage, non-cancer effects of radiation include cell death, neuroinflammation, oxidative stress and mitochondrial dysfunction. Their incidence and severity increase above a threshold dose with increasing dose, which can lead to cardiovascular, neurovascular and neurodegenerative diseases, gastrointestinal symptoms, bone marrow failure, skin disturbance, cataracts and necrosis (Picano et al. 2012). While the effects of high-dose radiation are well documented, the health effects of low doses are not clearly understood (Vaiserman et al. 2018). Epidemiological data provide no evidence for detrimental health effects below 100 millisieverts (mSv) and hormesis theory propounds that low dose radiation can even induce protective, radioadaptive and reparative mechanisms (Betlazar 2016). Several factors including age at exposure, sex and genetics can however influence the outcome post-exposure but there is no clear consensus about their respective role and interaction (Ricoul et al. 1998; Roughton et al. 2013; Bakhmutsky et al. 2014; Kunze et al. 2015; Alsbeih et al. 2016; Stricklin et al. 2020; Wen et al. 2019).
The Viability of Microdosing Psychedelics as a Strategy to Enhance Cognition and Well-being - An Early Review
Published in Journal of Psychoactive Drugs, 2020
Lastly, it is important to note that there is no consensus on the precise definition of a microdose. In terms of psilocybin, for example, the experimental evidence here reviewed ranges in their definition of a “very low dose” from 12 μg/kg body weight (i.e., 0.84 mg/70 kg; e.g., Wackermann et al. 2008) to 45 μg/kg body weight (i.e., 3.15 mg/70 kg; e.g., Hasler et al. 2004). In some of the studies using the higher end of this spectrum, participants selectively reported some perceptual distortions and visual illusions (Griffiths et al. 2016; Hasler et al. 2004), violating the working definition employed by many researchers requiring a microdose to be sub-perceptual. Even without the perceptual aspect, however, it is still a reasonable expectation that there might be significant differences between a dose of 1/10th of a normal dose, and a dose of 1/20th. Failing to distinguish these two dose levels may make comparisons between studies more difficult. Standardized experimental procedures are needed to address confusion and confounds related to this issue. Research experiments within this 1/10th to 1/20th range may find the dose that maximizes the effects of the substances while still preserving the sub-perceptual nature of the experience. With regards to LSD, for example, Bershad et al. (2019) recently suggested a threshold dose of 13 µg. In terms of psilocybin, the range still seems ambiguous (i.e., somewhere between 14 and 43 µg/kg or 1 and 3 mg/70 kg).