I'm going to post the conversion factors for converting animal dosages, such as are described in "nutrition" articles in terms of mg of substance per kg of diet, into mg/kg body weight. This will help me avoid having to look up the equations in the future. I have to do these types of calculations, in some cases, along with some sort of between-species dosage scaling calculation, in order to be able to evaluate these articles in a meaningful way. This is actually kind of enjoyable to do, but it's disturbing to see the way small changes in the scaling "factors" can drastically alter the way one interprets the results of a given animal study.
I don't think that many doctors or scientists would be able to do these types of calculations in their heads or remember the conversion or scaling factors off the tops of their heads, and that limits the cross-disciplinary appeal of research in these areas. Researchers, particularly those who aren't working in nutrition research, wouldn't be able to appreciate the significance of the results. In some cases, it's literally not possible to tell what the concentrations or dosages are in an article, given the way the information is presented. An article might have important results, but, without a sense of the physiological contexts of the dosages that are producing the different responses, it's not possible to get much out of the article.
Here's one of a series of terrific articles on the anticonvulsant effects of oral guanosine or guanosine 5'-monophosphate: (http://www.ncbi.nlm.nih.gov/pubmed/17682941). The authors give the dosage in mg/kg bw and give the weights of the rats.
Many articles still express dosages in terms of mg/kg diet or percent of diet in (w/w). An expression of a dosage as, say, "guanosine at 0.0425 percent of diet (w/w)" (I'm writing this to help myself remember and allow me to not have to think about it in the future) is the same as an expression of the dosage as "0.0425 g guanosine/100 g diet." To convert "% of substance in diet (w/w)" to "mg substance/kg diet," multiply by 10^4 (10,000).
The conversion factors for converting mg/kg diet to mg/kg bw (along with the masses of typical animals) are from the WHO document I linked to in a past posting on interspecific scaling (http://www.who.int/entity/ipcs/food/jecfa/en/tox_guidelines.pdf). The authors of the WHO document evidently compiled those from multiple sources, and the numbers look similar to ones I've seen before. The mass of an adult rat looks high to me (400 g). I'd switch their number to 300 g (.3 kg), but I'm worried that that would require me to change their food intake values, etc.
The other equation is a dosage scaling equation, derived from allometric data across multiple species, from this article: (http://www.ncbi.nlm.nih.gov/pubmed/17612951), and I think the equation is basically the ratio of two separate solutions of the equations from this paper (one for the animal and one for the human): (http://www.springerlink.com/content/kn360g725382p2m6/). But here are all the relevant conversion factors and the "equation":
mass of adult rat: 0.4 kg (use 0.3 kg, or more typical range of .25 to .35 kg, if only doing scaling and no food conversions)
mass of post-weanling, young rat: 0.1 kg
mass of adult mouse: 0.02 kg (range: 0.01 to 0.03, if only doing scaling and no food conversions)
mass of chick: 0.4 kg
mass of guinea pig: 0.75 kg
mass of rabbit: 2 kg
To convert Y mg/kg diet into mg/kg bw for adult rats, multiply Y by 0.05
To convert Y mg/kg diet into mg/kg bw for young rats, multiply Y by 0.10
To convert Y mg/kg diet into mg/kg bw for adult mice, multiply Y by 0.15
For chicks, multiply Y mg/kg diet by 0.125
For guinea pigs, multiply Y mg/kg diet by .04
For rabbits, multiply Y mg/kg diet by .03
I'm sorry if this looks like a third-grade math assignment, but I always have to look these things up and try to remember where to look. Here's the "equation" for the scaling factor, using a p value of 0.7 (the mass units cancel out, obviously, but this will help to obviate the need for me to think about it in the future):
dosage-scaling factor = [(mass of human (in kg or other units)) / (mass of animal (in kg))]^(0.3)
The exponent of (0.3) is (1-p), and the scaling factors, the p values, range from 0.6 to 0.8 (the "p," here, is referred to as the scaling factor in the literature, but both I and others are applying the terminology loosely), depending on the type of variable one is considering. In the above equation, different p values basically take into account different allometric variables, as far as I understand it. Some of them are the specific metabolic rate, expressed in terms of calories per gram body mass, and the surface area of the body in relation to the mass (which also relates to mass-specific metabolic rate).
These are the "dosage-scaling factors," (I'm calling them that for ease of reference) based on that value of p = 0.7 (I'm using a body mass of 70 kg for a human, just because everyone uses that number):
Adult Rat: 4.71
Young Rat: 7.14
Adult Mouse: 5.79
Chick: 4.71
Guinea Pig: 3.90
Rabbit: 2.91
In the rat dose for oral guanosine monophosphate, used in those studies, is 7.5 mg/kg bw (their rats were actually .25-.35 kg, making the conversion factor different, but let's say it's 4.71), the human dose would be scaled to 1.6 mg/kg (112 mg/day for a human?). That sounds low to me, but it's clear that the effects of guanosine are stronger than those, for example, of inosine, which generally produces therapeutic effects at 100-200 mg/kg in all of the animal models.
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