I’m looking for a drug calculator on the internet that you could put in a patient’s sex, weight, age, etc. and the dosage of a particular medication. And if that medication were taken as prescribed, the concentration of that drug that a tox screen should show.
Obviously there will be variations, but is there anything like that out there? Thanks.
What you are looking for is pharmacokinetics, which was one of my most hated classes in pharmacy school. I don’t know of any public programs to do PK, but if you do find one it would probably be for vancomycin dosing, not probably what you are looking for.
Is there a particular drug you want the info in? I might be able to set up an equation to figure it out.
Yeah. Let’s say that there is a hypothetical patient taking 8mg tab of hydromorphone 4 times per day. Is there any way that he could have a .81mg/L concentration in his blood from taking as prescribed?
I understand that you aren’t giving legal advice. It’s just a conversation I’m having. I contend that there is no possible way and that he was taking extra to get such a high amount in his system.
I’m aware of such a calculation, as clinical chemistry fellows I worked with had to know it. Unfortunately, I never learned it. I do know you need to know the volume of distribution of that particular drug. Newer algorithms are being developed to take into account metabolizer status (slow, fast, ultrafast) based on what mutations might be present in the P450 CYP genes (i.e. 2D6, 2C9, 2C19, 1A1, 1A2 and 3A4) that metabolize drugs.
Even knowing the level in the blood, you won’t be able to determine the dose the person was taking/receiving. The concentration of a drug in the blood reflects not just what goes in, but, of course, also what comes out. These, in turn, can be affected in a major way by problems in the liver, kidney, or heart, other medications the person is taking, nutritional status, smoking, and more. Even things like a recent viral illness or vaccination can affect the ultimate concentration of certain drugs in someone’s bloodstream.
It’s worth emphasizing that for the same amount of hydromorphone taken, different blood levels can result depending on what other medications a person may be taking. There are over six hundred drugs that have an interaction with hydromorphone. Some will only potentiate its effect, but others will actually lead to an increased blood level of hydromorphone.
Another typical list of hydromorphone drug interactions. http://cancer.emedtv.com/hydromorphone-er/drug-interactions-with-hydromorphone-er.html
See here for the commonest table you’ll find on the pharmacokinetics for hydromorphone.
In the table, the listed Cmax for that study occurred within an average of 45 minutes of taking 8 mg of Dilaudid and was “5.5 ng” without identifiying the volume. I suspect the volume was per 1 mL, but you need a smarter guy like Hirka T’Bawa to help me out here. (The AUC “Area Under Curve” is probably more indicative of things like relative binding and interactions and so on, for what it’s worth.)
Here’s a reference showing a Cmax of 2.5 ng/mL in young adults following a single 4 gm “immediate release” oral dose
Make sure the tox test was blood, by the way. They are often urine, which is not very reflective of blood and is way more dependent on free water being cleared (concentration of urine). As mentioned above, many many factors play into pharmacokinetics including co-ingested food and various absorption paramaters such as level of acid in the stomach and so on, as well as formulation (plain v controlled-release, e.g).
In this paper, for example, an 8mg dose of controlled release hydromorphone would yield a Cmax of about 1 nanogram/mL (if I am reading it correctly, which is highly in doubt considering the Pedant’s marginal quanitative skills). Controlled release is a very slow release form; note the Tmax here is closer to 6 or 8 hours.
Is my math right that 0.81 mg/L is 810 ng/mL? If so, that number you give seems really high based on the cites above. However I do not trust my arithmetic.
“See here for the commonest table you’ll find on the pharmacokinetics for hydromorphone.”
Sorry; fixing broken link, I hope.
Sounds like a hell of a research project with an iphone/droid app attached.
Kudos to Hirka, ChiefP and KarlG for taking this one on.
I fiddled around with the question for a bit, but after doing a google image search to find a decent acetaminophen nomogram to illustrate just how tricky it was to take in all the variables, I dropped the ball.
Why? I was startled to find that searching Google images for Acetaminophen nomogram (no quote marks) called up porno images along with more traditional results.
Then I got distracted by researching the results of the image search…
Yes. That is correct. The number seems absurdly high to me such that it would be nearly impossible to achieve by taking the meds as directed, even if in reaction to other drugs. Many thanks for the replies.
Wow. Rule 34 is real! :eek: 
Thank you for the compliment, but I wouldn’t say “smarter” just skilled in another area. You are an expert on diagnosing, and I’m an expert on drug therapy. You tell me what they have, I’ll tell you the drug to treat them with. For the record though, a quick look through the data supports what you posted.
810 ng/mL is what I came up with when I did the math too.
I know! Hence why I haven’t posted anything in so long. It is hard to do the research on a phone, and I haven’t been on my desktop recently.
The number is high, but I do have a couple questions. First, are you sure about the unit? Might it have been mcg instead of mg? Second, how was the level gathered? Hydromorphone is excreted through the kidneys, so would be concentrated in the urine. The levels we have been giving are all from the blood. Third, does the person have any kidney or liver issues? The level could spike greatly if either of those organs are damaged.
It was taken from the blood. The patient is deceased and the ME ruled hydromorphone overdose as the cause. The autopsy did show a fair amount of “fatty liver” but no kidney damage. It is definitely .81 mg/L and the ME notes that .2 mg/L is considered a lethal dose.