Drug Concentration: Estimating Drug Levels in the Body

[madoxx]

If you ingest a drug, is there a mathematical formula that models how much of the drug is left in the system?

 

[Monique]

Pharmacology deals with such questions, which I'm not an expert in. There are a number of variables that are needed to do any predictions, such as the rate with which a drug is taken up and the rate with which it is broken down. Then there are variables as the weight of a person ingesting the drug. Animal studies give us indications of the uptake and metabolism of drugs, I guess they can make models based on such information (which will be different for each drug).

There are always modifiers of the system, one of them is grapefruit juice. Grapefruit juice reduces the intestinal efflux of P-glycoprotein substrates, thereby raising the blood concentration of some drugs which can then reach dangerous levels. It's important to know such interactions.

 

[TRCSF]

Yes, there's something called the plasma concentration curve which monitors how quickly a drug is absorbed and how quickly it's eliminated.

There's something called the minimum effective concentration and the minimum toxic concentration and doctors and pharmacists try to keep the drug concentration somewher in between in order to maximize the efficacy of the drug.

Of course it will change depending on the drug, how it's introduced (e.g. oral vs. IV), health of the patient, drug-drug interactions, etc. But it's still very important for doctors and pharmacists to get right.

It's also very important, as you might imagine, for anesthesiologists. That's basically what they do while a patient is in or recovering from surgery- making sure the patient is within that therapeutic window.

 

[Tide]

The simplest model of drug concentration in the body is a half-life model. Many drugs do list their half-lives. A good textbook on pharmacokinetics should provide details.