There aren't (weren't?) many pharmacometricians on #Twitter, weirdly. Most of us lurk on #LinkedIn and #Facebook. This may be a #Pharma thing.

I already introduced myself but it occurs to me that it might be fun to go into a bit more detail about my tiny corner of science and #OpenSource! Buckle up, this might get a bit dry and boring. Hope not. But there will be #Beer!

So what is #Pharmacometrics?

Wikipedia defines #Pharmacometrics (#PMx) as a field of study of the methodology and application of #models for disease and pharmacological measurement. It applies mathematical models of #biology, #pharmacology, #disease, and #physiology to describe and quantify interactions between #xenobiotics (drugs) and patients (human and non-human), including both beneficial and adverse effects.
It is normally applied to combine data from drugs, diseases and clinical trials to aid efficient #DrugDevelopment, #Regulatory decisions and #RationalDrugTreatment in patients.

Pharmacometrics rolls up modeling and simulation for #Pharmacokinetics, #Pharmacodynamics, and #DiseaseProgression, with a focus on populations and variability. A major focus is to understand variability in drug response, which can be predictable (e.g. due to differences in body weight or kidney function) or unpredictable (differences between subjects seem random, but likely reflect a lack of knowledge or data).

https://en.wikipedia.org/wiki/Pharmacometrics

Pharmacometrics - Wikipedia

#QuantitativeSystemsPharmacology (#QSP) is also considered to be a part of the PMx ecosystem, but applies a more theoretical and less data-driven approach to building models. QSP models are often much more complex than PK/PD models, with less of a populations focus.
What this boils down to is using mathematical/statistical models to help explain and predict what the body does to the drug (#Pharmacokinetics, #PK) and what the drug does to the body (#Pharmacodynamics, #PD) - these are often combined to produce #PKPD or #ExposureResponse models.
We build these using data collected from clinical trials (e.g. blood samples, clinical observations, scores, X-rays and suchlike - multiple samples, over time, from many subjects), which we use to build compartmental models which approximate what is happening over time using ordinary differential equations (#ODEs).
This sounds complicated - and it can be - but it's based on the well-stirred compartmental model for PK, a well-established set of principles for how systems like these can be approximated. Here's a more detailed explainer, but it's not for the faint of heart. https://en.wikipedia.org/wiki/Multi-compartment_model
Multi-compartment model - Wikipedia

I promised you #Beer! It's actually a pretty good example. PK describes what happens to the alcohol (ethanol) you consume between the glass and the bathroom, and PD describes what it does while it's circulating in your blood (quite a few things, including making you tipsy). Ethanol is a pretty interesting case, because it's eye-wateringly complex. The #DrinkMe simulation on Nick Holford's website is a fun interactive example of how it fits together! #PMx

http://holford.fmhs.auckland.ac.nz/research/ethanol

Ethanol PKPD

So #Pharmacometrics can help us understand how drugs behave in different people. The #DrinkMe model includes body weight - the bigger you are, the bigger your organs are (usually) and the more machinery you have for metabolizing substances like ethanol, so the slower you get drunk, and if you've eaten something, the alcohol will take longer to get into your system (although these are just two aspects of a very complex system).
These principles apply to every drug we take, from aspirin to metformin (which is commonly used for treating diabetes). We use these models to figure out what an appropriate dose is, and what might affect it.
We can use #Pharmacometric models like these to #Simulate clinical trials, dose regimens and so on, in silico, so that we can predict what will happen when we actually give a drug to a human, and whether the design we have proposed for our clinical trial will actually work when we run it.
Later on in drug development, as we get close to registration, we can use these models to identify #Covariates whcih might inform differences in exposure and effect between patients (like age, weight, and sex), and to quantify the relationships between dose, exposure, and response for efficacy (e.g. how well the drug does at reducing or eliminating a tumour) and safety (e.g. how many unwanted side effects the drug generates at a useful dose).

It's not just about the drugs themselves. #DrugDisease and #DiseaseProgression models are also an area in which #Pharmacometrics continues to have an impact - #FDA maintains a list the ones they've developed internally, including examples for #Alzheimers and #Diabetes, although there are many, many more.

https://www.fda.gov/about-fda/center-drug-evaluation-and-research-cder/division-pharmacometrics

Division of Pharmacometrics

Pharmacometrics at FDA

U.S. Food and Drug Administration
The best thing about being a #Pharmacometrician (IMHO) is that you never stop learning, and every job is different. Right now I work a lot in #Immunooncology, the use of monocolonal antibodies (#mAbs) for treating #Cancer. mAbs have their own interesting set of complexities. (Well, they're interesting after we've figured them out. Before that that they're just maddening.)
So far I've mostly talked about empirical, data-driven models, but #Pharmacometrics goes further, especially now that the computers are getting so fast (models take time to fit to data, and the more complex they are, and the more patients you have, the longer they take).
Physiologically-based PK (#PBPK) models, for example, find the middle ground between PK and #QSP, having a more mechanistic bent by taking into account anatomical, physiological, physical, and chemical descriptions of the phenomena involved in complex absorption, distribution, metabolic and elimination (#ADME) processes, while remaining fundamentally driven by observed data.
I'm on fosstodon.org because I do a lot of #rstats development, most notably as a member of the #nlmixr2 development team. nlmixr2 is a set of packages - let's call it the #mixrverse - for R that provides an #OpenSource alternative for nonlinear mixed-effects (#NLME) model development, which are the core of most #Pharmacometrics workflows (amongst others).

Modeling tools in our area are largely closed-source and massively expensive, and are a gigantic entry barrier for new people, especially in low and middle-income countries (and borderline unaffordable even for CROs like mine). #nlmixr2 is intended to be a solution to this problem. I also maintain the #pmxTools package, which provides a handy set of general #PMx functions.

@nlmixr2

https://www.nlmixr2.org

Nonlinear Mixed Effects Models in Population PK/PD

Fit and compare nonlinear mixed-effects models in differential equations with flexible dosing information commonly seen in pharmacokinetics and pharmacodynamics (Almquist, Leander, and Jirstrand 2015 <doi:10.1007/s10928-015-9409-1>). Differential equation solving is by compiled C code provided in the rxode2 package (Wang, Hallow, and James 2015 <doi:10.1002/psp4.12052>).

For those interested, there are lots of journals that publish in #PMx, including

- Journal of Pharmacokinetics and Pharmacodynamics (JPKPD)
- Clinical Pharmacology and Therapeutics: Pharmacometrics and Systems Pharmacology (CPT:PSP)
- The AAPS Journal (AAPS J)

The International Society of Pharmacometrics (#ISoP) is the professional scientific association for #PMx. I was a member of its Board of Directors, and it's one of the most fun and rewarding things I've done.

https://www.isop.org

ISoP

Finally, some pharmacometricians are here:

@FlyingGardener
@francois_mercier
@MikeKSmith
@Tensfeldt

(I told you there weren't many of us around...)

If I've missed someone or something - and I'm sure I have - shout out! #Pharmacometrics is, to put it mildly, complicated, and I've tried to provide a (very) high-level view of what we do. There will be gaps.

@justinwilkins yup pharmacometrics fosstodon here! #pharmacometrics is generally on Linkedin for some reason. Something about the field likes suits moreso than plain black t-shirts.
@chrisrackauckas I skew more towards hoodies myself, but these are admittedly also usually black
@justinwilkins Get back on Facebook. Or maybe the Metaverse if it's a graphic hoodie.
@chrisrackauckas Nah, I like it here. I'm going to change the dress code from within
@chrisrackauckas I also cannot help but notice that that's a button-down shirt in your profile pic. And it isn't black 😀
@justinwilkins I came to Mastadon and put a pharmacometrics-style LinkedIn picture on. You can never over-dress you know? I'm still catching the lay of the land: it might change to a barefoot picture with my dog. Who knows. I'll let you be the trendsetter though haha.