MaatiRx
Source

MaatiRx

Watch a dose move.

Cmax
9.3mg/L
AUC
74.2mg·h/L
Time in window
48%

Educational model, not for clinical dosing. The default scenario: 500 mg by mouth, half-life 4 h, window 2–12 mg/L.

Every dose

drawn from the model.

Simulate. Change a drug, a patient or a regimen and the concentration and effect curves respond.

Compare. Set two regimens side by side, or freeze a baseline, and see what moved and why.

Learn. 36 guided lessons ask for a prediction first, and 16 graded cases use each patient's own numbers.

Check. The engine is compared with an independent solver on 146 scenarios, in your browser.

Simulate

Doses arrive as pulses.

500 mg by mouth every 8 hours, six doses, over 48 hours: each dose adds to what is left of the ones before.

Learn

200 patients, one median.

200 virtual patients on the default regimen, with clearance varying 30% and volume 20% between them, as in the app's population mode. Each vial holds one patient's level at 4 hours; sorted, the middle two give the median, 7.0 mg/L, and the middle 90% runs from 5.2 to 9.4 mg/L.

Cases

Two phases, one patient.

16 graded cases. Here, a two-compartment drug after an IV bolus: its distribution and elimination phases, on a log scale. The two glass chambers hold the amounts in the central and peripheral compartments, which exchange at k12 and k21.

Exposure

Time above the MIC, counted.

Piperacillin 3 g every 6 hours against an MIC of 16 mg/L, 70% unbound. Over a steady-state interval the unbound level is above the MIC for 47% of the time as a 30-minute infusion and 69% as a 3-hour infusion, the same 12 g a day. Each dish dims by its share of time above the MIC: a visual cue, not a model of bacterial killing.

Rebound

The level returns after dialysis.

A two-compartment drug, 1000 mg IV, through a 4-hour hemodialysis session from 6 hours (the app's rebound lesson). The level falls 53% while the dialyzer clears the blood, then rises again to 6.3 mg/L within 1.6 hours as drug returns from the peripheral compartment: 13% of the fall. The course is shown from 4 hours.

Validated

Every check within tolerance.

146 scenarios against an independent SciPy solver: 584 readings of peak, trough, AUC and time in the window, one point each.

Open MaatiRx

Free, in your browser.

No account, nothing to install. Educational model, not for clinical dosing.

MaatiRx

Educational model, not for clinical dosing.Open in MaatiRx (new tab)

Watch a dose move through the body, in real time.

Change a drug, a patient or a regimen and see the concentration and effect curves respond. Compare regimens side by side, build your own dose schedules, and learn the ideas behind them with guided lessons, practice problems and graded clinical cases.

Educational model, not for clinical dosing.

Quick comparisons
Editing
Editing
1Change any setting on the left. The curve updates instantly.
2Set a baseline, then change something. The panel below explains what moved and why.
3Drag across the chart, or press Play, to read the concentration at any moment.
Plasma concentration–timeSingle oral dose

Select a readout to see how it's worked out, with these numbers.

Sensitivity: which input matters most? (each ±20%)

One input moved at a time, everything else held: clearance with the volume held, volume with clearance held, F capped at 1. A regular regimen is read at steady state; anything else over the time window. Educational model, not for clinical dosing.

Compare against a baseline. Freeze this curve, change anything, and MaatiRx explains what moved and why.
Understand the modelTap a concept
FBioavailability›
The fraction of an oral dose that survives absorption and first-pass metabolism to reach the bloodstream. IV routes bypass this entirely, so F = 1. Halving F halves every concentration on the curve.
kₐAbsorption rate›
How fast drug moves from the gut into plasma. High kₐ → sharp early peak; low kₐ (extended-release) → flatter, later peak with the same total exposure (AUC). Try sliding it and watch Tmax move.
t½Half-life & kₑ›
Time for concentration to fall by half. Linked to the elimination constant by kₑ = ln2 / t½. On the LOG scale, elimination becomes a straight line — its slope is −kₑ. That's the classic way pharmacologists read half-life off a plot.
VVolume of distribution›
The apparent volume the dose dissolves into: C = amount / V. Drugs that hide in tissue have huge V and low plasma levels. V scales with body weight — move the patient weight slider and watch the whole curve rescale.
CLClearance›
The volume of plasma cleared of drug per hour: CL = kₑ·V. Reduced organ function lowers CL, stretching the half-life and raising accumulation — simulate it with the organ function slider.
AUCExposure›
Area under the curve — total drug exposure. For first-order kinetics AUC = F·D / CL, independent of absorption speed. That's why an ER formulation changes the shape but not the area.
SSSteady state›
With repeated dosing, drug accumulates until input = elimination. ~90% of steady state arrives after 3.3 half-lives regardless of dose or interval. A loading dose jumps you there immediately — toggle it and compare.
TWTherapeutic window›
The band between minimum effective (MEC) and toxic (MTC) concentration. Good regimens maximize time in window — tracked live in the readouts. Narrow-window drugs like theophylline make this a genuine engineering problem.
LDLoading dose›
Getting to a target and staying there are different jobs. Conceptually, LD ≈ C_target·V / F: filling the volume sets the load. The maintenance rate ≈ C_target·CL / F: clearance sets what it takes to stay. A load changes how fast you arrive, not where you settle.
✕Missed dose›
Skipping a dose leaves a gap in the input while elimination carries on, so the next trough dips well below the usual one. Recovery back to the regular pattern takes roughly as long as reaching steady state in the first place, which is a few half-lives. Set one with the missed dose slider.
LessonsOne-click scenarios. Each replaces the baseline with its own.

Glossary

Loading the cases…

Practice problemsGenerated problems with worked solutions, every answer checked against the model
Streak 0
Solved 0/0

Fit the data
Get a set of measured concentrations, then move the model's settings until its curve runs through them. It's how a half-life and a volume of distribution are estimated from measurements.
Hit the window
A made-up drug and a concentration window. Choose a dose and a dosing interval so that, once the regimen settles, both the peak and the trough stay inside the window.
Worksheet
A set of problems from the topic chosen above, to work on screen or print, with a worked answer key on its own page. Its link rebuilds the same sheet.

Keyboard shortcuts

KeysWhat they do
On the chart (focus it with Tab)
← →Move the time cursor 0.5 h
Shift + ← →Move it 5 h
Home EndJump to the start or the end of the window
SpacePlay or pause
EscClear the cursor (or cancel a dose you're dragging)
On the dose timeline (a custom schedule)
↑ ↓Pick the previous or next dose
← →Move the picked dose 0.5 h (Shift: 2 h)
Anywhere, unless you're typing (single-key shortcuts)
SpacePlay or pause
← →Move the time cursor, when nothing else has focus
LSwitch between linear and log scale
BSet the baseline
?Open this list
Everywhere else
Tab Shift + TabMove between controls
← → ↑ ↓Change a slider by one step; in the tab bar, move between tabs (Home End for the first and last)
Page Up Page DownChange a slider by a larger step
EnterCheck a practice answer; save a name in the library
EscClose a dialog; cancel a rename

The ⟨ dose ⟩, ⟨ peak ⟩ and ⟨ trough ⟩ buttons under the chart move the cursor to the previous or next dose, peak or trough.

Scenario library

Saved scenarios stay in this browser unless you export or share them. Clearing your browser data removes them. Don't use patient-identifying names.