How a concentration curve is drawn

Updated 29 September 2026

The model Dose uses, the numbers it needs for each compound, and what happens when one is missing.

The short version

Dose estimates a curve for each dose you log, from a standard model of how a compound enters and leaves the body. The model uses values recorded for the compound in the catalogue, adjusted by what your profile says about you. When a value it cannot do without is missing, Dose does not put a default in its place: it draws no curve, and the calculation names the missing value.

Omeprazole 20 mg, oralExample data

Estimated concentration, ng/mL

Figure 1. One oral dose, taken at hour 1, for an invented person. Example data: the values behind it are illustrative, not the catalogue's.

The model

Dose uses a one-compartment model with first-order absorption and first-order elimination.

One compartment means the body is treated as a single space that the compound spreads through evenly. First order means that in each hour, a fixed share of what is left is absorbed, or removed. So the curve rises while absorption outpaces elimination, reaches a peak, and then falls.

An intravenous dose is modelled as a single injection: the whole dose is in the bloodstream at once, so its curve starts at its peak and only falls. A dose logged as an infusion is different: see Infusions.

When doses of the same compound overlap, Dose adds their curves together. After seven half-lives, it treats a dose as cleared.

Infusions

Some medicines are pumped in steadily over hours or days, such as a 46-hour or a 96-hour infusion. If you log a dose as an infusion, with a start time and a planned stop, Dose draws the input as a steady flow instead of a single injection. The level climbs while the pump runs, levels off if it runs long compared with the compound's half-life, and falls after it stops.

The curve uses the actual stop you record, not only the planned one. If the pump was stopped early, paused or changed rate, and you recorded those periods, the curve follows them. If no periods are recorded, Dose assumes one constant rate from the start to the planned stop and says so. While a pump may still be running and no stop is recorded, the curve is drawn only up to now, because the stop is not known.

A subcutaneous infusion is drawn as a steady input into a depot under the skin, absorbed from there at the compound's recorded rate. That is an approximation, and the curve says so.

What an infusion curve cannot tell you: it is a one-compartment approximation unless the catalogue records two-compartment values for the compound, and long-infusion cancer medicines often need more than one compartment. The curve is an estimate from population values, illustrative only. It is not a measurement, it does not judge whether a level is right for you, and it is not dosing advice. If the half-life or volume of distribution is not recorded, there is no curve, and Dose says which value is missing.

What Dose needs for each compound

Three values come from the compound's record in the catalogue. Without any one of them there is no curve.

Half-life: How long it takes for the amount in your body to fall by half. It sets how fast the curve falls.
Bioavailability for the route you took: The share of a dose that reaches your bloodstream. It can differ by route, so Dose looks for the value that matches how you took the dose. For an intravenous dose it is the whole dose.
Volume of distribution, with its unit: How widely the compound spreads through the body. The same amount spread through a larger volume gives a lower concentration.

Dose models ten routes: oral, intramuscular, subcutaneous, intravenous, inhaled, transdermal, sublingual, intranasal, buccal and rectal. A patch is modelled like any other absorbed dose, not as the slow, steady release a real patch gives.

Volume of distribution is recorded in one of three ways: per kilogram of body weight, per square metre of body surface area, or as one volume for the whole body. Dose reads the unit along with the number, and does not draw a curve when the unit is too uncertain to trust.

Dose also needs how quickly the compound is absorbed by your route. Where the catalogue records it, Dose uses it. Where it does not, Dose uses a default rate for the route and marks it as assumed. The default rates are approximations, so the timing and height of the peak are approximate too.

What adjusts it for you

Two of those values are adjusted using your profile.

Volume of distribution is scaled to your body:

A value recorded per kilogram is scaled to your weight. If you have recorded your body fat, Dose uses it; for compounds that dissolve in fat it also needs your height. If you have not recorded body fat, Dose adjusts for sex instead.
A value recorded per square metre uses your body surface area, from your height and weight.
A value given for the whole body is not rescaled.
Pregnancy is taken into account in all three cases.

Half-life is adjusted for liver function when the compound is cleared by the liver, and for kidney function when it is cleared by the kidneys. Your age, sex, metabolic rate, a recorded drug-metabolism status, smoking and pregnancy can also make it longer or shorter. A recorded drug-metabolism status applies to every compound cleared by the liver; Dose does not model individual enzymes.

Where your profile does not record liver or kidney function, Dose assumes typical function and marks it as assumed.

When a value is missing

For the values a curve cannot be drawn without, Dose does not fill the gap with a stand-in. If the compound has no recorded half-life, no bioavailability for your route, no volume of distribution, or a volume of distribution with no usable unit, there is no curve, and the calculation names the value that is missing.

It also says where the gap is. A gap in the catalogue is not something you can fix. A gap in your profile, such as a missing height or weight, is one you can fill in yourself.

A recorded zero is not a gap. If a compound is recorded as not absorbed by a route at all, its curve is flat.

Not every screen shows the missing value's name yet. Where one does not, a compound with no curve can show as zero. That zero means no estimate, not a level of zero.

What the curve is not

The curve is an estimate. It comes from population values for the compound, adjusted by your profile. It is not a measurement of your blood, and it is not a blood test. Your own levels can differ from it.

KYNYTYX is not a medical device and does not give medical advice. If a decision depends on a level, talk to your prescriber.

Dose: what it keeps track of.
What Course is, and what it is not.
Security: what protects your account.