This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
How isotretinoin courses are planned
Isotretinoin is an oral retinoid used for severe acne and acne that has not responded to other treatments. A course is usually planned around a cumulative dose, the total amount taken over the whole treatment divided by body weight. Studies have found fewer relapses when the total reaches about 120 to 150 mg/kg, although some dermatologists now go higher, or use lower daily doses for longer.
Calculations
- Daily dose per kilo = daily dose ÷ weight. The usual range is 0.5 to 1 mg/kg a day. Low-dose regimens, around 0.25 to 0.4 mg/kg, are often better tolerated.
- Cumulative dose to reach = target in mg/kg × weight
- Treatment length = cumulative dose ÷ daily dose
Example
A person weighing 60 kg (132 lb) taking 40 mg a day takes 0.67 mg/kg a day. To reach 120 mg/kg, the course needs 7,200 mg, or 180 days, about 6 months. At 150 mg/kg, it would take 225 days.
If the dose changes during treatment, enter the days already taken at the current dose, or add up the milligrams taken at each dose and divide by your weight.
Safety
Isotretinoin causes severe birth defects. In the United States it is only available through the iPLEDGE program: people who can become pregnant must use two forms of contraception and have regular pregnancy tests before, during and for a month after treatment. Other points your prescriber will check:
- Dry skin, lips and eyes, the most common side effects
- Blood lipids and liver tests
- Mood changes, which must be reported straight away
- No blood donation during treatment and for a month after
- No wax, laser or dermabrasion during treatment
Limits
The cumulative target is a guide, not a fixed rule. The dermatologist adjusts the dose and duration to the response, the side effects and the severity of the acne. Never change your dose without medical advice.