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Isotretinoin (Accutane) Dosing Calculator

Calculate your daily isotretinoin (Accutane) dose based on body weight and prescribed dose intensity using the standard weight-based formula.

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Daily Isotretinoin Dose

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Daily Isotretinoin Dose—mg

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How the Isotretinoin Dosing Calculator Works

Isotretinoin, commonly known by the brand name Accutane, is an oral retinoid prescribed for severe nodular acne and acne vulgaris that has not responded to conventional therapies. Because the drug's efficacy and safety profile are both dose-dependent, clinicians use a precise weight-based formula to determine each patient's daily dose and to plan the full treatment course.

The Core Dosing Formula

The daily isotretinoin dose is calculated as follows:

Ddaily = Wkg × dmg/kg

Where:

  • Ddaily — total daily dose expressed in milligrams (mg)
  • Wkg — patient body weight expressed in kilograms (kg)
  • dmg/kg — prescribed dose intensity expressed in milligrams per kilogram per day (mg/kg/day)

If the patient's weight is recorded in pounds, convert to kilograms by dividing by 2.2046 before applying the formula. The calculator performs this conversion automatically when pounds are selected.

Therapeutic Dose Ranges and Titration

According to the FDA Isotretinoin Clinical Pharmacology Review, the established therapeutic range is 0.5 to 1.0 mg/kg/day. Treatment conventionally begins at the lower end of this range — 0.5 mg/kg/day — so the prescribing physician can assess tolerability before escalation. Common early adverse effects include cheilitis (lip dryness), xerosis (skin dryness), and transient elevations in serum triglycerides and liver enzymes. When these side effects remain manageable, the dose is titrated upward toward 1.0 mg/kg/day to maximize therapeutic benefit and shorten course duration.

The American Academy of Dermatology (AAD) Guidelines for the Management of Acne Vulgaris recommend targeting a cumulative dose of 120 to 150 mg/kg over the entire treatment course. Meeting this cumulative threshold is strongly associated with durable remission and reduced relapse rates. Prescribers calculate both the daily dose and the cumulative target at the outset so treatment duration can be planned from the first prescription.

Cumulative Dose Formula

The total dose a patient should receive over the full course is:

Dcumulative = Wkg × target (mg/kg)

Using a target of 120 mg/kg for a 70 kg patient yields a cumulative goal of 8,400 mg; at 150 mg/kg the goal is 10,500 mg. The daily dose determines how quickly that total accumulates and therefore how many months of therapy are required.

Worked Examples

Example 1 — 70 kg Patient, Starting Dose

  • Weight: 70 kg
  • Dose intensity: 0.5 mg/kg/day
  • Daily dose: 70 × 0.5 = 35 mg/day
  • Cumulative target: 8,400 mg to 10,500 mg
  • Estimated course length: 240 to 300 days (approximately 8 to 10 months)

Example 2 — 70 kg Patient, Full Therapeutic Dose

  • Weight: 70 kg
  • Dose intensity: 1.0 mg/kg/day
  • Daily dose: 70 × 1.0 = 70 mg/day
  • Cumulative target: 8,400 mg to 10,500 mg
  • Estimated course length: 120 to 150 days (approximately 4 to 5 months)

Example 3 — 50 kg Patient

  • Weight: 50 kg
  • Dose intensity: 0.5 mg/kg/day (starting): 50 × 0.5 = 25 mg/day
  • Dose intensity: 1.0 mg/kg/day (full): 50 × 1.0 = 50 mg/day
  • Cumulative target range: 6,000 mg to 7,500 mg

Capsule Strengths and Rounding

Isotretinoin capsules are commercially available in strengths of 10 mg, 20 mg, 30 mg, and 40 mg in the United States. Calculated doses are rounded to the nearest achievable combination. For example, a calculated dose of 35 mg/day is commonly dispensed as one 20 mg capsule plus one 10 mg capsule (30 mg) or one 20 mg plus one 20 mg (40 mg), depending on the prescriber's clinical judgment. Dividing the daily dose into two administrations taken with meals improves bioavailability by approximately 50%, since dietary fat significantly enhances intestinal absorption of isotretinoin.

iPLEDGE and Prescribing Requirements

In the United States, isotretinoin is dispensed exclusively through the iPLEDGE risk evaluation and mitigation strategy (REMS) program, administered by the FDA, due to the drug's severe teratogenicity. Patients, prescribers, and dispensing pharmacies must all be registered. Monthly pregnancy tests, lab monitoring (lipid panel, liver function tests, complete blood count), and confirmed contraception are required for patients of childbearing potential throughout the treatment course.

Disclaimer

This calculator delivers an educational estimate based on published weight-based dosing guidelines and is not a substitute for professional medical advice. All dosing decisions must be made by a licensed dermatologist or physician who reviews the patient's complete clinical picture, laboratory values, and individual risk factors before issuing a prescription under the iPLEDGE program.

Reference

Frequently asked questions

What is the standard isotretinoin dose per kilogram of body weight?
The standard isotretinoin dose ranges from 0.5 mg/kg/day to 1.0 mg/kg/day. Prescribers typically start at 0.5 mg/kg/day to assess tolerability, then titrate to 1.0 mg/kg/day as clinically appropriate. For a 70 kg patient, this means beginning at 35 mg/day and potentially increasing to 70 mg/day based on side effect profile and acne response.
How is the cumulative isotretinoin dose calculated and why does it matter?
The cumulative dose equals patient weight in kilograms multiplied by the target dose intensity, typically 120 to 150 mg/kg. For a 75 kg patient, this gives a target total of 9,000 mg to 11,250 mg. Reaching this threshold is clinically significant because patients who complete a full cumulative course experience substantially lower relapse rates compared to those who receive sub-therapeutic totals. Dermatologists use this figure to plan treatment duration from the first visit.
Why is isotretinoin dosed based on body weight rather than a flat milligram amount?
Weight-based dosing ensures proportional drug exposure across patients of different sizes. Isotretinoin is lipophilic, extensively metabolized by the liver, and distributed throughout body tissues in proportion to body mass. A fixed flat dose would under-treat heavier patients, reducing efficacy, and over-expose lighter patients to dose-dependent adverse effects such as hypertriglyceridemia, elevated liver enzymes, and severe mucocutaneous dryness.
What is the difference between starting at 0.5 mg/kg/day versus 1.0 mg/kg/day?
Starting at 0.5 mg/kg/day is a conservative approach designed to minimize early adverse effects including severe cheilitis, epistaxis, skin fragility, and lipid abnormalities. A dose of 1.0 mg/kg/day represents the full therapeutic target and is associated with faster acne clearance and a shorter overall course duration. The AAD guidelines support titrating to 1.0 mg/kg/day once the lower starting dose is tolerated without significant side effects.
How long does a typical isotretinoin treatment course last?
Course length depends on both the daily dose and the cumulative target of 120 to 150 mg/kg. At 1.0 mg/kg/day, a full course lasts approximately 120 to 150 days, or 4 to 5 months. At 0.5 mg/kg/day, reaching the same cumulative total requires 240 to 300 days, or 8 to 10 months. Most dermatologists prescribe a 5 to 6 month course at moderate to full dosing, adjusting based on acne clearance and laboratory monitoring.
Is this isotretinoin dosing calculator a replacement for a dermatologist's prescription?
No. This calculator provides an educational estimate based on published weight-based dosing guidelines and does not constitute medical advice or a prescription. In the United States, isotretinoin is dispensed exclusively through the FDA's iPLEDGE risk management program due to its severe teratogenicity. A licensed dermatologist must evaluate each patient's weight, lipid panel, liver function, complete blood count, medical history, and pregnancy status before prescribing the medication.