ISOTRETINOIN
Clinical safety rating: avoid
Contraindicated (not allowed)
Reduces sebum production, inhibits sebaceous gland activity, and induces apoptosis in sebocytes. Binds to retinoic acid receptors (RARs) and retinoid X receptors (RXRs) to regulate gene expression.
| Metabolism | Primarily metabolized by CYP3A4 and CYP2B6; also metabolized by CYP2C8 and CYP2C9. Isoenzymes convert isotretinoin to 4-oxo-isotretinoin and other metabolites. |
| Excretion | Primarily hepatic metabolism; metabolites excreted in urine (65-80%) and feces (15-35%). Less than 1% excreted unchanged in urine. |
| Half-life | Terminal elimination half-life is approximately 20 hours (range 10-30 hours) for the parent drug. Clinical significance: steady-state achieved in ~5 days with repeated dosing; prolongation in renal impairment is minimal. |
| Protein binding | 99.9% bound, primarily to albumin. |
| Volume of Distribution | 1.4 L/kg (range 0.5-2.5 L/kg). High Vd indicates extensive tissue distribution, including accumulation in skin and sebaceous glands. |
| Bioavailability | Absolute bioavailability is approximately 25% (highly variable 20-30%) due to first-pass metabolism. Bioavailability is markedly increased (up to 2-fold) when taken with food. |
| Onset of Action | Oral administration: Clinical improvement in acne vulgaris typically observed within 4-8 weeks; maximal effect by 12-16 weeks. |
| Duration of Action | Effects persist for several months after discontinuation; therapeutic benefit may last 6-12 months; sebum production returns to baseline within 6-8 weeks after drug cessation. |
0.5-1 mg/kg/day orally in two divided doses for 15-20 weeks; cumulative dose 120-150 mg/kg.
| Dosage form | CAPSULE |
| Renal impairment | No dose adjustment required in renal impairment. Not studied in ESRD; contraindicated in severe renal impairment. |
| Liver impairment | Contraindicated in hepatic impairment (Child-Pugh class A, B, or C). |
| Pediatric use | Weight-based dosing: 0.5-1 mg/kg/day orally in two divided doses; minimum age 12 years due to risk of premature epiphyseal closure. |
| Geriatric use | No specific dose adjustment; caution due to potential hypersensitivity reactions and increased risk of drug interactions. Use lowest effective dose. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
No significant drug interactions Highly teratogenic and can cause severe skin irritation.
| Breastfeeding | Isotretinoin is excreted in human breast milk with a milk-to-plasma ratio of approximately 0.3-1.4. Due to potential adverse effects in the nursing infant, breastfeeding is contraindicated during isotretinoin therapy. |
| Teratogenic Risk | Isotretinoin is a known human teratogen. First trimester exposure is associated with up to 35% risk of major congenital malformations affecting the central nervous system, cardiovascular system, and craniofacial structures. Second and third trimester exposure can cause spontaneous abortion, preterm delivery, and neurocognitive impairment. Contraindicated in pregnancy. |
■ FDA Black Box Warning
Isotretinoin must not be used by female patients who are or may become pregnant. There is an extremely high risk of severe birth defects if pregnancy occurs while taking isotretinoin. Contraception is required for all female patients of childbearing potential.
| Common Effects | Skin dryness |
| Serious Effects |
Pregnancy or potential pregnancy (Category X), hypersensitivity to isotretinoin or any component, concomitant use of tetracyclines (increased risk of pseudotumor cerebri), and concurrent use of vitamin A supplements (risk of hypervitaminosis A). Relative: breastfeeding, liver disease, hyperlipidemia, diabetes.
| Precautions | Pancreatitis, pseudotumor cerebri (intracranial hypertension), psychiatric disorders (depression, psychosis, suicide), severe skin reactions (Stevens-Johnson syndrome), hepatotoxicity, inflammatory bowel disease, lipid abnormalities (hypertriglyceridemia), decreased night vision, corneal opacities, and premature epiphyseal closure. Monitor pregnancy status, lipids, liver function, and mental health. |
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| Fetal Monitoring | Women of childbearing potential must have two negative pregnancy tests before initiation, monthly pregnancy tests during therapy, and one post-therapy. Use two forms of effective contraception simultaneously for 1 month before, during, and 1 month after treatment. Monitor for psychiatric symptoms, lipid profiles, liver enzymes, and signs of pseudotumor cerebri. |
| Fertility Effects | Isotretinoin may cause reversible alterations in spermatogenesis in males, but no evidence of permanent impairment. In females, no direct effect on fertility beyond the mandatory contraceptive requirements. Use of isotretinoin does not appear to affect long-term fertility. |