MYORISAN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MYORISAN (MYORISAN).
Isotretinoin, the active ingredient, reduces sebaceous gland size and sebum production, inhibits sebaceous gland differentiation, and has anti-inflammatory and immunomodulatory effects. It binds to retinoic acid receptors (RARs) and retinoid X receptors (RXRs), altering gene expression.
| Metabolism | Isotretinoin is highly protein-bound (>99.9%). It is metabolized in the liver primarily by CYP2C8, CYP2C9, CYP3A4, and CYP2B6. Major metabolites include 4-oxo-isotretinoin, tretinoin, and 4-oxo-tretinoin. Excretion is through urine and feces. |
| Excretion | Renal (approximately 60-80% as unchanged drug and minor metabolites) and biliary/fecal (approximately 20-30%, mostly as glucuronide conjugates). |
| Half-life | 14-20 hours (terminal elimination half-life in steady state; may be prolonged in elderly or renal impairment). |
| Protein binding | Approximately 99.9% bound to albumin; distributes to tissues including sebaceous glands. |
| Volume of Distribution | 1.3-2.1 L/kg (indicates extensive tissue distribution; accumulates in adipose tissue and skin). |
| Bioavailability | Oral: Approximately 25% (highly variable due to first-pass metabolism and food effect; absorption enhanced with high-fat meals). |
| Onset of Action | Oral: Clinical improvement in acne lesions typically observed within 4-8 weeks of continuous therapy. |
| Duration of Action | Acne remission may persist for several months to years after cessation of therapy; therapeutic effect decreases once drug is discontinued. |
Myorisan (isotretinoin) dosing: 0.5-1 mg/kg/day orally in two divided doses for 15-20 weeks.
| Dosage form | CAPSULE |
| Renal impairment | No dose adjustment recommended for renal impairment; caution in severe renal impairment due to possible accumulation. |
| Liver impairment | Contraindicated in patients with hepatic impairment (Child-Pugh class B and C). Use with caution and monitor LFTs in mild impairment. |
| Pediatric use | Pediatric use: Not recommended in children <12 years; for adolescents ≥12 years, dose per adult weight-based guidelines. |
| Geriatric use | No specific geriatric dose adjustment; caution due to potential for increased adverse effects (e.g., hypertriglyceridemia) and renal function decline. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MYORISAN (MYORISAN).
| Breastfeeding | Contraindicated; M/P ratio unknown; likely excreted in breast milk; potential for severe adverse effects in nursing infant. |
| Teratogenic Risk | First trimester: Major congenital malformations (CNS, cardiovascular, facial dysmorphism) in up to 40% of exposed fetuses; Second trimester: CNS and growth abnormalities; Third trimester: Premature epiphyseal closure, cranial bone anomalies. |
| Fetal Monitoring |
■ 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. Also, isotretinoin is associated with inflammatory bowel disease.
| Serious Effects |
["Pregnancy (Pregnancy Category X)","Women of childbearing potential not using effective contraception","Hypersensitivity to isotretinoin or any component of the formulation","Elevated blood lipids (hypertriglyceridemia, hypercholesterolemia)","Concomitant use with tetracyclines (due to increased risk of pseudotumor cerebri)"]
| Precautions | ["Pseudotumor cerebri (benign intracranial hypertension): risk increased with tetracycline use","Psychiatric disorders: depression, psychosis, suicidal ideation","Pancreatitis: serum triglycerides should be monitored","Hepatotoxicity: monitor liver function","Inflammatory bowel disease","Severe skin reactions (e.g., Stevens-Johnson syndrome)","Photosensitivity","Hyperostosis with prolonged use","Ocular effects: dry eyes, corneal opacities, decreased night vision","Auditory impairment: tinnitus, hearing loss","Lipid abnormalities: hypertriglyceridemia, hypercholesterolemia","Allergic reactions","Skeletal muscle toxicity: rhabdomyolysis"] |
Loading safety data…
| Pregnancy test prior to initiation and monthly during therapy; fetal ultrasound before, at 4-6 weeks, and at 16-20 weeks gestation; avoid supplementation with vitamin A. |
| Fertility Effects | Reversible impairment in spermatogenesis and ovulation in animal studies; human data limited but potential for reduced fertility. |