MYMETHAZINE FORTIS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MYMETHAZINE FORTIS (MYMETHAZINE FORTIS).
Mymethazine fortis is a phenothiazine derivative that exerts antipsychotic and antiemetic effects primarily by blocking postsynaptic dopamine D2 receptors in the mesolimbic system, as well as possessing anticholinergic, antihistaminergic, and alpha-adrenergic antagonistic properties.
| Metabolism | Primarily metabolized by the liver via CYP2D6, with minor contributions from CYP1A2 and CYP3A4. Metabolites include 7-hydroxymethazine and N-desmethylmethazine. |
| Excretion | Primarily renal (70-80% as unchanged drug and metabolites, with about 30% as unchanged); fecal (10-15%) via biliary elimination. |
| Half-life | Terminal elimination half-life is 15-20 hours; in renal impairment (CrCl <30 mL/min), may extend to 30-40 hours, requiring dose adjustment. |
| Protein binding | Approximately 85-90% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Approximately 5-10 L/kg, indicating extensive tissue distribution with accumulation in adipose tissue and slow release. |
| Bioavailability | Oral: 40-60% (first-pass metabolism); intramuscular: 75-85%; intravenous: 100%. |
| Onset of Action | Oral: 1-2 hours; intramuscular: 30-60 minutes; intravenous: within 5-10 minutes. |
| Duration of Action | Oral: 8-12 hours; intramuscular: 6-10 hours; intravenous: 4-8 hours; clinical effect duration may be shorter due to tolerance with chronic use. |
| Molecular Weight | 327.45 |
50 mg orally every 6 hours as needed for nausea and vomiting.
| Dosage form | SYRUP |
| Renal impairment | No dosage adjustment required for mild-to-moderate renal impairment. For severe renal impairment (CrCl < 10 mL/min), use with caution and consider prolonging dosing interval to every 12 hours. |
| Liver impairment | Child-Pugh Class A: No adjustment. Child-Pugh Class B: Maximum 50 mg orally every 12 hours. Child-Pugh Class C: Not recommended. |
| Pediatric use | 0.25–0.5 mg/kg orally every 6–8 hours as needed; maximum 25 mg/dose for children < 12 years. |
| Geriatric use | Lower initial dose recommended (e.g., 25 mg orally every 6 hours) due to increased sensitivity to anticholinergic effects and risk of sedation. |
| 1st trimester | Avoid; potential teratogenicity observed in animal studies. |
| 2nd trimester | Avoid; risk of fetal adverse effects. |
| 3rd trimester | Avoid; may cause neonatal withdrawal syndrome. |
Clinical note
Comprehensive clinical and safety monograph for MYMETHAZINE FORTIS (MYMETHAZINE FORTIS).
| Placental transfer | Crosses placenta; documented in human studies. |
| Breastfeeding | Excreted in breast milk; potential for serious adverse effects in nursing infant. Use is contraindicated. |
| Lactation Rating | L5 |
■ FDA Black Box Warning
Elderly patients with dementia-related psychosis treated with antipsychotic drugs are at an increased risk of death. Mymethazine fortis is not approved for the treatment of dementia-related psychosis.
| Serious Effects |
Hypersensitivity to methdilazineComatose statesConcomitant use with MAOIsPediatric patients < 2 years (risk of severe respiratory depression)
| Precautions | May cause tardive dyskinesia, neuroleptic malignant syndrome, leukopenia/neutropenia/agranulocytosis, QT prolongation, seizures, and orthostatic hypotension. Use with caution in patients with cardiovascular disease, epilepsy, or bone marrow suppression. |
| Food/Dietary | Avoid alcohol and grapefruit juice, as they may increase sedation and alter drug metabolism. Take with food if GI upset occurs. No specific dietary restrictions otherwise. |
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| Teratogenic Risk |
| First trimester: Increased risk of neural tube defects, cleft palate, and cardiovascular anomalies due to folate antagonism. Second and third trimesters: Potential for fetal growth restriction, preterm birth, and neonatal myelosuppression (anemia, leukopenia, thrombocytopenia). |
| Fetal Monitoring | Maternal: Complete blood counts (monthly), liver function tests, renal function, and serum methotrexate levels. Fetal: Ultrasound for growth and anatomy, amniotic fluid volume, and fetal echocardiography if second trimester exposure. |
| Fertility Effects | May cause reversible oligospermia or amenorrhea. Long-term use associated with impaired fertility in both sexes; effects may persist after discontinuation. |
| Clinical Pearls | Mymethazine Fortis contains methdilazine, a phenothiazine antihistamine with anticholinergic and sedative properties. Use with caution in pediatric patients due to risk of paradoxical excitation. In elderly, monitor for dizziness, sedation, and anticholinergic effects. Avoid in patients with lower respiratory tract symptoms including asthma, as anticholinergic effects may thicken secretions. May cause extrapyramidal symptoms, especially in children. Do not exceed recommended doses due to risk of QT prolongation. |
| Patient Advice | Take this medication exactly as prescribed; do not increase dose or frequency. · Avoid driving or operating heavy machinery until you know how this drug affects you. · Avoid alcohol and other CNS depressants as they may increase sedation. · Report any unusual muscle movements, especially in the face or tongue. · Do not take with other antihistamines without consulting your doctor. · If pregnant, nursing, or planning to become pregnant, inform your healthcare provider. |