METROLOTION
Clinical safety rating: caution
Comprehensive clinical and safety monograph for METROLOTION (METROLOTION).
Metrolotion is a formulation of metronidazole, a nitroimidazole antibiotic. Its exact mechanism is not fully understood, but it is believed to involve reduction of the nitro group in anaerobic bacteria and protozoa, leading to DNA disruption and cell death. It also has anti-inflammatory and immunosuppressive properties, possibly by inhibiting neutrophil chemotaxis and reactive oxygen species.
| Metabolism | Hepatic via oxidation and glucuronidation; CYP450 isoenzymes including CYP2A6, CYP2B6, CYP2C19, CYP2D6, CYP3A4; also undergoes reduction of nitro group. |
| Excretion | Renal: 70% as unchanged drug; biliary/fecal: 30% as metabolites. |
| Half-life | Terminal elimination half-life is 18-24 hours; allows once-daily dosing. |
| Protein binding | 99% bound to albumin. |
| Volume of Distribution | Vd 2.5 L/kg; indicates extensive tissue distribution. |
| Bioavailability | Topical: 10-15% systemic absorption; oral: 100%. |
| Onset of Action | Topical: 2 weeks; oral: 1 week (clinical effect). |
| Duration of Action | Topical: 8-12 hours; oral: 24 hours. |
| Molecular Weight | 318.47 |
Topical metronidazole (Metrolotion) 1%: Apply a thin layer to affected areas once daily.
| Dosage form | LOTION |
| Renal impairment | No dosage adjustment required for renal impairment. |
| Liver impairment | No dosage adjustment provided; use caution in severe hepatic disease. |
| Pediatric use | Safety and efficacy in pediatric patients have not been established. |
| Geriatric use | No specific geriatric dose adjustments; use caution due to potential age-related hepatic impairment. |
| 1st trimester | Avoid due to potential teratogenic effects; use only if clearly needed and no alternative. |
| 2nd trimester | Use with caution; limited data but risk of preterm labor and low birth weight. |
| 3rd trimester | Avoid near term; may cause premature closure of ductus arteriosus and pulmonary hypertension in neonate. |
Clinical note
Comprehensive clinical and safety monograph for METROLOTION (METROLOTION).
| Placental transfer | Crosses placenta readily; fetal concentrations approach maternal levels. |
| Breastfeeding | Excreted in breast milk; potential for adverse effects in nursing infant. Avoid breastfeeding or discontinue drug. |
| Lactation Rating |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Hypersensitivity to metronidazole or any componentFirst trimester of pregnancy (unless alternative not available)Active neurological disorder
| Precautions | Avoid contact with eyes; if severe skin irritation occurs, discontinue use; known carcinogen in animal studies (avoid prolonged use); neurological toxicity (e.g., peripheral neuropathy, seizures) with systemic absorption; use with caution in patients with blood dyscrasias or history of central nervous system disorders. |
| Food/Dietary | No significant food interactions with topical metronidazole. Oral metronidazole has interactions with alcohol (disulfiram-like reaction), but topical use systemic absorption is minimal, so alcohol consumption is not contraindicated. However, avoid applying immediately after eating or with greasy foods that may affect absorption. |
Loading safety data…
| L4 (Possibly Hazardous) |
| Teratogenic Risk | Pregnancy Category D. First trimester: associated with cardiovascular defects (e.g., septal defects), neural tube defects, and limb reduction anomalies. Second and third trimesters: risk of fetal nephrotoxicity, oligohydramnios, and premature closure of ductus arteriosus. Avoid use in pregnancy unless absolutely necessary. |
| Fetal Monitoring | Monitor maternal renal function (serum creatinine, BUN), urinalysis, blood pressure, and fetal ultrasound for amniotic fluid volume and ductus arteriosus flow. Perform fetal echocardiography if exposed in second or third trimester. |
| Fertility Effects | May impair female fertility via disruption of prostaglandin synthesis affecting ovulation and implantation. Reversible upon discontinuation. No direct male fertility effects reported, but testicular atrophy observed in animal studies. |
| Clinical Pearls | Metrolotion (metronidazole) is a topical nitroimidazole antibiotic effective against anaerobic bacteria and certain parasites. For rosacea, it reduces inflammatory lesions and erythema. Avoid contact with eyes, mucous membranes, and open wounds. Can cause skin dryness; use with moisturizer if needed. Not effective for demodex-related conditions alone. Warn patients about potential metallic taste if accidentally ingested. |
| Patient Advice | Apply a thin layer to affected areas once or twice daily as directed. · Do not use on broken skin or near eyes, mouth, or nose. · Avoid sun exposure and use sunscreen; may increase sun sensitivity. · Report any severe burning, stinging, or allergic reaction. · May cause skin dryness; use a non-comedogenic moisturizer if needed. · Do not swallow or ingest; for external use only. |