RONDOMYCIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for RONDOMYCIN (RONDOMYCIN).
Binds to the 30S ribosomal subunit, inhibiting protein synthesis by blocking the attachment of aminoacyl-tRNA to the mRNA-ribosome complex.
| Metabolism | Primarily hepatic via CYP450 isoenzymes; undergoes enterohepatic recirculation. |
| Excretion | Renal (40-50% unchanged), biliary/fecal (10-20% as metabolites and unchanged drug). Approximately 30% undergoes enterohepatic circulation. |
| Half-life | Terminal elimination half-life is 6-8 hours in patients with normal renal function; may extend to 20-30 hours in severe renal impairment. |
| Protein binding | 65-75% bound to serum proteins (albumin). |
| Volume of Distribution | 0.9-1.1 L/kg; indicates distribution into total body water and tissues. |
| Bioavailability | Oral: approximately 60-70% (first-pass metabolism reduces bioavailability). |
| Onset of Action | Oral: 1-2 hours (therapeutic plasma levels). |
| Duration of Action | 12-24 hours (typical dosing interval is 12 hours). |
| Molecular Weight | 444.44 |
150 mg orally twice daily or 300 mg orally once daily.
| Dosage form | SYRUP |
| Renal impairment | CrCl >50 mL/min: no adjustment; CrCl 10-50 mL/min: 150 mg every 24 hours; CrCl <10 mL/min: 150 mg every 48 hours. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: contraindicated. |
| Pediatric use | 8-12 years: 4 mg/kg initially, then 2 mg/kg orally twice daily; >12 years: adult dosing. |
| Geriatric use | No specific adjustment; monitor renal function and reduce dose if CrCl <50 mL/min. |
| 1st trimester | Avoid; tetracyclines can cause fetal harm, including delayed skeletal development and congenital anomalies. |
| 2nd trimester | Avoid; risk of enamel hypoplasia and skeletal growth retardation. |
| 3rd trimester | Avoid; risk of permanent tooth discoloration and inhibition of bone growth. |
Clinical note
Comprehensive clinical and safety monograph for RONDOMYCIN (RONDOMYCIN).
| Placental transfer | Crosses placenta; forms stable calcium complexes in fetal bone and teeth. |
| Breastfeeding | Excreted into breast milk in small amounts; potential for tooth discoloration and bone growth inhibition in nursing infants. Use caution, especially with prolonged use. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to tetracyclinesSevere hepatic impairmentPregnancyLactation (relative)Children under 8 years
| Precautions | Photosensitivity reactions; hepatotoxicity; renal impairment; use in pregnancy (Category D) may cause fetal harm; tooth discoloration and enamel hypoplasia in children <8 years; esophageal ulceration; superinfection with resistant organisms; exacerbation of systemic lupus erythematosus; intracranial hypertension; caution in patients with myasthenia gravis. |
| Food/Dietary | Avoid dairy products, calcium-fortified foods, and antacids containing aluminum, calcium, or magnesium within 2-3 hours of dosing. Iron, zinc, and bismuth subsalicylate also reduce absorption. Take on an empty stomach. |
Loading safety data…
| L3 (Moderately Safe) |
| Teratogenic Risk | RONDOMYCIN (methacycline) is a tetracycline antibiotic. Tetracyclines cross the placenta and can cause fetal harm. First trimester: No well-controlled studies, but animal data suggest risk; avoid unless no alternative. Second and third trimesters: Use is contraindicated due to risk of permanent tooth discoloration (yellow-gray-brown) and enamel hypoplasia in the fetus. Also associated with reduced fibula growth and skeletal development. Risk is greatest after 20 weeks gestation. |
| Fetal Monitoring | Monitor maternal renal and hepatic function, complete blood count, and signs of hepatotoxicity or superinfection. For the fetus, no specific monitoring is required if used early in pregnancy; however, avoid use during second and third trimesters. If inadvertent exposure occurs, document gestational age. |
| Fertility Effects | Tetracyclines have been associated with reversible impairment of spermatogenesis in animal studies. In females, no specific effects on fertility are reported. However, use during pregnancy is not recommended; for men, temporary reduction in sperm count is possible but reversible upon discontinuation. |
| Clinical Pearls | RONDOMYCIN (methacycline) is a bacteriostatic tetracycline derivative. It is not first-line for any infection; use only if preferred tetracyclines are contraindicated. Avoid in children under 8 years and during pregnancy/lactation due to teeth discoloration and bone growth inhibition. Renal impairment requires dose adjustment. Monitor for photosensitivity reactions. May increase INR in patients on warfarin. |
| Patient Advice | Take on an empty stomach (1 hour before or 2 hours after meals) with a full glass of water. · Avoid milk, dairy products, antacids, iron, calcium, magnesium, and zinc supplements within 2-3 hours of dosing. · Finish the entire prescription even if you feel better. · Use sunscreen and protective clothing; avoid prolonged sun exposure. · Notify your doctor if you experience severe diarrhea, rash, or yellowing of eyes/skin. |