DYNABAC
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DYNABAC (DYNABAC).
Dirithromycin is a macrolide antibiotic that binds to the 50S subunit of the bacterial ribosome, specifically to the 23S rRNA, inhibiting peptide chain elongation by blocking the translocation step. It also interferes with the assembly of the 50S ribosomal subunit. This action is primarily bacteriostatic but can be bactericidal at higher concentrations.
| Metabolism | Dirithromycin is not extensively metabolized; it is converted to its active metabolite, erythromycylamine, via non-enzymatic hydrolysis. Minor metabolism may involve CYP3A4, but this is not a major pathway. |
| Excretion | Approximately 65% of a dose is excreted unchanged in the urine via glomerular filtration and tubular secretion; about 15% is excreted unchanged in the bile; fecal elimination accounts for <5%. |
| Half-life | Terminal elimination half-life is 9–12 hours in adults with normal renal function; may extend to 20–30 hours in severe renal impairment (CrCl <30 mL/min). |
| Protein binding | Approximately 15–20% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | 0.9–1.2 L/kg, indicating extensive distribution into total body water and tissues; achieves high intracellular concentrations. |
| Bioavailability | Oral: Approximately 85–95% (fasting); food may delay absorption but does not significantly reduce extent. |
| Onset of Action | Oral: Clinical improvement typically begins within 24–48 hours; peak serum concentrations achieved 2–3 hours after oral administration. |
| Duration of Action | Serum concentrations remain above MIC for susceptible organisms for approximately 12 hours; clinical effect persists for 12–24 hours, supporting twice-daily dosing. |
500 mg orally once daily or 250 mg orally twice daily; usual duration 5-14 days depending on infection
| Dosage form | TABLET, DELAYED RELEASE |
| Renal impairment | CrCl 30-49 mL/min: 250 mg once daily; CrCl 10-29 mL/min: 250 mg every 48 hours; CrCl <10 mL/min: 250 mg every 48 hours (not studied in dialysis) |
| Liver impairment | No adjustment recommended; however, monitor for adverse effects in severe hepatic impairment (Child-Pugh C) due to limited data |
| Pediatric use | Safety and efficacy not established in children below 12 years; for ages ≥12 years, same as adult dosing |
| Geriatric use | No specific dose adjustment; consider monitoring renal function and adjusting based on CrCl due to age-related decline in renal function |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DYNABAC (DYNABAC).
| Breastfeeding | Excreted in human milk; M/P ratio unknown. Use caution due to potential for serious adverse reactions in nursing infants, including disruption of infant gut flora and allergic reactions. Consider withholding breastfeeding or discontinuing drug. |
| Teratogenic Risk | Pregnancy Category C: Animal studies have shown adverse effects (e.g., increased skeletal variations in rats) but no adequate human studies. Avoid in first trimester unless benefit outweighs risk; risk of fetal harm cannot be ruled out in all trimesters. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to dirithromycin, erythromycin, or any macrolide antibiotic. Concomitant use with pimozide, cisapride, ergotamine, or dihydroergotamine (risk of ergotism or cardiac arrhythmias). History of cholestatic jaundice or hepatic dysfunction associated with prior macrolide use.
| Precautions | Hepatic dysfunction: May cause hepatocellular toxicity, including elevated liver enzymes and hepatitis; monitor liver function. QT prolongation: Risk of cardiac arrhythmias (e.g., torsades de pointes) in patients with preexisting QT prolongation, electrolyte disturbances, or those taking other QT-prolonging drugs. Pseudomembranous colitis: Consider Clostridioides difficile infection in patients with diarrhea. Exacerbation of myasthenia gravis: May worsen symptoms. Drug interactions: Avoid concomitant use with pimozide, ergot alkaloids, cisapride, and HMG-CoA reductase inhibitors metabolized by CYP3A4 (e.g., lovastatin, simvastatin) due to risk of toxicity. Use with caution in patients with renal impairment. |
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| Fetal Monitoring |
| Monitor maternal liver function tests (AST, ALT) and renal function periodically. Fetal monitoring including ultrasound for growth and anatomy if used in pregnancy; no specific guidelines but standard prenatal care recommended. |
| Fertility Effects | Animal studies showed no impaired fertility. Human data limited; no known adverse effects on male or female fertility based on current evidence. |