KETEK
Clinical safety rating: caution
Comprehensive clinical and safety monograph for KETEK (KETEK).
Telithromycin binds to the 50S subunit of bacterial ribosome, inhibiting protein synthesis by blocking peptide chain elongation.
| Metabolism | Metabolized primarily by CYP3A4 and to a lesser extent by CYP1A2. Undergoes first-pass metabolism. |
| Excretion | Primarily fecal (≈70%) via biliary excretion of unchanged drug; renal excretion accounts for ≈13% (mostly unchanged), with additional minor metabolism (<30%). |
| Half-life | Terminal half-life (t½) is 9.8–10.6 hours in young healthy adults, allowing once-daily dosing. In elderly or severe hepatic impairment, t½ may be prolonged. |
| Protein binding | Serum protein binding ≈60–70%, primarily to albumin and α1-acid glycoprotein. |
| Volume of Distribution | Volume of distribution (Vd) ≈2.5–3 L/kg, indicating extensive tissue penetration (high intracellular concentrations). |
| Bioavailability | Oral bioavailability ≈57% (increases by ≈40% with food; take with food to enhance absorption). |
| Onset of Action | Oral: Time to maximum plasma concentration (Tmax) 0.5–3 hours; clinical effect (e.g., symptom improvement in respiratory infections) typically within 24–48 hours. |
| Duration of Action | Once-daily dosing (800 mg) maintains therapeutic concentrations over 24 hours due to long half-life and post-antibiotic effect. Duration of clinical effect continues for entire dosing interval. |
| Molecular Weight | 812 |
Telithromycin 800 mg orally once daily for 7-10 days.
| Dosage form | TABLET |
| Renal impairment | CrCl >=30 mL/min: no adjustment; CrCl <30 mL/min: 400 mg orally once daily. |
| Liver impairment | Child-Pugh A or B: no adjustment; Child-Pugh C: contraindicated. |
| Pediatric use | Not approved for use in pediatric patients. |
| Geriatric use | No specific dose adjustment recommended; monitor for adverse effects and drug interactions. |
| 1st trimester | Avoid. Telithromycin is a macrolide antibiotic; animal studies have shown teratogenicity at high doses. Human data limited; use only if clearly needed and no safer alternatives. |
| 2nd trimester | Use with caution. May be used if benefit outweighs risk, but safer alternatives (e.g., azithromycin) are preferred. |
| 3rd trimester | Use with caution. Risk of fetal effects unknown; avoid near term due to potential for gastrointestinal disturbances in neonate. |
Clinical note
Comprehensive clinical and safety monograph for KETEK (KETEK).
| Placental transfer | Telithromycin crosses the placenta; animal studies show fetal exposure. Human data limited but transfer is expected. |
| Breastfeeding | Telithromycin is excreted into breast milk in small amounts. Risk to infant is unclear; monitor for diarrhea and rash. Use only if essential and with infant monitoring. |
■ FDA Black Box Warning
Telithromycin is contraindicated in patients with myasthenia gravis due to risk of rapid onset of respiratory failure or death. Fatal and life-threatening respiratory failure has been reported in myasthenia gravis patients.
| Serious Effects |
Hypersensitivity to telithromycin or any macrolideHistory of hepatitis/jaundice with macrolidesConcurrent use with cisapride, pimozide, or ergot alkaloidsMyasthenia gravisQTc prolongation or concurrent use with QT-prolonging drugs
| Precautions | Hepatotoxicity (including severe liver injury and fatalities), exacerbation of myasthenia gravis, QT interval prolongation, visual disturbances (loss of consciousness, blurred vision, diplopia), Clostridium difficile-associated diarrhea, and potential for drug interactions with CYP3A4 substrates. |
| Food/Dietary | Avoid grapefruit and grapefruit juice during treatment, as CYP3A4 inhibition increases telithromycin levels. Take with or without food; food does not significantly affect absorption. Maintain adequate hydration. |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Telithromycin is classified as FDA Pregnancy Category C. Animal studies have shown embryotoxicity and fetotoxicity at doses 2-4 times the human dose. No adequate human studies exist; risk cannot be ruled out. Avoid use in first trimester unless benefit outweighs risk. |
| Fetal Monitoring | Monitor liver function tests (ALT, AST, bilirubin) due to risk of hepatotoxicity. Monitor for QT prolongation via ECG in patients with predisposing conditions. Assess for visual disturbances and loss of consciousness. |
| Fertility Effects | No specific human data on fertility impairment. Animal studies at high doses showed no adverse effects on fertility. |
| Clinical Pearls | Ketek (telithromycin) is a ketolide antibiotic, not a macrolide, but shares class effects. Avoid in myasthenia gravis due to risk of rapid onset respiratory depression. Monitor for hepatotoxicity; contraindicated in patients with prior hepatic reactions to penicillins/macrolides. Potent CYP3A4 inhibitor; check for drug interactions with statins, warfarin, and antiarrhythmics. Do not use in patients with prolonged QTc interval or electrolyte disturbances. |
| Patient Advice | Take exactly as prescribed; do not skip doses or stop early even if you feel better. · Report any muscle weakness, double vision, or difficulty breathing immediately. · Avoid alcohol during treatment, as it may increase risk of liver toxicity. · Watch for signs of liver problems: dark urine, yellowing skin/eyes, severe abdominal pain. · Tell your doctor about all other medications you take, including over-the-counter. · Do not take with antacids containing aluminum or magnesium; separate by at least 2 hours. · Store at room temperature, away from moisture and heat. |