BETHKIS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BETHKIS (BETHKIS).
Tobramycin, an aminoglycoside antibiotic, binds to the 30S ribosomal subunit, causing misreading of mRNA and inhibiting protein synthesis, leading to bacterial cell death.
| Metabolism | Primarily excreted unchanged in urine via glomerular filtration; minimal hepatic metabolism. |
| Excretion | Primarily renal excretion of unchanged drug via glomerular filtration; ~90% of absorbed dose excreted in urine within 24 hours; biliary/fecal elimination <5%. |
| Half-life | Terminal elimination half-life 2-3 hours in patients with normal renal function; prolonged to 20-40 hours in severe renal impairment (CrCl <30 mL/min). |
| Protein binding | Low protein binding: 10-20%; primarily binds to albumin. |
| Volume of Distribution | 0.2-0.4 L/kg; distributes primarily into extracellular fluid; limited intracellular penetration. |
| Bioavailability | Inhalation: ~50-60% of nominal dose reaches systemic circulation; oral: negligible (<1% due to poor gastrointestinal absorption). |
| Onset of Action | Inhalation: within 15-30 minutes of inhalation; optimal peak serum concentrations at 1 hour. |
| Duration of Action | 12 hours (recommended dosing interval every 12 hours); clinical effect persists for the dosing interval with consistent trough levels. |
4 IU/kg (1 mg/kg) intramuscularly or subcutaneously once weekly for 4 weeks, then a maintenance dose of 2 IU/kg (0.5 mg/kg) once weekly.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for renal impairment. Not removed by hemodialysis. |
| Liver impairment | No dose adjustment recommended for mild to moderate hepatic impairment (Child-Pugh A or B). Use with caution in severe hepatic impairment (Child-Pugh C) due to lack of data. |
| Pediatric use | Weight-based dosing: 4 IU/kg (1 mg/kg) intramuscularly or subcutaneously once weekly for 4 weeks, then 2 IU/kg (0.5 mg/kg) once weekly. Safety and efficacy in children <18 years not established. |
| Geriatric use | No specific dose adjustments recommended. Use with caution due to potential age-related decline in renal and hepatic function. Monitor for adverse effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for BETHKIS (BETHKIS).
| Breastfeeding | Unknown if excreted in human breast milk; M/P ratio not available. Caution advised due to risk of infant bowel flora alteration and potential for tobramycin-related ototoxicity or nephropathy. |
| Teratogenic Risk | Insufficient human data; animal studies show no teratogenic effects at doses up to 4 times the human dose. Risk cannot be ruled out; use only if clearly needed. |
| Fetal Monitoring |
■ FDA Black Box Warning
Risk of nephrotoxicity and ototoxicity; monitor renal function and hearing during therapy.
| Serious Effects |
Hypersensitivity to tobramycin or other aminoglycosides.
| Precautions | Nephrotoxicity, ototoxicity (vestibular and auditory), neuromuscular blockade, hypersensitivity, superinfection. |
| Food/Dietary | No specific food interactions. Maintain adequate hydration; avoid excessive salt intake if concurrent diuretics are used. |
| Clinical Pearls | Administer via inhalation only using a suitable nebulizer; do not mix with other drugs in the nebulizer. Monitor for bronchospasm; consider pretreatment with a bronchodilator in patients with reactive airway disease. Assess renal function before and during therapy due to potential nephrotoxicity. Obtain audiometric testing at baseline and periodically due to ototoxicity risk. Avoid concurrent use of loop diuretics or other nephrotoxic drugs. Trough serum tobramycin concentrations should be measured after 2–3 doses when systemic absorption is suspected. |
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| Monitor renal function, audiometry, and serum tobramycin trough levels (target <2 mcg/mL) during prolonged therapy; assess fetal growth and amniotic fluid volume with ultrasound if used in pregnancy. |
| Fertility Effects | No documented adverse effects on fertility in animal studies; human data lacking. |
| Patient Advice | Use Bethkis exactly as prescribed; do not skip doses or double up. · Do not swallow or inject Bethkis; it is for inhalation only. · Use a nebulizer with a mouthpiece; do not use a face mask unless necessary. · Store vials in the refrigerator; protect from light. · Clean and disinfect the nebulizer after each use. · Report hearing loss, ringing in the ears, dizziness, or changes in urine output immediately. · Avoid other inhaled medications within 30 minutes of Bethkis unless directed. · Inform your healthcare provider of all other medications, especially diuretics and other antibiotics. |