What is the recommended intravenous (IV) dosing of tobramycin for an adult female?

Tobramycin IV Dosing for Adult Female

For adult females with normal renal function, the recommended intravenous (IV) tobramycin dosing is 3 mg/kg/day administered in 3 equal doses (1 mg/kg every 8 hours). 1

Standard Dosing Regimens

Normal Renal Function

• Standard dose for serious infections: 3 mg/kg/day divided into 3 equal doses (1 mg/kg every 8 hours) 1
• Life-threatening infections: Up to 5 mg/kg/day in 3 or 4 equal doses 1
  • Should be reduced to 3 mg/kg/day as soon as clinically indicated
  • Serum concentration monitoring is required when exceeding 5 mg/kg/day

Special Populations

Patients with Cystic Fibrosis

• Initial dosing: 10 mg/kg/day in 4 equally divided doses 1
• Serum concentration monitoring is essential due to altered pharmacokinetics

Patients with Burns

• Initial dosing: 10 mg/kg/day 2
• Monitoring serum concentration is crucial as pharmacokinetics are altered
• Burn patients with <20% TBSA and adequate renal function can be candidates for once-daily dosing 2

Postpartum Patients

• May require higher than standard doses 3
• Serum level monitoring is essential as standard dosing may not achieve therapeutic levels

Dosing in Renal Impairment

Following a loading dose of 1 mg/kg, subsequent dosing must be adjusted using one of two methods 1:

1. Reduced doses at 8-hour intervals

   • Calculate dose based on creatinine clearance using a nomogram

2. Normal doses at prolonged intervals

   • If creatinine clearance is unavailable, determine dosing frequency by multiplying serum creatinine by 6.2

Duration of Treatment

• Standard duration: 7-10 days 1
• Complicated infections may require longer therapy
• For treatments exceeding 10 days, monitoring of renal, auditory, and vestibular functions is essential due to increased risk of neurotoxicity 1

Administration Guidelines

1. Reconstitute and dilute prior to IV administration
2. Administer as IV infusion over 20-60 minutes
3. Do not administer as direct, undiluted IV injection
4. Infusion periods less than 20 minutes are not recommended (may cause peak serum concentrations to exceed 12 mcg/mL) 1

Therapeutic Drug Monitoring

• Measure peak and trough serum concentrations periodically
• Target levels:
  • Peak: Below 12 mcg/mL
  • Trough: Below 2 mcg/mL
• Rising trough levels (above 2 mcg/mL) may indicate tissue accumulation, potentially leading to ototoxicity and nephrotoxicity 1
• Timing of sample collection:
  • Peak: 30 minutes after IV infusion
  • Trough: 8 hours after dose or just before next dose

Important Considerations

• Elderly patients may be at higher risk for nephrotoxicity and may require dose adjustment 4
• Tobramycin should not be physically premixed with other drugs
• Drug incompatibilities must be considered when administering through the same IV line

Monitoring for Adverse Effects

• Baseline assessment: Audiogram, vestibular testing, Romberg testing, and serum creatinine
• Monthly monitoring: Renal function and questioning about auditory or vestibular symptoms
• Repeat audiogram and vestibular testing if symptoms of eighth nerve toxicity develop 5

Remember that tobramycin is primarily eliminated by the kidneys, making dose adjustment essential in patients with renal impairment to prevent toxicity while maintaining efficacy.