Global RPH Gentamicin Dosing Calculator

Gentamicin Dose Formula:

\[ \text{Dose} = \frac{\text{target\_peak} \times Vd \times (1 - e^{-ke \times \tau})}{e^{-ke \times \text{inf}/2} - e^{-ke \times (\text{inf}/2 + \tau)}} \]

Target Peak (mg/L):

Volume of Distribution (L):

Elimination Rate (1/h):

Dosing Interval (h):

Infusion Time (h):

Dose (mg):

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1. What is the Gentamicin Dosing Calculator?

Definition: This calculator determines the appropriate gentamicin dose using extended interval (once-daily) dosing based on pharmacokinetic principles.

Purpose: It helps healthcare professionals optimize gentamicin therapy to achieve target peak concentrations while minimizing toxicity risks.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \text{Dose} = \frac{\text{target\_peak} \times Vd \times (1 - e^{-ke \times \tau})}{e^{-ke \times \text{inf}/2} - e^{-ke \times (\text{inf}/2 + \tau)}} \]

Where:

Dose — Gentamicin dose in milligrams (mg)
target_peak — Desired peak concentration (mg/L)
Vd — Volume of distribution in liters (L)
ke — Elimination rate constant (1/hour)
tau — Dosing interval (hours)
inf — Infusion time (hours)

Explanation: The formula accounts for drug distribution, elimination, and infusion time to calculate the optimal dose.

3. Importance of Proper Gentamicin Dosing

Details: Correct dosing ensures therapeutic efficacy while minimizing risks of nephrotoxicity and ototoxicity associated with aminoglycosides.

4. Using the Calculator

Tips: Enter the target peak concentration (typically 15-20 mg/L for once-daily dosing), patient's volume of distribution, elimination rate, dosing interval (usually 24h), and infusion time (typically 1h).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical volume of distribution for adults?
A: For gentamicin, Vd is typically 0.25 L/kg of ideal body weight (about 15-20L for average adults).

Q2: How do I estimate the elimination rate (ke)?
A: ke can be estimated from creatinine clearance: ke ≈ 0.00293 × CrCl + 0.014.

Q3: Why use extended interval dosing?
A: Once-daily dosing maximizes concentration-dependent killing while allowing trough periods that may reduce toxicity.

Q4: When should I check serum levels?
A: Check peak (30 min post-infusion) and trough (just before next dose) levels after the first dose.

Q5: Are there patients who shouldn't use extended interval dosing?
A: Yes, patients with CrCl <30 mL/min, burns >20% BSA, or endocarditis may need conventional dosing.