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Effect of reducing the paediatric stavudine dose by half: a physiologically-based pharmacokinetic model
Sherwin K B Sy1, Ruben Malmberg1, Aoi Matsushima1
1Department of Pharmaceutics, College of Pharmacy, University of Florida, Gainesville, FL, USA.
Insights
Reducing the pediatric stavudine dose could significantly lower mitochondrial toxicity risks. Halving the dose to 0.5 mg/kg may maintain antiviral efficacy while improving safety profiles for children.
Area of Science:
- Pharmacology and Toxicology
- Pediatric Antiviral Therapy
- Pharmacokinetic Modeling
Background:
- The adult dose of stavudine was reduced in 2007 due to toxicity, but the pediatric dose remains unchanged.
- Current pediatric dosing may lead to higher intracellular stavudine triphosphate (d4T-TP) levels than original adult doses, increasing toxicity risks.
- Both antiviral efficacy and mitochondrial toxicity are linked to intracellular d4T-TP concentrations.
Purpose of the Study:
- To simulate the pharmacokinetic and pharmacodynamic effects of reducing the pediatric stavudine dose.
- To evaluate the impact of a halved pediatric dose (0.5 mg/kg) on intracellular d4T-TP levels compared to current dosing and adult doses.
- To assess the potential for reducing mitochondrial toxicity without compromising antiviral efficacy in pediatric patients.
Main Methods:
- A physiologically-based pharmacokinetic model with 13 tissue compartments and an ADAM model was used to simulate stavudine elimination.
- Simulated volume of distribution and oral clearance were compared with literature data.
- A biochemical reaction model simulated intracellular d4T-TP levels for standard (1.23 mg/kg) and reduced (0.5 mg/kg) pediatric doses, and compared them to adult doses (40 mg and 20 mg).
Main Results:
- Simulated and observed stavudine exposure showed good agreement.
- The current mean pediatric dose (1.23 mg/kg b.i.d.) resulted in a mean d4T-TP of 27.9 fmol/10(6) cells, 25% higher than the original 40 mg adult dose.
- A reduced pediatric dose of 0.5 mg/kg b.i.d. yielded d4T-TP levels of 13.2 fmol/10(6) cells, comparable to the 20 mg adult dose (11.5 fmol/10(6) cells) associated with less toxicity and good efficacy.
Conclusions:
- Current pediatric stavudine dosing may result in supratherapeutic intracellular d4T-TP levels, increasing mitochondrial toxicity risk.
- Halving the pediatric dose to 0.5 mg/kg is predicted to significantly reduce mitochondrial toxicity.
- The proposed dose reduction offers a favorable balance between maintaining antiviral efficacy and enhancing safety in pediatric patients.
Abstract:
Owing to significant dose-related toxicity, the adult stavudine dose was reduced in 2007. The paediatric dose, however, has not been reduced. Although the intended paediatric dose is 1 mg/kg twice daily (b.i.d.), the current weight-band dosing approach results in a mean actual dose of 1.23±0.47 mg/kg. Both efficacy and mitochondrial toxicity depend on the concentration of the intracellular metabolite stavudine triphosphate (d4T-TP). We simulated the effect of reducing the paediatric dose to 0.5 mg/kg. A physiologically-based pharmacokinetic model consisting of 13 tissue compartments plus a full ADAM model was used to describe the elimination of stavudine. The volume of distribution at steady-state and apparent oral clearance were simulated and the resulting AUC profile was compared with literature data in adult and paediatric populations. A biochemical reaction model was utilised to simulate intracellular d4T-TP levels for both the standard and proposed reduced paediatric doses. Simulated and observed exposure after oral dosing showed adequate agreement. Mean steady-state d4T-TP for 1.23 mg/kg b.i.d. was 27.9 (90% CI 27.0-28.9) fmol/10(6) cells, 25% higher than that achieved by the 40 mg adult dose. The 0.5 mg/kg dose resulted in d4T-TP of 13.2 (12.7-13.7) fmol/10(6) cells, slightly higher than the adult dose of 20 mg b.i.d. [11.5 (11.2-11.9) fmol/10(6) cells], which has excellent antiviral efficacy and substantially less toxicity. Current paediatric dosing may result in even higher d4T-TP than the original 40 mg adult dose. Halving the paediatric dose would significantly reduce the risk of mitochondrial toxicity without compromising antiviral efficacy.
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