ALPHA-1-ANTITRYPSIN DEFICIENCY

Alpha-1-antitrypsin deficiency: optimal therapeutic regimen based on population pharmacokinetics

D Soy¹, C de la Roza², B Lara², C Esquinas², A Torres², M Miravitlles²

¹ Pharmacy Service, Hospital Clínic (IDIBAPS), Barcelona, Spain
² Department of Pneumology, Institut Clínic del Tòrax, Hospital Clínic (IDIBAPS), Barcelona, Spain

Correspondence to:
Dr M Miravitlles
Department of Pneumology, Clinical Institute of Thorax, Hospital Clínic Barcelona, Villarroel 170, Barcelona 08036, Spain; marcm{at}clinic.ub.es

Background: Exogenous doses of 60 mg/kg ₁-antitrypsin (AAT) every 7 days are recommended in patients with severe AAT deficiency. However, long term administration of weekly doses is not well accepted by patients. Using pharmacokinetic simulations, we evaluated whether steady state minimum concentrations of total AAT can be maintained above the threshold of 0.5 g/l with longer intervals between doses.

Methods: Several sets of exogenous AAT versus time simulations were studied using a non-linear mixed effect approach with dosage regimens every 7, 14, 21, and 28 days. For each regimen the mean exogenous AAT trough concentrations and 5/95th percentiles were determined. The results obtained were applied to estimate the individual optimal dose at 7, 14, and 21 days in six patients using Bayesian analysis.

Results: The simulations showed that a dose of 50 mg/kg AAT every 7 days was sufficient to obtain nadir concentrations. Doses of 120 and 100 mg/kg every 14 days were also adequate, but 180 mg/kg given every 21 days required total AAT monitoring to avoid underdosage. Longer intervals were inappropriate. Dosage individualisation confirmed that AAT infusions given every 14 days maintained the nadir level of 0.5 g/l without a significant dose increase compared with current practice. When the time span between doses was fixed at 21 days, a mean relative AAT dose enhancement of 91% and 13%, respectively, was required to achieve sustained total AAT concentrations above the target level for 100% and 85% of the interval between doses.

Conclusions: It is feasible to extend the interval between doses of AAT to 14 or 21 days to achieve adequate trough total AAT concentrations. This study might be used as a starting point for clinical evaluation of the regimens described.

Abbreviations: AAT, ₁-antitrypsin; CL, clearance; C_min^SS, expected exogenous minimum AAT concentration at steady state conditions

Keywords: 1-antitrypsin deficiency; dosage; population pharmacokinetics; replacement therapy

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