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JAC Advance Access published online on November 9, 2006
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkl436
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© The Author 2006. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Received July 1, 2006
Revised October 1, 2006
Accepted October 4, 2006

Brief report

Influence of body temperature on indinavir crystallization under loop of Henle conditions

Saima Salahuddin 1, Dik J. Kok 2, and Noor N.-P. Buchholz 3 *

1 Department of Experimental Urology, Erasmus Medical Centre, Dr Molenwaterplein, 3010 GD, Rotterdam, The Netherlands; Department of Urology, St Bartholomew's Hospital, Barts and The London NHS Trust, London EC1A 7BE, UK
2 Department of Experimental Urology, Erasmus Medical Centre, Dr Molenwaterplein, 3010 GD, Rotterdam, The Netherlands
3 Department of Urology, St Bartholomew's Hospital, Barts and The London NHS Trust, London EC1A 7BE, UK

* To whom correspondence should be addressed.
Noor N.-P. Buchholz, E-mail: nielspeter{at}yahoo.com


  Abstract

Objectives: Indinavir is a protease inhibitor used in the therapy of HIV-1+ patients. It causes indinavir stone formation. It has been shown to precipitate in the loop of Henle (LH) at plasma concentrations (conc[P]) of ~8 mg/L. Those experiments were performed at room temperature. Given the influence of temperature on crystallization in general, and solubility of indinavir in particular, we repeated the experiments under physiological (body) temperature conditions.

Methods: Test solutions contained indinavir concentrations of 100-750 mg/L at ionic strengths varying from 0 to 800 mM simulating conditions in the proximal tubule and the LH. Solutions were titrated with base (NaOH) to find the pH value where nucleation is initiated. Experiments were conducted at room temperature (20°C) and repeated under constantly monitored (body) temperature (37°C).

Results: Experiments at 20°C confirmed our previous results. At 37°C, the relationship between pH and indinavir concentration remained inversely proportional. Again, the LH was confirmed as the most likely localization of crystallization. However, at 37°C precipitation occurred at a lower urinary concentration (100 versus 125 mg/L) and within a lower pH range (6.67-7.26 versus 7.23-7.44). This lower urinary concentration corresponds to a lower conc[P] [critical value (CV)] of 6.41 mg/L, as compared with 8.01 mg/L at 20°C.

Conclusions: The CV is even lower at 37°C than previously assumed. Plasma peak concentration above the CV of 6.4 mg/L will induce crystallization in the LH and should be avoided.

Keywords: protease inhibitors; drug kinetics; dosages; in vitro experiments.
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