3rd International AIDS Society Conference on HIV Pathogenesis and Treatment Rio de Janeiro - July 24 - 27, 2005

EFFECT ON ATAZANAVIR (ATZ) AND RITONAVIR (RTV) PLASMA LEVELS OF INCREASING ATZ/RTV DAILY DOSING FROM 300/100 MG TO 300/200 MG AND 400/200 MG

IAS Conf HIV Pathog Treat 2005 Jul 24-27;3rd: Abstract No. WePe3.2C07

Harris M., Alexander C., Joy R., Guillemi S., Phillips E., Langridge S., Harrigan R., Montaner J.
British Columbia Centre for Excellence in HIV/AIDS, Vancouver, Canada

INTRODUCTION: The effects on plasma drug levels of increasing ATZ/rtv doses from 300/100mg daily to 300/200mg and 400/200mg daily are described.

METHODS: Pharmacokinetic (PK) testing was performed on HIV+ adults receiving ATZ/rtv 300/100mg daily. After >2 weeks on stable therapy, blood was collected before dosing and at ~1, 2, and 3 hours post-dose. If ATZ trough was low on 300/100mg, rtv was increased to 200mg and PK repeated after >2 weeks. If ATZ levels remained suboptimal, ATZ dose was increased to 400/200mg and PK repeated. Plasma drug concentrations were determined by a validated assay using HPLC coupled with tandem mass spectrometry. ATZ levels were compared between regimens using Wilcoxon Rank Sum Tests. The analysis includes only patients with no change in co-administered medications.

RESULTS: 25 patients had PK performed on 300/100mg and again on 300/200mg. Plasma ATZ levels were not different between the two regimens at trough (median 612.5 and 672.5 ng/mL, respectively, p=0.4), nor at 2 or 3 hours post-dose (P=0.4 for both). However, 1 hour ATZ levels increased slightly from 690.5 to 871 ng/mL (p=0.01). Ritonavir levels were detectable (>80 ng/mL) at trough in 5/22 patients on 300/100mg and 13/22 on 300/200mg. Eight patients had dose increased further to 400/200mg. Compared to 300/100mg, this increased ATZ levels at all time points tested: trough (median) from 346.5 to 1034.5 ng/mL (p=0.004), 1 hour from 393 to 1350 (p=0.008), 2 hour from 356 to 1765 (p=0.03), 3 hour from 412 to 4490 (p=0.02).

CONCLUSIONS: A subset of patients with suboptimal ATZ levels on ATZ/rtv 300/100mg daily will experience improved ATZ levels when rtv alone is increased to 200mg daily. However, increasing both ATZ and rtv to 400/200mg daily may more reliably increase ATZ levels without increasing cost (compared to 300/200mg daily). The effect of this dose increase on ATZ-related toxicity remains to be determined.

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Clinical | WePe3.2C07 | Harris M
Pharmacological Monitoring of ARV Therapy

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