School of Pharmacy, Medical Biology Centre, Queen's University of Belfast, 97 Lisburn Road, Belfast BT9 7BL, Northern Ireland, UK
Received 21 June 2005; returned 12 August 2005; revised 17 August 2005; accepted 17 August 2005
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Abstract |
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Methods: Core-type, silicone elastomer vaginal rings containing TMC120 were manufactured, and in vitro release studies performed under sink conditions. The experimental release data, as determined by HPLC, were correlated with estimates of vaginal TMC120 concentrations required to inhibit HIV replication.
Results: Continuous, zero-order release of TMC120 from core-type vaginal rings was observed in vitro over a 71 day period, equivalent to 136 µg/day. The release rate is predicted to maintain vaginal concentrations of the antiretroviral in the range of several orders of magnitude in excess of reported HIV inhibitory concentration values.
Conclusions: Continuous and prolonged zero-order release of TMC120 from a silicone vaginal ring device at quantities predicted to prevent HIV infection was observed.
Keywords: antiviral , diffusion , drug release , zero order
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Introduction |
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As of June 2005, 15 HIV microbicide candidates, including the potent experimental non-nucleoside reverse transcriptase inhibitor (NNRTI) TMC120,35 were undergoing clinical trials.6 Most of these compounds are being evaluated in conventional semi-solid gel formulations designed to provide a single dose of the microbicidal agent, applied immediately before intercourse. The potential for developing controlled release formulations for long-term administration of vaginal microbicides has only recently been considered,2 and may overcome many of the compliance, acceptability and efficacy issues associated with single-dose, gel-based products.7
Several in vitro and animal model studies have demonstrated that TMC120 is a potent NNRTI that effectively prevents both cell-free and cell-associated HIV infection at concentrations in the nanomolar range.35 In an in vitro model using monocyte-derived dendritic cells and autologous CD4+ T cell co-cultures designed to mimic sustained antiretroviral delivery, TMC120 blocked primary infection with monotropic HIV-1 Ba-L at a 0.01 µM concentration and secondary cultures at 0.1 µM.3 In addition, the low cytotoxicity and high therapeutic index of TMC120 make it an ideal candidate for development as an HIV vaginal microbicide. Currently, microbicidal gel formulations of TMC120 are being tested in Phase 1 trials.
The emergence of resistance to NNRTIs is well documented. Although initial studies have demonstrated that TMC120 is active against both wild-type and drug-resistant strains of HIV, the whole issue of resistance, particularly in long-term use as a prophylactic vaginal microbicide, will need to be closely monitored in subsequent clinical investigations.
In this study, we report for the first time the prolonged and controlled release of a lead candidate vaginal microbicide, TMC120, from a silicone elastomer vaginal ring. Vaginal rings have already been commercialized for the sustained release of steroids for hormone replacement therapy (Femring®, Estring®) and contraception (Nuvaring®).7
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Materials and methods |
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TMC120 was kindly provided by Tibotec-virco (Mechelen, Belgium). MED6382 medical grade silicone elastomer was supplied by Warner Chilcott UK. Tetrapropyl orthosilicate (95%) and tin(II) 2-ethylhexanoate (95%) were purchased from SigmaAldrich (Gillingham, UK). Isopropanol (99.8%) and HPLC-grade acetonitrile were purchased from Riedel-de Haën and ultra-pure water was obtained using an Elga Purelab Maxima system.
Manufacture of core-type silicone vaginal rings loaded with TMC120
Core-type vaginal rings (also known as reservoir-type rings) containing 400 mg of TMC120 in a full-length silicone elastomer core and encapsulated with a non-medicated silicone elastomer sheath layer were manufactured on a laboratory-scale, ring-making machine according to a standard method already described in the literature.8 The rings had the following characteristics: 5.5 mm core cross-sectional diameter; 9.0 mm ring cross-sectional diameter; 55.0 mm overall ring diameter; 10.0 (±0.2) g mean weight of rings.
In vitro release studies
Each TMC120-loaded vaginal ring was suspended in a stoppered 250 mL conical flask containing 200 mL of a 1:1 mixture of isopropanol/water (to ensure sink conditions), and the flasks were placed in an orbital (60 rpm; 32 mm orbital diameter) shaking incubator at 37°C (Sanyo Gallenkamp IOX400.XX2.C). Sampling followed by complete replacement of the release medium was performed every day for the first 14 days and at regular intervals thereafter.
Quantification of release of TMC120 using HPLC analysis
The amount of TMC120 released from the rings was quantified using reversed-phase HPLC with ultraviolet detection (Waters Breeze HPLC system; Phenomenex Synergi 4µ Fusion-RP80 column 4.6 mm i.d.x150 mm; temp. 25°C; isocratic mode; mobile phase 1:1 acetonitrile/0.01 M pH 2.7 phosphate buffer; flow rate 1.0 mL/min; detection wavelength 290 nm; 10 µL injection volume; TMC120 retention time 2.9 min). A linear calibration plot for TMC120 was obtained over the range 0.1100 µg/mL (r2 = 0.999).
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Results and discussion |
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Acknowledgements |
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References |
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