- Email: [email protected]
Comparison of the rheological properties of Advantage-S and Replens☆
Contraception 64 (2001) 393–396
Original research article
Comparison of the rheological properties of Advantage-S and Replens夞 Derek H. Owena,*, Jennifer J. Petersa, David F. Katza,b a
b
Department of Biomedical Engineering, Duke University, Durham, NC, USA Department of Obstetrics and Gynecology, Duke University, Durham, NC, USA
Abstract The rheological properties of Advantage-S and Replens were measured at body (37°C) and room temperature (25°C) over a range of physiologically relevant shear rates. The viscosity of Replens was found to differ from that of Advantage-S, particularly at room temperature. In addition, the two materials differed in their miscibility with a vaginal fluid simulant. © 2002 Elsevier Science Inc. All rights reserved. Keywords: Microbicide; Contraceptive gel; Vagina; Rheology; Viscosity
1. Introduction Our laboratory has recently been studying the rheological properties of several commercially available contraceptive gels. These gels (Conceptrol, Advantage-S, Gynol II, and KY Plus) have been studied at room and at body temperatures, both whole and diluted with a vaginal fluid simulant [1–3]. A recent study named COL-1492, described at the Thirteenth International AIDS Conference, involved the use of one of these products, Advantage-S (Columbia Laboratories, Inc.; Aventura, FL) [4]. In this triple-blind, randomized, multicenter study, Advantage-S (containing nonoxynol-9) was used intravaginally before heterosexual vaginal intercourse, and the rate of new HIV infections was compared with that of a control group using the same gel vehicle without nonoxynol-9, the commercially available product Replens (Columbia Laboratories, Inc.). Preliminary results indicate that the rate of new HIV infections per 100 personyears was 10.2 for Replens and 15.5 for Advantage-S. This difference has been attributed to the detrimental effect of the surfactant nonoxynol-9 on the vaginal epithelial tissue. Our previous work indicates that the composition of a gel can strongly influence its rheological properties. These properties, in turn, affect its ability to coat the vaginal 夞 Support for this study was provided by the American Foundation for AIDS Research. * Corresponding author. Tel.: ⫹1-919-660-5182; fax: ⫹1-919-6844488. E-mail address: [email protected] (D.H. Owen)
epithelia and to be retained on this surface during and after coitus [5]. For the control in a clinical study to be a true placebo, it should differ in only one respect, the absence of the active compound under study. We, therefore, thought it would be of interest to measure the rheological properties of Replens and compare them with those of Advantage-S.
2. Materials and methods Two polyacrylic acid-based commercial gels were studied: Advantage-S and Replens (both made by Columbia Laboratories, Inc.). These gels differ in composition in that Advantage-S contains nonoxynol-9 and Replens does not. Rheological properties measurements were made over a range of increasing shear rates (0.1 to 1000 s⫺1) at 25°C (room temperature) and at 37°C (body temperature). These shear rates bracket those experienced by formulations in vivo. Three to six replicates were performed for each experiment and the results averaged. Measurements were highly reproducible with coefficients of variation around 5% in all cases. Both Replens and Advantage-S were packaged in the commercially available tubes. All measurements were performed on a Brookfield Model DV-III Digital Rheometer (Brookfield Engineering Laboratories, Inc.; Stoughton, MA) as described in our previous work [2]. In this instrument, the test material is placed between two surfaces, one surface is rotated, and the torque resisting flow is measured. This allows the determination of the relationship between applied shear rate and shear stress experienced by the material. All measurements
0010-7824/01/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII: S 0 0 1 0 - 7 8 2 4 ( 0 1 ) 0 0 2 7 8 - 5
394
D.H. Owen et al. / Contraception 64 (2001) 393–396
Fig. 1. Viscosity versus shear rate for Advantage-S and Replens, room temperature.
were conducted with a cone and plate configuration (three configurations were used, with cone angles and diameters of 3° - 4.8 cm, 3° - 2.4 cm, and 0.8° - 4.8 cm). The viscosity versus shear rate data were analyzed to determine the significance of temperature and gel type. An ANCOVA was performed on the data, with the shear rate being the covariate variable while gel type and temperature were the simple main effects; viscosity was the dependent variable. The number of variables and interactions was small enough to permit an “all possible models” approach to model evaluation [6]. The model containing the covariate alone was then compared to all models containing additional terms (gel type, temperature, and interaction terms) to determine the significance of these additional terms. Statistical analysis was performed by using the software package “R” [7].
3. Results and discussion Results for the measurements made at room temperature and at body temperature are shown in Figs. 1 and 2, respectively. Fig. 3 shows the ratio of the viscosity of Replens to that of Advantage-S as a function of shear rate at the two temperatures. We can see from these results that at room temperature, Replens has a higher viscosity than Advantage-S, but that this difference decreases with increasing shear rate. At low shear rates, the viscosity of Replens is 1.5 times higher than that of Advantage-S. At body temperature, the difference is less pronounced, although the same relationship to shear rate applies. This is because, for Advantage-S, the viscosity at the higher temperature is higher than that at the lower temperature; this is not the case with Replens.
Fig. 2. Viscosity versus shear rate for Advantage-S and Replens, body temperature.
D.H. Owen et al. / Contraception 64 (2001) 393–396
395
Fig. 3. Ratio of viscosities Replens/Advantage-S vs. shear rate.
This anomalous viscosity-temperature relationship has been observed with other polyacrylic acid derivatives [8]. Both gels exhibited shear thinning behavior over the range of shear rates studied. The relatively constant slope of these curves indicates that, under these flow conditions, all product mixtures can be modeled by using the power law equation for the viscosity () as a function of shear rate (␥˙ ) [9]:
⫽ m ␥䡠 n-1 where m and n are constants. It is this linear relationship between the log of the viscosity and the log of the shear rate that allows that us to use shear rate as the covariate in our ANCOVA. The ANCOVA model containing the shear rate alone was then compared to all models containing additional terms by using ANOVA methods. The three models of greatest relevance are the following: Model I: shear rate alone; Model II: shear rate plus gel type; Model III: shear rate plus temperature. When Model II was compared with Model I it was found that gel type was significant (F ⫽ 19.649, Pr(⬎F) ⫽ 3.8 ⫻ 10⫺5). Note: Pr(⬎F) is the probability of obtaining a greater F value by chance alone. When Model III was compared with Model I, it was found that temperature was also significant (F ⫽ 4.014, Pr(⬎F) ⫽ 4.9 ⫻ 10⫺2). A similar analysis demonstrated that shear rate/gel type; temperature/ gel type and; to a lesser extent, shear rate/temperature interaction terms were also significant. When the room temperature data were analyzed separately it was found that almost 60% of the variance not described by shear rate was due to gel type. In our previous studies, we diluted the gels with a
vaginal fluid simulant (pH ⫽ 4.2) developed in this lab. In the present study, we attempted a similar dilution with Replens, but found that it is not soluble with the simulant. Advantage-S, however, mixes with the vaginal fluid simulant to form a suspension that is stable for several hours at room temperature. Replens has essentially the same chemical composition as Advantage-S except that it does not include nonoxynol-9, a nonionic surfactant spermicide. This difference in solubility between the two formulations may be due to the presence of nonoxynol-9 or to some difference in the ratio of ingredients used. Our results indicate that Advantage-S and Replens, although differing in only one constituent, have significantly different rheological properties and that these differences are temperature dependent. Moreover, they exhibit quite different responses to contact with a fluid similar to that found in the vagina. Both the rheology of a formulation, and its inherent miscibility with ambient vaginal fluid, have paramount effects on its deployment (distribution and retention) in the vagina [5]. Deployment, in turn, may profoundly affect the functionality of a formulation as a prophylactic agent against infection. Current studies in our lab are addressing specific relationships of formulation rheology and miscibility to measures of deployment. Our results call into question whether the epithelial coatings in the COL-1492 study were similar for the placebo Replens and the test formulation Advantage-S.
Acknowledgments The authors thank Columbia Laboratories for providing the formulations studied.
396
D.H. Owen et al. / Contraception 64 (2001) 393–396
References [1] Owen DH, Katz DF. A vaginal fluid simulant. Contraception 1999; 59:91–5. [2] Owen DH, Peters JJ, Katz DF. Rheological properties of contraceptive gels. Contraception 2001;62:321– 6. [3] Owen DH, Peters JJ, Lavine ML, Katz DF. Effect of temperature and pH on contraceptive gel viscosity, submitted for publication. [4] Van Damme L, Laga, et al. Vaginal microbicides: an update. Plenary presentation, 13th International AIDS Conference. Durban, South Africa. July 2000:12. [5] Katz DF, Henderson MH, Owen DH, Plenys AM, Walmer DK. What
[6] [7] [8] [9]
is needed to advance vaginal formulation technology? In: Rencher WF, editor. Vaginal microbicide formulations workshop. Philadelphia: Lippincott-Raven Publishers, 1998. p. 90 –9. Pagano M, Gauvreau. Principles of biostatistics. Belmont, CA: Duxbury Press, 1993. Venables WN, Smith DM, R Development Core Team. An introduction to R. published online, 2001. Park NA, Irvine TF. Anomalous viscosity-temperature behavior of aqueous carbopol solutions. J Rheol 1997;41:167–73. Bird RB, Armstrong RC, Hassager O. Dynamics of polymerics liquids. Vol. 1. Fluid Mechanics. 2nd ed. NewYork: John Wiley and Sons, 1987.
Original research article
Comparison of the rheological properties of Advantage-S and Replens夞 Derek H. Owena,*, Jennifer J. Petersa, David F. Katza,b a
b
Department of Biomedical Engineering, Duke University, Durham, NC, USA Department of Obstetrics and Gynecology, Duke University, Durham, NC, USA
Abstract The rheological properties of Advantage-S and Replens were measured at body (37°C) and room temperature (25°C) over a range of physiologically relevant shear rates. The viscosity of Replens was found to differ from that of Advantage-S, particularly at room temperature. In addition, the two materials differed in their miscibility with a vaginal fluid simulant. © 2002 Elsevier Science Inc. All rights reserved. Keywords: Microbicide; Contraceptive gel; Vagina; Rheology; Viscosity
1. Introduction Our laboratory has recently been studying the rheological properties of several commercially available contraceptive gels. These gels (Conceptrol, Advantage-S, Gynol II, and KY Plus) have been studied at room and at body temperatures, both whole and diluted with a vaginal fluid simulant [1–3]. A recent study named COL-1492, described at the Thirteenth International AIDS Conference, involved the use of one of these products, Advantage-S (Columbia Laboratories, Inc.; Aventura, FL) [4]. In this triple-blind, randomized, multicenter study, Advantage-S (containing nonoxynol-9) was used intravaginally before heterosexual vaginal intercourse, and the rate of new HIV infections was compared with that of a control group using the same gel vehicle without nonoxynol-9, the commercially available product Replens (Columbia Laboratories, Inc.). Preliminary results indicate that the rate of new HIV infections per 100 personyears was 10.2 for Replens and 15.5 for Advantage-S. This difference has been attributed to the detrimental effect of the surfactant nonoxynol-9 on the vaginal epithelial tissue. Our previous work indicates that the composition of a gel can strongly influence its rheological properties. These properties, in turn, affect its ability to coat the vaginal 夞 Support for this study was provided by the American Foundation for AIDS Research. * Corresponding author. Tel.: ⫹1-919-660-5182; fax: ⫹1-919-6844488. E-mail address: [email protected] (D.H. Owen)
epithelia and to be retained on this surface during and after coitus [5]. For the control in a clinical study to be a true placebo, it should differ in only one respect, the absence of the active compound under study. We, therefore, thought it would be of interest to measure the rheological properties of Replens and compare them with those of Advantage-S.
2. Materials and methods Two polyacrylic acid-based commercial gels were studied: Advantage-S and Replens (both made by Columbia Laboratories, Inc.). These gels differ in composition in that Advantage-S contains nonoxynol-9 and Replens does not. Rheological properties measurements were made over a range of increasing shear rates (0.1 to 1000 s⫺1) at 25°C (room temperature) and at 37°C (body temperature). These shear rates bracket those experienced by formulations in vivo. Three to six replicates were performed for each experiment and the results averaged. Measurements were highly reproducible with coefficients of variation around 5% in all cases. Both Replens and Advantage-S were packaged in the commercially available tubes. All measurements were performed on a Brookfield Model DV-III Digital Rheometer (Brookfield Engineering Laboratories, Inc.; Stoughton, MA) as described in our previous work [2]. In this instrument, the test material is placed between two surfaces, one surface is rotated, and the torque resisting flow is measured. This allows the determination of the relationship between applied shear rate and shear stress experienced by the material. All measurements
0010-7824/01/$ – see front matter © 2002 Elsevier Science Inc. All rights reserved. PII: S 0 0 1 0 - 7 8 2 4 ( 0 1 ) 0 0 2 7 8 - 5
394
D.H. Owen et al. / Contraception 64 (2001) 393–396
Fig. 1. Viscosity versus shear rate for Advantage-S and Replens, room temperature.
were conducted with a cone and plate configuration (three configurations were used, with cone angles and diameters of 3° - 4.8 cm, 3° - 2.4 cm, and 0.8° - 4.8 cm). The viscosity versus shear rate data were analyzed to determine the significance of temperature and gel type. An ANCOVA was performed on the data, with the shear rate being the covariate variable while gel type and temperature were the simple main effects; viscosity was the dependent variable. The number of variables and interactions was small enough to permit an “all possible models” approach to model evaluation [6]. The model containing the covariate alone was then compared to all models containing additional terms (gel type, temperature, and interaction terms) to determine the significance of these additional terms. Statistical analysis was performed by using the software package “R” [7].
3. Results and discussion Results for the measurements made at room temperature and at body temperature are shown in Figs. 1 and 2, respectively. Fig. 3 shows the ratio of the viscosity of Replens to that of Advantage-S as a function of shear rate at the two temperatures. We can see from these results that at room temperature, Replens has a higher viscosity than Advantage-S, but that this difference decreases with increasing shear rate. At low shear rates, the viscosity of Replens is 1.5 times higher than that of Advantage-S. At body temperature, the difference is less pronounced, although the same relationship to shear rate applies. This is because, for Advantage-S, the viscosity at the higher temperature is higher than that at the lower temperature; this is not the case with Replens.
Fig. 2. Viscosity versus shear rate for Advantage-S and Replens, body temperature.
D.H. Owen et al. / Contraception 64 (2001) 393–396
395
Fig. 3. Ratio of viscosities Replens/Advantage-S vs. shear rate.
This anomalous viscosity-temperature relationship has been observed with other polyacrylic acid derivatives [8]. Both gels exhibited shear thinning behavior over the range of shear rates studied. The relatively constant slope of these curves indicates that, under these flow conditions, all product mixtures can be modeled by using the power law equation for the viscosity () as a function of shear rate (␥˙ ) [9]:
⫽ m ␥䡠 n-1 where m and n are constants. It is this linear relationship between the log of the viscosity and the log of the shear rate that allows that us to use shear rate as the covariate in our ANCOVA. The ANCOVA model containing the shear rate alone was then compared to all models containing additional terms by using ANOVA methods. The three models of greatest relevance are the following: Model I: shear rate alone; Model II: shear rate plus gel type; Model III: shear rate plus temperature. When Model II was compared with Model I it was found that gel type was significant (F ⫽ 19.649, Pr(⬎F) ⫽ 3.8 ⫻ 10⫺5). Note: Pr(⬎F) is the probability of obtaining a greater F value by chance alone. When Model III was compared with Model I, it was found that temperature was also significant (F ⫽ 4.014, Pr(⬎F) ⫽ 4.9 ⫻ 10⫺2). A similar analysis demonstrated that shear rate/gel type; temperature/ gel type and; to a lesser extent, shear rate/temperature interaction terms were also significant. When the room temperature data were analyzed separately it was found that almost 60% of the variance not described by shear rate was due to gel type. In our previous studies, we diluted the gels with a
vaginal fluid simulant (pH ⫽ 4.2) developed in this lab. In the present study, we attempted a similar dilution with Replens, but found that it is not soluble with the simulant. Advantage-S, however, mixes with the vaginal fluid simulant to form a suspension that is stable for several hours at room temperature. Replens has essentially the same chemical composition as Advantage-S except that it does not include nonoxynol-9, a nonionic surfactant spermicide. This difference in solubility between the two formulations may be due to the presence of nonoxynol-9 or to some difference in the ratio of ingredients used. Our results indicate that Advantage-S and Replens, although differing in only one constituent, have significantly different rheological properties and that these differences are temperature dependent. Moreover, they exhibit quite different responses to contact with a fluid similar to that found in the vagina. Both the rheology of a formulation, and its inherent miscibility with ambient vaginal fluid, have paramount effects on its deployment (distribution and retention) in the vagina [5]. Deployment, in turn, may profoundly affect the functionality of a formulation as a prophylactic agent against infection. Current studies in our lab are addressing specific relationships of formulation rheology and miscibility to measures of deployment. Our results call into question whether the epithelial coatings in the COL-1492 study were similar for the placebo Replens and the test formulation Advantage-S.
Acknowledgments The authors thank Columbia Laboratories for providing the formulations studied.
396
D.H. Owen et al. / Contraception 64 (2001) 393–396
References [1] Owen DH, Katz DF. A vaginal fluid simulant. Contraception 1999; 59:91–5. [2] Owen DH, Peters JJ, Katz DF. Rheological properties of contraceptive gels. Contraception 2001;62:321– 6. [3] Owen DH, Peters JJ, Lavine ML, Katz DF. Effect of temperature and pH on contraceptive gel viscosity, submitted for publication. [4] Van Damme L, Laga, et al. Vaginal microbicides: an update. Plenary presentation, 13th International AIDS Conference. Durban, South Africa. July 2000:12. [5] Katz DF, Henderson MH, Owen DH, Plenys AM, Walmer DK. What
[6] [7] [8] [9]
is needed to advance vaginal formulation technology? In: Rencher WF, editor. Vaginal microbicide formulations workshop. Philadelphia: Lippincott-Raven Publishers, 1998. p. 90 –9. Pagano M, Gauvreau. Principles of biostatistics. Belmont, CA: Duxbury Press, 1993. Venables WN, Smith DM, R Development Core Team. An introduction to R. published online, 2001. Park NA, Irvine TF. Anomalous viscosity-temperature behavior of aqueous carbopol solutions. J Rheol 1997;41:167–73. Bird RB, Armstrong RC, Hassager O. Dynamics of polymerics liquids. Vol. 1. Fluid Mechanics. 2nd ed. NewYork: John Wiley and Sons, 1987.