Parenteral Texture Control: Vaginal Delivery Products

VAGINAL DELIVERY

The vaginal route of administration offers a promising option for local and systemic delivery of drugs.

Suppositories, creams, gels and tablets are commonly used vaginal drug delivery systems. These conventional vaginal formulations, however, are associated with limitations of poor retention, leakage, and messiness, thereby causing inconvenience to users. 

To overcome these limitations, formulations that adhere to the vaginal mucosa for a sufficient period of time need to be developed. Bioadhesion and retention are desirable characteristics of a vaginal formulation to achieve desired efficacy. These properties can be built in during formulation development by the use of bioadhesive polymers and tested by similar methods to those already discussed for bioadhesion. The limitations have also necessitated the development of other novel drug delivery systems.

Vaginal Rings

Vaginal rings (also known as intravaginal rings, or V-Rings) are soft, flexible, 'doughnut-shaped' polymeric drug delivery devices designed to provide controlled release of drugs to the vagina over extended periods of time. The rings, typically measuring 54mm in diameter, are easily inserted and removed and are held in place by the walls of the vagina. Although their exact location within the vagina is not critical for clinical efficacy, rings commonly reside next to the cervix. Vaginal ring devices are already commonly used for contraception and hormone replacement therapy but the potential for exploiting vaginal ring technology for the prolonged delivery of HIV microbicides is now being considered by researchers from the School of Pharmacy at Queen’s University (see Woolfson et al).

The development of an effective HIV microbicide could play an important role in preventing women becoming infected with the virus by preventing or decreasing the likelihood of viral transmission and subsequent infection. In turn, a microbicidal vaginal ring would essentially replace conventional poorly retentive semi-solid formulations and place a woman in greater control of her own sexual health which would have a significant impact on HIV transmission rates amongst the poorest women in the developing world.

Measuring Vaginal Ring Mechanical Properties

There is the possibility that inclusion of excipients into Intravaginal Ring formulations may adversely influence their mechanical properties. The mechanical properties of an IVR must ensure optimal vaginal compatibility and user acceptability. If the mechanical strength is too low, the ring could either be expulsed from the vagina or be prone to rupture. If the mechanical strength is too high, the inflexibility of the device could cause irritation/ulceration of the vaginal tissue. It is therefore necessary to assess the mechanical characteristics of the rings before and after release, since both incorporation of such excipients into the rings and the subsequent release/uptake of drug/excipients/release medium are likely to influence their mechanical characteristics.

The compressional strength of each formulation can be evaluated on a Texture Analyser. Compressional force required to depress the vaginal rings through a specified distance is measured. The ring is placed vertically in a holder (Figure 13) and subjected to a compression cycle to a distance of 5mm, at a rate of 2mm/s for 5 cycle counts using an aluminium probe. The rings are tested before and after the 4-week dissolution period. Any further physical modifications to the ring design, such as core length or sheath thickness, would also need to be assessed to assess any potential compromise on the mechanical properties.

There is a Texture Analysis test for virtually any physical property. Contact Stable Micro Systems today to learn more about our full range of solutions.

---

For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

No-one understands texture analysis like we do!

To discuss your specific test requirements, click here...