International Active Surveillance Study of Women Taking Oral Contraceptives (INAS-OC)

Drospirenone is a novel progestogen with antiandrogenic and antimineralocorticoid properties. A large active post-marketing surveillance study has demonstrated that a 21-day regimen of 3mg drospirenone and 30mcg ethinylestradiol can be used safely for oral contraception. This study investigates the risks of short and long-term use of a 24-day regimen of drospirenone/ethinylestradiol in comparison to established OCs in a study population that is representative of the actual users of the individual preparations.

INAS-OC is a prospective, controlled, non-interventional cohort study with two study arms: OCs containing drospirenone and OCs containing any other progestogen. The study was started in the USA in April 2005 and was extended to several European countries in September 2008 based on the launch status of the 24-day regimen. New users of an OC (starters, switchers without a pill intake break and recurrent users with a pill intake break [same or different OC]) are accrued by a network of prescribing physicians. Baseline and follow-up information are collected via a self-administered questionnaire. Data analysis will be based on life-table methods comparing the cohorts. All analyses will make allowance for confounding, using methods that will include multivariate techniques such as Cox regression.

Inclusion criteria

• First-ever OC users ("starters")
• Women switching OC use without a pill intake break ("switchers")
• Recurrent users with a pill intake break ("recurrent users")
• Women willing to participate in the active surveillance

Exclusion criteria

• Women who do not agree to participate
• Long-term users