### Effects of Drospirenone on Other Drugs

#### Metabolic Interactions

Metabolism of DRSP and potential effects of DRSP on hepatic cytochrome P450 (CYP) enzymes have been investigated in in vitro and in vivo studies (see Metabolism). In in vitro studies, DRSP did not affect turnover of model substrates of CYP1A2 and CYP2D6, but had an inhibitory influence on the turnover of model substrates of CYP1A1, CYP2C9, CYP2C19 and CYP3A4 with CYP2C19 being the most sensitive enzyme. The potential effect of DRSP on CYP2C19 activity was investigated in a clinical pharmacokinetic study using omeprazole as a marker substrate. In the study with 24 postmenopausal women [including 12 women with homozygous (wild type) CYP2C19 genotype and 12 women with heterozygous CYP2C19 genotype] the daily oral administration of 3mg DRSP for 14 days did not affect the systemic clearance of the CYP2C19 substrate omeprazole (40 mg) and the CYP2C19 product 5-hydroxy-omeprazole. Furthermore, no significant effect of DRSP on the systemic clearance of the CYP3A4 product omeprazole sulfone was found. These results demonstrated that DRSP did not inhibit CYP2C19 and CYP3A4 in vivo. 

Two further clinical drug-drug interaction studies using simvastatin and midazolam as marker substrates for CYP3A4, were each performed in 24 healthy, postmenopausal women. The results of these studies demonstrated that pharmacokinetics of the CYP3A4 substrates were not influenced by steady-state DRSP concentrations achieved after administration of 3 mg DRSP/day.

Based on the available results of in vivo and in vitro studies, it can be concluded that, at clinical dose level, DRSP is unlikely to interact significantly with cytochrome P450 enzymes.

In vitro and in vivo studies have shown that estrogens are metabolized partially by cytochrome P450 3A4 (CYP3A4). Therefore, inducers or inhibitors of CYP3A4 may affect estrogen drug metabolism. Inducers of CYP3A4 such as St. John's Wort preparations (Hypericum perforatum), phenobarbital, carbamazepine, and rifampin may reduce plasma concentrations of estrogens, possibly resulting in a decrease in therapeutic effects and/or changes in the uterine bleeding profile. Inhibitors of CYP3A4 such as erythromycin, clarithromycin, ketoconazole, itraconazole, ritonavir and grapefruit juice may increase plasma concentrations of estrogens and may result in side effects. 

### Co-Administration with Drugs that Have the Potential to Increase Serum Potassium 

There is a potential for an increase in serum potassium in women taking drospirenone with other drugs that may affect electrolytes, such as angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers, or non-steroidal anti-inflammatory drugs (NSAIDs). 

Electrolytes were studied in 230 postmenopausal women with hypertension and/or diabetes mellitus requiring an ACE inhibitor or angiotensin receptor blocker (ARB). Of these, 26 patients had a creatinine clearance >50 mL/min to <80 mL/min. Patients were given 1 mg estradiol (E2) and 3 mg drospirenone (DRSP) (n=112) or placebo (n=118) over 28 days. Non-diabetic patients also received ibuprofen 1200 mg/day for 5 days during the study. There was a single case of serum potassium >6.0 mEq/L and a single case of serum sodium <130 mEq/L on treatment, both occurring following five days of ibuprofen therapy in two women taking E2/DRSP. Serum potassium levels ≥5.5 mEq/L were observed in 8 (7.3%) E2/DRSP-treated subjects (3 diabetic and 5 non-diabetic) and in 3 (2.6%) placebo-treated subjects (2 diabetic and 1 non-diabetic). After 28 days of exposure, the mean change from baseline in serum potassium was 0.11 mEq/L for the E2/DRSP group and 0.08 mEq/L for the placebo group. None of the subjects with serum potassium levels ≥5.5 mEq/L had cardiovascular adverse events. A drug-drug interaction study of DRSP 3 mg/estradiol (E2) 1 mg versus placebo was performed in 24 mildly hypertensive postmenopausal women taking enalapril maleate 10 mg twice daily. Potassium levels were obtained every other day for a total of 2 weeks in all subjects. Mean serum potassium levels in the DRSP/E2 treatment group relative to baseline were 0.22 mEq/L higher than those in the placebo group. Serum potassium concentrations also were measured at multiple timepoints over 24 hours at baseline and on Day 14. On Day 14, the ratios for serum potassium Cmax and AUC in the DRSP/E2 group to those in the placebo group were 0.955 (90% CI: 0.914, 0.999) and 1.010 (90% CI: 0.944, 1.080), respectively. No patient in either treatment group developed hyperkalemia (serum potassium concentrations >5.5 mEq/L). 

Of note, occasional or chronic use of NSAID medication was not restricted in any of the ANGELIQ clinical trials.