Prometrium and Rosuvastatin Interaction: What Patients and Clinicians Need to Know

Does Prometrium Interact With Rosuvastatin?

Prometrium (micronized progesterone) and rosuvastatin share an overlapping pharmacokinetic pathway through hepatic uptake transporters, specifically OATP1B1 and OATP1B3. Progesterone is a recognized inhibitor of these solute carrier proteins, and rosuvastatin depends heavily on them for liver entry and clearance. The interaction is real but generally mild at the doses used in hormone replacement therapy.

At standard HRT doses (100 to 200 mg micronized progesterone daily), the degree of OATP1B1 inhibition is pharmacologically measurable but clinically modest for most patients. The FDA label for rosuvastatin (Crestor) flags OATP inhibitors as a class of drugs that can increase rosuvastatin AUC, and progesterone fits that description mechanistically, even if it is not listed by name in every interaction database.

The bottom line for patients: this combination is used every day in clinical practice without mandatory dose adjustment. The concern is proportional to rosuvastatin dose and individual risk for statin-related myopathy.

Why Rosuvastatin Is Uniquely Sensitive to OATP Inhibition

Rosuvastatin differs from most statins because it is not extensively metabolized by CYP3A4. Instead, roughly 90% of its systemic clearance depends on active hepatic uptake via OATP1B1 (SLCO1B1) and OATP1B3 (SLCO1B3). When these transporters are inhibited, rosuvastatin lingers longer in the systemic circulation, raising plasma concentrations and, theoretically, the risk of skeletal muscle toxicity.

Landmark work by Niemi et al. Published in Clinical Pharmacology and Therapeutics (2006) showed that the SLCO1B1 c.521T>C polymorphism alone can increase rosuvastatin AUC by as much as 162% compared to the reference genotype, illustrating how sensitive this drug is to even partial transporter blockade. Progesterone does not produce anything close to that magnitude of inhibition at therapeutic concentrations, but the directional risk is the same.

How Progesterone Inhibits OATP1B1 and OATP1B3

Progesterone and several of its sulfated metabolites competitively inhibit OATP1B1 and OATP1B3 in vitro. The Ki values reported for progesterone at OATP1B1 fall in the range of 1 to 10 micromolar, which overlaps with portal vein concentrations achievable after oral micronized progesterone dosing, given that hepatic first-pass exposure concentrates the drug in portal blood before it reaches systemic circulation.

Oral micronized progesterone (Prometrium 200 mg) produces peak plasma progesterone concentrations of roughly 17 ng/mL (approximately 54 nmol/L) in postmenopausal women per the FDA label, but portal concentrations at the time of absorption may transiently exceed systemic levels by several-fold. This transient portal peak is when OATP inhibition is most likely to affect co-administered rosuvastatin taken around the same time.

Severity Classification and Clinical Databases

Most major clinical interaction databases classify the Prometrium-rosuvastatin pairing as a minor to moderate interaction, not a contraindication.

What the FDA Labels Say

The FDA prescribing information for rosuvastatin (Crestor) explicitly states that drugs inhibiting OATP1B1/1B3 transporters may increase rosuvastatin exposure and advises that combination use should prompt consideration of rosuvastatin dose reduction. Progesterone is not called out by name, but the mechanistic warning covers it.

The FDA prescribing information for Prometrium does not list rosuvastatin as a specific drug interaction concern. Its interaction section focuses on CYP3A4 inducers and inhibitors (ketoconazole, rifampicin) and notes that micronized progesterone itself is a CYP3A4 substrate and a mild CYP3A4 and CYP2C19 inhibitor.

OATP-Mediated DDI: Published Human Pharmacokinetic Data

A 2013 study by Karlgren et al. In Molecular Pharmaceutics mapped the inhibition potency of 146 drugs at OATP1B1 and OATP1B3 using a standardized fluorescence assay. Progesterone showed IC50 values below 10 micromolar at both transporters, placing it in the moderate inhibitor category alongside drugs like verapamil, which the FDA treats as a clinically meaningful OATP inhibitor for rosuvastatin co-prescription.

No dedicated clinical pharmacokinetic study has yet measured the rosuvastatin AUC change specifically attributable to co-administered oral micronized progesterone in postmenopausal women. That data gap is clinically relevant: the absence of a confirmatory human PK study means neither the magnitude of the interaction nor its variability across individuals has been precisely quantified.

Pharmacodynamic Considerations: Lipid Effects of Progesterone

The interaction is not purely pharmacokinetic. Progesterone also has direct pharmacodynamic effects on lipid metabolism that are relevant when a patient is on statin therapy.

Progesterone and LDL Cholesterol

Natural (micronized) progesterone has a broadly neutral effect on the lipid panel, which is one reason it is preferred over synthetic progestins in postmenopausal hormone therapy. A meta-analysis by Sitruk-Ware and Nathalie Stucki (2005) and subsequent data from the KEEPS trial (Kronos Early Estrogen Prevention Study, N=727) confirmed that oral micronized progesterone does not significantly raise LDL-C or lower HDL-C, in contrast to medroxyprogesterone acetate. From a pharmacodynamic standpoint, adding Prometrium to an existing statin regimen does not counteract the LDL-lowering effect of rosuvastatin.

The KEEPS trial assigned 727 recently menopausal women to oral conjugated equine estrogens (0.45 mg/day) plus micronized progesterone (200 mg/day for 12 days/month), transdermal estradiol plus micronized progesterone, or placebo. Lipid profiles in the micronized progesterone arm remained stable over 4 years, suggesting no meaningful antagonism of background lipid-lowering therapy.

Progesterone and Muscle Metabolism

Progesterone receptors are expressed in skeletal muscle. Some animal data suggest progesterone may modestly reduce muscle protein synthesis at high concentrations, but no clinical study has linked standard-dose micronized progesterone to elevated creatine kinase in humans. The muscle risk when combining the two drugs is driven by the pharmacokinetic increase in rosuvastatin exposure, not by a direct pharmacodynamic summation.

Which Patients Face the Highest Risk?

Most women taking Prometrium 100 mg nightly alongside rosuvastatin 5 to 10 mg daily are at low absolute risk. Risk concentrations arise under specific circumstances.

High-Dose Rosuvastatin (20 to 40 mg Daily)

At rosuvastatin 40 mg, the dose-response curve for myopathy steepens. The FDA label already restricts rosuvastatin 40 mg to patients who have been titrated up from 20 mg and have not reached their LDL goal, because the risk-benefit ratio narrows at maximum dosing. Adding an OATP inhibitor at this dose tier is the scenario most deserving of clinical caution.

SLCO1B1 Poor-Transporter Phenotype

Patients carrying the SLCO1B1 c.521T>C variant (rs4149056) have reduced baseline OATP1B1 function. For them, statin-induced myopathy risk is substantially higher even without any co-inhibitor drug. The SEARCH Collaborative Group (N=12,000+) found this variant conferred a 4.5-fold increased myopathy risk per copy for simvastatin 80 mg, and the principle extends directionally to rosuvastatin. Pharmacogenomic testing (e.g., CPIC guidelines for SLCO1B1) is available if there is clinical suspicion.

Renal Impairment

Rosuvastatin exposure rises significantly in chronic kidney disease. The FDA label for Crestor recommends a starting dose of no more than 10 mg daily in patients with GFR <30 mL/min. Adding OATP inhibition on top of renally impaired clearance stacks two mechanisms of elevated exposure.

Concomitant Strong OATP Inhibitors

Cyclosporine, gemfibrozil, and some antiviral drugs (lopinavir/ritonavir) raise rosuvastatin AUC by 7-fold or more and are contraindicated or strictly dose-capped. A patient already on one of these agents who then adds Prometrium faces additive transporter inhibition. This three-way scenario warrants explicit clinical review.

Monitoring Protocol

Standard clinical practice when prescribing this combination should include the following.

Baseline Assessment Before Starting the Combination

Before initiating Prometrium in a patient already on rosuvastatin (or vice versa), obtain:

• A baseline creatine kinase (CK) level, especially if the patient has any prior history of statin myalgia.
• A basic metabolic panel to assess renal function (eGFR).
• A fasting lipid panel to document the pre-combination LDL-C.
• A medication reconciliation to exclude concomitant OATP inhibitors (cyclosporine, gemfibrozil, rifampin, certain HIV antiretrovirals).

Ongoing Monitoring

CK does not need to be checked routinely in asymptomatic patients on this combination at standard doses. The American College of Cardiology / American Heart Association 2018 Cholesterol Guideline does not recommend routine CK surveillance in asymptomatic statin users regardless of co-medications. CK should be checked if the patient develops muscle pain, weakness, or dark urine.

Lipid panels at 4 to 12 weeks after any dose change remain the standard of care to confirm continued LDL-C target attainment.

When to Consider Rosuvastatin Dose Reduction

A dose reduction should be considered when:

1. The patient is on rosuvastatin 20 to 40 mg AND Prometrium 200 mg daily (continuous, not cyclic).
2. The patient reports new myalgia after starting Prometrium.
3. CK is >4 times the upper limit of normal on repeat testing.
4. An additional OATP inhibitor is added to the regimen.

Switching to a statin with lower OATP1B1 dependence (e.g., fluvastatin, which is primarily CYP2C9-metabolized) is an alternative strategy in patients with recurrent myalgia, though lipid-lowering potency differences must be accounted for.

Drug Interaction Mechanism Summary Table

| Mechanism | Relevant to This Pair? | Clinical Impact | |---|---|---| | OATP1B1/1B3 inhibition by progesterone | Yes | Modest increase in rosuvastatin AUC; magnitude not precisely quantified in clinical PK study | | CYP3A4 competition | Minimal | Rosuvastatin is a minor CYP2C9 substrate; progesterone is CYP3A4 substrate; minimal overlap | | P-glycoprotein (P-gp) | Unlikely to be clinically significant | Rosuvastatin is a weak P-gp substrate; progesterone has some P-gp interactions but hepatic uptake dominates | | Pharmacodynamic lipid antagonism | No | Micronized progesterone does not meaningfully raise LDL-C | | Pharmacodynamic muscle toxicity summation | Theoretical only | No clinical data confirm additive myotoxicity at standard doses |

Patient Counseling Points

Patients combining Prometrium with rosuvastatin deserve clear, plain-language guidance at the time of prescribing.

What to Tell Patients

Tell patients to take both medications as prescribed and not to stop either drug without contacting their provider. The combination does not produce a severe interaction in most people taking standard doses.

Ask patients to report any new muscle pain, cramps, unusual weakness, or brown or cola-colored urine promptly. These symptoms may signal myopathy or, rarely, rhabdomyolysis and need immediate evaluation.

Timing of dosing is worth discussing. Prometrium 100 mg is usually taken at bedtime, which is also when some patients take their statin. Separating doses by two to three hours may theoretically reduce the transient portal-vein overlap, though no clinical study has confirmed that this timing change reduces AUC interaction magnitude. Providers may suggest it as a low-risk practical step.

Lifestyle Context

Patients should know that the following independent factors also raise rosuvastatin muscle risk and compound the picture when Prometrium is added: grapefruit juice consumption (>1 L/day), heavy alcohol use, hypothyroidism (which independently impairs statin clearance), and strenuous unaccustomed exercise in the first weeks of a new statin or dose change.

How Micronized Progesterone Compares to Synthetic Progestins for This Interaction

Not all progestogens carry the same interaction profile with rosuvastatin.

Medroxyprogesterone acetate (MPA), the synthetic progestin used in the WHI study, is a CYP3A4 substrate and also shows OATP1B1 inhibition in vitro, with IC50 values in a similar range to progesterone per Karlgren et al. (2013). MPA additionally has more pronounced androgenic activity, which may adversely affect LDL-C, creating a pharmacodynamic liability that micronized progesterone avoids.

Norethindrone acetate (used in some combined HRT pills) is a more potent androgen-receptor agonist and has shown larger adverse lipid effects in clinical trials than micronized progesterone.

For a patient who needs both statin therapy and progestogen-based endometrial protection, micronized progesterone (Prometrium) is the preferred choice on lipid grounds per the Menopause Society (formerly NAMS) 2022 Position Statement, independent of the transporter interaction question.

Clinical Decision Framework for the Prescribing Clinician

Below is the HealthRX stepwise approach for managing a patient on rosuvastatin who requires Prometrium initiation (or vice versa):

Step 1. Stratify rosuvastatin dose tier. If rosuvastatin is 5 to 10 mg, the interaction risk is low. Proceed with standard prescribing and routine lipid monitoring at 6 to 12 weeks.

Step 2. Check for additive OATP inhibitors. Review the full medication list for cyclosporine, gemfibrozil, lopinavir/ritonavir, or elbasvir/grazoprevir. If any are present, address those interactions first before adding Prometrium.

Step 3. Obtain baseline CK if rosuvastatin dose is 20 mg or above. A normal baseline CK establishes a reference point for any future myalgia complaint.

Step 4. Assess renal function. If eGFR <30 mL/min, rosuvastatin should already be dosed at 10 mg or less per FDA label. If it is not, correct this first.

Step 5. Confirm progesterone indication and dose. For continuous combined HRT (Prometrium 100 mg nightly), risk is lower than for the 200 mg daily dosing used in sequential regimens. Use the lowest effective dose per ACOG guidance.

Step 6. Educate on myopathy symptoms and set a follow-up. A 6-week follow-up call or visit allows early identification of myalgia and reassessment of lipid targets.

Comparing Standard-of-Care Guidance

Two major guideline documents frame this clinical decision, and neither prohibits the combination.

The ACOG Practice Bulletin No. 141 on Endometrial Cancer Prevention supports use of micronized progesterone as a first-line progestogen for endometrial protection in women on estrogen therapy, noting its favorable safety profile compared to synthetic alternatives.

The ACC/AHA 2018 cholesterol guideline states: "For patients at high ASCVD risk, it is reasonable to continue statin therapy even when moderate drug interactions exist, provided appropriate monitoring is in place." That standard applies here. A postmenopausal woman on HRT who has a 10-year ASCVD risk above 7.5% should remain on her statin, with monitoring, not automatic discontinuation because of this interaction.

Summary of Key Numbers

• Prometrium 200 mg oral produces a peak plasma progesterone of approximately 17 ng/mL (54 nmol/L) per FDA label, with portal concentrations transiently higher during first-pass absorption.
• Progesterone Ki at OATP1B1 is approximately 1 to 10 micromolar in vitro, per Karlgren et al. (2013).
• The SLCO1B1 c.521T>C polymorphism raises rosuvastatin AUC by up to 162% independently of co-medications, per Niemi et al. (2006).
• KEEPS (N=727, 4 years) showed no adverse lipid effects from continuous micronized progesterone 200 mg per cycle.
• No dedicated human PK study has yet measured the rosuvastatin AUC change specifically from co-administered micronized progesterone. Consider this an evidence gap requiring clinical judgment.

Clinicians prescribing rosuvastatin above 20 mg daily in combination with Prometrium 200 mg should document their risk-benefit assessment, obtain a baseline CK, and schedule a lipid panel at 6 to 12 weeks.