Norethisterone (Norethindrone) — Drug Profile

• Binds progesterone receptors -> suppresses the LH surge and inhibits ovulation
• Thickens cervical mucus (impairs sperm penetration)
• Induces endometrial changes unfavorable to implantation
• Also carries notable intrinsic androgenic activity and weak estrogenic/anabolic activity, which accounts for several of its side effects - Langman's Medical Embryology.

• Oral contraceptives: combined with ethinylestradiol (e.g., 0.035 mg EE + 1 mg norethisterone) or as norethisterone acetate in various combined pill brands (e.g., Loestrin) - Park's Textbook, Table 20.
• Progestogen-only tablets: 5 mg tablets used for contraception and for menstrual disorders.
• Injectable depot: Norethisterone enantate (NET-EN), 200 mg IM every 60 days - a progestogen-only injectable contraceptive in use since 1966, though less widely used than DMPA - Park's Textbook, "NET-EN" section.
• Menstrual disorders: dysfunctional/heavy uterine bleeding, endometriosis-related pain (often combined with an aromatase inhibitor such as letrozole), dysmenorrhea, and to delay menstruation.
• Hormone replacement therapy: combined with estrogen (e.g., estradiol) in postmenopausal women to provide endometrial protection against unopposed estrogen.

• Androgenic effects: acne, hirsutism, weight gain, voice changes
• Risk of masculinization of a female fetus if taken inadvertently in early pregnancy (clitoromegaly, labial fusion) due to androgenic potency - Langman's Medical Embryology
• Breakthrough bleeding/spotting, headache, mood changes, breast tenderness
• Mild adverse lipid profile changes; small increase in venous thromboembolism risk (lower than estrogen-containing preparations)

• Confirmed or suspected pregnancy
• Undiagnosed abnormal vaginal bleeding
• Active or past hormone-sensitive breast cancer
• Active thromboembolic disease or severe liver disease

• Acetazolamide is a sulfonamide derivative. Sulfonamide-related compounds have a weak, non-enzymatic ability to interfere with folate metabolism (similar structural family to folate-antagonist antimicrobials, though far weaker than agents like methotrexate or trimethoprim).
• The prescribing information explicitly notes: "Acetazolamide may increase the effects of other folic acid antagonists." This is a pharmacodynamic effect - it doesn't change absorption, distribution, metabolism, or excretion of folic acid/iron; it can potentiate anti-folate activity if co-administered with true folate antagonists.
• This is distinct from classic pharmacokinetic interactions involving iron (e.g., iron chelating tetracyclines, fluoroquinolones, levothyroxine, or bisphosphonates in the gut, which reduce absorption of those drugs) - acetazolamide does not chelate iron and iron does not meaningfully alter acetazolamide absorption.

• Classified by most drug-interaction checkers as "minor" or "low-risk" - the combination can generally be co-administered with standard monitoring, not a contraindicated or major pairing.
• In practice, these two are sometimes used together clinically rather than against each other - e.g., in high-altitude illness, acetazolamide is used for acute mountain sickness prophylaxis, while iron/folic acid supplementation is used to manage altitude-related polycythemia/chronic mountain sickness. This is a complementary therapeutic use, not an adverse interaction.