Norethisterone and Ciprofloxacin Drug Interactions
Direct Answer
There is no clinically significant pharmacokinetic or pharmacodynamic interaction between norethisterone and ciprofloxacin, and these medications can be safely co-administered without dose adjustment. 1
Evidence Base
A randomized, double-blind, placebo-controlled crossover trial specifically evaluated ciprofloxacin 500 mg twice daily with a low-dose oral contraceptive containing ethinyl estradiol and desogestrel (a progestogen similar to norethisterone) and found no interaction. 1 The study demonstrated:
- No significant differences in ethinyl estradiol area under the curve during ciprofloxacin versus placebo administration 1
- No changes in sex hormone binding globulin levels, indicating stable estrogen exposure 1
- Complete ovarian suppression maintained in all subjects, with progesterone levels <2 ng/ml confirming no ovulation occurred 1
- No subjects had estradiol levels above early-follicular-phase range during ciprofloxacin treatment 1
Clinical Implications
Contraceptive efficacy is maintained when norethisterone-containing contraceptives are used with ciprofloxacin. 1 Unlike broad-spectrum antibiotics such as rifampicin or certain anticonvulsants (phenobarbital, phenytoin, carbamazepine) that induce cytochrome P450 enzymes and reduce contraceptive steroid levels, ciprofloxacin does not affect the metabolism of contraceptive hormones. 2
No backup contraception is required when ciprofloxacin is prescribed to patients taking norethisterone-containing contraceptives. 1
Important Safety Considerations for Ciprofloxacin
While there is no interaction with norethisterone, ciprofloxacin has several important drug interactions and precautions:
- QT prolongation risk: Ciprofloxacin blocks cardiac potassium channels and should be used cautiously with other QT-prolonging medications including class IA/III antiarrhythmics, tricyclic antidepressants, macrolides, and antipsychotics 3, 4
- Warfarin interaction: Ciprofloxacin increases bleeding risk when combined with warfarin 3
- Theophylline toxicity: Ciprofloxacin increases theophylline serum levels, requiring dose reduction and monitoring 3
- Absorption interactions: Separate ciprofloxacin administration from calcium, iron, magnesium, and antacids by 1-2 hours before or 4 hours after 3
- Tendon rupture risk: Increased in patients >60 years, on corticosteroids, or with renal impairment 3
Contraindications for Ciprofloxacin
Ciprofloxacin is contraindicated in pregnancy and nursing women. 3 If a patient taking norethisterone for contraception becomes pregnant or is breastfeeding, alternative antibiotics must be selected.