Levonorgestrel + ethinylestradiol is the combined contraceptive pill: a progestogenic hormone and an oestrogen that together prevent ovulation. When taken correctly it is more than 99% effective.
Also known as: Pílula combinada, Microgynon, Levlen
Rifampicin markedly reduces the effectiveness of hormonal contraception (levonorgestrel + ethinylestradiol), with risk of unintended pregnancy.
Enzyme induction (CYP3A4) accelerates oestrogen and progestogen metabolism; Annex 7 lists rifampicin among drugs reducing oral contraceptive efficacy.
Ask about intermenstrual bleeding and missed periods.
Intermenstrual bleeding, missed period.
Recommend additional barrier contraception throughout treatment and for 4 weeks after; consider a non-hormonal method while on rifampicin.
INFARMED Prontuário Terapêutico (11th ed., 2012), Annex 7 — Oestrogens: "Rifampicin" (reduced oral contraceptive efficacy); DailyMed — Rifampin Capsule label [RLD Rifadin]: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=50f706f9-5003-4e15-bece-85b6213b1f5c
Carbamazepine reduces hormonal contraceptive efficacy through enzyme induction, with risk of unintended pregnancy.
Enzyme inducers accelerate oestrogen/progestogen metabolism (Annex 7: "See also Carbamazepine"; the Tegretol label documents contraceptive failure).
Intermenstrual bleeding, missed periods.
Intermenstrual bleeding, unintended pregnancy.
Recommend additional barrier contraception or a non-hormonal method; do not rely on the oral contraceptive alone during co-administration.
DailyMed — Tegretol (carbamazepine) label, Drug Interactions (contraceptive failure): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d0121be3-b904-41d3-a81a-292aa4176491; INFARMED Prontuário Terapêutico (11th ed., 2012), Annex 7 — Oestrogens.
Phenytoin reduces hormonal contraceptive efficacy through enzyme induction, with risk of unintended pregnancy.
Phenytoin is a microsomal metabolism inducer; Annex 7 (Oestrogens): "Phenytoin" among drugs increasing oestrogen metabolism.
Intermenstrual bleeding, missed periods.
Intermenstrual bleeding, unintended pregnancy.
Recommend additional barrier contraception; consider non-hormonal methods; pregnancy in women with epilepsy also requires planning with the neurologist.
INFARMED Prontuário Terapêutico (11th ed., 2012), Annex 7 — Oestrogens: "Phenytoin"; DailyMed — Phenytoin Tablet label [RLD Dilantin]: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=46d5c0d1-a97b-46d9-8cf4-994780673337
No clinically relevant food interaction is documented; vomiting/diarrhoea within 3–4 h of the dose reduces efficacy (not a food interaction, dose loss).
Take with or without food, always at the same time; if vomiting within 3–4 h, follow missed-dose instructions.
EMC-UK — combined oral contraceptive SmPC 4.2/4.4 (vomiting/diarrhoea).
The combined contraceptive is contraindicated in active/past VTE — oestrogen raises VTE risk.
Exclude history of DVT/PE before prescribing; discontinue 4 weeks before high-risk surgery.
Site monograph (levonorgestrel-EE — thrombosis history); EMC-UK combined pill SmPC 4.3.
Contraindicated in uncontrolled hypertension — oestrogen raises blood pressure.
Measure blood pressure before prescribing; if BP raised, choose an oestrogen-free method.
Site monograph (levonorgestrel-EE — hypertension); EMC-UK combined pill SmPC 4.3.
Hormonal contraceptive: should not be used during pregnancy (no indication), but inadvertent exposure is not harmful — Annex 1 records "See Oral contraceptives: epidemiological data suggest no danger to the fetus" (factor C). Discovering pregnancy on the pill is an indication to stop, not to terminate.
Discontinue on confirming pregnancy; inadvertent 1st-trimester exposure is not an indication for abortion — reassure and follow normal surveillance.
Oestrogens reduce milk production and impair lactation; prefer progestogen-only or non-hormonal methods while breastfeeding (especially in the first 6 months).
Prontuário Terapêutico INFARMED — Annex 1: "Levonorgestrel — See Oral contraceptives" (l. 40803) and "Oral contraceptives" (l. 39861-62). WHO — Medical eligibility criteria for contraceptive use (category 4 in pregnancy; inadvertent exposure without risk).
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Ovulation suppression (> 99% efficacy with correct dosing); cycle regulation.
Levonorgestrel binds the progesterone receptor strongly; ethinylestradiol binds the oestrogen receptor and keeps the endometrium stable and FSH/LH feedback suppressed.
Rapid complete oral absorption; ethinylestradiol undergoes significant first-pass (bioavailability ~ 40%).
Levonorgestrel: hepatic CYP3A4; ethinylestradiol: CYP3A4 hydroxylation and sulphation; both renally and biliary excreted.
Levonorgestrel ~ 30 h; ethinylestradiol ~ 13–27 h.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
