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Oral contraceptive prescribing

Oral contraceptive prescribing. clinical pharmacology mechanism of action ADME interactions adverse reactions benefits and harms. what are they. around since late 1950’s social revolution progestogen /oestrogen variety of components and doses changes over time in both. oestrogen

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Oral contraceptive prescribing

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  1. Oral contraceptive prescribing

  2. clinical pharmacology • mechanism of action • ADME • interactions • adverse reactions • benefits and harms

  3. what are they • around since late 1950’s • social revolution • progestogen /oestrogen • variety of components and doses • changes over time in both

  4. oestrogen ethinyoestradiol mestranol progestogen norethisterone norgestrel Levonorgestrel medroxyprogesterone ethynodiol diacetate gestodene desogestrel components

  5. doses • monophasic • oestrogen - up to 50g/day • progestogen - up to 1mg/day • biphasic • oestrogen: constant • progestogen: eg 11 days @50, 10 @125 g • triphasic • oestrogen 30/40/30 • progestogen 50/75/125

  6. clinical pharmacology • mechanism of action • inhibit secretion of FSH, LH - inhibit ovulation • additional actions on endometrium tubal motility, cervical mucosa

  7. clinical pharmacology • absorption • well absorbed orally • distribution • bound to plasma proteins • albumin, SBG, others

  8. metabolism • Oestrogens • first pass clearance • metabolised in liver, conjugated • excreted in the bile - (estradiol vs EE) • enterohepatic circulation • Progestogens • depends on which one - “natural” progestogen extensive first pass metabolism

  9. excretion • urinary • remember the bile duct STO HV PV CBD About 40-60 % of estrogen removed in the first pass through the liver HMW conjugates are excreted in bile

  10. interactions (1) • antibiotics • impaired absorption (effect on gut enzymes) reduced bacterial sulfatase leading to reduced entero-hepatic recycling • enzyme induction -> increased clearance, lower plasma estrogen concentrations (eg rifampicin, griseofulvin, anticonvulsants, St John’s Wort)

  11. interactions (2) • anticonvulsants • Older drugs are enzyme inducers -> increased clearance and reduced concentration and failure (phenytoin, phenobarbitone, primidone, carbamazepine). No effect of sodium valproate • Newer drug have variable effects (no change with gabapentin, lamotrigine, tiagabine, levetiracetam) (induction with topiramate and oxcarbazepine) • try higher dose estrogen pills, double product dosing • valproate less of a problem

  12. adverse reactions • estrogen excess • late cycle breakthrough bleeding • menorrhagia/dysmenorrhoea • nausea/vomiting • fluid retention • breast tenderness

  13. adverse reactions • progestogen excess • amenorrhoea • acne/oily skin • weight gain • mood changes • depressed libido • breast tenderness

  14. other risks • thromboembolic disorder • high dose oestrogen - Inman, dose response relationship • worse with other risk factors (age, smoking) • ?third generation progestogens • differentiating effects on VTE and other cardiovascular disease

  15. big picture risks • endometrial cancer • progestogen is protective • ovarian cancer • protective • breast cancer • jury out /data unconvincing • cervical cancer • confounded

  16. other benefits • reduction in menstrual flow - may lower incidence of anemia • reduction in dysmenorrhoea • possible reduction in auto-immune thyroid disease, rheumatoid arthritis • some protection against PID

  17. risk of nonfatal VTE

  18. other issues • compliance • gastro. • missing pills • alternative forms of hormonal contraception

  19. benefits effective contraception other health benefits long-term health and social impact harms immediate adverse effects risk of failure long-term health effects balance sheet

  20. other uses • morning after pill • EE 100mcg + norgestrel 1mg within 72 hours, 2 doses • Failure rate of about 1%

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