Pharmacology Flashcards
What are pharmacokinetic drug interactions and how can they affect contraception?
Pharmacokinetics is the movement of drugs through the body - how the drug changes the body
Pharmacokinetic interactions alter the four stages: absorption, distribution, metabolism, and excretion
Interactions that Reduce Effectiveness:
Drugs INDUCE cytochrome P450 enzymes INCREASE hormone CLEARANCE, therefore REDUCING the effectiveness of most combined hormonal methods, progestogen-only pills, implants, and oral emergency contraception.
Injectable contraception (DMPA), copper IUDs, and levonorgestrel IUS are unaffected.
Drugs causing vomiting, diarrhoea, or altering gut pH and transit may also reduce absorption.
Clinical relevance
Antibiotics and Contraceptives:
Non-enzyme-inducing antibiotics, despite potentially altering gut flora, do not significantly affect combined hormonal contraception.
No additional precautions are needed unless the antibiotic is an enzyme inducer or causes vomiting/diarrhea.
Interactions that Increase Hormone Exposure:
Drugs REDUCE cytochrome P450 enzymes make blood more RICH in contraceptive hormone levels, potentially leading to increased RISK of side effects like thrombosis.
Effects on Other Drugs:
