Oral Contraceptives, birth control

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Oral Contraceptives - Interactions and Warnings


Drug interactions that decrease the efficacy of contraception or that limit the efficacy of concomitant medications can occur. The most frequent clinically encountered interactions involve antibiotics or anticonvulsants.
- J Gend Specif Med 1999 Nov-Dec;2(6):26-9 -- Oral contraceptive therapy in women: drug interactions and unwanted outcomes. -- Schwartz JB.

Oral contraceptive plasma concentrations may be reduced by induction of hepatic metabolism in the case of griseofulvin, rifampicin (rifampin) and several anticonvulsant drugs; valproic acid (sodium valproate) does not have this effect. Antibiotics may interfere with enterophepatic recirculation of ethinyl estradiol and reduce plasma levels of active hormone.
- Drug Saf 1993;9(1):21-37 -- Oral contraceptives: are drug interactions of clinical significance? -- Shenfield GM.

Plasma concentrations of ethinyl estradiol may be increased by ascorbic acid (vitamin C) and paracetamol (acetaminophen) which compete with it for sulphation in the gut wall. Theoretically, problems may arise if these agents are stopped suddenly.
- Drug Saf 1993;9(1):21-37 -- Oral contraceptives: are drug interactions of clinical significance? -- Shenfield GM.

A number of anticonvulsants (phenobarbital, phenytoin, carbamazepine) are enzyme-inducing agents and thereby increase the clearance of the oral contraceptive steroids. Broad spectrum antibiotics have been implicated in causing pill failure. The problem remains that there is still no firm clinical pharmacokinetic evidence which indicates that blood concentrations of oral contraceptive steroids are altered by antibiotics.
- Clin Pharmacokinet 1990 Jun;18(6):472-84 -- Pharmacokinetic drug interactions with oral contraceptives. -- Back DJ, Orme ML.

Although on theoretical grounds adsorbents (e.g. magnesium trisilicate, aluminium hydroxide, activated charcoal and kaolin) could be expected to interfere with oral contraceptive efficacy, there is no firm evidence that this is the case.
- Clin Pharmacokinet 1990 Jun;18(6):472-84 -- Pharmacokinetic drug interactions with oral contraceptives. -- Back DJ, Orme ML.

St. John's wort interaction caused irregular bleeding with oral contraception.
- Schweiz Rundsch Med Prax 2001 May 10;90(19):843-9 -- St. John's wort: a pharmaceutical with potentially dangerous interactions -- Ratz AE, von Moos M, Drewe J.

Oral contraceptives should not be the primary method of birth control in women of child-bearing potential who are treated with nevirapine.
- J Acquir Immune Defic Syndr 2002 Apr 15;29(5):471-7 -- Pharmacokinetic interaction between nevirapine and ethinyl estradiol/norethindrone when administered concurrently to HIV-infected women. -- Mildvan D, Yarrish R, Marshak A, Hutman HW, McDonough M, Lamson M, Robinson P.

Observation suggests that the oral contraceptive increased the plasma concentration of chlorpromazine.
- Ther Drug Monit 2001 Oct;23(5):556-8 -- Oral contraceptives increase the plasma concentrations of chlorpromazine. -- Chetty M, Miller R.

Not recommended if you are a smoker.
- J Gend Specif Med 1999 Nov-Dec;2(6):26-9 -- Oral contraceptive therapy in women: drug interactions and unwanted outcomes. -- Schwartz JB.

Dietary boron supplementation enhanced the action of estrogen.
- Biol Trace Elem Res 2001 Summer;82(1-3):109-23 -- Dietary boron supplementation enhanced the action of estrogen, but not that of parathyroid hormone, to improve trabecular bone quality in ovariectomized rats. -- Sheng MH, Taper LJ, Veit H, Qian H, Ritchey SJ, Lau KH.

Oral contraceptives can interact with many prescription medications and over the counter medications. Consult with your physician before using with other drugs.

Use caution with herbs and Oral Contraceptives especially St. John's wort and red clover. Consult with your physician to avoid dangerous interactions.





last update: November 2008



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