Re: Grrrrr for Doctors, Yay for Pharmacists


Lossandra wrote:
> So that is my rant for the day. Hopefully, the interference has not
> resulted in anything unplanned. A word for all other women who might be
> reading this: ASK about drug interactions when starting a new
> medication because your doctors may fail to inform you.

Lossandra, this is a vital heads-up for a lot of us wimmin-folk!

oral contraceptives have a pretty high drug-drug and drug-herb
interaction rate. some meds decrease the amount of contraceptive
hormones, others will *increase* it, and they can actually cause
changes in certain lab tests.

here's a (partial) list of interactions -- many of the drugs on the
list are commonly prescribed with M.S., including anti-convulsant and
pain meds. also included are herbs -- St. John's Wort prominently --
tha can cause changes in the contraceptive hormone levels and hoze
stuff up.

good on ya for bringing it up!
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DRUG INTERACTIONS
Changes in Contraceptive Effectiveness Associated With
Co-Administration of Other Drugs:

Contraceptive effectiveness may be reduced when hormonal contraceptives
are co-administered with some antibiotics, antifungals,
anticonvulsants, and other drugs that increase metabolism of
contraceptive steroids. This could result in unintended pregnancy or
breakthrough bleeding. Examples include barbiturates, griseofulvin,
rifampin, phenylbutazone, phenytoin, carbamazepine, felbamate,
oxcarbazepine, topiramate and possibly with ampicillin.

The proposed mechanism of interaction of antibiotics is different from
that of liver enzyme-inducing drugs. Literature suggests possible
interactions with the concomitant use of hormonal contraceptives and
ampicillin or tetracycline. In a pharmacokinetic drug interaction
study, oral administration of tetracycline HCl, 500 mg q.i.d. for 3
days prior to and 7 days during wear of ORTHO EVRAÒ did not
significantly affect the pharmacokinetics of norelgestromin or EE.

Several of the anti-HIV protease inhibitors have been studied with
co-administration of oral combination hormonal contraceptives;
significant changes (increase and decrease) in the mean AUC of the
estrogen and progestin have been noted in some cases. The efficacy and
safety of oral contraceptive products may be affected; it is unknown
whether this applies to ORTHO EVRAÒ. Healthcare professionals should
refer to the label of the individual anti-HIV protease inhibitors for
further drug-drug interaction information.

Herbal products containing St. John's Wort (hypericum perforatum) may
induce hepatic enzymes (cytochrome P450) and p-glycoprotein transporter
and may reduce the effectiveness of contraceptive steroids. This may
also result in breakthrough bleeding.

Increase in Plasma Hormone Levels Associated With Co-Administered
Drugs:

Co-administration of atorvastatin and certain oral contraceptives
containing ethinyl estradiol increase AUC values for ethinyl estradiol
by approximately 20%. Ascorbic acid and acetaminophen may increase
plasma ethinyl estradiol levels, possibly by inhibition of conjugation.
CYP 3A4 inhibitors such as itraconazole or ketoconazole may increase
plasma hormone levels.

Changes in Plasma Levels of Co-Administered Drugs:

Combination hormonal contraceptives containing some synthetic estrogens
(e.g., ethinyl estradiol) may inhibit the metabolism of other
compounds. Increased plasma concentrations of cyclosporine,
prednisolone, and theophylline have been reported with concomitant
administration of oral contraceptives. In addition, oral contraceptives
may induce the conjugation of other compounds. Decreased plasma
concentrations of acetaminophen and increased clearance of temazepam,
salicylic acid, morphine and clofibric acid have been noted when these
drugs were administered with oral contraceptives.

Although norelgestromin and its metabolites inhibit a variety of P450
enzymes in human liver microsomes, the clinical consequence of such an
interaction on the levels of other concomitant medications is likely to
be insignificant. Under the recommended dosing regimen, the in vivo
concentrations of norelgestromin and its metabolites, even at the peak
serum levels, are relatively low compared to the inhibitory constant
(Ki) (based on results of in vitro studies).

Health care professionals are advised to also refer to prescribing
information of co-administered drugs for recommendations regarding
management of concomitant therapy.

Interactions With Laboratory Tests

Certain endocrine and liver function tests and blood components may be
affected by hormonal contraceptives:

a. Increased prothrombin and factors VII, VIII, IX, and X; decreased
antithrombin 3; increased norepinephrine-induced platelet
aggregability.

b. Increased thyroid binding globulin (TBG) leading to increased
circulating total thyroid hormone, as measured by protein-bound iodine
(PBI), T4 by column or by radioimmunoassay. Free T3 resin uptake is
decreased, reflecting the elevated TBG, free T4 concentration is
unaltered.

c. Other binding proteins may be elevated in serum.

d. Sex hormone binding globulins are increased and result in elevated
levels of total circulating endogenous sex steroids and corticoids;
however, free or biologically active levels either decrease or remain
unchanged.

e. Triglycerides may be increased and levels of various other lipids
and lipoproteins may be affected.

f. Glucose tolerance may be decreased.

g. Serum folate levels may be depressed by hormonal contraceptive
therapy. This may be of clinical significance if a woman becomes
pregnant shortly after discontinuing ORTHO EVRA.
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