Rifampin with oral contraceptives

Clinically important, potentially hazardous interactions with diuretics, estrogens, ketoconazole, live vaccines, oral contraceptives, phenytoin, rifampin, warfarin... 

The effects of the progestins are decreased when administered with anticonvulsants, barbiturates, or rifampin. Administration of the penicillins or tetracyclines with the oral contraceptives decreases the effects of the oral contraceptives. 

Stopping oral contraceptives - For women not taking carbamazepine, phenytoin, phenobarbital, primidone, or rifampin, the maintenance dose of lamotrigine may need to be decreased by as much as 50% of the maintenance dose with concurrent oral contraceptives. 

Certain concomitantly administered drugs may interfere with the effectiveness of the oral contraceptives or lead to an increased incidence of breakthrough bleeding. These include rifampin, isoniazid, ampiciUin, neomycin, penicillin V, chloramphenicol, sulfonamides, nitrofurantoin, phenytoin, barbiturates, primidone, analgesics, and phenothiazines. 

Meanwhile, the currently marketed CYP3A4 inducers can profoundly affect the pharmacokinetics of coadministered CYP3A4 substrates, e.g., rifampin on midazolam (139) or triazolam (140). Clearly, the most frequent outcome is a loss of efficacy, which is perhaps less serious than inhibition interactions, although the consequences of coadministering rifampin with the oral contraceptive pill can lead to contraceptive failure (141-143). 

UGT1A6 is a high-affinity (Km = 2.2 mM), low-capacity enzyme. UGT1A1 has intermediate affinity (9 mM) with high capacity, and UGT1A9 is a low-affinity, high-capacity enzyme (21 mM) (59). With a kinetic model, Court et al. estimated that at typical therapeutic concentrations (0.05-5 mM), UGT1A9 was the most important enzyme (>55% of total activity). Consequently, the mechanism of induction by oral contraceptives, phenytoin, and rifampin is unclear and may involve multiple enzymes. 

Decreased levels with enzyme inducers (rifampin). Increased levels wHh VPA. increased sedation with other CNS depressants. Decreased effectiveness of warfarin, CBZ, metronidazole, oral contraceptives. 

Clinically important, potentially hazardous interactions with alprazolam, astemizole, carbamazepine, cisapride, clarithromycin, dexamethasone, diltiazem, docetaxel, ifosfamide, imatinib, irinotecan, itraconazole, ketoconazole, methylprednisolone, midazolam, nefazodone, oral contraceptives, paroxetine, phenytoin, pimozide, rifampin, ritonavir, terfenadine, tolbutamide, trabectedin, troleandomycin, vinblastine, vincristine, warfarin... 

Clinically important, potentially hazardous interactions with benzodiazepines, carbamazepine, chlordiazepoxide, ciclesonide, clonazepam, clorazepate, dasatinib, diazepam, dihydroergotamine, ergot alkaloids, eszopiclone, eucalyptus, fentanyl, fesoterodine, flurazepam, ivabradine, lapatinib, lorazepam, methysergide, midazolam, oral contraceptives, oxazepam, phenytoin, pimozide, quazepam, rifampin, sildenafil, solifenacin, St John s wort, temazepam, temsirolimus, tolvaptan... 

Clinically important, potentially hazardous interactions with aluminum, aminophylline, aspirin, chlorambucil, cimetidine, clarithromycin, cyclophosphamide, cyclosporine, dicumarol, diuretics, docetaxel, estrogens, grapefruit juice, indomethacin, influenza vaccines, itraconazole, ketoconazole, lansoprazole, live vaccines, methotrexate, montelukast, omeprazole, oral contraceptives, pancuronium, phenobarbital, phenytoin, ranitidine, rifampicin, rifampin, timolol, tolbutamide, vitamin A... 

Clinically important, potentially hazardous interactions with alfentanil, alfuzosin, alprazolam, amiodarone, amprenavir, aprepitant, astemizole, atazanavir, bepridil, buprenorphine, bupropion, carbamazepine, chlordiazepoxide, ciclesonide, clozapine, conivaptan, cyclosporine, cyproterone, dasatinib, diazepam, dihydroergotamine, ergot alkaloids, estazolam, eszopidone, etravirine, ezetimibe, fentanyl, fesoterodine, flecainide, flurazepam, fluticasone, halazepam, ivabradine, ixabepilone, ketoconazole, lapatinib, levothyroxine, meperidine, meptazinol, methysergide, midazolam, nifedipine, nilotinib, oral contraceptives, phenytoin, pimozide, piroxicam, propafenone, propoxyphene, quazepam, quinidine, ranolazine, rifabutin, rifampin, rifapentine, rimonabant, rivaroxaban, saquinavir, sildenafil, silodosin, simvastatin, solifenacin, St John s wort, tadalafil, temsirolimus, trabectedin, triazolam, vardenafil, voriconazole, zolpidem... 

Rofecoxib is metabolized in the liver, primarily by cytosolic enzymes, with little renal excretion of unchanged drug. Rofecoxib at 75 mg daily modestly increased methotrexate concentrations, and at 50 mg daily modestly elevated the International Normalized Ratios (INRs) of warfarin patients. Additionally, rifampin can decrease rofecoxib concentrations. Clinically significant interactions were not observed when rofecoxib was administered with crmetidine, digoxin, oral contraceptives, or ketoconazole. Rofecoxib inhibits CYP450 1A2 and may increase serum theophylline area under the curve. 

Hepatic cirrhosis, congestive heart failure, and acute pulmonary edema all increase the tj of theophylline, as does concurrent therapy with cimetidine or erythromycin. In contrast, clearance is increased twofold by phenytoin or barbiturates, whereas cigarette smoking, rifampin, and oral contraceptives induce smaller changes. 

On her release from hospital, the patient is advised not to rely solely on oral contraceptives to avoid pregnancy since they may be less effective while she is being maintained on antimycobacterial drugs. The agent most likely to interfere with the action of oral contraceptives is (A) Ethambutol Isoniazid Pyrazinamide Rifampin Streptomycin... 

Drug Interactions Contraceptive effects are decreased when "the pill" is taken with ANTIDIOTICS (ampicillin, isoniazid, neomycin, pen V, rifampin, sulfonamides, tetracycline) or CNS AGENTS (barbiturates, benzodiazepines, phenytoin). Contraceptives increase the effects of corticosteroids and worsen side effects of tricyclic antidepressants. Oral contraceptives decrease the effectiveness of oral anticoagulants, anticonvulsants, and oral hypoglycemic agents. 

With the introduction of RiF in 1967, the duration of combination therapy for the treatment of TB was significantiy reduced (from 18 to 9 months). Rifampin is nearly always used in combination with one or more other antitubercuiin agents. The drug is potentially hepatotoxic and may produce Gl disturbances, rash, and thrombocytopenic purpura. Rifampin is known to induce hepatic microsomai enzymes (cytochrome P450) and may decrease the effectiveness of oral contraceptives, corticosteroids, warfarin, quinidine, methadone, zidovudine, clarithromycin, and the azoie antifungai agents (see Chapter 10) (33). 

Gambertoglio et al (131) have given in a detailed review the pharmacokinetics of prednisolone in healthy volunteers, patients with different diseases as well as effect of other drugs such as barbiturates, phenytoin, rifampin and oral contraceptives. 

Carbamazepine levels are increased by CYP3A4 inhibitors (cimetidine, macrolides, diltiazem, fluoxetine, ketoconazole, verapamil, valproate) levels are decreased by CYP3A4 inducers (cisplatin, doxorubicin, felbamate, phenobarbital, phenytoin, primidone, rifampin, theophylline). Carbamazepine may increase levels of clomipramine, phenytoin, and primidone and lithium toxicity may decrease levels of phenytoin, warfarin, oral contraceptives, doxycycline, theophylline, haloperidol, alprazolam, clozapine, ethosuximide, and valproate may interfere with other anticonvulsants. 

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