Interference with laboratory and diagnostic tests
Therapeutic levels of rifampicin have been shown to inhibit standard microbiological assays for serum folate and Vitamin B12. Thus alternative assay methods should be considered. Transient elevation of BSP and serum bilirubin has been reported. Rifampicin may impair biliary excretion of contrast media used for visualization of the gallbladder, due to competition for biliary excretion. Therefore, these tests should be performed before the morning dose of rifampicin.
Pharmacodynamic Interactions
When rifampicin is given concomitantly with the combination saquinavir/ritonavir, the potential for hepatotoxicity is increased. Therefore, concomitant use of Rifampicin with saquinvir/ritonavir is contraindicated (see section 4.3 Contraindications).
When rifampicin is given concomitantly with either halothane or isoniazid, the potential for hepatotoxicity is increased. The concomitant use of rifampicin and halothane should be avoided. Patients receiving both rifampicin and isoniazid should be monitored closely for hepatotoxicity.
The concomitant use of rifampicin with other antibiotics causing vitamin K dependent coagulopathy such as cefazolin (or other cephalosporins with N-methyl-thiotetrazole side chain) should be avoided as it may lead to severe coagulation disorders, which may result in fatal outcome (especially in high doses).
Effect of Rifampicin capsules on other medicinal products
Induction of Drug Metabolizing Enzymes and Transporters
Rifampicin capsules are a well characterized and potent inducer of drug metabolizing enzymes and transporters. Enzymes and transporters reported to be affected by Rifampicin capsules include cytochromes P450 (CYP) 1A2, 2B6, 2C8, 2C9, 2C19, and 3A4, UDP-glucuronyltransferases (UGT), sulfotransferases, carboxylesterases, and transporters including P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2). Most drugs are substrates for one or more of these enzyme or transporter pathways, and these pathways may be induced by Rifampicin capsules simultaneously. Therefore, Rifampicin capsules may accelerate the metabolism and reduce the activity of certain co-administered drugs, and has the potential to perpetuate clinically important drug-drug interactions against many drugs and across many drug classes (Table 1). To maintain optimum therapeutic blood levels, dosages of drugs may require adjustment when starting or stopping concomitantly administered Rifampicin capsules.
Rifampicin is contraindicated with medicines strongly affected by its potential to induce drug metabolizing enzymes and transporters such as: lurasidone, sofosbuvir, antiretrovirals: cabotegravir, fostemsavir and lenacapavir. Significant decrease in their plasma concentrations is observed because of potent induction of CYP 3A4, P-gp, UGT1A1 by rifampicin which is likely to result in loss of their therapeutic effectiveness.
Examples of drugs or drug classes affected by rifampicin:
• Antiarrhythmics (e.g. disopyramide, mexiletine, quinidine, propafenone, tocainide),
• Antiepileptics (e.g. phenytoin),
• Hormone antagonist (antiestrogens e.g. tamoxifen, toremifene, gestinone),
• Antipsychotics (e.g. haloperidol, aripiprazole),
• Anticoagulants (e.g. coumarins),
• Antifungals (e.g. fluconazole, itraconazole, ketoconazole, voriconazole),
• Antivirals (e.g. saquinavir, indinavir, efavirenz, amprenavir, nelfinavir, atazanavir, lopinavir, nevirapine),
• Barbiturates
• Beta-blockers (e.g. bisoprolol, propanolol),
• Anxiolytics and hypnotics (e.g. diazepam, benzodiazepines, zolpicolone, zolpidem),
• Calcium channel blockers (e.g. diltiazem, nifedipine, verapamil, nimodipine, isradipine, nicardipine, nisoldipine),
• Antibacterials (e.g. chloramphenicol, clarithromycin, dapsone, doxycycline, fluoroquinolones, telithromycin),
• Corticosteroids
• Cardiac glycosides (digitoxin, digoxin),
• Clofibrate,
• Systemic hormonal contraceptives including estrogens and progestogens,
• Antidiabetic (e.g. chlorpropamide, tolbutamide, sulfonylureas, rosiglitazone),
• Immunosuppressive agents (e.g. ciclosporin, sirolimus, tacrolimus)
• Irinotecan,
• Thyroid hormone (e.g. levothyroxine),
• Losartan,
• Analgestics (e.g. methadone, narcotic analgesics),
• Praziquantel,
• Quinine,
• Riluzole,
• Selective 5-HT3 receptor antagonists (e.g. ondansetron)
• Statins metabolised by CYP 3A4 (e.g. simvastatin),
• Theophylline,
• Tricyclic antidepressants (e.g. amitriptyline, nortriptyline),
• Cytotoxics (e.g. imatinib),
• Diuretics (e.g. eplerenone)
• Enalapril: decrease enalapril active metabolite exposure. Dosage adjustments should be made if indicated by the patient's clinical condition
• Hepatitis-C antiviral drugs (eg, daclatasvir, simeprevir, sofosbuvir, telaprevir): Concurrent use of treatment of hepatitis-C antiviral drugs and rifampicin should be avoided.
• Morphine: Plasma concentrations of morphine may be reduced by rifampicin. The analgesic effect of morphine should be monitored and doses of morphine adjusted during and after treatment with rifampicin.
• fesoterodine - used for overactive bladder
• tadalafil - used for impotence
• cimetidine - used for ulcer-healing drugs.
Rifampicin treatment reduces the systemic exposure of oral contraceptives.
Patients on oral contraceptives should be advised to use alternative, non-hormonal methods of birth control during Rifampicin therapy. Also diabetes may become more difficult to control.
Short-term treatment
Women on treatment with Rifampicin or herbal products should be advised that the efficacy of contraceptives may be reduced. An additional barrier contraceptive method should be used. The barrier method must be used during the whole time of Rifampicin treatment and for 28 days after discontinuation.
Long-term treatment
For women on long-term Rifampicin treatment, an additional alternative method of contraception unaffected by enzyme-inducing medicinal products should be considered.
Concurrent use of ketoconazole and rifampicin has resulted in decreased serum concentrations of both drugs.
If p-aminosalicylic acid and rifampicin are both included in the treatment regimen, they should be given not less than eight hours apart to ensure satisfactory blood levels.
Effect of other medicinal products on Rifampicin capsules
Concomitant antacid administration may reduce the absorption of rifampicin. Daily doses of rifampicin should be given at least 1 hour before the ingestion of antacids.
Other drug interactions with Rifampicin capsules
When the two drugs were taken concomitantly, decreased concentrations of atovaquone and increased concentrations of rifampicin were observed.
Rifampicin