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 daily administration of Rifadin for Infusion.
Pharmacodynamic Interactions
When rifampicin is given concomitantly with the combination saquinavir/ritonavir, the potential for hepatotoxicity is increased. Therefore, concomitant use of Rifadin with saquinvir/ritonavir is contraindicated (see section 4.3).
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 Rifadin Infusion on other medicinal products
Induction of Drug Metabolizing Enzymes and Transporters
Rifadin infusion is a well characterized and potent inducer of drug metabolizing enzymes and transporters. Enzymes and transporters reported to be affected by Rifadin infusion 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 Rifadin infusion simultaneously. Therefore, Rifadin infusion may accelerate the metabolism and decrease the activity of certain co-administered drugs or increase the activity of a co-administered pro-drug (where metabolic activation is required) and has the potential to perpetuate clinically important drug-drug interactions against many drugs and across many drug classes. To maintain optimum therapeutic blood levels, dosages of drugs may require adjustment when starting or stopping concomitantly administered Rifadin infusion.
Rifampicin is contraindicated with medicines strongly affected by its potential to induce drug metabolizing enzymes and transporters such as: lurasidone, sofosbuvir, daclatasvir, telaprevir, 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 (anti-oestrogens e.g. tamoxifen, toremifene, gestinone)
• Antipsychotics (e.g. haloperidol, aripiprazole)
• Anticoagulants (e.g. coumarins)
• Antivirals (e.g. saquinavir, indinavir, efavirenz, cabotegravir, fostemsavir, lenacapavir, amprenavir, nelfinavir, atazanavir, lopinavir, nevirapine)
• Barbiturates
• Beta-blockers (e.g. bisoprolol, propanolol)
• Anxiolytics and hypnotics (e.g. diazepam, benzodiazepines, zopiclone, 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
• Immunosuppressive agents (e.g. ciclosporin, sirolimus, tacrolimus)
• Irinotecan
• Thyroid hormone (e.g. levothyroxine)
• Losartan
• Analgesics (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)
Cabotegravir, fostemsavir, lenacapavir: Rifampicin 600 mg daily reduced cabotegravir exposure (AUC) by 59% most likely via induction of UGTs.
Rifampicin 600 mg daily reduced fostemsavir exposure (AUC) by 82% most likely via induction of CYP3A4.
Rifampicin 600 mg daily reduced lenacapavir exposure (AUC) by 84% most likely via induction of CYP3A4, UGT1A1 and P-gp.
Lurasidone: Rifampicin 600mg was shown to decrease lurasidone AUC by 81%. Therefore, markedly reduced exposure of lurasidone can be expected when lurasidone is given concomitantly with a CYP3A4 inducer such as rifampicin (see section 4.3).
Enalapril: Decrease enalapril active metabolite exposure. Dosage adjustments should be made if indicated by the patient's clinical condition
Hepatitis-C antiviral drugs (e.g, daclatasvir, simeprevir, sofosbuvir, telaprevir): Concurrent use of treatment of simeprevir and rifampicin should be avoided. For daclatasvir, sofosbuvir and telaprevir see section 4.3.
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.
Clopidogrel: Increases active metabolite exposure. Rifadin strongly induces CYP2C19, resulting in both an increased level of clopidogrel active metabolite and platelet inhibition, which in particular might potentiate the risk of bleeding. As a precaution, concomitant use of clopidogrel and rifampicin should be discouraged.
Dapsone: Rifampicin has also been shown to increase the clearance of dapsone and the production of the hydroxylamine metabolite of dapsone which could increase the risk of methaemoglobinaemia, haemolytic anaemia, agranulocytosis, and haemolysis.
Systemic hormonal contraceptives including oestrogens and progestogens: 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 Rifadin therapy.
Mifepristone: Rifampicin was shown to decrease mifepristone AUC by 6.3-fold and its metabolites 22-hydroxy mifepristone and N-demethyl mifepristone by 20-fold and 5.9-fold, respectively. Therefore, reduced efficacy can be expected when mifepristone is given concomitantly with a potent CYP inducer such as rifampicin.
Antidiabetic (e.g. chlorpropamide, tolbutamide, sulfonylureas, rosiglitazone): diabetes may become more difficult to control.
Antifungals (e.g. fluconazole, itraconazole, ketoconazole, voriconazole, caspofungin): Concurrent use of ketoconazole and rifampicin has resulted in decreased serum concentrations of both drugs. After two weeks of repeated administration of rifampicin, trough levels of caspofungin were 30% lower than in adult subjects who received caspofungin alone.
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 Rifadin infusion
Antacids: 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.
Paracetamol: Concomitant use of paracetamol with rifampicin may increase the risk of hepatotoxicity.
Other drug interactions with Rifadin infusion
When the two drugs were taken concomitantly, decreased concentrations of atovaquone and increased concentrations of rifampicin were observed.