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Darunavir and cobicistat: Darunavir is an inhibitor of CYP3A, a weak inhibitor of CYP2D6 and an inhibitor of P-gp. Cobicistat is a mechanism based inhibitor of CYP3A, and a weak CYP2D6 inhibitor. Cobicistat inhibits the transporters p-glycoprotein (P-gp), BCRP, MATE1, OATP1B1 and OATP1B3. Cobicistat is not expected to inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9 or CYP2C19. Cobicistat is not expected to induce CYP1A2, CYP3A4, CYP2C9, CYP2C19, UGT1A1, or P-gp (MDR1).
Co-administration of Symtuza and medicinal products primarily metabolised by CYP3A or transported by P-gp, BCRP, MATE1, OATP1B1 and OATP1B3 may result in increased systemic exposure to such medicinal products, which could increase or prolong their therapeutic effect and adverse reactions (see Contraindications or Table 8).
Symtuza must not be combined with medicinal products that are highly dependent on CYP3A for clearance and for which increased systemic exposure is associated with serious and/or life-threatening events (narrow therapeutic index).
Co-administration of Symtuza and medicinal products that have active metabolite(s) formed by CYP3A may result in reduced plasma concentrations of these active metabolite(s) potentially leading to loss of their therapeutic effect. These interactions are described in the interaction table as follows.
Darunavir and cobicistat are metabolised by CYP3A. Medicinal products that induce CYP3A activity would be expected to increase the clearance of darunavir and cobicistat, resulting in lowered plasma concentrations of darunavir and cobicistat (e.g. efavirenz, carbamazepine, phenytoin, phenobarbital, rifampicin, rifapentine, rifabutin, St. John's Wort) (see Contraindications and Table 8).
Co-administration of Symtuza and other medicinal products that inhibit CYP3A may decrease the clearance of darunavir and cobicistat and may result in increased plasma concentrations of darunavir and cobicistat (e.g. azole antifungals like clotrimazole). These interactions are described in the interaction table as follows.
Unlike ritonavir, cobicistat is not an inducer of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19 or UGT1A1. If switching from ritonavir as a pharmacoenhancer to this regimen with cobicistat, caution is required during the first two weeks of treatment with Symtuza, particularly if doses of any concomitantly administered medicinal products have been titrated or adjusted during use of ritonavir.
Emtricitabine: In vitro and clinical pharmacokinetic interaction studies have shown that the potential for CYP-mediated interactions involving emtricitabine with other medicinal products is low.
Emtricitabine did not inhibit the glucuronidation reaction of a non-specific UGT substrate in vitro. Co-administration of emtricitabine with medicinal products that are eliminated by active tubular secretion may increase concentrations of emtricitabine, and/or the co-administered medicinal product. Medicinal products that decrease renal function may increase concentrations of emtricitabine.
Tenofovir alafenamide: Tenofovir alafenamide is transported by P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP). Medicinal products that strongly affect P-gp activity and BCRP may lead to changes in tenofovir alafenamide absorption. Medicinal products that induce P-gp activity (e.g., rifampicin, rifabutin, carbamazepine, phenobarbital) are expected to decrease the absorption of tenofovir alafenamide, resulting in decreased plasma concentration of tenofovir alafenamide, which may lead to loss of therapeutic effect of tenofovir alafenamide and development of resistance. Co-administration of tenofovir alafenamide with other medicinal products that inhibit P-gp (e.g., cobicistat, ritonavir, ciclosporin) are expected to increase the absorption and plasma concentration of tenofovir alafenamide. It is not known whether the co-administration of tenofovir alafenamide and xanthine oxidase inhibitors (e.g. febuxostat) would increase systemic exposure to tenofovir.
Tenofovir alafenamide is not an inhibitor of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, or CYP2D6 in vitro. It is not an inhibitor of CYP3A4 in vivo. Tenofovir alafenamide is a substrate of OATP1B1 and OATP1B3 in vitro. The distribution of tenofovir alafenamide in the body may be affected by the activity of OATP1B1 and OATP1B3.
Interaction table: Expected interactions between Symtuza with potential concomitant medicinal products are listed in Table 8 as follows and are based on the studies conducted with the components of Symtuza, as individual agents or combined, or are potential interactions that may occur.
Interaction trials with the components of Symtuza have only been performed in adults.
The interaction profile of darunavir depends on whether ritonavir or cobicistat is used as a pharmacokinetic enhancer; therefore, there may be different recommendations for the use of darunavir with concomitant medicines. Refer to the prescribing information for darunavir for further information.
The following list of examples of interactions is not comprehensive and therefore the label of each medicinal product that is co-administered with Symtuza should be consulted for information related to the route of metabolism, interaction pathways, potential risks, and specific actions to be taken with regards to co-administration. (See Tables 8a, 8b, 8c and 8d.)
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