Table 18. Drug Interactions Between Antiretrovirals and Other Drugs: Protease Inhibitors (PIs)

Drug Interactions Requiring Dose Modifications or Cautious Use
Drugs Affected Zidovudine
(ZDV)
Stavudine
(d4T)
Didanosine
(ddI)
Tenofovir
METHADONE No dataLevels: d4TImage f3644_down-arrow.jpg27%, methadone unchanged.
No dose adjustment.
Levels: ddIImage f3644_down-arrow.jpg41%, methadone unchanged.
Consider ddI dose increase.
No data
MISCELLANEOUS
Ribavirin Ribavirin inhibits phosphorylation of ZDV; this combination should be avoided if possible.No dataNo dataNo data
Didanosine buffered tablets No data No data No data
  • ddI AUC increase by 44%, Cmax increased by 28%
  • Monitor for ddIassociated toxicities
Cidofovir,
Ganciclovir,
Valganciclovir
No data No data No data
  • Possibly competes for active tubular secretion with tenofovir, may increase serum concentration of these drugs and/or tenofovir
  • Monitor for doserelated toxicities

* Drugs for which plasma concentrations may be decreased by coadministration with Ritonavir: anticoagulants (warfarin), anticonvulsants (phenytoin, divaproex, lamotrigine), antiparasitics (atovaquone).

+

Some drug interaction studies were conducted with Invirase. May not necessarily apply to use with Fortovase.

+# These recommendations apply to regimens that do not include PIs, which can substantially increase rifabutin levels.

From: Guidelines for the Use of Antiretroviral Agents in HIV-Infected Adults and Adolescents

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