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

Drug Interactions Requiring Dose Modifications or Cautious Use
Drugs Affected Nelfinavir
(NFV)
Amprenavir
(APV)
Lopinavir
(LPV)
ANTIFUNGALS
Ketoconazole No dose adjustment necessaryLevels: APV Image f3644_up-arrow.jpg 31%
Keto Image f3644_up-arrow.jpg 44%. Combination under investigation
Levels: LPV AUC Image f3644_down-arrow.jpg 13%.
Keto Image f3644_up-arrow.jpg 3-fold
ANTI-MYCOBACTERIALS
Rifampin Levels Image f3644_down-arrow.jpg 82%
Contraindicated
Levels: APV AUC Image f3644_down-arrow.jpg 82%
No change in rifampin AUC.
Avoid concomitant use.
Levels: LPV AUC Image f3644_down-arrow.jpg 75%
Avoid concomitant use
Rifabutin Levels: NFV Image f3644_down-arrow.jpg32%
RifabutinImage f3644_up-arrow.jpg2X
Dose: Image f3644_down-arrow.jpgrifabutin to 150 mg qd
Or 300 mg 2-3x/week
Image f3644_up-arrow.jpgNFV dose to 1000 mg tid.
Levels: APV AUC Image f3644_down-arrow.jpg15%
Rifabutin Image f3644_up-arrow.jpg193%
Dose: No change in APV dose;
Decrease rifabutin to 150 mg qd or 300 mg 2-3x/week.
Levels: Rifabutin AUC Image f3644_up-arrow.jpg 3-fold
25-O-desacetyl metabolite Image f3644_up-arrow.jpg 47.5-fold.
Decrease rifabutin dose to 150 mg qod
LPV/r: Standard
Clarithromycin No dataLevels: APV AUC Image f3644_up-arrow.jpg 18%.
No change in clarithromycin AUC.
No dose adjustment
No data
ORAL CONTRACEPTIVES Levels: NorethindroneImage f3644_down-arrow.jpg 18%
Ethinyl estradiolImage f3644_down-arrow.jpg47%
Use alternative or additional method
Levels: Potential for metabolic interactions; use alternative or additional method.Levels: ethinyl estradiol Image f3644_down-arrow.jpg 42%
Use alternative or additional method
LIPID LOWERING AGENTS
Simvastatin

Lovastatin

Atorvastatin

Pravastatin
Levels: Potential for large increase in statin levels. Avoid concomitant use.
Atorvastatin AUC Image f3644_up-arrow.jpg 74% -- use with caution. Simvistatin AUC Image f3644_up-arrow.jpg 505% -- not recommended. Potential for large increase in Lovastatin AUC -- not recommended.
Levels: Potential for large increase in statin levels. Avoid concomitant use with lovastatin and simvastatin.Levels: Potential for large increase in statin levels. Avoid concomitant use.
Atorvastatin AUC Image f3644_up-arrow.jpg 5.88-fold. Use with caution and monitoring.
Pravastatin AUC Image f3644_up-arrow.jpg 33%; no dosage adjustment necessary
ANTICONVULSANTS
Phenobarbitol
Phenytoin
Carbamazepine
Unknown, but may decrease NFV levels substantially
Monitor anticonvulsant levels.
Unknown, but may decrease APV levels substantially
Monitor anticonvulsant levels.
Unknown, but may decrease LPV levels substantially.
Monitor anticonvulsant levels.
METHADONE NFV may decrease methadone levels, but minimal effect on maintenance dose. Monitor and titrate dose if needed.
May require Image f3644_up-arrow.jpg methadone dose.
No dataMethadone AUC Image f3644_down-arrow.jpg 53%
Monitor and titrate dose if needed.
May require Image f3644_up-arrow.jpg methadone dose.
SILDENAFIL Sildenafil AUC Image f3644_up-arrow.jpg 2-11 fold. Do not exceed 25 mg in a 48 hr periodSildenafil AUC Image f3644_up-arrow.jpg 2-11 fold. Do not exceed 25 mg in a 48 hr period.Probable substantial Image f3644_up-arrow.jpg in sildenafil AUC.
Do not exceed 25 mg in a 48 hr period.

* 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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