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Labeling update for Lexiva ((fosamprenavir)

The  Lexiva (fosamprenavir) label was recently updated to include new drug-drug interaction information regarding phenytoin (an anticonvulsant)  and paroxetine (an antidepressent).

Details of the newly added information are shown below.

Table 6. Established And Other Potentially Significant Drug Interaction

Concomitant Drug Class: Drug Name Effect on Concentration of Amprenavir or Concomitant Drug Clinical Comment
Anticonvulsants: Phenytoin LEXIVA/ritonavir
↑amprenavir
↓phenytoin
Plasma phenytoin concentrations should be monitored and phenytoin dose should be increased as appropriate. No change in LEXIVA/ritonavir dose is recommended.
Antidepressant:
Paroxetine, trazodone
↓Paroxetine Coadministration of paroxetine with LEXIVA/ritonavir significantly decreased plasma levels of paroxetine. Any paroxetine dose adjustment should be guided by clinical effect (tolerability and efficacy).

In addition, section 12.3 Pharmacokinetics, Table 10 and 12, were updated to show the results of the interaction study with phenytoin as follows:

Table 10. Drug Interactions: Pharmacokinetic Parameters for Amprenavir After Administration of LEXIVA in the Presence of the Coadministered Drug(s)

Coadministered Drug(s) and Dose(s) Dose of LEVIVA n % Change in Pharmacokinetic Parameters of Coadministered Drug (90% CI)
Cmax AUC Cmin
Phenytoin
300 mg q.d. for 10 days
700 mg b.i.d. plus ritonavir 100 mg b.i.d. for 10 days 13 ↑ 20
(↑ 8 to ↑ 34)
↑ 19
(↑ 6 to ↑ 13)

Table 12. Drug Interactions: Pharmacokinetic Parameters for Coadministered Drug in the Presence of Amprenavir After Administration of LEXIVA

Coadministered Drug(s) and Dose(s) Dose of LEVIVA n % Change in Pharmacokinetic Parameters of Coadministered Drug (90% CI)
Cmax AUC Cmin
Phenytoin
300 mg q.d. for 10 days
700 mg b.i.d. plus ritonavir 100 mg b.i.d. for 10 days 14 ↓ 20
(↓ 12 to ↓ 27)
↓ 22
(↓ 17 to ↓ 27)
↓ 29
(↓ 23 to ↓ 34)

The complete revised label is available at  http://www.fda.gov/cder/foi/label/2007/021548s014lbl.pdf 

Richard Klein
Office of Special Health Issues
Food and Drug Administration

Kimberly Struble
Division of Antiviral Drug Products
Food and Drug Administration