• Influence of 50mg, 100mg and 200mg of Ritonavir (RTV) on the Pharmacokinetics (PK) of Amprenavir (APV) After Multiple Doses in Healthy Volunteers for Once-Daily (QD) and Twice-Daily (BID) Regimens (Poster 351)
  Authored by Kurowski, M.; Auguste-Viktoria Krankenhaus, Berlin, Germany

The reason for this study is similar to that of abstract 4: to determine if once-daily dosing of amprenavir is possible. The way that this is done is by boosting the drug with ritonavir. The same issues that make once-daily dosing superior to twice-daily dosing will be addressed here, ease, simplicity and adherence to the medication. If it is possible to take amprenavir once daily, it could be combined with 3TC and ABC given once daily, with DDI and 3TC given once daily, or with DDI and ABC given once daily.

This is a pretty standard study design performed in healthy volunteers for a total of 21 days. All patients in the BID group received APV 600mg twice daily for seven days, then 600 of APV with 50mg of RTV for seven days and then 600 of APV and 100 of RTV for the last seven days.

The once-daily group received APV 1,200mg daily for seven days, then RTV was added at 100mg for the next seven days and increased to 200mg per day for the last seven days. All patients received the drugs for 21 days.

The results basically show that the C min (the level of drug which is the lowest of the day) of the APV 1,200mg/RTV 100mg once-daily group is equivalent to the APV 1,200mg/RTV 200mg group. This is good news for two reasons. It demonstrates that APV can be given once daily with RTV boosting, and that the low dose (and less toxic) RTV is equivalent to the higher dose group. So it should be possible to administer APV with low dose RTV once daily without sacrificing efficacy.

This study was done in normal volunteers, so it is difficult to say what will happen in the studies done in HIV patients. Based on the results of this trial, a trial in HIV patients will be done (probably already underway) to show that efficacy against the virus is equivalent or similar to the previous study. At least pharmacokinetically, the once-daily dose of amprenavir with ritonavir for boosting seems like a good idea and may lead to further investigation. This is not enough data for people to start taking these drugs this way yet, however. They should stay on the twice-daily regimen for now.

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