By Harvey S. Bartnof, MD, Staff Physician at AVERI, AIDS Virus Education and Research Institute in San Francisco, California

PART 4: Once-Daily Reports about Saquinavir Plus Ritonavir

• Once daily saquinavir 1,600 mg plus ritonavir 100 mg and 2 NRTI drugs leads to high level of viral undetectability and favorable saquinavir drug levels, and ought to be considered for study in once daily Direct Observed Therapy (DOT).
• Safety and tolerability is reviewed below.
• Equal benefits and similar drug levels reported below in African-American and Caucasian patients.
• No effect on methadone levels found, including those with chronic hepatitis C (all were HIV negative).
• Weight may be associated with drug blood levels. Lower body weight may be associated with higher drug levels, and higher weight may be associated with lower drug blood levels .

There were many presentations about the protease inhibitor (PI) drug saquinavir (SQV, Fortovase, Invirase) at the Workshop, including several that addressed once-daily dosing of SQV 1,600 mg plus low-dose ritonavir (RTV, Norvir, PI drug). Once daily dosing may be associated with increased patient adherence to dosing, particularly in "directly observed therapy" (DOT).

(editorial comment from Jules Levin: it has not yet been established that self-administered once daily dosing improves adherence. An additional concern about some once daily dosing regimens is that if a person misses one dose it may be more harmful than if a person misses a dose when taking a twice daily regimen, with regards to resistance developing. But, certainly an effective once daily PI regimen would be useful in DOT).

An impressive poster about the pharmacokinetics (PK, drug concentrations), safety and clinical benefits of once daily saquinavir (Fortovase) plus RTV and 2 NRTI (nucleoside analog) drugs was authored by Edward P. Acosta, PharmD of the University of Alabama at Birmingham and colleagues. Close examination of the virologic results showed that 88% of 33 patients who took once-daily SQV 1,600 mg plus RTV 100mg (and 2 NRTI drug) for 32-72 weeks achieved an undetectable viral load (limit 50 copies per milliliter). However, the PK study appeared to be observational and likely represents an "as-treated" analysis (not a stricter "intent-to-treat") that was not primarily intended to measure viral efficacy. It is likely that the 49 treatment-naïve (no previous therapy) patients included in the "PK" and safety study represent very adherent ones and possibly excluded patients who dropped off study. Using a less sensitive lower limit of 400 copies per milliliter, 97% of those same 33 patients achieved undetectability. Interestingly, a significantly larger viral load reduction at week 4 occurred among those older than 38 years, compared to those 38 years and younger, that was not related to 24-hour SQV levels or body mass index (height ¸weight squared).

Six patients had complete serial PK profile after 4 weeks and had a median (average, half above, half below) 24-hour (end of dosing interval, minimum) SQV concentration of 429 nanograms per milliliter (ng/mL), more than 8-fold greater than the "EC50" (effective inhibitory concentration for 50% of HIV growth, 50 ng/mL) for treatment-naïve patients. The median total drug exposure ("area-under-the-curve" or AUC concentration) was 66,920 "nanogram-hours per milliliter." Both of these measurements are similar to those previously reported for healthy volunteers. The same once-daily combination of SQV plus RTV led to minimum SQV concentrations that were increased 5.5-fold and AUC concentrations increased 8-fold, when compared to standard SQV dosing of 1,200 mg 3-times daily without RTV. In healthy volunteers, Cmax (peak SQV levels in blood) increased 7.6-fold using the 1600/100 once daily regimen compared to standard 1200 SQV 3-times per day.

For all 49 patients, the median SQV level at 24 hours was 376 ng/mL and included some statistical modeling or estimations. These 49 patients included 31% women, 41% African Americans, 10% Hispanics, with a mean baseline of 367 CD4 cells per microliter and an HIV RNA of 4.9 log (72,443) copies per milliliter. Interestingly, among those 49 patients on treatment for at least 32 weeks, two patients with a low SQV 24-hour blood level of level less the 50 ng/mL (EC50) still had an undetectable viral load (levels were 28 and 33 ng/mL, respectively). This suggests that the AUC might be an important measurement for some, or that viral suppression was due to other drugs in their regimens.

Safety information was tabulated for a larger group of 78 patients taking the same once daily dosing of SQV and RTV for 4-24 weeks. Moderate or severe (grades 2-3) adverse events were mostly "gastro-intestinal" (stomach-colon) and included nausea in 10%, diarrhea in 5%, vomiting in 3%, and headache in 3%. Grade 3-4 (severe to life threatening) laboratory abnormalities included 4% each with low neutrophils (white cell), low glucose (sugar, this might have been a "typo" and meant to be high glucose) and high potassium (blood salt) and 1% each with low hemoglobin (oxygen-carrying molecule, anemia), low sodium (salt), and increased "PTT" (bleeding time due to low clotting proteins). There were no major increases (from grade 0 to 3 or 4 or from grade 1 to 4) in liver enzymes or triglycerides (fats). An accompanying graph without absolute numbers did show mild increases in triglycerides, total cholesterol, LDL (low density or "bad"), and HDL (high density of "good") cholesterol. Overall, these safety results reveal no unexpected or new findings. The discontinuation rate in the 78 patients was 17%, with only 8% due to an adverse event (AE) and none of 5 AEs that were drug-related. There was one death due to heart attack in a patient with multiple risk factors.

--[Editorial note: The accompanying graph showed mean fasting serum triglycerides, HDL (good cholesterol), LDL (bad cholesterol), and total cholesterol levels for most of the patients on drug at 24 weeks. Total cholesterol appeared to increase from about 160 to 200 mg/dL (upper limit of noraml listed as 199). Triglycerides went from about 125 to 150 mg/dL (upper limit of normal listed as 199). LDL went from about 100 to 125 mg/dL (upper limit of normal listed as 129 mg/dL). HDL appeared to remain about the same at about 45 mg/dL or maybe went up a very little, with upper limit of normal listed as 35 mg/dL. These 24 week preliminary lipid data show results that remain within the normal ranges but show trends of increase.

Acosta reported that for the 6 patients evaluated for PK-

• --median Cmax was 6,435 (95% confidence interval: 3728, 10422) ng/mL
• --median AUC-24 was 66,920 (95% CI: 29484, 103493) ng-h/mL
• --median 24 hr minimum concentration (C24H) was 429 (95% CI: 75, 1087) ng/mL

PK levels were assessed in 5 patients after 25 hours from dosing. C24H was estimated assuming a halflife of 5 hours for SQV for the elimination phase between 12-24 hours post dosage. After 26.10 hours the Cmin was 76 ng/mL. This compares to SQV 24 hour Cmin of 376 ng/ml, and 50 ng/mL in vivo EC50. At 28.58 hours, the Cmin was 90 ng/ml. After 35.25 hours, the Cmin was 75 ng/mL. And after 38 hours, it was 78 ng/mL.]--

In a separate poster presentation about the same 49 patients as above, race-ethnic differences were reported by Robert Schwartz, MD of Associates in Research in Fort Myers, Florida and colleagues. Patients received 1600 mg SQV-100 mg RTV once daily. The 41% each who were African American (AA) and Caucasian were compared; the 10% who were Hispanic represented too small of a number for adequate comparison. Caucasians included 10% women, and the African-Americans had 45% women. The results showed non-significant differences when comparing Caucasians to African Americans and for all African Americans, men to women. In nanograms per milliliter, the minimum SQV concentration was 359 for Caucasians, 470 for African-Americans, 392 for AA men and 594 for AA women. The minimum SQV concentrations were still more than 9-fold greater (African-Americans) and more than 7-fold greater (Caucasians) than the EC50 (effective inhibitory concentration for 50% of HIV) for treatment-naïve patients. Some of the differences in minimum blood concentrations might have been due to weight; however, only a statistical trend (p=0.08) towards a difference in body mass index (weight ÷ height squared) was observed when comparing AA to Caucasians. For the 15 AA on study for at least 24 weeks, 73% achieved viral undetectability (limit 50 copies) with 100% having less than 400 copies per milliliter. For the 19 Caucasians who were on study for at least 24 weeks 89% achieved undetectability (limit 50 copies) with 95% having less than 400 copies per milliliter. These results indicate similar potent anti-viral benefits and "PK" results for AA and Caucasian patients for this once daily combination of SQV and RTV, plus 2 NRTI drugs.

A similar presentation about once daily SQV 1,600 mg plus RTV 100 mg and 2 NRTI drugs in 35 patients was authored by Dr. G. Peytavin of Bichat-Cl Bernard Hospital in Paris, France and colleagues. The results in this prospective study (IMEA 015) showed that the calculated median minimum SQV concentration was 191 ng/mL, 5-fold greater than the reported "IC95" (inhibitory concentration to block 95% of HIV growth in the laboratory, 38 ng/mL). In 95 samples from 35 patients measured at 2, 4 and 12 weeks, 99% of them had a calculated minimum SQV concentration that was greater than the IC95. Dr. Peytavin also measured intracellular levels of SQV in a sub-group of 13 patients and found they were a mean 3.6-fold greater than levels in blood plasma (without cells). However, there was a trend towards this decreasing over time, with only a 2.7-fold greater concentration than plasma at 12 weeks, possibly due to effects from "p-glycoprotein" (drug transport protein) or "MRP-1" (multi-drug resistance protein). However, there was a direct correlation between intracellular and plasma levels of SQV. Yet, all of these measurements showed wide inter-patient variability. "AUC" concentrations were not reported.

For 17 treatment-experienced patients (median baseline CD4 count 601 cells/µL and viral load 2.3 log or 199 copies/mL while on previous regimen), 10 of 10 (100%) who completed 3 months of treatment maintained an undetectable viral load (limit 200 copies/mL) with a CD4 count increase of 56 cells/µL. For the 18 treatment-naïve patients (median baseline CD4 count 219 cells/µL, viral load 4.97 log or 93,325 copies), 9 of 14 (64%) who completed 3 months achieved viral undetectability and another 3 of 14 (21%) had at least a 1 log copies/mL decrease in viral load (note this is shorter follow-up than the Acosta/Schwartz reports above), with an overall CD4 increase of 83 cells/µL. The remaining two discontinued treatment due to adverse events. Overall, of the 3 patients who discontinued due adverse events, only one was due to drug effects (gastrointestinal). In summary, these results from an entirely different group than the Acosta and Schwartz reports above indicate that minimum SQV drug concentrations with the same once daily regimen of SQV/RTV (plus 2 NRTI drugs) are quite good and that virologic and immunologic results in the short-term are quite good in a small group of patients, both treatment-naïve and treatment-experienced.

Yet another presentation about once-daily SQV 1,600 mg plus RTV 100 mg, along with 2 NRTI drugs, was authored by Rolf P.G. van Heeswijk, PharmD, PhD of HIV-NAT (HIV Netherlands Australia Thailand Research Collaboration). In that study, 69 treatment-experienced patients from Thailand (% women not reported) with an undetectable viral load (limit 50 copies/mL) while taking SQV 1,400 mg twice daily with 2 NRTI drugs were switched to once daily SQV/RTV (1,600/100 mg) while maintaining their NRTI drugs. The results after 24 weeks showed that 93% maintained an undetectable viral load (limit 50 copies/mL), with 100% maintaining undetectability using a lower limit of 400 copies/mL. The median baseline CD4 count of 534 cells/µL increased by a median 123 cells/µL. A sub-analysis found a significantly greater increase during those 24 weeks than during the pre-switch period with twice-daily SQV.

The regimen was reported to be "generally well tolerated." Adverse events that occurred among at least 6% of patients included: mild (grade 1) nausea in 7%, with one of those patients also reporting vomiting; grade 3-4 (severe or life threatening) increases in triglycerides (blood fats) occurred in 9%; grade 3-4 increases in ALT (liver enzyme) occurred in 6% (possible hepatitis virus co-infection was not reported). However, none changed their drug regimen due to toxicity.

Detailed pharmacokinetic (drug level) analyses were performed on 12 patients (50% women). The median (average, half above, half below) trough (minimum concentration) of SQV was 168 ng/mL, although there was a wide 27-fold variation between patients. Yet, all patients had levels that were greater than and the median minimum concentration was more than 3-fold greater than the "proposed threshold concentration of 50 ng/mL." The median "AUC" ("area-under-the-curve," total drug exposure) was 48,147 ng-hours/mL. Dr. van Heeswijk reported a significant inverse correlation between body weight and both the minimum and AUC concentrations of SQV. (Higher bodyweight was associated with lower minimum and AUC concentrations, while lower bodyweight was associated with higher minimum and AUC concentrations.) The latter case was particularly true for 5 of the women who had lower bodyweights than all the men but one. It would have been useful to compare the SQV levels to those before the switch; however, this was not reported.

The authors concluded that switching to the once-daily regimen of SQV/RTV (1,600/100 mg) (plus 2 NRTI drugs) represents a "convenient regimen to maintain suppression of viral replication..." They hypothesized that the improvement in the CD4 cell increases after the switch might have been due to improved HIV suppression, but this was not measurable with their assay (test). An alternative explanation might relate to the lower SQV dosing before the switch than is FDA-approved. A 6% rate of grade 3-4 increases in ALT is somewhat worrisome; whether this is related to the race-ethnicity (100% Thai) or possible unreported hepatitis virus co-infection is not known.

In another presentation, researchers from Roche attempted to determine whether the saquinavir minimum concentration or total exposure ("area-under-the-curve" concentration) was better in determining the likelihood of achieving viral undetectability (limit 50 copies/mL). Patients from Study NR15720 were treatment-naïve (no previous treatment) and received 2 NRTI drugs plus once-daily SQV 1,600 mg and RTV 100 mg. Using very complex modeling and a retrospective (after the fact) statistical analyses, there appeared to be significant associations with both of the concentration measurements with viral load reduction. The lead author was Dr. Brian Jahns of Hoffmann-LaRoche.

In a last report about once-daily SQV/RTV (1,600/100 mg), Dr. Mark J. Shelton of the University of Buffalo in New York tested potential drug interactions with methadone, an opiate substitute for those with heroin addiction. A total of 12 health volunteers (HIV negative) included 42% men, 17% African American, 25% Hispanic, and 58% with chronic hepatitis C. The mean, stable, baseline methadone dose was 67 mg daily. SQV/RTV/ methadone and a meal were given once daily for 14 days under "DOT" (directly observed therapy). The results showed that there were no significant effects by SQV/RTV on the pharmacokinetics (drug levels) of total methadone "isomers" (R- and S-methadone breakdown products) or on clinical tolerance to methadone. There were minor reductions in both the unbound (active, not bound to protein) R-methadone (-8%) and S-methadone (-17%). There were no significant differences by gender (sex) or by hepatitis C status. The medications "appeared to be well tolerated," and there were no grade 3-4 (severe to life threatening) adverse events. Two patients (17%) "discussed a methadone dose increase, but opted not to change methadone dose and completed the study." The results suggest that the once-daily regimen of SQV/RTV (with NRTI drugs) likely represents a viable treatment option for patients who are taking methadone maintenance therapy. However, the study would need to be repeated among HIV positive persons taking methadone, preferably including those with and without co-infection with hepatitis C virus.

References
Acosta EP and others. Pharmacokinetics and safety of once daily saquinavir soft gel capsules/ritonavir in HIV-infected antiretroviral naïve patients. Abstract and poster presentation 3.14 at the 2nd International Workshop of Clinical Pharmacology of HIV Therapy; April 2-4, 2001; Noordwijk, the Netherlands.

Jahns BE and others. Relationships between saquinavir exposure and antiviral effect in study NV15107, and NV15720-the Fortovase once-daily study. Abstract and poster presentation 5.14 at the 2nd International Workshop of Clinical Pharmacology of HIV Therapy; April 2-4, 2001; Noordwijk, the Netherlands.

Peytavin G and others. Saquinavir plasma and intracellular concentrations in a once daily combination of Fortovase (SQV-SGC)- low dose ritonavir in a prospective study (IMEA 015) in HIV-infected patients. Abstract and poster presentation 3.16 at the 2nd International Workshop of Clinical Pharmacology of HIV Therapy; April 2-4, 2001; Noordwijk, the Netherlands.

Peytavin G and others. Saquinavir population pharmacokinetics in HIV-infected patients treated with ritonavir baby dose-saquinavir hard gel capsule. Abstract and poster presentation 3.17 at the 2nd International Workshop of Clinical Pharmacology of HIV Therapy; April 2-4, 2001; Noordwijk, the Netherlands.

Schwartz R and others. Pharmacokinetic evaluation of HIV (+) African Americans and Caucasians on once daily saquinavir soft gel capsules and mini dose ritonavir. Abstract and poster presentation 3.13 at the 2nd International Workshop of Clinical Pharmacology of HIV Therapy; April 2-4, 2001; Noordwijk, the Netherlands.

Shelton MJ and others. Effects of once daily saquinavir/mini-dose ritonavir on the pharmacokinetics of methadone isomers. Abstract and poster presentation 1.17 at the 2nd International Workshop of Clinical Pharmacology of HIV Therapy; April 2-4, 2001; Noordwijk, the Netherlands.

van Heeswijk RPG and others. Once-daily dosing of 1,600 mg saquinavir (soft-gelatin capsules) plus low dose ritonavir (100 mg) in HIV-1-infected Thai patients: pharmacokinetics and clinical experience (HIV-NAT 001.3). Abstract and poster presentation 3.9 at the 2nd International Workshop of Clinical Pharmacology of HIV Therapy; April 2-4, 2001; Noordwijk, the Netherlands.