Interfast

Interfast in combination with ritonavir and other antiretroviral agents is indicated for the treatment of HIV-1 infection in adults (over the age of 16 years).

The following points should be considered when initiating therapy with Interfast:

• The twice daily administration of Interfast in combination with ritonavir is supported by safety data from the MaxCmin 1 trial and pharmacokinetic data.
• The efficacy of Interfast with ritonavir has not been compared against the efficacy of antiretroviral regimens currently considered standard of care.
• The number of baseline primary protease inhibitor mutations affects the virologic response to Interfast/ritonavir.

Interfast must be used in combination with ritonavir because ritonavir significantly inhibits saquinavir's metabolism to provide increased plasma saquinavir levels.

Cobicistat is not interchangeable with ritonavir to increase systemic exposure of saquinavir.

Recommended Dose

• Interfast 1000-mg twice daily (5 x 200-mg capsules or 2 x 500-mg tablets) in combination with ritonavir 100-mg twice daily.
• Ritonavir should be taken at the same time as Interfast.
• Interfast and ritonavir should be taken within 2 hours after a meal.
• For patients already taking ritonavir 100-mg twice daily as part of their antiretroviral regimen, no additional ritonavir is needed.
• Pediatric dose recommendations that are both reliably effective and below thresholds of concern for QT and PR interval prolongation could not be determined.

Administration For Patients Unable To Swallow Capsules

Open the Interfast capsules and place the contents into an empty container. Add 15 mL of either sugar syrup or sorbitol syrup (for patients with Type 1 diabetes or glucose intolerance) OR 3 teaspoons of jam to the contents of Interfast capsules that are in the container. Stir with a spoon for 30 to 60 seconds. Administer the full amount prepared for each dose. Suspensions should be at room temperature before administering.

QT interval prolongation and torsades de pointes have been reported rarely with Interfast/ritonavir use. Do not use in patients with congenital long QT syndrome, those with refractory hypokalemia or hypomagnesemia, and in combination with drugs that both increase saquinavir plasma concentrations and prolong the QT interval.

Interfast is contraindicated in patients with complete atrioventricular (AV) block without implanted pacemakers, or patients who are at high risk of complete AV block.

Interfast is contraindicated in patients with clinically significant hypersensitivity (e.g., anaphylactic reaction, Stevens-Johnson syndrome) to saquinavir, saquinavir mesylate, or any of its ingredients.

Interfast when administered with ritonavir is contraindicated in patients with severe hepatic impairment.

Coadministration of Interfast/ritonavir is contraindicated with drugs that are CYP3A substrates for which increased plasma levels may result in serious or life-threatening reactions. These drugs and potentially related adverse events are listed in Table 1.

Table 1 : Drugs That Are Contraindicated With Interfast/ritonavir

WARNINGS

Included as part of the PRECAUTIONS section.

PRECAUTIONS

Interfast must be used in combination with ritonavir. Please refer to the ritonavir full prescribing information for additional precautionary measures.

Interfast is not recommended for use in combination with cobicistat. Dosing recommendations for this combination have not been established. Cobicistat is also not recommended in combination with regimens containing ritonavir due to similar effects of cobicistat and ritonavir on CYP3A. Please refer to the cobicistat full prescribing information for additional precautionary measures.

If a serious or severe toxicity occurs during treatment with Interfast, Interfast should be interrupted until the etiology of the event is identified or the toxicity resolves. At that time, resumption of treatment with full-dose Interfast may be considered. For antiretroviral agents used in combination with Interfast, physicians should refer to the complete product information for these drugs for dose adjustment recommendations and for information regarding drug-associated adverse reactions.

Risk Of Serious Adverse Reactions Due To Drug Interactions

Initiation of Interfast/ritonavir, a CYP3A inhibitor, in patients receiving medications metabolized by CYP3A or initiation of medications metabolized by CYP3A in patients already receiving Interfast/ritonavir, may increase plasma concentrations of medications metabolized by CYP3A. Initiation of medications that inhibit or induce CYP3A may increase or decrease concentrations of Interfast/ritonavir, respectively. These interactions may lead to:

• Clinically significant adverse reactions potentially leading to severe, life threatening, or fatal events from greater exposures of concomitant medications.
• Clinically significant adverse reactions from greater exposures of Interfast/ritonavir.
• Loss of therapeutic effect of Interfast/ritonavir and possible development of resistance.

See Table 3 for steps to prevent or manage these possible and known significant drug interactions, including dosing recommendations. Consider the potential for drug interactions prior to and during Interfast/ritonavir therapy; review concomitant medications during Interfast/ritonavir therapy; and monitor for the adverse reactions associated with the concomitant medications.

PR Interval Prolongation

Saquinavir/ritonavir prolongs the PR interval in a dose-dependent fashion. Cases of second or third degree atrioventricular block have been reported rarely. Patients with underlying structural heart disease, pre-existing conduction system abnormalities, cardiomyopathies and ischemic heart disease may be at increased risk for developing cardiac conduction abnormalities. ECG monitoring is recommended in these patients.

The impact on the PR interval of co-administration of saquinavir/ritonavir with other drugs that prolong the PR interval (including calcium channel blockers, beta-adrenergic blockers, digoxin and atazanavir) has not been evaluated. As a result, co-administration of saquinavir/ritonavir with these drugs should be undertaken with caution, particularly with those drugs metabolized by CYP3A, and clinical monitoring is recommended.

QT Interval Prolongation

Saquinavir/ritonavir causes dose-dependent QT prolongation. Torsades de pointes has been reported rarely post-marketing. Avoid saquinavir/ritonavir in patients with long QT syndrome. ECG monitoring is recommended if therapy is initiated in patients with congestive heart failure, bradyarrhythmias, hepatic impairment and electrolyte abnormalities. Correct hypokalemia or hypomagnesemia prior to initiating saquinavir/ritonavir and monitor these electrolytes periodically during therapy. Do not use in combination with drugs that both increase saquinavir plasma concentrations and prolong the QT interval (see Tables 1 and 3).

Patients initiating therapy with Interfast/ritonavir

An ECG should be performed prior to initiation of treatment. Patients with a QT interval > 450 msec should not receive ritonavir-boosted Interfast. For patients with a QT interval < 450 msec, an on-treatment ECG is suggested after approximately 3 to 4 days of therapy; patients with a QT interval > 480 msec or prolongation over pre-treatment by > 20 msec should discontinue Interfast/ritonavir.

Patients Requiring Treatment With Medications With The Potential To Increase The QT Interval And Concomitant Interfast/Ritonavir

Such combinations should only be used where no alternative therapy is available and the potential benefits outweigh the potential risks. An ECG should be performed prior to initiation of the concomitant therapy, and patients with a QT interval > 450 msec should not initiate the concomitant therapy. If baseline QT interval < 450 msec, an on-treatment ECG should be performed after 3-4 days of therapy. For patients demonstrating a subsequent increase in QT interval to > 480 msec or increase by > 20 msec after commencing concomitant therapy, the physician should use best clinical judgment to discontinue either Interfast/ritonavir or the concomitant therapy or both.

A cardiology consult is recommended if drug discontinuation or interruption is being considered on the basis of ECG assessment.

Diabetes Mellitus / Hyperglycemia

New onset diabetes mellitus, exacerbation of preexisting diabetes mellitus and hyperglycemia have been reported during postmarketing surveillance in HIV-1-infected patients receiving protease-inhibitor therapy. Some patients required either initiation or dose adjustments of insulin or oral hypoglycemic agents for the treatment of these events. In some cases diabetic ketoacidosis has occurred. In those patients who discontinued protease-inhibitor therapy, hyperglycemia persisted in some cases. Because these events have been reported voluntarily during clinical practice, estimates of frequency cannot be made and a causal relationship between protease-inhibitor therapy and these events has not been established.

Hepatotoxicity

In patients with underlying hepatitis B or C, cirrhosis, chronic alcoholism and/or other underlying liver abnormalities, there have been reports of worsening liver disease.

Hemophilia

There have been reports of spontaneous bleeding in patients with hemophilia A and B treated with protease inhibitors. In some patients additional factor VIII was required. In the majority of reported cases treatment with protease inhibitors was continued or restarted. A causal relationship between protease inhibitor therapy and these episodes has not been established.

Hyperlipidemia

Elevated cholesterol and/or triglyceride levels have been observed in some patients taking saquinavir in combination with ritonavir. Marked elevation in triglyceride levels is a risk factor for development of pancreatitis. Cholesterol and triglyceride levels should be monitored prior to initiating combination dosing regimen of Interfast with ritonavir, and at periodic intervals while on such therapy. In these patients, lipid disorders should be managed as clinically appropriate.

Lactose Intolerance

Each capsule contains lactose (anhydrous) 63.3 mg. This quantity should not induce specific symptoms of intolerance.

Fat Redistribution

Redistribution/accumulation of body fat including central obesity, dorsocervical fat enlargement (buffalo hump), facial wasting, peripheral wasting, breast enlargement, and “cushingoid appearance” have been observed in patients receiving antiretroviral therapy. The mechanism and long-term consequences of these events are currently unknown. A causal relationship has not been established.

Immune Reconstitution Syndrome

Immune reconstitution syndrome has been reported in patients treated with combination antiretroviral therapy, including Interfast. During the initial phase of combination antiretroviral treatment, patients whose immune system responds may develop an inflammatory response to indolent or residual opportunistic infections (such as Mycobacterium avium infection, cytomegalovirus, Pneumocystis jiroveci pneumonia [PCP], or tuberculosis), which may necessitate further evaluation and treatment.

Autoimmune disorders (such as Graves' disease, polymyositis, and Guillain-Barré syndrome) have also been reported to occur in the setting of immune reconstitution; however, the time to onset is more variable, and can occur many months after initiation of treatment.

Resistance/Cross-resistance

Varying degrees of cross-resistance among HIV-1 protease inhibitors have been observed. Continued administration of Interfast therapy following loss of viral suppression may increase the likelihood of cross resistance to other protease inhibitors.

Patient Counseling Information

• Advise the patient to read the FDA-approved patient labeling (Medication Guide).

A statement to patients and health care providers is included on the product's bottle label: ALERT: Find out about medicines that should NOT be taken with Interfast.

Interfast is not a cure for HIV-1 infection and patients may continue to experience illnesses associated with HIV-1 infection, including opportunistic infections. Patients should remain under the care of a physician when using Interfast.

Advise patients to avoid doing things that can spread HIV-1 infection to others.

• Do not share needles or other injection equipment.
• Do not share personal items that can have blood or body fluids on them, like toothbrushes and razor blades.
• Do not have any kind of sex without protection. Always practice safe sex by using a latex or polyurethane condom to lower the chance of sexual contact with semen, vaginal secretions, or blood.
• Do not breastfeed. We do not know if Interfast can be passed to your baby in your breast milk and whether it could harm your baby. Also, mothers with HIV-1 should not breastfeed because HIV-1 can be passed to the baby in the breast milk.

Pregnancy

An Antiretroviral Pregnancy Registry has been established. See Pregnancy for information on how to enroll.

Drug Interactions

Interfast may interact with some drugs; therefore, advise patients to report to their doctor the use of any other prescription, nonprescription medication, or herbal products, particularly St. John's wort.

PR and QT Interval Prolongation

Inform patients that Interfast may produce changes in the electrocardiogram (PR interval or QT interval prolongation). Patients should consult their health care provider if they are experiencing symptoms such as dizziness, lightheadedness, or palpitations.

Fat Redistribution

Inform patients that redistribution or accumulation of body fat may occur in patients receiving protease inhibitors and that the cause and long-term health effects of these conditions are not known at this time.

Dosing Instructions

Advise patients that Interfast must be used in combination with ritonavir, which significantly inhibits saquinavir's metabolism to provide increased plasma saquinavir levels.

Advise patients that Interfast administered with ritonavir should be taken within 2 hours after a full meal. When Interfast is taken without food, concentrations of saquinavir in the blood are substantially reduced and may result in no antiviral activity. Advise patients of the importance of taking their medication every day, as prescribed, to achieve maximum benefit. Patients should not alter the dose or discontinue therapy without consulting their physician. If a dose is missed, patients should take the next dose as soon as possible. However, the patient should not double the next dose.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment Of Fertility

Carcinogenesis

Carcinogenicity studies found no indication of carcinogenic activity in rats and mice administered saquinavir for approximately 2 years. Because of limited bioavailability of saquinavir in animals, the plasma exposures (AUC values) in the respective species were approximately 29% (using rat) and 65% (using mouse) of those obtained in humans at the recommended clinical dose combined with ritonavir.

Mutagenesis

Mutagenicity and genotoxicity studies, with and without metabolic activation where appropriate, have shown that saquinavir has no mutagenic activity in vitro in either bacterial (Ames test) or mammalian cells (Chinese hamster lung V79/HPRT test). Saquinavir does not induce chromosomal damage in vivo in the mouse micronucleus assay or in vitro in human peripheral blood lymphocytes, and does not induce primary DNA damage in vitro in the unscheduled DNA synthesis test.

Impairment of Fertility

No adverse effects were reported in fertility and reproductive performance study conducted in rats. Because of limited bioavailability of saquinavir in animals, the maximal plasma exposures achieved in rats were approximately 26% of those obtained in humans at the recommended clinical dose combined with ritonavir.

Use In Specific Populations

Pregnancy

Pregnancy Category B

Reproduction studies conducted with saquinavir have shown no embryotoxicity or teratogenicity in both rats and rabbits. Because of limited bioavailability of saquinavir in animals and/or dosing limitations, the plasma exposures (AUC values) in the respective species were approximately 29% (using rat) and 21% (using rabbit) of those obtained in humans at the recommended clinical dose combined with ritonavir. Clinical experience in pregnant women is limited. Saquinavir should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Antiretroviral Pregnancy Registry

To monitor maternal-fetal outcomes of pregnant women exposed to antiretroviral medications, including Interfast, an Antiretroviral Pregnancy Registry has been established. Physicians are encouraged to register patients by calling 1-800-258-4263.

Nursing Mothers

The Centers for Disease Control and Prevention recommend that HIV-infected mothers not breastfeed their infants to avoid risking postnatal transmission of HIV-1.

It is not known whether saquinavir is excreted in human milk. Because of both the potential for HIV-1 transmission and the potential for serious adverse reactions in nursing infants, mothers should be instructed not to breastfeed if they are receiving Interfast.

Pediatric Use

The safety and activity of saquinavir have been evaluated in 68 pediatric subjects 4 months to less than 16 years of age treated with Interfast combined with either ritonavir or with lopinavir/ritonavir in two clinical trials. Data from the NV20911 trial demonstrated that saquinavir combined with low dose ritonavir provided plasma levels of saquinavir that were significantly higher than those historically observed in adults at the approved dose. The HIVNAT 017 trial provided long term 96-week activity and safety data; however, pharmacokinetic data from this study could not be validated.

HIVNAT 017 was an open-label, single-arm trial at two centers in Thailand that evaluated the use of Interfast (50 mg per kg twice daily given as 200 mg capsules) with lopinavir/ritonavir (230/57.5 mg/m² twice daily) for 96 weeks. Fifty subjects 4 years to less than 16 years of age were enrolled. In this trial population, treatment resulted in HIV-1 RNA < 400 copies/mL at week 96 in 78% of subjects (HIV-1 RNA < 50 copies per mL at week 96 in 66%). Mean CD4 lymphocyte percentage increased from 8% at screening to 22% at week 96.

NV20911 was an open label, multinational trial that evaluated the pharmacokinetics, safety, and activity of Interfast (50 mg per kg twice daily as 200 mg capsules, up to the adult dose of 1000 mg twice daily) and ritonavir oral solution plus ≥ 2 background ARVs. Eighteen subjects 4 months to less than 6 years of age were enrolled. Treatment with Interfast/ritonavir resulted in HIV-1 RNA < 400 copies per mL at week 48 in 72% of subjects (HIV-1 RNA < 50 copies per mL at week 48 in 61%). The percentage of subjects with HIV-1 RNA < 50 copies per mL at week 48 was 61%. Mean CD4 lymphocyte percentage increased from 29% at screening to 34% at week 48.

Steady state saquinavir exposures observed in pediatric trials were substantially higher than historical data in adults where dose- and exposure-dependent QTc and PR prolongation were observed. Although electrocardiogram abnormalities were not reported in these pediatric trials, the trials were small and not designed to evaluate QT or PR intervals. Modeling and simulation assessment of pharmacokinetic/pharmacodynamic relationships in pediatric subjects suggest that reducing the Interfast dose to minimize risk of QT prolongation is likely to reduce antiviral efficacy. In addition, no clinical efficacy data are available at Interfast doses less than 50 mg per kg in pediatric subjects. Therefore, pediatric dose recommendations that are both reliably effective and below thresholds of concern with respect to QT and PR prolongation could not be determined.

Geriatric Use

Clinical trials of Interfast did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. In general, dosing Interfast in elderly patients should be undertaken with caution keeping in mind the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Impaired Renal Function

Renal clearance is a minor elimination pathway; the principal route of excretion for saquinavir is by hepatic metabolism. Therefore, no initial dose adjustment is necessary for patients with renal impairment. However, patients with severe renal impairment or end-stage renal disease (ESRD) have not been studied, and caution should be exercised when prescribing Interfast in this population.

Impaired Hepatic Function

No dosage adjustment is necessary for HIV-1-infected patients with mild or moderate hepatic impairment based on limited data. In patients with underlying hepatitis B or C, cirrhosis, chronic alcoholism and/or other underlying liver abnormalities, there have been reports of worsening liver disease. Interfast when administered with ritonavir is contraindicated in patients with severe hepatic impairment.

The following adverse reactions are discussed in greater detail in other sections of the labeling:

• PR Interval Prolongation
• QT Interval Prolongation

Clinical Trial Experience In Adult Subjects

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

The original Interfast safety database consisted of a total of 574 adult subjects who received saquinavir 600 mg alone or in combination with ZDV or ddC. Combination dosing with ritonavir is based on 352 HIV-1 infected subjects and 166 healthy subjects who received various combinations of either saquinavir (hard gel or soft-gel capsules) with ritonavir.

The recommended dose of Interfast is 1000 mg twice daily co-administered with ritonavir 100 mg twice daily, in combination with other antiretroviral agents. Table 2 lists grade 2, 3 and 4 adverse events that occurred in ≥ 2% of subjects receiving saquinavir soft gel capsules with ritonavir (1000/100 mg bid).

Table 2 : Grade 2, 3 and 4 Adverse Events (All Causality^a) Reported in ≥ 2% of Adult Subjects in the MaxCmin 1 Study of Saquinavir Soft Gel Capsules in Combination with Ritonavir 1000/100 mg twice a day

Limited experience is available from three trials investigating the pharmacokinetics of the Interfast 500 mg film-coated tablet compared to the Interfast 200 mg capsule in healthy volunteers (n=140). In two of these trials saquinavir was combined with ritonavir; in the other trial, saquinavir was administered as single drug. The Interfast tablet and the capsule formulations were similarly tolerated. The most common adverse events were gastrointestinal disorders (such as nausea, vomiting, and diarrhea). Similar bioavailability was demonstrated and no clinically significant differences in saquinavir exposures were seen. Thus, similar safety profiles are expected between the two Interfast formulations.

A study investigating the drug-drug interaction of rifampin 600 mg/day daily and Interfast 1000 mg/ritonavir 100 mg twice daily enrolled 28 healthy volunteers. Eleven of 17 healthy volunteers (65%) exposed concomitantly to rifampin and Interfast/ritonavir developed severe hepatocellular toxicity which presented as increased hepatic transaminases. In some subjects, transaminases increased up to > 20-fold the upper limit of normal and were associated with gastrointestinal symptoms, including abdominal pain, gastritis, nausea, and vomiting. Following discontinuation of all three drugs, clinical symptoms abated and the increased hepatic transaminases normalized.

Additional Adverse Reactions Reported During Clinical Trials with Saquinavir

Blood and lymphatic system disorders: anemia, hemolytic anemia, leukopenia, lymphadenopathy, neutropenia, pancytopenia, thrombocytopenia

Cardiac disorders: heart murmur, syncope

Ear and labyrinth disorders: tinnitus

Eye disorders: visual impairment

Gastrointestinal disorders: abdominal discomfort, ascites, dyspepsia, dysphagia, eructation, flatulence, gastritis, gastrointestinal hemorrhage, intestinal obstruction, mouth dry, mucosal ulceration, pancreatitis

General disorders and administration site conditions: anorexia, asthenia, chest pain, edema, lethargy, wasting syndrome, weight increased

Hepatobiliary disorders: chronic active hepatitis, hepatitis, hepatomegaly, hyperbilirubinemia, jaundice, portal hypertension

Immune system disorders: allergic reaction

Investigations: ALT increase, AST increase, blood creatine phosphokinase increased, increased alkaline phosphatase, GGT increase, raised amylase, raised LDH

Metabolism and nutrition disorders: increased or decreased appetite, dehydration, hypertriglyceridemia

Musculoskeletal and connective tissue disorders: arthralgia, muscle spasms, myalgia, polyarthritis

Neoplasms benign, malignant and unspecified (incl cysts and polyps): acute myeloid leukemia, papillomatosis

Nervous system disorders: confusion, convulsions, coordination abnormal, dizziness, dysgeusia, headache, hypoaesthesia, intracranial hemorrhage leading to death, loss of consciousness, paresthesia, peripheral neuropathy, somnolence, tremor

Psychiatric disorders: anxiety, depression, insomnia, libido disorder, psychotic disorder, sleep disorder, suicide attempt

Renal and urinary disorders: nephrolithiasis

Respiratory, thoracic and mediastinal disorders: cough, dyspnea

Skin and subcutaneous tissue disorders: acne, alopecia, dermatitis bullous, drug eruption, erythema, severe cutaneous reaction associated with increased liver function tests, Stevens-Johnson syndrome, sweating increased, urticaria

Vascular disorders: hypertension, hypotension, thrombophlebitis, peripheral vasoconstriction

Clinical Trial Experience In Pediatric Subjects

Limited safety data are available from two pediatric clinical trials of saquinavir hard gel capsules (approximately 50 mg per kg twice daily) used in combination with either low dose ritonavir or lopinavir/ritonavir. These trials enrolled pediatric subjects aged 4 months to 16 years old. In the HIVNAT 017 study (Interfast + lopinavir/ritonavir), adverse events were reported in 90% of the 50 subjects enrolled. The most commonly reported adverse events considered related to study treatment were diarrhea (18%) and vomiting (10%). In the NV20911 study (Interfast + ritonavir), 4 subjects (22% of 18 enrolled) experienced adverse events that were considered related to Interfast + ritonavir. These events (n) were vomiting (3), abdominal pain (1) and diarrhea (1). All reported adverse events were mild or moderate in intensity. The adverse reaction profile of Interfast in the pediatric trials is similar to that observed in adult trials.

Postmarketing Experience

Additional adverse events identified during postmarketing use are similar to those observed in clinical trials with Interfast and saquinavir soft gel capsules alone or in combination with ritonavir. Because these events are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to Interfast exposure. In addition, torsades de pointes has been reported rarely.

There is limited experience of overdose with saquinavir.

No acute toxicities or sequelae were noted in 1 subject who ingested 8 grams of Interfast as a single dose. The subject was treated with induction of emesis within 2 to 4 hours after ingestion. A second subject ingested 2.4 grams of Interfast in combination with 600 mg of ritonavir and experienced pain in the throat that lasted for 6 hours and then resolved. In an exploratory Phase II study of oral dosing with Interfast at 7200 mg per day (1200 mg q4h), there were no serious toxicities reported through the first 25 weeks of treatment.

Treatment of overdose with saquinavir should consist of general supportive measures including monitoring of vital signs and ECG and observations of the patient's clinical status. Since saquinavir is highly protein bound, dialysis is unlikely to be beneficial in significant removal of the active substance.

QTcS interval was evaluated in a randomized, placebo and active (moxifloxacin 400 mg once daily) controlled crossover study in 59 healthy adults, with ECG measurements on Day 3. The maximum mean (95% upper confidence bound) differences in QTcS interval from placebo after baseline-correction were 18.9 (22.0) and 30.2 (33.4) ms for 1000/100 mg twice daily and supratherapeutic 1500/100 mg twice daily of Interfast/ritonavir, respectively. There is a delayed effect between QTc interval change and drug concentrations, with the maximum placebo-adjusted baseline-corrected QTcS observed at about 12-20 h post-dose. Interfast/ritonavir 1500/100 mg twice daily resulted in a Day 3 mean Cmax of Interfast approximately 1.4-fold higher than the mean Cmax observed on Day 3 with the approved therapeutic dose in healthy volunteers (within the same study). QTcS in this study was QT/RR^0.319 for males and QT/RR^0.337 for females, which are similar to Fridericia's correction (QTcF=QT/RR^0.3333).

PR and QRS interval prolongations were also noted in subjects receiving Interfast/ritonavir in the same study on Day 3. The maximum mean (95% upper confidence bound) difference from placebo in the PR interval after baseline-correction were 28.6 (31.6) and 38.4 (41.4) ms for 1000/100 mg twice daily and supratherapeutic 1500/100 mg twice daily saquinavir/ritonavir respectively. The maximum mean (95% upper confidence bound) difference from placebo in QRS interval after baseline correction were 2.9 (3.9) and 4.4 (5.3) ms for 1000/100 mg twice daily and supratherapeutic 1500/100 mg twice daily Interfast/ritonavir respectively. In this study using healthy subjects, PR interval prolongation of > 200 ms was also observed in 40% and 47% of subjects receiving Interfast/ritonavir 1000/100 mg bid and 1500/100 mg bid, respectively, on Day 3. Three (3%) of subjects in the active control moxifloxacin arm and 5% in the placebo arm experienced PR prolongation of > 200 ms.

The HIV-1 antiviral drugs didanosine, tenofovir, and zidovudine are not predicted to have any clinically significant effect on the pharmacokinetics of saquinavir with and without ritonavir. No clinically significant effect on the pharmacokinetic parameters of enfuvirtide was observed with coadministration of Interfast/ritonavir. No clinically significant effect on the pharmacokinetic parameters of saquinavir was observed with coadministration of fosamprenavir.

Microbiology

Mechanism of Action

Saquinavir is an inhibitor of HIV-1 protease. HIV-1 protease is an enzyme required for the proteolytic cleavage of viral polyprotein precursors into individual functional proteins found in HIV-1 particles. Saquinavir is a peptide-like substrate analogue that binds to the protease active site and inhibits the activity of the enzyme. Saquinavir inhibition prevents cleavage of the viral polyproteins resulting in the formation of immature noninfectious viral particles.

Antiviral Activity

The antiviral activity of saquinavir was assessed in lymphoblastoid and monocytic cell lines and in peripheral blood lymphocytes in cell culture. Saquinavir inhibited HIV-1 activity in both acutely and chronically infected cells. EC50 and EC90 values (50% and 90% inhibitory concentrations) ranged from 1 to 30 nM and 5 to 80 nM, respectively. In the presence of 40% human serum, the mean EC50 of saquinavir against laboratory strain HIV-1 RF in MT4 cells was 37.7± 5 nM representing a 4-fold increase in the EC50 value. In cell culture, saquinavir demonstrated additive to synergistic effects against HIV-1 in combination with reverse transcriptase inhibitors (didanosine, lamivudine, nevirapine, stavudine and zidovudine) without enhanced cytotoxicity. Saquinavir in combination with the protease inhibitors amprenavir, atazanavir, or lopinavir resulted in synergistic antiviral activity. Saquinavir displayed antiviral activity in cell culture against HIV-1 clades A-H (EC50 values ranged from 0.9 to 2.5 nM). The EC50 and EC90 values of saquinavir against HIV-2 isolates in cell culture ranged from 0.25 nM to 14.6 nM and 4.65 nM to 28.6 nM, respectively.

Resistance

HIV-1 isolates with reduced susceptibility to saquinavir have been selected during passage in cell culture. Genotypic analyses of these isolates showed several amino acid substitutions in the HIV-1 protease. Only the G48V and L90M substitutions were associated with reduced susceptibility to saquinavir, and conferred an increase in the EC50 value of 8- and 3-fold, respectively.

HIV-1 isolates with reduced susceptibility ( ≥ 4-fold increase in the EC50 value) to saquinavir emerged in some subjects treated with Interfast. Genotypic analysis of these isolates identified resistance conferring primary amino acid substitutions in the protease G48V and L90M, and secondary substitutions L10I/R/V, I54V/L, A71V/T, G73S, V77I, V82A and I84V that contributed additional resistance to saquinavir. Forty-one isolates from 37 subjects failing therapy with Interfast had a median decrease in susceptibility to saquinavir of 4.3-fold.

The degree of reduction in cell culture susceptibility to saquinavir of clinical isolates bearing substitutions G48V and L90M depends on the number of secondary substitutions present. In general, higher levels of resistance are associated with greater number of substitutions only in association with either or both of the primary substitutions G48V and L90M. No data are currently available to address the development of resistance in patients receiving saquinavir/ritonavir.

Cross-resistance

Among protease inhibitors, variable cross-resistance has been observed. In one clinical study, 22 HIV-1 isolates with reduced susceptibility ( > 4-fold increase in the EC50 value) to saquinavir following therapy with Interfast were evaluated for cross-resistance to amprenavir, indinavir, nelfinavir and ritonavir. Six of the 22 isolates (27%) remained susceptible to all 4 protease inhibitors, 12 of the 22 isolates (55%) retained susceptibility to at least one of the protease inhibitors and 4 out of the 22 isolates (18%) displayed broad cross-resistance to all protease inhibitors. Sixteen (73%) and 11 (50%) of the 22 isolates remained susceptible ( < 4-fold) to amprenavir and indinavir, respectively. Four of 16 (25%) and nine of 21 (43%) with available data remained susceptible to nelfinavir and ritonavir, respectively.

After treatment failure with amprenavir, cross-resistance to saquinavir was evaluated. HIV-1 isolates from 22/22 subjects failing treatment with amprenavir and containing one or more substitutions M46L/I, I50V, I54L, V32I, I47V, and I84V were susceptible to saquinavir.

Clinical Studies

Description Of Clinical Studies In Adults

In a randomized, double-blind clinical study NV14256 in zidovudine-experienced, HIV-1-infected adult subjects, Interfast in combination with zalcitabine² was shown to be superior to either Interfast or zalcitabine monotherapy in decreasing the cumulative incidence of clinical disease progression to AIDS-defining events or death. In another randomized study ACTG229/NV14255, subjects with advanced HIV-1 infection with history of prolonged zidovudine treatment were administered Interfast 600 mg (three times daily) + zidovudine + zalcitabine. Subjects receiving this regimen experienced greater increases in CD4⁺ cell counts as compared to those who received Interfast + zidovudine or zalcitabine + zidovudine. It should be noted the HIV treatment regimens that were used in these clinical trials are no longer considered standard of care.

In the MaxCmin1 trial, saquinavir gel capsule 1000 mg twice daily coadministered with ritonavir 100 mg twice daily was evaluated in a heterogeneous population of 148 HIV-1-infected subjects. A total of 42 subjects enrolled were treatment naïve, and 106 subjects were treatment experienced (of which 52 subjects had HIV-1 RNA < 400 copies/mL at baseline). Results showed that 91/148 (61%) subjects achieved and/or sustained an HIV-1 RNA < 400 copies per mL at the completion of 48 weeks treatment.

²No longer available in the US.