Introduction
HIV-1, a retrovirus, can induce acquired immunodeficiency syndrome if not treated. According to data from the World Health Organization (WHO), an estimated 39 million individuals worldwide are living with HIV-1 [
1‐
4]. Because HIV-1 has significant genetic diversity, monotherapy with the authorized therapies for this virus frequently leads to the selection of resistant variants. However, combined antiretroviral treatment (cART) combining various classes of HIV-1 medications has been confirmed to be extremely successful in HIV-1-positive individuals, making the infection a long-term chronic condition [
5,
6].
However, the emergence of drug-resistant and multidrug-resistant strains remains a key factor in the failure of cART, leading to higher odds of HIV disease progression and mortality [
7]. HIV medications are classified into six types based on whether they target viral proteins or the virus’s attachment to host cells. These categories include nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), protease inhibitors (PIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), entrance inhibitors, integrase strand transfer inhibitors (INSTIs), and capsid inhibitors. Entry inhibitors are further classified as pre-attachment inhibitors, post-attachment inhibitors, CCR5 antagonists, and fusion inhibitors [
8].
New mutations cause limitations of cART drug regimen. Other limitations of this treatment regimen include the high cost of treatment and drug-drug interactions [
9,
10].. According to the World Health Organization’s most current HIV Drug Resistance Report, the prevalence of acquired and transmitted HIV drug resistance has increased significantly and rapidly among people who have not yet received ART. This growth presents a significant barrier to attaining the aim of eliminating the HIV-1 pandemic as a public health issue by 2030. According to the findings, 10% of HIV-positive persons who begin HIV therapy are already resistant to non-nucleoside reverse transcriptase inhibitors (NNRTI) [
11].
Pre-attachment inhibitors, such as FTR, hinder the virus’s first attachment to host cells by inhibiting interactions between gp120 and CD4 [
12]. Post-attachment inhibitors, such as ibalizumab, promote alterations in the CD4-gp120 complex, blocking fusion between the virus and the cell [
13,
14]. CCR5 antagonists, such as maraviroc and leronlimab, prevent viral docking by binding to the CCR5 co-receptor [
15]. Fusion inhibitors, such as the synthetic peptide enfuvirtide (T-20; ENF), are a kind of ARV that prevents the virus from entering host cells [
16].
FTR, originally BMS-663,068/GSK-3,684,934, is an FDA-approved medication marketed under the brand name Rukobia [
17].
FTR attaches to the viral envelope glycoprotein 120 (gp120), inhibiting the conformational shift required for the virus to enter host T cells and other immune cells [
18,
19]. During its development, it was revealed that FTR is converted into a more permeable derivative termed TMR by the action of alkaline phosphatase near the surface of the gut epithelium [
18,
20,
21].
HIV-MDR has a limited response to most existing HIV medicines, making it difficult to develop effective treatment regimens to reduce viral replication in these individuals. HIV-MDR infection has been associated with increased risks of clinical deterioration and fatality [
22,
23]. Individuals who have previously used ARV medications have a threefold increased probability of acquiring resistance to the NNRTI drug class [
24,
25]. The BRIGHT trial’s findings did not consistently demonstrate a link between virologic failure (the inability to reduce viral replication) and particular gp120 mutations. Furthermore, there have been no instances of FTR developing cross-resistance to other ARV medications. FTR is considered an essential therapy option for individuals with HIV who are resistant to other drugs, perhaps saving lives [
26‐
29].
Interaction of FTR with ARVs
Evidence has indicated few significant interactions between FTR and other ARVs or medications frequently used for HIV-associated comorbidities. FTR is often metabolized by a hydrolysis pathway mediated by esterase. Also, it is partly metabolized through an oxidative pathway mediated by CYP3A4. Researchers and collaborators at ViiV Healthcare (USA) compiled data from 11 studies on drug-drug interaction to report the potential use of FTR with other ARVs and with drugs commonly used by HIV-infected people. Strong CYP3A inducers (e.g., rifampin) and anti-HCV drug (e.g., elbasvir/grazoprevir) are contraindicated with FTR. As the metabolization of TMR is performed by CYP3A4, strong CYP3A inducers considerably mitigate TMR plasma concentrations and may cause impairment in virologic response to FTR. TMR prevents the transporter OATP1B1/3, which may result in higher grazoprevir concentrations, therefore increasing liver enzymes [
60].
The Data Documentation Initiative from 13 investigations was collected to report the effect of 17 drugs or drug combinations on TMR. FTR with CYP3A4, P-glycoprotein (P-gp), and/or breast cancer resistance protein (BCRP) inhibitors raised TMR concentrations; however, they do not cause clinical concern at therapeutic dose. TMR may be given with weak/moderate inducers with or without co-administration, such as ritonavir (RTV) or cobicistat (COBI). FTR can be administered with drugs raising stomach pH; famotidine did not influence TMR pharmacokinetics (PK). Temsavir may enhance the concentrations of drugs that are substrates of organic-anion transporting polypeptide 1B1/3 and BCRP. Thus, the majority of statins need dose reduction [
61]. Wire et al., showed that co-administration of maraviroc and FTR did not result in clinically relevant changes in TMR. These two drugs may be co-administered without dose adjustment of either ARV agent [
62].
High concentrations of grazoprevir may enhance the risk of alanine aminotransferase (ALT) elevations. Thus, administration of FTR with elbasvir/grazoprevir is not recommended. Dose alterations and/or careful titration of dose are recommended for certain statins that are substrates of OATP1B1/3 or BCRP (rosuvastatin, atorvastatin, pitavastatin, simvastatin, and fluvastatin) when co-administered with FTR. Following the co-administration of FTR with tenofovir/alafenamide (TAF), TMR is speculated to raise the plasma concentrations of TAF by blocking OATP1B1/3 and/or BCRP. The recommended TAF dose is 10 mg when co-administered with FTR. Due to drug interaction of COBI and RTV, FTR may be administered combined with strong CYP3A4, BCRP, and/or P-gp inhibitors (such as clarithromycin, itraconazole, posaconazole, and voriconazole) without dose adjustment [
63].
One study investigated 99 patients who had no active drugs as treatment options. However, FTR was added to their optimized ARV regimen. Of these 99 patients, 38 cases obtained an HIV viral load of < 40 copies/mL at 48 weeks. Co-administration of FTR with strong cytochrome P450 3 A inducers is contraindicated as the plasma concentrations of TMR considerably decreased. Etravirine, another ARV agent, may lower TMR plasma concentrations. However, after its combination with a ritonavir-boosted protease (strong) inhibitor, the impact on TMR metabolism is insignificant and does not need dose alteration [
64].
Safety, efficacy and side effects
FDA approved FTR based on the findings of phase 3 BRIGHTE clinical trial research for the medical therapy of HIV-1 infection in adult patients with MDR HIV-1 virus infection who are suffering from treatment failure and unable to construct an effective regime [
74]. FTR has undergone several clinical trials to ensure its effectiveness and safety before its approval in many research projects.
Treatment with more potent ARV medications, such as FTR, improves HIV-1 patient survival while increasing the risk of complications, such as chronic kidney and liver disease. In the HIV-infected population, liver diseases are becoming more frequent, so in the phase 1 study, researchers evaluated renal and hepatic dysfunction of FTR. In renal (NCT02674581) and hepatic (NCT02467335) clinical trial studies, following a single dose of FTR renal and hepatic dysfunction showed no clinically relevant effect on TMR pharmacokinetics [
75]. Also, in an eight-day monotherapy trial study, the antiviral activity, safety, and pharmacokinetics of BMS-488,043, were evaluated. The antiviral activity and safety of this inhibitor were affirmed, but it had weak PK, and its oral bioavailability was limited [
76]. In phase 2a (NCT01009814) of the study conducted by Nettles and co-workers focused on the pharmacokinetics, pharmacodynamics, and drug safety of FTR, patients were given varying doses of FTR with or without RTV for eight days. On day eight, the mean reduction in the plasma HIV-1 RNA level at baseline was in the range of 1.21–1.73 log10 copies/mL, and a mean elevation in the CD4 + count from baseline was detected in all regimen groups, with no clinically relevant alterations in the percentages of CD4 and CD8 + T cells. These findings along with the favorable pharmacokinetic profile and usually good tolerability were reported in this clinical trial study [
77].
In phase 2b of the study (NCT01384734), 251 patients were placed into five groups through 48 weeks: four in different dosages of FTR and one for atazanavir/ ritonavir (ATV/r) as a control group. During the study, all of these groups received backbone regimes consisting of teltegravir and tenofovir. The FTR groups’ mean CD4 + T-cell count experienced an increase of 145–186 cells/l, while the (ATV/r) group had a mean CD4 + T-cell count increase of 142 cells/l. In this study, FTR doses were safe and there were no FTR-related adverse effects that led to the drug’s withdrawal and indicated similar efficacy compared to (ATV/r) [
78]. In another phase 2b study, a randomized, active-controlled trial (NCT01384734), 254 participants enrolled to receive different doses of FTR. The included participants had HIV-1 RNA ≥ 1000 copies/mL and CD4 + cell count > 50 cells/µL and experienced treatment with ARV. Eligible cases were randomized into five groups. All groups received 300 mg of the backbone of Tenofovir disoproxil fumarate (TDF) daily and 400 mg of raltegravir every 12 h. Two cases of each of the first and second groups withdrew consent, and one case of the first group was randomized in error. At week 24, 80%, 69%, 76%, and 72% of treatment groups 1, 2, 3, and 4 obtained an HIV-1 RNA viral load of more than 50 copies/mL, as compared to 75% of the control group [
79].
In study conducted by Aberg et al., they have reported 240-week efficacy and safety of FTR + OBT in adults with HIV-1. The results show that 66% of the NRC and 82% of the RC had virologic response. At Week 240, mean change from baseline in CD4 + T-cell count was 296 cells/mm3 (RC) and 240 cells/mm3 (NRC); mean CD4+/CD8 + ratio increased between Weeks 96 and 240. From the Weeks 96 to 240, one additional participant experienced a drug-related serious adverse effect, and six deaths happened. Totally, this study have reported that virologic responses and clinically significant improvements in CD4+/CD8 + ratio and CD4 + T-cell count was observed. The safety and tolerability profile of FTR-based ARV regimens remained consistent with previous studies through 96 weeks, and no new safety trends occurred [
80]. In a study conducted by Anderson and co-workers in the 2021 Patient‑Reported Outcomes in phase 3 clinical trial, 371 participants were included in the study and were given at least one dosage of FTR; 272 in the randomized control (RC) (69 placeboes, 203 FTR ) and 99 in the none randomized control (NRC). Through 8 days of functional monotherapy, effectiveness and safety evaluations revealed that FTR (added to the failed regimen) was more effective than placebo. Virologic success (40 copies/ mL, intention-to-treat snapshot analysis) was shown in 53 and 54% of the RC and 37 and 38% of the NRC, respectively, at weeks 24 and 48. FTR was generally well tolerated, with only a small number of adverse events resulting in treatment cessation.
The EQ-5D-3 L, EQ-VAS, and Functional Assessment of HIV Infection (FAHI) tests were used to measure PRO. At week 24, both groups had improved their EQ-5D-3 L US and UK-referenced utility scores from baseline. At week 24, mean visual analog scale (VAS) scores in the RC and NRC rose from baseline by 8.7 (95% CI 6.2–11.2) and 5.6 points (95%CI 1.5–9.7), respectively, and at week 48, they climbed by 9.8 (95% CI 7.0–12.6) and 4.9 points (95% CI 0.6–9.2). From baseline to weeks 24 and 48 in the RC, mean increases in FAHI total score were 6.9 (95% CI 4.2–9.7) and 5.8 (95% CI 2.7–9.0), respectively. Improvements in key EQ-VAS and FAHI domains through week 48, in combination with efficacy and safety data, support the use of FTR for Heavily treatment-experienced people living with HIV-1 [
81].
In the BRIGHTE (the name of clinical trial) study, 81% of patients had mild to moderate complications. At week 96, 7% of participants had stopped taking FTR due to an adverse event. Common side effects of the therapeutic dose of FTR (600 mg BID) with optimized backbone therapy include nausea, headache and diarrhea. Most adverse effects were less than 4%, including abdominal pain, pyrexia, dyspepsia, fatigue, asthenia, sleep disorders, vomiting, myalgia, dizziness, pruritus, peripheral neuropathy and immune reconstitution inflammatory syndrome that may occur in patients treated with FTR and backbone therapy [
27,
82]. The most important laboratory abnormalities in these patients are related to increases in serum creatinine (greater than 1.8 times the upper limit of normal (ULN)), creatinine kinase (greater than 10 times ULN), bilirubin (greater than 2.6 times ULN), ALT levels (greater than 0.5 times ULN) and AST (Aspartate Aminotransferase) levels (greater than 0.5 times ULN). Other less common laboratory abnormalities like increases in lipase levels (greater than 0.3 times ULN), LDL (low-density lipoprotein) cholesterol levels (greater than 190 mg/dl), triglycerides (greater than 500 mg/dl), urate levels (greater than 12 mg/dl) and blood sugar (greater than 250 mg/dl) may occur. Possible hematological abnormalities such as decreased neutrophil count and hemoglobin levels may also be seen in these patients.
FTR has few adverse reactions at low doses, so it doesn’t require dosage adjustments in patients with renal or hepatic impairment. Immune reconstitution inflammatory is one of the most considerable side effects of using this drug in patients on cART which includes FTR. It may also develop an inflammatory reaction to opportunistic infections like
Mycobacterium avium infection,
Pneumocystis jirovecii, cytomegalovirus (CMV), tuberculosis, or pneumonia [
82]. Because the use of FTR in patients with hepatitis B or C virus coinfection is linked to an increase in hepatic transaminases, liver function tests should be monitored [
27]. At therapeutic levels, FTR has no major negative effects, but doses greater than 2400 mg twice daily can cause QTc prolongation. As a result, FTR should be used with caution in individuals on other medications that can prolong the QT interval [
73].
Some medicines like Ethinyl estradiol and statins, when taken together with FTR may increase their concentration and induce side effects [
61,
83]. There are inadequate human data on the use of RUKOBIA during pregnancy to accurately estimate the risk of birth abnormalities and miscarriage related with the medicine. During organogenesis, oral administration of FTR to pregnant rats and rabbits had no adverse developmental effects at clinically relevant TMR exposures in animal reproduction experiments. However, research is still ongoing to ensure that the FTR is safe during pregnancy.
Information on using FTR during pregnancy is not sufficient to precisely evaluate the risk of birth defects and miscarriage related to drugs. It’s unclear whether FTR is found in human breast milk, whether it affects human milk production, or whether it affects the breastfed child. A FTR-related medication was found in rat milk after it was given to nursing rats. Therefore, the use of this drug during breastfeeding should be done with caution. FTR is not approved for children use and in pediatric patients; the safety and efficacy of FTR have not been demonstrated. The number of patients aged 65 and older in FTR clinical studies was insufficient to assess if they respond differently than younger ones. In general, while administering FTR to older patients with reduced hepatic, renal, or cardiac function, as well as concurrent illness or other pharmacological therapy, caution should be given [
82,
84].
Conclusion and outlook
For more than a decade, therapeutic HIV recommendations have included ART, which has saved the lives of countless HIV/AIDS patients. Extraordinary increased usage of HIV medications has coincided with the establishment of HIV drug resistance. Due to the advent of drug-resistant virus, all ARV medications, including those from newer pharmacological classes, are in danger of becoming partially or completely inactive. HIV medication resistance, if not controlled might impair the efficacy of HIV treatments leading to an increase in HIV infections. FTR is currently in an ongoing phase 4 and post-marketing studies. Also, many studies on the effectiveness and side effects of this drug in children, elderly patients, pregnant and lactating women are under investigation. However, after passing 3 phases of clinical trial studies, this drug has the appropriate effectiveness with minimal side effects and interactions. Heavily treatment-experienced adults with MDR HIV-1 have many problems, including using multiple drugs with low efficacy. They also experience high side effects and high drug interactions due to polypharmacy. Therefore, it seems logical that considering the risk/benefit ratio, FTR can be a suitable alternative treatment for these patients.
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