Atazanavir is indicated for the treatment of human immunodeficiency virus (HIV)-1 infection. Once the establishment of infection, HIV cannot be eradicated from the body, although an undetectable viral load equates with the virus being untransmittable sexually, so long as antiviral therapy continues. The goal of lifelong drug treatment in HIV-infected patients is to suppress viral replication and sustain viral target CD4+ T lymphocyte counts to prevent the development of clinical conditions associated with acquired immunodeficiency syndrome (AIDS) and prevent viral transmission to others.
Atazanavir therapy works in combination with other anti-HIV drugs. The high error rate of HIV polymerase creates extensive mutations and promotes the development of antiretroviral drug-resistant strains. The administration of multiple medications addresses this problem with at least two different modes of action. The combination of protease inhibitors, such as atazanavir, paired with two nucleoside analogs, can reduce the HIV viral load to undetectable concentrations in the blood.
Because of cross-resistance among antiretroviral agents, information on the baseline mutations in the virus, as determined by genotype testing, should guide the drug regimen selection, especially in patients who have had prior treatment with protease inhibitors.
Atazanavir is not recommended to children younger than three months of age, and the optimal dosage remains unestablished. Atazanavir may cause kernicterus in this group as it is a competitive inhibitor of an enzyme that catalyzes bilirubin glucuronidation. Atazanavir is also not recommended for use during lactation. Atazanavir may be given to HIV-infected pregnant patients, as it has not shown an increased risk of teratogenicity or genotoxicity in human and animal studies. However, elevated bilirubin concentrations are observable in neonates whose mothers were taking atazanavir during pregnancy, and the selection of other available protease inhibitor combinations may reduce potential adverse effects to the infant.
Mechanism of Action
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Human immunodeficiency virus is a lentivirus in the retrovirus family. It is an enveloped RNA virus. The virus contains two identical linear positive-strand RNA molecules that form its genome, along with the enzymes reverse transcriptase (RNA-dependent DNA polymerase), integrase, protease, as well as structural proteins, envelope proteins, regulatory proteins, accessory proteins, and transfer RNAs needed for viral replication.
The life cycle of HIV provides several drug targets. Viral entry to host cells is initiated by binding of the viral envelope glycoprotein to host cell surface receptor CD4 and chemokine co-receptors. Once the fusion of the viral membrane with the host cell membrane occurs, the contents of the HIV capsid get released into the host cytosol, and double-stranded DNA is produced by the HIV reverse transcriptase using the viral RNA genome as a template. Then, the viral DNA is transported into the nucleus and integrated into host chromosomes, using viral integrase enzymes. Using the host cellular transcription machinery leads to the synthesis of viral mRNAs and the production of proteins. Most viral proteins are made as precursor proteins and assembled with other components of the virus. After budding of the newly formed virions, HIV protease cleaves the precursor proteins into individual functional proteins. The newly synthesized viral particles are then capable of infecting subsequent host cells.
The first drug approved as an anti-HIV agent was azidothymidine (zidovudine), a nucleoside analog of thymidine without 3’-hydroxyl group on the sugar. Cellular tri-phosphorylation of the 5’-hydroxyl group of azidothymidine results in viral reverse transcriptase incorporation of this nucleotide during reverse transcription. However, due to the lack of the 3’-hydroxyl group, the DNA chain elongation is prematurely terminated. Other nucleoside reverse transcriptase inhibitors include dideoxycytidine, dideoxyinosine, idoxuridine, ribavirin, stavudine, trifluridine, and others. Lamivudine has a modified sugar, and idoxuridine, ribavirin, and trifluridine have modified bases.
Non-nucleoside reverse transcriptase inhibitors also bind to the enzyme, but not at the same sites where the nucleotide substrate binds. Non-nucleoside reverse transcriptase inhibitors are non-competitive inhibitors of reverse transcriptase. The six FDA-approved non-nucleoside reverse transcriptase inhibitors are delavirdine, doravirine, efavirenz, etravirine, nevirapine, and rilpivirine. These drugs only inhibit the reverse transcriptase of HIV-1 and not HIV-2, which is less common than HIV-1 in HIV infections worldwide.
Viral integrase enzyme is essential for the integration of proviral DNA into the host chromosome. The four FDA-approved viral integrase inhibitors are bictegravir, dolutegravir, elvitegravir, and raltegravir are integrase inhibitors.
Due to the essential role of HIV protease in the production of the mature virus, HIV protease has been the target for anti-HIV drugs. The ten FDA approved protease inhibitors are amprenavir, atazanavir, darunavir, fosamprenavir, indinavir, lopinavir, nelfinavir, saquinavir, and tipranavir. These drugs are peptide mimetics that compete with the Gag and Gag-Pol proteins, which are natural substrates of HIV protease. Inhibition of the protease cleavage of these precursor proteins results in incomplete packaging of the virus. Protease inhibitors also have various off-target interactions, such as atazanavir's inhibition of the UGT1A1 enzyme (responsible for bilirubin glucuronidation), leading to the accumulation of bilirubin in the serum. However, atazanavir use is associated with fewer cardiac and lipid profile adverse effects than other protease inhibitors.
Additionally, enfuvirtide and maraviroc are viral entry inhibitors. Enfuvirtide is a peptide mimic to the region of the HIV-1 glycoprotein 41 that is essential for the entry of HIV-1 to the host cells. Maraviroc is a chemokine receptor CCR5 inhibitor. The CCR5 is a co-receptor that HIV uses for host cell entry.
These therapeutics are used in various combinations, called antiretroviral treatment (ART), to combat the rapid mutation rate that leads to the evolution of drug resistance seen in HIV. HIV protease inhibitors are a key component of highly active antiretroviral combination therapy (HAART) for patients infected with HIV; mutations in HIV protease lead to their drug resistance. Atazanavir was the first protease inhibitor that received approval for once-daily dosing. Protease inhibitors have shown improved efficacy in reducing HIV viral load over other antiretroviral therapeutics alone but also contribute to the most severe antiretroviral adverse effects, impacting patient pharmacotherapy adherence.
Atazanavir administration is via the oral route. Administration with food has demonstrated enhanced bioavailability and reduced pharmacokinetic variability. Gastric acid is necessary for the dissolution of atazanavir. Therefore, co-administration of antacids, buffered medications, proton pump inhibitors, and histamine H2-receptor antagonists requires a careful plan for separated dosing time.
Atazanavir is the first once-daily administered protease inhibitor; administration is with low dose ritonavir or cobicistat. Cobicistat and ritonavir are cytochrome P450 (CYP3A4) inhibitors. Because the same enzyme metabolizes atazanavir, co-administration with cobicistat or ritonavir will increase the bioavailability of atazanavir. Atazanavir without these pharmacokinetic boosts may be administered in patients with underlying hyperlipidemia, as ritonavir-boosted therapy may enhance the risk of hyperlipidemia.
Common adverse effects are hyperbilirubinemia (35 to 49% in adults, 16% in children), rash (up to 21%), hypercholesterolemia (6 to 25%), hyperamylasemia (14 to 33%), jaundice (5 to 9% in adults, 13 to 15% in children), nausea (3 to 14%), cough (21% in children), and fever (2% in adults, 18-19% in children). Severe adverse effects are Stevens-Johnson syndrome, toxic skin eruptions, erythema multiforme, angioedema, cholecystitis, pancreatitis, interstitial nephritis, diabetic ketoacidosis, and AV block. Other potential adverse effects are nephrolithiasis, cholelithiasis, hyperlipidemia, hypertriglyceridemia, bleeding, pancreatitis, exacerbation of diabetes mellitus or hyperglycemia, and lactic acidosis in combination with nucleoside analogs.
Although immune reconstitution inflammatory syndrome (IRIS) is not a direct side effect of atazanavir, a pathological inflammatory response may occur after initiation of antiretroviral treatment for HIV infection. Up to a 75% mortality rate in IRIS with tuberculosis in the central nervous system has been reported. There have been suggestions that successful treatment with antiretroviral drugs enables the recovery of the immune function but may also exacerbate existing opportunistic infections (paradoxical IRIS) or unmasks opportunistic infections (unmasking IRIS). Clinical symptoms may vary depending on the type of opportunistic infections, but a common feature includes acute generalized or local inflammation responses such as fever or localized tissue edema. The timing of initiating antiretroviral therapy, therefore, is crucial to prevent IRIS.
Hypersensitivity reaction to atazanavir in the form of a mild rash, Stevens-Johnson syndrome, toxic skin eruptions, or erythema multiforme may occur. Atazanavir should be discontinued in patients who develop serious hypersensitivity reactions.
Atazanavir metabolism occurs via CYP3A4 and inhibits CYP3A4, CYP1A2, and CYP2C9. Patients who also take drugs that inhibit or are substrates of these enzymes with a narrow therapeutic index should not take atazanavir. For example, significant drug interactions may occur with warfarin, irinotecan, diltiazem, simvastatin, lovastatin, phosphodiesterase inhibitors, Saint John’s wort, and tenofovir.
Human immunodeficiency virus is highly mutatable due to the lack of proofreading capability of viral reverse transcriptase, which creates a higher risk for the development of drug resistance. Viral genetic testing should take place to monitor the occurrence of drug resistance, especially when the viral titer increases.
Research has reported first-degree AV block in patients treated with ritonavir and atazanavir co-administration. An electrocardiogram is necessary for patients who have pre-existing conduction diseases or simultaneously take medications that may cause PR prolongation. Cardiac complications may present as patient complaints of dizziness or lightheadedness.
Delayed hypersensitivity to atazanavir or any of its components may develop. A mild rash may often develop but can disappear after 1 to 2 weeks and does not require stopping atazanavir. However, the development of serious reactions to the drug requires monitoring, especially the development of a severe rash, flu-like symptoms, fever, muscle or joint aches, conjunctivitis, blisters, mouth sores, facial swelling, painful/inflamed skin lesions.
Clinicians should monitor the development of acute immune reconstitution inflammatory syndrome following the initiation of antiretroviral therapy.
Drug interactions with co-administrated medications should require monitoring, as do hepatic function and renal function. Signs of hepatic impairment include hyperbilirubinemia, elevated liver enzymes in the serum, jaundice, dark-colored urine, light-colored bowel movements, nausea, itching, and abdominal pain. Signs of renal impairment include back pain (due to kidney stones), crystalluria, or bloody urine. These symptoms may occur within weeks (acute kidney injury (AKI)) or years (chronic kidney disease (CKD)) after initiation of atazanavir therapy.
There is no specific antidote for atazanavir toxicity. Healthcare staff should provide symptomatic and supportive care. Patient monitoring for signs of respiratory distress and other vital signs is necessary. Electrocardiogram monitoring of the patient is recommended as the atazanavir may worsen AV block due to PR interval prolongation. If the simultaneous overdose with nucleoside reverse transcriptase inhibitors is suspected, clinicians should monitor patients for symptoms of lactic acidosis.
Enhancing Healthcare Team Outcomes
Estimates are that more than a million people in the United States have HIV infection. Once diagnosed with HIV infection, immediate initiation of antiretroviral treatment is the recommended course to delay the disease progression from HIV infection to acquired immunodeficiency syndrome (AIDS) in the infected patient. This approach requires an interprofessional team effort.
Adherence to the treatment plan is equally crucial to prevent HIV transmission to others by reducing viral load. Additionally, studies have shown that the stigma associated with HIV infection negatively impacted treatment adherence. This factor poses a non-trivial challenge to the entire healthcare team to not only monitor the patient for adverse drug events to improve adherence to drug therapy and test for the occurrence of drug resistance but also to provide effective counseling on the importance of therapy adherence and behavioral modifications to reduce patient risk for opportunistic infections and minimize public risk for the spread of HIV infections. Treatment adherence improves by the healthcare team when it is attentive to patient concerns about adverse events, providing strategies to reduce dosing forgetfulness, and increasing disease and health literacy.
Recently, research has shown that a single-tablet regimen improved pharmaceutical adherence over multi-tablet regimens. Nurses play a vital role in performing patient counseling to emphasize the importance of strict regimen adherence. A failure in this regard can render entire classes of antiretroviral drugs impotent. A pharmacist, preferably with infectious disease board certification, who also specializes in HIV regimens, should verify the agents chosen and dosing, as well as carefully check for drug interactions that could produce adverse effects or inhibit therapeutic effectiveness, and alert the prescriber of any issues.
In summary, interprofessional healthcare teams can enhance HIV treatment outcomes in various ways, especially by improving drug adherence through education, careful monitoring, and consideration of the patient's needs and lifestyle. [Level 5]
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