Avifix250 mg

Avifix is an HIV-1 protease inhibitor indicated, in combination with other antiretroviral agents, for the treatment of HIV-1 infection.

Evidence-based classification of use

• Established/FDA-approved use: Treatment of HIV-1 infection in adults and pediatric patients (2 years of age and older), always as part of a combination antiretroviral regimen with at least two other antiretroviral agents. Avifix must never be used as monotherapy.
• Guideline status: Current HIV treatment guidelines (e.g., DHHS/WHO) no longer list Avifix as a preferred or alternative first-line agent because of the availability of protease inhibitors and other antiretroviral classes with better tolerability, lower pill burden, and fewer food/interaction restrictions. Avifix may still be used in select, guideline-directed circumstances (for example, in patients already virologically suppressed on it, or where other agents are unsuitable), under specialist supervision.
• Combination-only agent: Efficacy depends entirely on combining Avifix with other active antiretroviral drugs; it is not effective and is not indicated as a standalone therapy.

All use of Avifix should be directed by a physician experienced in the management of HIV infection.

Each tablet typically contains Nelfinavir mesylate equivalent to 250 mg or 625 mg of Nelfinavir base. An oral powder formulation (typically 50 mg of Nelfinavir base per gram of powder) is also available for patients who cannot swallow tablets, mixed with a small amount of liquid or food before dosing. Strengths and available dosage forms may vary by manufacturer and market.

Avifix is a synthetic, non-peptidic antiretroviral drug belonging to the HIV protease inhibitor class. It works by inhibiting the HIV-1 protease enzyme, blocking a critical step in the viral replication cycle.

Avifix is administered orally, taken with food, and is used only as part of a multi-drug combination antiretroviral regimen — never alone.

Antiretroviral agent - HIV protease inhibitor (PI).

Mechanism of Action

Nelfinavir is a selective, reversible inhibitor of HIV-1 and HIV-2 protease, the viral enzyme responsible for cleaving the Gag and Gag-Pol polyprotein precursors into the individual functional proteins required for the assembly of infectious HIV virions. By inhibiting this enzyme, Nelfinavir causes the formation of immature, non-infectious viral particles, preventing the virus from establishing new infectious cycles.

Pharmacokinetics

• Absorption: Oral bioavailability is enhanced by food; absorption is reduced in an achlorhydric (low-acid) gastric environment, which is why co-administration with acid-reducing agents (e.g., proton pump inhibitors) is contraindicated.
• Protein binding: Highly protein-bound (approximately 98%).
• Metabolism: Extensively metabolized in the liver, primarily by CYP3A4 and CYP2C19, with an active metabolite (M8) contributing to antiviral activity. Nelfinavir is also a potent CYP3A4 inhibitor, accounting for its extensive drug-interaction profile.
• Elimination: Predominantly eliminated via the feces (mainly as metabolites), with a plasma elimination half-life of approximately 3.5 to 5 hours.

Avifix tablets should be swallowed with food. The oral powder can be mixed with a small amount of water, milk, formula, soy formula, or dietary supplement (not acidic food/juice, which may produce a bitter taste) and consumed immediately. Do not administer with only water for children who require the powder form without an appropriate mixing agent per label instructions.

Avifix is both a substrate and a potent inhibitor of CYP3A4, giving it an extensive drug interaction profile. Only clinically significant, well-verified interactions are listed below.

• Proton pump inhibitors (e.g., omeprazole): Significantly reduce Avifix absorption and plasma concentration by raising gastric pH; co-administration is contraindicated.
• Rifampin: Substantially reduces Avifix plasma concentrations via CYP3A4 induction, risking loss of antiviral efficacy; co-administration is contraindicated.
• Ergot derivatives (e.g., ergotamine, dihydroergotamine): Risk of acute ergot toxicity (peripheral vasospasm, ischemia) due to increased ergot levels; co-administration is contraindicated.
• Certain statins (lovastatin, simvastatin): Markedly increased statin levels raise the risk of myopathy/rhabdomyolysis; co-administration is contraindicated.
• Amiodarone and other QT-prolonging agents (e.g., quinidine): Increased plasma concentrations of these drugs raise the risk of serious arrhythmias; co-administration is contraindicated.
• Sildenafil (when used for pulmonary arterial hypertension), midazolam, triazolam, cisapride, pimozide: Increased plasma levels raise the risk of serious or life-threatening effects (extended sedation, respiratory depression, arrhythmia); co-administration is contraindicated.
• St. John's Wort and other strong CYP3A4 inducers: Reduce Avifix concentrations significantly, risking loss of virologic response and resistance; concomitant use should be avoided.
• Hormonal contraceptives: Avifix may reduce ethinyl estradiol concentrations, reducing contraceptive efficacy; an alternative or additional non-hormonal contraceptive method is recommended.

Because of the complexity of these interactions, all concomitant medications (including over-the-counter drugs and herbal supplements) should be reviewed by a physician or pharmacist before starting Avifix.

Common

• Diarrhea (the most common adverse effect, often dose-related)
• Nausea, flatulence, abdominal pain
• Rash
• Headache, fatigue

Less Common but Clinically Important

• Hyperglycemia and new-onset or worsening diabetes mellitus
• Elevated liver transaminases
• Fat redistribution/accumulation (lipodystrophy) with long-term use
• Increased bleeding episodes in patients with hemophilia A or B
• Immune reconstitution inflammatory syndrome (in patients with advanced HIV starting combination antiretroviral therapy)

Patients should promptly report severe or persistent diarrhea, signs of high blood sugar, unusual bleeding, or jaundice to their physician.

Avifix should be used during pregnancy only as part of a current guideline-directed antiretroviral regimen, and only if the potential benefit to the mother and reduction of mother-to-child HIV transmission justifies the potential risk to the fetus. Use only under the direction of a physician experienced in HIV management, following current national/WHO perinatal HIV treatment guidelines.

Breastfeeding is generally not recommended for mothers with HIV infection where safe formula feeding is available, regardless of antiretroviral therapy, due to the risk of postnatal HIV transmission; a physician should be consulted for individualized guidance.

• Hyperglycemia: New-onset diabetes mellitus, exacerbation of pre-existing diabetes, and hyperglycemia have been reported with protease inhibitors including Avifix; monitor blood glucose periodically.
• Lipid abnormalities and fat redistribution: Increases in cholesterol and triglycerides, and redistribution/accumulation of body fat, have been observed with long-term use; monitor lipid profile.
• Hepatic impairment: Use with caution and enhanced monitoring in patients with underlying liver disease, including chronic hepatitis B or C.
• Hemophilia: Increased spontaneous bleeding has been reported in patients with hemophilia A and B receiving protease inhibitors.
• Drug interactions: Extensive CYP3A4-mediated interaction potential; see Interactions and Contraindications.
• Adherence and resistance: Strict adherence to the prescribed dose and schedule of Avifix, in combination with other antiretroviral agents, is essential. Missing doses, taking Avifix without food, or discontinuing therapy without medical advice can lead to the development of viral resistance and treatment failure. Take exactly as prescribed by your physician; do not stop, extend, skip doses, or share this medicine with others without medical advice.

There is limited clinical experience with Avifix overdose. In case of suspected overdose, seek immediate medical attention or contact a poison control center. General supportive measures should be provided as directed by a physician; there is no specific antidote for Avifix overdose, and it is not significantly removed by hemodialysis.

Store at room temperature (below 30°C), away from light and moisture. Keep out of reach of children.

• Pediatric patients: Approved for use in children 2 years of age and older, using weight-based dosing; safety and efficacy in children under 2 years have not been established.
• Elderly: Clinical studies of Avifix did not include sufficient numbers of patients aged 65 and over to determine whether they respond differently from younger patients; use with caution, considering the greater frequency of decreased hepatic or renal function and concomitant disease in this population.
• Hepatic impairment: Use with caution; not well studied in significant hepatic impairment (see Precautions).
• Renal impairment: No dosage adjustment required.
• Pregnancy and lactation: See Pregnancy and Lactation section.

Avifix, as part of combination antiretroviral therapy, is generally continued long-term/indefinitely for chronic suppression of HIV-1 infection, as directed by the treating physician based on virologic and immunologic response. Treatment should not be interrupted or discontinued without medical supervision.

HIV Protease Inhibitor; Antiretroviral agent.

Nelfinavir selectively and reversibly binds to the active site of HIV-1 protease, preventing cleavage of the Gag-Pol polyprotein precursor. This results in the production of immature, non-infectious HIV particles that are unable to initiate new rounds of infection, thereby reducing viral load when used with other antiretroviral agents.

B (FDA legacy pregnancy category)

Avifix is approved for use in children 2 years of age and older, in combination with other antiretroviral agents, using weight-based dosing (tablets or oral powder). Safety and efficacy in children under 2 years of age have not been established. Close monitoring for growth, tolerability, and adherence is recommended in pediatric patients.