Fosamprenavir

Fosamprenavir is an antiretroviral agent belonging to the protease inhibitor class, commonly co-administered with ritonavir, which enhances its plasma concentration and therapeutic effectiveness by acting as a pharmacokinetic booster. Approved in the United States in October 2003 and in the European Union in July 2004, fosamprenavir targets the HIV-1 protease enzyme, a key component in viral replication. By inhibiting this enzyme, it reduces the production of infectious virus, thereby lowering viral load. This antiviral activity supports immune function and decreases the risk of complications associated with HIV. While not a cure, fosamprenavir remains a vital part of combination antiretroviral therapy for managing HIV infection.

BRAND NAMES:

Lexiva - Lexiva is available as oral administration tablets in a strength of 700mg of fosamprenavir as fosamprenavir calcium.

Telzir – Each film coated tablet contains 700mg of fosamprenavir as fosamprenavir calcium.

MECHANISM OF ACTION:

Fosamprenavir is a prodrug that is rapidly converted to its active form, amprenavir, by cellular phosphatases in the intestinal epithelium during absorption. Amprenavir functions as an inhibitor of HIV-1 protease, an enzyme essential for viral replication. During the replication cycle, HIV-1 protease cleaves the Gag and Gag-Pol polyproteins to produce structural proteins and enzymes necessary for the maturation of infectious viral particles. By binding to the active site of the protease enzyme, amprenavir blocks this cleavage process, leading to the production of immature, non-infectious virions.

PHARMACOKINETICS:

Absorption: After administration of fosamprenavir, it is rapidly hydrolyzed by enzymes in the intestinal wall and liver to produce the active drug amprenavir. The oral bioavailability of amprenavir is moderate but improved with a high-fat meal.

Distribution: The volume of distribution of fosamprenavir is approximately 90%.

Metabolism: It is extensively metabolized in the liver, primarily by cytochrome P4503A4(CYP3A4).

Excretion: Fosamprenavir is primarily excreted in feces and lesser extent in urine.

PHARMACODYNAMICS:

Fosamprenavir is converted by cellular phosphatases into amprenavir, an antiretroviral protease inhibitor. This enzymatic conversion enables a sustained release of amprenavir, thereby decreasing the pill burden for patients.

DOSAGE AND ADMINISTRATION:

Fosamprenavir is available in tablets and is prescribed to the patient depending on the person weight, severity of the disease and other considerations.

For adults suffering from HIV infection,

Without Ritonavir, the recommended dose is 1400mg orally twice a day.
With ritonavir, the prescribed dose is 1400mg plus ritonavir 100 or 200mg orally once a day. Fosamprenavir 700mg plus ritonavir 100mg orally twice a day.

For adult patients suffering from Non Occupational Exposure,

The recommended dose is 1400mg orally twice a day for 28 days.

For adults suffering from Occupational Exposure,

The recommended dose with ritonavir is, fosamprenavir 1400mg plus ritonavir 100mg orally once a day.
Without ritonavir, the prescribed dose is 1400mg orally twice a day.

The paediatric dose for HIV infection is, without ritonavir, the prescribed dose for oral suspension is 30mg/kg orally twice a day, and the maximum dose is 1400mg/dose.

DRUG INTERACTIONS:

Some medications may change how the actual medications work and also increase the risk of side effects. So it is necessary to discuss with the doctor before if the patient is taking any other medication. Below are some drugs that should be avoided while taking fosamprenavir.