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Fosamprenavir oral

Updated 2 Feb 2023 | Protease inhibitors


Oral formulations of fosamprenavir as fosamprenavir calcium

Drugs List

  • fosamprenavir 700mg tablets
  • TELZIR 700mg tablets
  • Therapeutic Indications


    HIV infection-combined with other antiretrovirals

    Treatment of Human Immunodeficiency Virus (HIV-1) infection in combination with low dose ritonavir and other antiretroviral agents.

    In moderately antiretroviral experienced adults, fosamprenavir in combination with low dose ritonavir has not been shown to be as effective as lopinavir with ritonavir. No comparative studies have been undertaken in children or adolescents.
    In heavily pre-treated patients, fosamprenavir in combination with low dose ritonavir has not been studied sufficiently.
    In protease inhibitor experienced patients, the choice of fosamprenavir should be based on individual viral resistance and treatment history.


    Fosamprenavir must be given with low dose ritonavir (as a pharmacokinetic enhancer of amprenavir) and in combination with other antiretroviral medications.

    Fosamprenavir is a pro-drug of amprenavir and must not be administered concurrently with any other amprenavir-containing product.

    The importance of complying with the full recommended dosing regimen should be highlighted to all patients.


    700 mg fosamprenavir twice daily in combination with ritonavir 100 mg twice daily.


    No dose recommendations can be made for this patient population.

    The pharmacokinetics of fosamprenavir have not been studied in patients over 65 years old.


    Children 6 to 18 years and weighing greater than or equal to 39 kg
    700 mg fosamprenavir twice daily in combination with ritonavir 100 mg twice daily.

    For children weighing less than 39 kg fosamprenavir oral suspension is the recommended option for the most accurate dosing in children based on body weight.

    Children 6 to 18 years and weighing 33 to 38 kg
    The recommended dose of fosamprenavir is 18 mg/kg twice daily in combination with ritonavir 100 mg twice daily.

    Children 6 to 18 years and weighing 25 to 32 kg
    The recommended dose of fosamprenavir is 18 mg/kg twice daily in combination with ritonavir 3 mg/kg twice daily.

    Children 6 to 18 years and weighing less than 25 kg
    No dosage recommendations can be made for children weighing less than 25 kg.

    Patients with Hepatic Impairment

    Even with the dosage adjustments below some patients may have higher or lower than anticipated plasma levels of amprenavir. Monitoring of safety and virologic response is warranted in patients with hepatic impairment.

    Mild hepatic impairment (Child-Pugh score: 5 to 6)
    700 mg fosamprenavir twice daily in combination with ritonavir 100 mg once daily.

    Moderate hepatic impairment (Child-Pugh score: 7 to 9)
    The recommended dose of fosamprenavir is 450 mg twice daily in combination with 100 mg of ritonavir once daily.

    Severe hepatic impairment (Child-Pugh score: 10 to 15)
    Use fosamprenavir with caution at a reduced dose of 300 mg twice daily in combination with 100 mg ritonavir once daily.

    No dose recommendation can be made for children and adolescents with hepatic impairment as no studies have been conducted in these age groups.


    Children under 6 years
    Acute porphyria

    Precautions and Warnings

    Patients over 65 years
    Diabetes mellitus
    Hepatic impairment
    Hepatitis B
    Hepatitis C

    Treatment does not prevent risk of transmission of HIV
    Advise ability to drive/operate machinery may be affected by side effects
    Must be used in combination with other antiretrovirals
    Treatment should be initiated by doctor experienced in HIV management
    Some formulations contain hydroxybenzoate
    Monitor blood glucose before treatment, after 3 to 6 months, then annually
    Monitor serum lipids before treatment, after 3 to 6 months, then annually
    Autoimmune disorders can occur many months after initiation of treatment
    Evaluate for physical signs of fat redistribution
    Advise patient to seek medical advice if joint aches or pain occur
    Advise patient to seek medical advice if movement becomes difficult
    Inflammatory symptoms should be evaluated and treated appropriately
    May exacerbate diabetes mellitus
    May precipitate diabetes mellitus
    Risk of developing opportunistic infections
    Discontinue if rash with systemic, allergic or mucosal symptoms occurs
    Discontinue if severe skin reaction occurs
    Advise patient not to take St John's wort concurrently
    Female: Barrier or non-hormonal contraception advised during treatment
    Advise haemophiliac patients of possibility of increased bleeding

    Fosamprenavir must be administered in combination with other antiretroviral agents.

    Fosamprenavir contains a sulfonamide moiety and should be used with caution in patients with a sulfonamide allergy.

    Patients with chronic hepatitis B or C who are treated with combination antiretroviral therapy have an increased risk of developing severe and potentially fatal hepatic adverse effects, and therefore should be closely monitored during treatment. The product literature relating to concurrent treatments for hepatitis B or C should be consulted. If hepatic disease worsens in these patients, interruption or discontinuation of therapy should be considered. Patients with pre-existing hepatic impairment, including chronic active hepatitis, have an increased risk of developing hepatic function abnormalities during therapy. These patients should be closely monitored and treatment interruption or discontinuation should be considered if hepatic disease worsens in these patients.

    Protease inhibitors have been associated with increased bleeding including spontaneous skin haematomas and haemarthroses in patients with haemophilia types A and B. In some patients the administration of factor VIII was required. Patients with haemophilia should be warned of an increased risk of bleeding.

    The redistribution of body fat (lipodystrophy) has occurred in HIV patients receiving combination antiretroviral therapy. The long term consequences and mechanisms of this effect are unknown, but a connection between visceral lipomatosis and protease inhibitors and lipoatrophy and nucleoside reverse transcriptase inhibitors has been suggested. There is believed to be an increased risk of lipodystrophy in older patients, and with a longer treatment duration and associated metabolic disturbances. Clinical examinations should include evaluation for physical signs of fat redistribution.

    When combination antiretroviral therapy is initiated in HIV-infected patients with severe immune deficiency, an inflammatory reaction to asymptomatic or residual opportunist pathogens may arise. This can lead to the aggravation of symptoms or other serious clinical conditions such as cytomegalovirus retinitis, mycobacterial infections or Pneumocystis carinii pneumonia. These reactions are usually observed within the first few weeks or months after treatment initiation. Any inflammatory symptoms should be evaluated and treated appropriately.

    Cases of osteonecrosis have been reported in patients with advanced HIV disease and/or long term exposure to combination antiretroviral therapy. The aetiology of this condition is thought to be due to several factors including corticosteroid use, alcohol consumption, severe immunosuppression, higher body mass index. Patients should be advised to seek medical advice if they experience joint aches or pains, joint stiffness or difficulty in movement.

    Pregnancy and Lactation


    Use fosamprenavir with caution in pregnancy.

    At the time of writing there is limited published experience concerning the use of fosamprenavir in pregnant women. In animal studies at systemic plasma exposures to amprenavir lower than therapeutic exposure in patients treated with fosamprenavir, some developmental toxicity was observed. The potential developmental toxicity of fosamprenavir has not been fully determined. The risk-benefit ratio to the mother and foetus should be considered when treatment with fosamprenavir is being considered and treatment should be based upon each individual. If indicated, protease inhibitors, including fosamprenavir should not be withheld in pregnancy because the expected benefit to the HIV positive mother outweighs the unknown risk to the foetus. Pregnant women taking protease inhibitors should be monitored for hyperglycaemia.

    Combination therapy does not prevent vertical transmission of HIV to the newborn.

    The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14 to 17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password on the internet ( ) or if this is unavailable at the backup site ( ).


    HIV is known to be transmitted in milk. Therefore, HIV infected mothers should avoid breastfeeding in order to prevent transmission of the disease.

    Fosamprenavir is contraindicated in breastfeeding.

    It is not known if amprenavir is excreted in human breast milk however, the molecular weight is low enough that excretion should be expected.

    Amprenavir-related material was found in rat milk. The offspring, who were exposed pre and post-natally to fosamprenavir, showed signs of developmental toxicity.

    Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
    Specialist advice is available from the UK Drugs in Lactation Advisory Service at

    Side Effects

    Abdominal pain
    Autoimmune disorders
    Autoimmune hepatitis
    Blood disorders
    Creatine phosphokinase increased
    Diabetes mellitus
    Elevated serum lipase
    Erythematous rash
    Exacerbation of diabetes
    Gastro-intestinal disturbances
    Graves' disease
    Hepatic impairment
    Hypersensitivity reactions
    Immune Reactivation/Reconstitution Syndrome
    Increase in serum ALT/AST
    Increased spontaneous bleeding (haemophiliacs)
    Insulin resistance
    Maculopapular rash
    Metabolic disorders
    Severe cutaneous skin eruptions
    Sleep disturbances
    Soft or liquid stools
    Stevens-Johnson syndrome
    Taste disturbances


    It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.

    The following number will direct the caller to the relevant local centre (0844) 892 0111

    Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( ) or if this is unavailable at the backup site ( ).

    Further Information

    Last Full Review Date: October 2014

    Reference Sources

    Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 2nd edition (2007) ed. Schaefer, C., Peters, P. and Miller, R. Elsevier, London.

    Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 9th edition (2011) ed. Briggs, G., Freeman, R. and Yaffe, S. Lippincott Williams & Wilkins, Philadelphia.

    Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press Accessed on 8 October, 2014.

    Paediatric Formulary Committee. BNF for Children (online) London: BMJ Group, Pharmaceutical Press, and RCPCH Publications Accessed on 8 October, 2014.

    Summary of Product Characteristics: Telzir 700mg film-coated tablets. ViiV Healthcare UK Ltd. Revised October 2018.
    Summary of Product Characteristics: Telzir oral suspension. ViiV Healthcare UK Ltd. Revised October 2018.

    US National Library of Medicine. Toxicology Data Network. Drugs and Lactation Database (LactMed).
    Available at:
    Fosamprenavir. Last revised: 1 August, 2014
    Last accessed: 8 October, 2014.

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