Fosamprenavir (Telzir, Lexiva)

Fosamprenavir (Telzir) is an anti-HIV drug that reduces the amount of virus in the body. Anti-HIV drugs such as fosamprenavir slow down or prevent damage to the immune system and reduce the risk of developing AIDS-related illnesses.

Fosamprenavir is a protease inhibitor. Protease (or proteinase) is the protein or enzyme that HIV uses to break up large viral proteins so new HIV particles can be made. For more information about how protease inhibitors work, see Protease inhibitors.

Fosamprenavir was approved in the European Union in July 2004 under the brand name Telzir for use in combination with low-dose ritonavir (Norvir) in HIV-positive adults.

In the United States, fosamprenavir was approved for use with or without ritonavir boosting in October 2003 and is marketed under the trade name Lexiva.

Effectiveness

Fosamprenavir (Telzir) is no longer recommended as a component of first-line antiretroviral combinations in British, European or US treatment guidelines. Fosamprenavir was shown to be inferior on some measures to the boosted protease inhibitor lopinavir/ritonavir (Kaletra) in treatment-experienced people and is not recommended for use after the failure of a previous protease inhibitor-containing regimen.[ref]

Taking it

The recommended dose of fosamprenavir (Telzir) in the European Union is 700mg with 100mg ritonavir (Norvir) twice daily in combination with at least two other antiretroviral drugs. In Europe, it is only approved for treatment-experienced people.

Tablets can be taken with or without food. Adults using the oral solution should take it without food, but children need to take the oral suspension with food.[ref] Oral suspension does not require refrigeration; shake well before using.

Fosamprenavir is available in 700mg tablets and as a liquid at a concentration of 50mg/ml.

Side-effects

The commonest side-effects are headache, nausea, rash, diarrhoea, vomiting and fatigue. These are usually mild. As a class, protease inhibitors have been associated with the lipodystrophy syndrome of fat redistribution and metabolic irregularities.

Less than 1% of people who have taken fosamprenavir have experienced severe and life-threatening skin reactions, including Stevens-Johnson syndrome.

Drug interactions

Glossary

protease

An enzyme that HIV uses to break up large proteins into smaller ones from which new HIV particles can be made.

oral

Refers to the mouth, for example a medicine taken by mouth.

syndrome

A group of symptoms and diseases that together are characteristic of a specific condition. AIDS is the characteristic syndrome of HIV.

 

enzyme

A protein which speeds up a chemical reaction.

treatment-experienced

A person who has previously taken treatment for a condition. Treatment-experienced people may have taken several different regimens before and may have a strain of HIV that is resistant to multiple drug classes.

Fosamprenavir (Telzir) is metabolised by the cytochrome P450 enzymes in the liver, particularly the CYP3A4 enzyme. Consequently, its levels are affected by other drugs that use the same pathway.

Many other drugs using the CYP3A4 enzyme should not be given with fosamprenavir, as their levels may be altered. These include:

  • Alfuzosin
  • Astemizole
  • Cisapride
  • Colchicine in people with renal or hepatic impairment
  • Diazepam
  • Ergotamine tartrate (Cafergot / Migril)
  • Flecainide acetate (Tambocor)
  • Flurazepam (Dalmane)
  • Fluticasone propionate (Flixotide): taking this with fosamprenavir can cause symptoms of Cushing’s syndrome and suppression of the adrenal glands, including weight gain, weakening of the skin, sweating, facial hair growth and psychological disturbances.
  • Halofantrine
  • Hypericin (St John’s wort)
  • Lovastatin
  • Lumefantrine
  • Midazolam (Hyponovel)
  • Pimozide (Orap)
  • Propafenone (Arythmol)
  • Rifampicin (Rifadin / Rimactane)
  • Simvastatin (Zocor)
  • Terfenadine
  • Triazolam.

Caution is advised when taking any protease inhibitor with the impotence drugs sildenafil (Viagra), tadalafil (Cialis) or vardenafil (Levitra). When taken with fosamprenavir, levels of these drugs may increase making side-effects more likely. Commencing the drugs at a reduced dose is advised. Sildenafil is contraindicated if used for treatment of pulmonary arterial hypertension.

Levels of the lipid-lowering drug atorvastatin (Lipitor) are increased by ritonavir-boosted fosamprenavir. A low dose of atorvastatin is recommended.

Other drugs that should be used cautiously or whose levels should be checked in people taking fosamprenavir include:

  • Amiodarone hydrochloride (Cordarone X)
  • Amitriptyline hydrochloride
  • Amlodipine (Istin)
  • Bepidril
  • Carbamazepine (Tegretol / Carbagen SR / Tegretol Retard)
  • Ciclosporin (Neoral / Sandimmun)
  • Dexamethasone hydrochloride
  • Diltiazem (Tildiem / Adizem-SR / Adizem-XL / Angitil SR / Angitil XL / Calcicard CR / Dilcardia SR / Dilzem SR / Dilzem XL / Slozem / Tildiem LA / Tildiem Retard / Viazem XL / Zemtard)
  • Felodipine (Plendil)
  • Imipramine hydrochloride
  • Isradipine (Prescal)
  • Itraconazole (Sporanox)
  • Ketoconazole (Nizoral)
  • Lidocaine hydrochloride (Minijet Lignocaine / Xylocaine)
  • Nicardipine hydrochloride (Cardene / Cardene SR)
  • Nifedipine (Adalat / Adalat LA / Adalat Retard / Adipine MR / Adipine XL / Cardilate MR / Coracten SR / Coracten XL / Fortipine LA 40 / Hypolar Retard 20 / Nifedipress MR / Nifopress Retard / Slofedipine / Slofedipine XL / Tensipine MR)
  • Nimodipine (Nimotop)
  • Nisoldipine (Syscor MR)
  • Phenobarbital
  • Phenytoin (Epanutin)
  • Quinidine (Kindin Dureles)
  • Rapamycin
  • Tacrolimus (Prograf / Protopic)
  • Verapamil hydrochloride (Cordilox / Securon / Half Securon SR / Securon SR / Univer / Verapress MR / Vertab SR 240)
  • Warfarin sodium.

Children

A liquid formulation of fosamprenavir was approved in the United States and European Union in 2007 for use in children aged 2 to 18. In the US, use of fosamprenavir is approved for use in children 2 years and older but is not recommended for use in children aged 2-5 years by US guidelines due to inadequate drug levels.

Pregnancy

A liquid formulation of fosamprenavir was approved in the United States and European Union in 2007 for use in children aged 2 to 18. In the US, use of fosamprenavir is approved for use in children 2 years and older but is not recommended for use in children aged 2-5 years by US guidelines due to inadequate drug levels.

Related topics