Drug Index

Fosamprenavir

 
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Mechanism :

Fosamprenavir is a prodrug that is rapidly hydrolysed to amprenavir by cellular phosphatases in the gut epithelium as it is absorbed. Amprenavir is an inhibitor of HIV-1 protease. During HIV replication, HIV protease cleaves viral polypeptide products of the Gag and Gag-Pol genes to form structural proteins of the virion core and essential viral enzymes. Amprenavir interferes with this process by binding to the active site of HIV-1 protease, thereby preventing the processing of viral Gag and Gag-Pol polyprotein precursors, resulting in the formation of immature non-infectious viral particles.


Indication :

• HIV infection


Contraindications :

Coadministration is contraindicated with drugs that are highly dependent on CYP3A4 for clearance and for which elevated plasma concentrations are associated with serious and/or life-threatening events. If amprenavir is coadministered with ritonavir, the antiarrhythmic agents flecainide and propafenone are also contraindicated. Because of the potential toxicity from the large amount of the excipient, propylene glycol, contained in the Oral Solution, that formulation is contraindicated in certain patient populations and should be used with caution in others. Contraindicated in patients with previously demonstrated clinically significant hypersensitivity to any of the components of this product.


Dosing :

Oral

Administered without ritonavir:

Protease Inhibitor (PI)-naive patients who are 2 years of age or older:

30 mg/kg (up to 1400 mg/dose) orally twice a day.

47 kg or more: 1400 mg orally twice a day.

Administered in combination with ritonavir:

PI-naive patients who are at least 4 weeks of age (including infants at a postnatal age of at least 28 days who were born at 38 weeks gestation or greater) and PI-experienced patients who are at least 6 months of age:

<11 kg: Fosamprenavir 45 mg/kg plus ritonavir 7 mg/kg orally twice a day.

11 to <15 kg: Fosamprenavir 30 mg/kg plus ritonavir 3 mg/kg orally twice a day.

15 to <20 kg: Fosamprenavir 23 mg/kg plus ritonavir 3 mg/kg orally twice a day.

≥20 kg: Fosamprenavir 18 mg/kg (up to 700 mg/dose) plus ritonavir 3 mg/kg (up to 100 mg/dose) orally twice a day.

39 kg or more: Fosamprenavir 700 mg plus ritonavir 100 mg orally twice a day.


Adverse Effect :

Nausea, vomiting, diarrhea, abdominal pain/discomfort, headache, fatigue, rash, increased serum lipase, ALT/AST in patients treated with concomitant ritonavir.


Interaction :

Rifabutin: An increase in the plasma concentrations of rifabutin and a decrease in the plasma concentrations of amprenavir.
Ketoconazole: An increase in the plasma concentrations of amprenavir, a dosage reduction should be considered.
Rifampin: Rifampin is a potent inducer of P450 (CYP3A4) which markedly diminishes plasma concentrations of amprenavir.
Other: Should not be administered concurrently with terfenadine, astemizole, cisapride, triazolam and midazolam because coadministration with inhibitors of P450 (CYP3A4) may result in inhibition of metabolism of these drugs and create the potential for serious and/or life-threatening events (i.e., cardiac arrhythmias or prolonged sedation).
Other drugs that induce CYP3A4 less potently than Rifampin, such as Phenobarbital, Phenytoin, Carbamazepine, and Dexamethasone: Should be used cautiously together since they could also diminish plasma concentrations of amprenavir.
Occupational Hazards: Dizziness and blurred vision have been reported. Patients should be advised to avoid driving or operating machinery if they experience these reactions.


07/21/2019 22:18:50 Fosamprenavir
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