Indications

In combination with other antiretroviral agents, for the treatment of HIV-1 infection. Proxivir is also indicated for the treatment of chronic hepatitis B in adults.

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Pharmacology

Mechanism of Action: Tenofovir inhibits the activity of HIV reverse transcriptase by competing with the natural substrate deoxyadenosine 5-triphosphate. Specifically, the drugs are analogues of the naturally occurring deoxynucleotides needed to synthesize the viral DNA and they compete with the natural deoxynucleotides for incorporation into the growing viral DNA chain.

Pharmacokinetics: Tenofovir is a water soluble diester prodrug of the active ingredient Tenofovir. The oral bioavailability of Tenofovir is approximately 25%. Following oral administration of a single dose of Tenofovir 245 mg to HIV-1 infected subjects in the fasted state, maximum serum concentrations (Cmax) are achieved in 1.0 10.4 hrs. Cmax and AUC values are 0.30 0.09 ug/mL and 2.29 + 0.69 ug hr/mL, respectively. Protein binding Very low. <0.7% to human plasma proteins and <7.2% to serum proteins. Half life Approximately 17 hours. Tenofovir is eliminated by a combination of glomerular filtration and active tubular secretion.

Dosage & Administration

The size and frequency of the dosage must be adjusted to the needs of the individual patient. Tenofovir disoproxil 245 mg oral tablets should be administered once daily orally, without regard to food.

Recommended Dose in Adults: For the treatment of HIV-1 or chronic hepatitis B: The dose is 245 mg Tenofovir tablet once daily taken orally, without regard to food. In the treatment of chronic hepatitis B, the optimal duration of treatment is unknown.

Recommended Dose in Pediatric Patients (12 years of age and older and greater than or equal to 35 kg): For the treatment of HIV-1 in pediatric patients 12 years of age and older with body weight greater than or equal to 35 kg: The dose is one 245 mg Tenofovir tablet once daily taken orally, without regard to food.

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Interaction

Didanosine: Coadministration of Proxivir and didanosine should be undertaken with caution and patients receiving Proxivir should be monitored dosely for didanosine-associated adverse reactions.

Atazanavir: Patients receiving atazanavir and Proxivir should be monitored for Proxivir associated adverse reactions.

Lopinavir, Ritonavir: Patients receiving lopinavir/ ritonavir and Proxivir should be monitored for Proxivir-associated adverse reactions.

Contraindications

Broken bone due to disease or illness, enlarged fatty liver, severe liver disease, acute kidney disease, decreased calcification or density of bone, a mother who is producing milk and breastfeeding, low amount of phosphate in the blood, increased blood acidity due to high levels of lactic acid and overweight.

Side Effects

As with any medicine, side effects are possible with Proxivir. If side effects do occur, in most cases, they are minor and either require no treatment or can easily be treated by you or your healthcare provider. Headache, diarrhea, nausea, and weakness appear to be some of the most common side effects of Proxivir. Other possible side effects include indigestion or heartburn, chest pain, and drowsiness. While most Proxivir side effects are minor, there are a number of side effects that should be reported to your healthcare provider immediately, including high cholesterol or triglycerides, kidney problems, depression, and anxiety.

Pregnancy & Lactation

Pregnancy category B. No adequate and well-controlled studies in pregnant women. Tenofovir should be used during pregnancy only if clearly needed. The centers for disease control and prevention recommend that HIV-1-infected mothers not breastfeed their infants to avoid risking postnatal transmission of HIV-1. Pediatric Use: For the treatment of HIV-1 in pediatric patients 12 years of age and older with body weight greater than or equal to 35 kg: The dose is 245 mg Tenofovir tablet is once daily taken orally Geriatric Use: Clinical trials of Tenofovir did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. In general, dose selection for the elderly patient should be cautious, keeping in mind the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Precautions & Warnings

Lactic acidosis/severe hepatomegaly with steatosis: Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with the use of nucleoside analogs, including Proxivir, in combination with other antiretrovirals. A majority of these cases have been in women. Exacerbation of hepatitis after discontinuation of treatment discontinuation of anti-HBV therapy, including Proxivir, may be associated with severe acute exacerbations of hepatitis. Patients infected with HBV who discontinue Proxivir should be closely monitored with both clinical and laboratory follow-up for at least several months after stopping treatment. New onset or worsening renal impairment: Proxivir is principally eliminated by the kidney. Renal impairment, including cases of acute renal failure and Fanconi syndrome (renal tubular injury with severe hypophosphatemial), has been reported with the use of Proxivir.

Coadministration with other products: Proxivir should not be used in combination with the fixed-dose combination products which contains Proxivir. Proxivir should not be administered in combination with adefovir disoproxil.

Patients Coinfected with HIV-1 and HBV: Due to the risk of development of HIV-1 resistance Proxivir should only be used in HIV-1 and HBV coinfected patients as part of an appropriate antiretroviral combination regimen. Fat Redistribution In HIV-infected patients redistribution/accumulation of body fat including central obesity, dorsocervical fat enlargement buffalo hump), peripheral wasting, facial wasting, breast enlargement have been observed in patients receiving combination antiretroviral.

Immune Reconstitution/Redistribution Syndrome: Immune reconstitution syndrome has been reported in HIV-infected patients treated with combination antiretroviral therapy, including Proxivir.

Use in Special Populations

Dose Adjustment for Renal Impairment in Adults: Significantly increased drug exposures occurred when Proxivir was administered to subjects with moderate to severe renal impairment Therefore, the dosing interval of Proxivir should be adjusted in patients with baseline creatinine clearance below 50 mL/min using the recommended 245 mg dosing interval every 24 hours, if the creatinine clearance is 30-49 (mL/min) recommended 245 mg dosing interval every 48 hours. If the creatinine clearance 10-29 (mL/min) recommended 245 mg dosing interval every 72 to 96 hours. In case of hemodialysis patients recommended 245 mg dosing interval every 7 days or after a total of approximately 12 hours of dialysis. No dose adjustment is necessary for patients with mild renal impairment (creatinine clearance 50-80 mL/min).

Therapeutic Class

Drugs for HIV / Anti-retroviral drugs, Hepatic viral infections (Hepatitis B)

Storage Conditions

Do not store above 25°C. Store in a cool and dry place, protected from light. Keep out of children’s reach.