Favolar

Uses

Favolar is used for prevention and treatment of high blood uric acid level and gout, prevents deposition of urate crystal in kidney, serous membranes of liver, heart, air sac and joints of poultry.

Favolar is also used to associated treatment for these conditions: Hyperuricemia, Primary Gout, Recurrent calcium oxalate calculi, Secondary gout, Calcium oxalate calculi Renal Calculi

How Favolar works

Favolar is a structural analog of the natural purine base, hypoxanthine. After ingestion, allopurinol is metabolized to its active metabolite, oxypurinol (alloxanthine) in the liver , which acts as an inhibitor of xanthine oxidase enzyme .

Favolar and its active metabolite inhibit xanthine oxidase, the enzyme that converts hypoxanthine to xanthine and xanthine to uric acid. Inhibition of this enzyme is responsible for the effects of allopurinol. This drug increases the reutilization of hypoxanthine and xanthine for nucleotide and nucleic acid synthesis by a process that involves the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRTase). This process results in an increased nucleotide concentration, which causes feedback inhibition of de novo purine synthesis. The end result is decreased urine and serum uric acid concentrations , which decreases the incidence of gout symptoms.

Accompanying the reduction of serum uric acid by allopurinol is an increase in the serum and urine concentrations of hypoxanthine and xanthine (due to inhibition of xanthine oxidase). In the absence of allopurinol, regular urinary excretion of oxypurines almost entirely occurs in the form of uric acid. After the ingestion of allopurinol, the contents of excreted urine are hypoxanthine, xanthine, and uric acid. Because each substance has its own individual solubility, the concentration of uric acid in plasma is decreased without exposing the renal tissues to a high load of uric acid, thereby decreasing the risk of crystalluria. By lowering the uric acid concentration in the plasma below its limits of solubility, allopurinol encourages the dissolution of gout tophi. Although the levels of hypoxanthine and xanthine are found to be increased after allopurinol ingestion, the risk of deposition in renal tissues is less than that of uric acid, as they become more soluble and are rapidly excreted by the kidney .

Dosage

Favolar dosage

Poultry- 25 mg/kg body or 2.5 gm/liter water for 3-5 days, or as directed by registered veterinarian.

Side Effects

The most frequent adverse reaction to Favolar is skin rash such as, pruritic maculopapular skin eruptions, sometimes scaly or exfoliative.

Toxicity

Oral TDLO (rat): 10 mg/kg; Oral LD50 (mouse): 78 mg/kg; Oral TDLO (mouse): 100 mg/kg

Use in pregnancy

Reproductive studies have been completed using rats and rabbit models at doses up to twenty times the normal human dose ( about 5 mg/kg per day), and it was concluded that fertility was not impaired and there was no fetal harm. There is a published report of a study in pregnant mice administered 50 or 100 mg/kg allopurinol intraperitoneally on gestation days 10 or 13. There were increased numbers of dead fetuses in dams administered 100 mg/kg allopurinol, however, death did not occur in those given 50 mg/kg. There were higher numbers of external malformations in fetuses at both doses of allopurinol on gestation day 10 and higher numbers of skeletal malformations in fetuses at both doses on gestation day 13. Despite the above findings, there are no adequate or well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if it is absolutely required .

Use in nursing

Both allopurinol and the metabolite oxipurinol have been found in the milk of a mother who was receiving allopurinol. Since the effect of allopurinol on the nursing infant is unknown, it is advisable to exercise caution when allopurinol is taken by a nursing woman .

Mutagenicity and carcinogenicity

Cytogenic studies demonstrate that allopurinol does not induce chromosomal abnormalities in human blood cells in vitro at concentrations up to 100 g/mL and in vivo at doses up to 60 mg/day for an average duration of 40 months. Favolar does not form nitroso compounds (which may be carcinogenic) or affect lymphocyte transformation in vitro. Evidence suggests that allopurinol does not have deleterious effects on DNA at any stage of the cell cycle and was not found to be mutagenic. No evidence of carcinogenicity has been observed in mice treated with allopurinol for up to a 2 year period .

Precaution

Before you use discuss with your doctor if you are allergic to it or its ingredients.

Interaction

Anticoagulant: Favolar prolongs the half life of the anticoagulant, dicumarol.

Diuretic: Concomitant use of Favolar and thiazide diuretics may contribute to the enhancement of Favolar toxicity.

Cytotoxic agent: Enhanced bone marrow suppression by cyclophosphamide and other cytotoxic agent has been reported among patients with neoplastic disease.

Food Interaction

• Avoid alcohol.
• Take with a full glass of water.
• Take with food.

Favolar Drug Interaction

Unknown: aspirin, aspirin, aspirin, aspirin, omega-3 polyunsaturated fatty acids, omega-3 polyunsaturated fatty acids, furosemide, furosemide, atorvastatin, atorvastatin, metoprolol, metoprolol, metoprolol, metoprolol, cyanocobalamin, cyanocobalamin, ascorbic acid, ascorbic acid, cholecalciferol, cholecalciferol

Favolar Disease Interaction

Moderate: bone marrow suppression, dehydration, liver disease, renal dysfunction

Volume of Distribution

Favolar and oxypurinol are both substrates for the enzyme xanthine oxidase, which is present in the cytoplasm of endothelial cells of capillaries, including sinusoids, with the highest activity demonstrated in the liver and intestinal lining. Tissue concentrations of allopurinol have not yet been reported in humans, however, it is probable that allopurinol and the metabolite oxypurinol would be measured in the highest concentrations in the abovementioned tissues. In animals, allopurinol concentrations are found to reach the highest levels in the blood, liver, intestine and heart, and lowest in the brain and lung tissues .

Elimination Route

This drug is about 90% absorbed from the gastrointestinal tract. Peak plasma levels normally occur at 1.5 hours and 4.5 hours post-dose for allopurinol and oxipurinol respectively. Following one oral dose of 300 mg of allopurinol, maximum plasma levels of about 3 mcg/mL of allopurinol and 6.5 mcg/mL of oxipurinol were measured .

Half Life

The plasma half-life of allopurinol is 1-2 hours, due to its rapid renal clearance .

Clearance

Since allopurinol and its metabolites are mainly eliminated by the kidney, accumulation of this drug can occur in patients with renal dysfunction or failure, and the dose of allopurinol should, therefore, be reduced. With a creatinine clearance of 10 to 20 mL/min, a daily dosage of 200 mg of allopurinol is suitable. When the creatinine clearance is less than 10 mL/min, the daily dosage should not be higher than 100 mg. With severe renal impairment (creatinine clearance measured at less than 3 mL/min) a longer interval between doses may be required .

Elimination Route

Approximately 80% of orally ingested allopurinol is found excreted in the urine as various metabolites . About 20% of ingested allopurinol is excreted in the feces .

Pregnancy & Breastfeeding use

Sufficient clinical data is not available. This drug should be used during pregnancy only if clearly indicated. Favolar has been found in breast milk, caution should be exercised when Favolar is administered to a lactating mother.

Contraindication

Patients who have developed a severe reaction to allopurinol should not be restarted the drug. Favolar should be withdrawn immediately when a skin rash or other evidence or sensitivity occurs. Dosage reduction should be considered in the presence of severe hepatic or renal disorder.

Acute Overdose

Over dosage may cause diarrhea, abdominal pain and neurotoxicity.

Interaction with other Medicine

Anticoagulant: Favolar prolongs the half life of the anticoagulant, dicumarol.

Diuretic: Concomitant use of Favolar and thiazide diuretics may contribute to the enhancement of Favolar toxicity.

Cytotoxic agent: Enhanced bone marrow suppression by cyclophosphamide and other cytotoxic agent has been reported among patients with neoplastic disease.

Storage Condition

Protect from light & keep in a cool and dry place. Keep out of reach of children.

Innovators Monograph

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