Page 17 - RxExam's Naplex Theory Book Part 2

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Dose Special Notes

Allopurinol 6). Allopurinol (Zyloprim) inhibits the enzymatic oxidation of
(Tablet) Mercaptopurine and Azathioprine, the sulfur-containing analogue of
(Injection) hypoxanthine, to 6-thiouric acid. This oxidation, which is catalyzed by
xanthine oxidase, inactivates Mercaptopurine. Hence, the inhibition of
such oxidation by Allopurinol (Zyloprim) may result in as much as a
75% reduction in the therapeutic dose requirement of Mercaptopurine
when the two compounds are given together.

7). The most frequent adverse reaction to Allopurinol (Zyloprim) is skin
rash. Skin reactions can be severe and sometimes fatal. Therefore,
treatment with Allopurinol (Zyloprim) should be discontinued
immediately if a rash develops. Some patients with the most severe
reaction also had fever, chills, arthralgias, cholestatic jaundice,
eosinophilia and mild leukocytosis or leukopenia.

Febuxostat 1. Hyperuricemia: 1). Febuxostat (Uloric) is a xanthine oxidase (XO) inhibitor, the enzyme
(Tablet) responsible for the conversion of hypoxanthine to xanthine and of
40 to 80 mg once xanthine to uric acid, the end product of purine metabolism in human.
daily without
regard to food or 2). Febuxostat (Uloric) is indicated for the chronic management of
antacids. hyperuricemia in patients with gout. It is NOT recommended for the
treatment of asymptomatic hyperuricemia.

3). Gout flares may occur after initiation of Febuxostat (Uloric) due to
changing serum uric acid levels resulting in mobilization of urate from
tissue deposits. Flare prophylaxis with a non-steroidal anti-
inflammatory drug (NSAID) or Colchicine is recommended upon
initiation of Febuxostat (Uloric). If a gout flare occurs during
Febuxostat (Uloric) treatment, Febuxostat (Uloric) need not be
discontinued.

4). Inhibition of xanthine oxidase (XO) enzyme may cause increased
plasma concentrations and toxicities of Mercaptopurine, Azathioprine
and Theophylline. Concurrent use should be strictly avoided.

5). Liver function abnormalities, nausea, arthralgia and rash are
commonly reported side effects of Febuxostat (Uloric).

B). Uric Acid Specific Enzyme

Pegloticase 1. Gout: 1). Pegloticase (Krystexxa) is a uric acid specific enzyme which is a
(Injection) 8 mg via slow (120 recombinant uricase and achieves its therapeutic effect by catalyzing
minutes) IV infusion the oxidation of uric acid to allantoin, thereby lowering serum uric
every 2 weeks. acid. Allantoin is an inert and water soluble purine metabolite. It is
readily eliminated, primarily by renal excretion.

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