THIOGUANINE (TG, 6-THIOGUANINE)

THIOGUANINE (TG, 6-THIOGUANINE)
(thye-oh-gwah'neen)
Lanvis , Tabloid
Classifications: antineoplastic; antimetabolite; purine antagonist;
Therapeutic: antineoplastic
; antimetabolite
Prototype: Mercaptopurine
Pregnancy Category: D

Availability

40 mg tablets

Action

Antimetabolite and purine antagonist with immunosuppressive activity. Highly toxic. Drug is incorporated into the DNA and RNa of human bone marrow cells.

Therapeutic Effect

Delays myelosuppression; has potential mutagenic and carcinogenic properties.

Uses

In combination with other antineoplastics for remission induction in acute myelogenous leukemia and as treatment of chronic myelogenous leukemia. Has little advantage over mercaptopurine.

Contraindications

Patients with prior resistance to this drug; severe bone marrow depression; pregnancy (category D), lactation.

Cautious Use

Hepatic disease.

Route & Dosage

Leukemia
Adult: PO 2 mg/kg/d, may increase to 3 mg/kg/d if no response after 4 wk

Administration

Oral
  • Withhold drug and notify physician if toxicity develops. There is no known antagonist; prompt discontinuation of the drug is essential to avoid irreversible myelosuppression from toxicity.
  • Store at 15°–30° C (59°–86° F) in airtight container.

Adverse Effects (≥1%)

Hematologic: Leukopenia, thrombocytopenia, anemia. GI: Jaundice, nausea, vomiting, anorexia, stomatitis, diarrhea. Urogenital: Hyperuricemia. Other: Hepatotoxicity (risk increased with long-term use).

Interactions

Drug: Severe hepatotoxicity with busulfan; may decrease immune response to vaccines; increase risk of bleeding with anticoagulants; nsaids, salicylates; platelet inhibitors, thrombolytic agents; effects may be reversed by filgrastim, sargramostim.

Pharmacokinetics

Absorption: Variable and incomplete absorption from GI tract. Peak: 8 h. Distribution: Crosses placenta. Metabolism: In liver. Elimination: In urine. Half-Life: 11 h.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Monitor blood counts weekly (CBC with differential and platelet count); periodic LFTs with long-term use.
  • Determine hematologic parameters for withholding drug.
  • Monitor I&O ratio and report oliguria.
  • Observe patient's skin and sclera for jaundice. It should be reported promptly as a symptom of toxicity; drug will be discontinued promptly.
  • Expect that the drop in leukocyte count may be slow over a period of 2–4 wk. Treatment is interrupted if there is a rapid fall within a few days.

Patient & Family Education

  • Maintenance doses are continued throughout remissions.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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