Probenecid

Trade Names:
Probenecid
- Tablets 0.5 g

Pharmacology

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Inhibits tubular reabsorption of urate, thus increasing urinary excretion of uric acid. Inhibits tubular secretion of most penicillin and cephalosporin antibiotics.

Pharmacokinetics

Absorption

Well absorbed. T _max is 2 to 4 h. C _max for a single 1 g dose is more than 30 mcg/mL. C _max for a single 2 g dose is 150 to 200 mcg/mL.

Distribution

Protein binding is 85% to 95%, albumin. Distributes into CSF, crosses the placenta, and appears in cord blood.

Metabolism

Rapid and extensive; hydroxylated to active metabolites and probenecid monacylglucuronide in the liver.

Elimination

Excreted in the urine (mainly in metabolite form) 5% to 10% unchanged. T _1/2 is dose-dependent and varies from less than 5 to greater than 8 h.

Peak

Uricosuric is 30 min.

Duration

Approximately 8 h.

Indications and Usage

Treatment of hyperuricemia associated with gout and gouty arthritis; adjunctive therapy with penicillins or cephalosporins to elevate and prolong serum levels.

Contraindications

Children less than 2 yr; blood dyscrasias or uric acid kidney stones. Do not start therapy until acute gout attack subsides.

Dosage and Administration

PO 250 mg twice daily initially (for 1 wk), followed by 500 mg twice daily. For maintenance therapy, may reduce by 500 mg every 6 mo until serum uric acid increases.

PO 2 g/day in divided doses.

PO 25 mg/kg or 0.7 g/m ² initially. Maintenance dose is 40 mg/kg/day or 1.2 g/m ² , divided into 4 doses.

Drug Interactions

Interacts with many other drugs by altering their clearance and elimination.

Increased serum levels and effects of these drugs.

Inhibition of uricosuric effect of either drug.

Laboratory Test Interactions

May produce false-positive results for glycosuria in some urine glucose tests and falsely high assays for theophylline with Schack and Waxler technique. May inhibit renal excretion of phenolsulfonphthalein, 17-ketosteroid, and sulfobromophthalein.

Adverse Reactions

CNS

Headaches; dizziness.

Dermatologic

Dermatitis; pruritus.

GI

Anorexia; nausea; GI distress; vomiting; sore gums.

Genitourinary

Urinary frequency; hematuria; renal colic; nephrotic syndrome.

Hematologic

Anemia; hemolytic anemia (possibly related to G-6-PD deficiency); aplastic anemia.

Hepatic

Hepatic necrosis.

Miscellaneous

Hypersensitivity reactions; anaphylaxis; fever; flushing; exacerbation of gout; uric acid stones; costovertebral pain.

Precautions

Pregnancy

Pregnancy category undetermined. Probenecid crosses placenta and appears in cord blood.

Children

Not recommended for children under 2 yr.

Hypersensitivity

Severe allergic reactions and anaphylaxis, although rare, have occurred. These have usually been associated with prior probenecid use.

Renal Function

May require increased doses for gout (not to exceed 2 g/day). Probenecid may be ineffective in chronic renal insufficiency (ie, glomerular filtration rate of less than 30 mL/min). Drug is not recommended for use with penicillin in cases of known renal function impairment.

Alkalinization of urine

May be needed to prevent hematuria, renal colic, costovertebral pain, formation of uric acid stones.

Exacerbation of gout

May occur; appropriate drug therapy (eg, colchicine or other appropriate therapy) is advisable.

History of peptic ulcer

Use with caution.

Overdosage

Symptoms

Nausea, vomiting, diarrhea, seizure.

Patient Information

• Instruct patient to take drug with food or antacids if GI upset occurs.
• Advise patient that drinking 6 to 8 full glasses of water daily may help prevent formation of kidney stones.
• If health care provider has recommended restriction of intake of foods high in purine, review foods to be avoided (eg, organ meats, meat gravy, anchovies, sardines). Explain that moderate amounts of purine are found in other meats, fish and other seafood, asparagus, spinach, peas, dried legumes, and wild game.
• Inform patient to notify health care provider if GI upset, anorexia, or headaches become bothersome.
• Instruct patient to report the following symptoms to health care provider: painful urination, bloody urine, severe lower back pain, difficulty breathing, or rash.
• Advise patient to avoid intake of alcoholic beverages.
• Instruct patient not to take OTC medications (including aspirin) without consulting health care provider.
• Caution patient not to discontinue drug without consulting health care provider.

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