Probenecid and Colchicine

Clinical summary

Indications and usage INDICATIONS & USAGE For the treatment of chronic gouty arthritis when complicated by frequent, recurrent acute attacks of gout. Dosage and administration DOSAGE & ADMINISTRATION Therapy with probenecid and colchicine should not be started until an acute gouty attack has subsided. However, if an acute attack is precipitated during therapy, probenecid and colchicine may be continued without changing the dosage, and additional colchicine or other appropriate therapy should be given to control the acute attack. The recommended adult dosage is 1 tablet of probenecid and colchicine daily for one week, followed by 1 tablet twice a day thereafter. Some degree of renal impairment may be present in patients with gout. A daily dosage of 2 tablets may be adequate. However, if necessary, the daily dosage may be increased by 1 tablet every four weeks within tolerance (and usually not above 4 tablets per day) if symptoms of gouty arthritis are not controlled or the 24 hour uric acid excretion is not above 700 mg. As noted, probenecid may not be effective in chronic renal insufficiency particularly when the glomerular filtration rate is 30 mL/minute or less. Gastric intolerance may be indicative of overdosage, and may be corrected by decreasing the dosage. As uric acid tends to crystallize out of an acid urine, a liberal fluid intake is recommended, as well as sufficient sodium bicarbonate (3 to 7.5 g daily) or potassium citrate (7.5 g daily) to maintain an alkaline urine (see PRECAUTIONS ). Alkalization of the urine is recommended until the serum urate level returns to normal limits and tophaceous deposits disappear, i.e., during the period when urinary excretion of uric acid is at a high level. Thereafter, alkalization of the urine and the usual restriction of purine-producing foods may be somewhat relaxed. Probenecid and colchicine (or probenecid) should be continued at the dosage that will maintain normal serum urate levels. When acute attacks have been absent for six months or more and serum urate levels remain within normal limits, the daily dosage of probenecid and colchicine may be decreased by 1 tablet every six months. The maintenance dosage should not be reduced to the point where serum urate levels tend to rise. Warnings and cautions WARNINGS Exacerbation of gout following therapy with probenecid and colchicine may occur; in such cases additional colchicine or other appropriate therapy is advisable. Probenecid increases plasma concentrations of methotrexate in both animals and humans. In animal studies, increased methotrexate toxicity has been reported. If probenecid and colchicine is given with methotrexate, the dosage of methotrexate should be reduced and serum levels may need to be monitored. In patients on probenecid and colchicine the use of salicylates in either small or large doses is contraindicated because it antagonizes the uricosuric action of probenecid. The biphasic action of salicylates in the renal tubules accounts for the so-called “paradoxical effect” of uricosuric agents. In patients on probenecid and colchicine who require a mild analgesic agent the use of acetaminophen rather than small doses of salicylates would be preferred. Rarely, severe allergic reactions and anaphylaxis have been reported with the use of probenecid and colchicine. Most of these have been reported to occur within several hours after readministration following prior usage of the drug. The appearance of hypersensitivity reactions requires cessation of therapy with probenecid and colchicine. Colchicine has been reported to adversely affect spermatogenesis in animals. Reversible azoospermia has been reported in one patient. Drug interactions DRUG INTERACTIONS When probenecid is used to elevate plasma concentrations of penicillin, or other beta-lactams, or when such drugs are given to patients taking probenecid therapeutically, high plasma concentrations of the other drug may increase the incidence of adverse reactions associated with that drug. In the case of penicillin, or other beta-lactams, psychic disturbances have been reported. The use of salicylates antagonizes the uricosuric action of probenecid (see WARNINGS ). The uricosuric action of probenecid is also antagonized by pyrazinamide. Probenecid produces an insignificant increase in free sulfonamide plasma concentrations but a significant increase in total sulfonamide plasma levels. Since probenecid decreases the renal excretion of conjugated sulfonamides, plasma concentrations of the latter should be determined from time to time when a sulfonamide and probenecid and colchicine are coadministered for prolonged periods. Probenecid may prolong or enhance the action of oral sulfonylureas and thereby increase the risk of hypoglycemia. It has been reported that patients receiving probenecid require significantly less thiopental for induction of anesthesia. In addition, ketamine and thiopental anesthesia were significantly prolonged in rats receivi