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Probenecid is an efficient preparation of no analgesic action prescribed for gout treatment. The medication started gaining popularity in the period when penicillin was still hardly accessible and expensive. The need in the preparation to prevent penicillin active excretion by the renal tubules, and thus the introducing of small doses to maintain a large concentration in the plasma grew. Probenecid was designed with that need it mind. Even though the price for penicillin experienced a significant decrease, the same effect can be achieved after considerable increase of the dosage.
Probenecid indications for use
Probenecid is sometimes used in infections, where unusually high level of penicillin in the plasma, e.g. in infective endocarditis, is required, or in treatment of children (where frequent administration of large doses of antibiotics is not recommended), and, if necessary, to get the maximum effect after a single dose of the drug, such as gonorrhea.
Early treatment increases the risk of joint crises, so it is necessary to prevent the same time appoint colchicine (2-3 times a day to 0.5 mg). The preparation is well tolerated, but in some cases, possible dyspepsia, allergic reactions (skin reactions, itching, fever). Prolonged treatment is not recommended to be taken in moderate and transient hyperuricemia, reduced glomerular filtration rate (less than 30 ml per minute), repetitive joint crises.
Probenecid pharmacological action
Probenecid inhibits transport of organic acids through the epithelium and, most importantly through the epithelium of the renal tubule. The effect was dose-dependent: low doses prevent tubular secretion and excretion of urate, but an adequate dose inhibits their reabsorption from the lumen of the tubules and has a beneficial uricosuric effect. The drug binds to plasma proteins to 90%; it is partially metabolized and partially excreted unchanged in the urine. The half-life varies depending on the dose taking 5 – 8 hours on average.
To prevent attack of gout, the 0.5g dosage orally once each 24 hours for the 1st week is prescribe, then the dosage is increased to 2.1 g/day. Plasma urate level initially decreases and sets, reaching 60% of initial. Because of the large loss of urate in the early period of treatment crystals in the urine may occur if the pH is not maintained at a level 6.0 or more in the first month of probenecid treatment (maintenance through using a mixture of potassium citrate to the water 12-24 g/day, or sodium hydrogencarbonate in powder form 5-10 g/day). The most commonly used daily dose of 1g increases uric acid excretion in the urine by 50% on average, and thus reduces lithemia.
The patient should drink plenty of liquids (3+ liters per day) to avoid the danger of mechanical obstruction or stone formation. Should strive to ensure that urine has an alkaline nature and is diluted; to this end, at night a 250 mg pill of acetazolamide is recommended to be taken. The treatment course in patients with renal insufficiency is needed to be carried out under the supervision of a treating doctor (potassium citrate may cause dangerous hyperkalemia). Probenecid is contraindicated in this case, since it may be ineffective; moreover, it can even exacerbate kidney disease.
In some patients it causes dysfunction of the gastrointestinal tract and sometimes allergy blocks tubular excretion and prolongs the effect of penicillins, cephalosporins, naproxen and indomethacin.
Probenecid is contraindicated in chronic renal failure and pregnancy.
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