Probenecid

About Probenecid

Probenecid is a uricosuric: it blocks the kidney from reabsorbing uric acid, so more leaves in the urine and the blood level falls. The label approves it for the hyperuricemia associated with gout and gouty arthritis, and as an adjunct to penicillin, ampicillin, methicillin, oxacillin, cloxacillin or nafcillin to raise and prolong the antibiotic’s plasma level. It must not be given to children under 2 years, and for the penicillin use children aged 2 to 14 are dosed by weight. For gout, treatment is not started during an acute attack; adults usually begin with 250 mg (half a tablet) twice a day for one week, then 500 mg twice a day, and the dose can be raised in 500 mg steps every four weeks, usually to no more than 2000 mg a day, if symptoms or uric acid levels call for it. After six months or more without attacks and with a normal uric acid level, the prescriber may lower the dose by 500 mg every six months. With penicillin the adult dose is 2000 mg a day in divided doses.

There is no boxed warning. Probenecid is contraindicated in anyone allergic to it and in children under 2, and the label says it is not recommended for people with known blood disorders or uric acid kidney stones. Gout attacks can become more frequent in the first months of treatment, so colchicine or another attack treatment is often prescribed alongside it. The label calls salicylates, including aspirin, contraindicated in people taking probenecid, because they cancel its effect; acetaminophen is suggested for mild pain. It raises blood levels of methotrexate, which may need a lower dose and level monitoring, and of several other medicines. Severe allergic reactions, including anaphylaxis, are rare and usually appear within hours of restarting the drug. Reported side effects include headache, dizziness, nausea, vomiting, loss of appetite, sore gums, urinary frequency, kidney stones and renal colic, flushing, rash and hair loss, with rare blood and liver reactions.

What is distinctive is the kidney stone risk and how it is managed: the label advises drinking plenty of fluid and, where the prescriber directs, taking an alkalizing agent such as sodium bicarbonate or potassium citrate to keep the urine less acidic, especially early in treatment. Probenecid may not work when kidney function is poor (a glomerular filtration rate of 30 mL per minute or less), and it is not recommended with penicillin in known kidney impairment. It crosses the placenta, so use in pregnancy is weighed against the benefit. It can cause a false positive on some urine sugar tests, so a glucose-specific test is used. The Benemid brand is discontinued in the US, and the drug is not a controlled substance.

Taking Probenecid

How to take it

Take it by mouth exactly as directed, usually twice a day for gout or four times a day with an antibiotic, with food or an antacid if it upsets your stomach. Drink at least six to eight full glasses of water a day unless the prescriber says otherwise, to help prevent kidney stones.

If you miss a dose

Take it as soon as you remember, unless it is almost time for the next dose; then skip the missed dose. Do not take a double dose.

Storage

In the original tightly closed container at room temperature, away from heat and moisture (not in the bathroom), out of reach of children.

Interactions to know about

Aspirin and other salicylates are contraindicated because they block its effect, and pyrazinamide does the same. Probenecid raises the levels of methotrexate, penicillins and other beta-lactam antibiotics, sulfa drugs, sulfonylurea diabetes pills, indomethacin, naproxen, ketoprofen, acetaminophen, lorazepam and rifampin. Tell the pharmacist and prescriber about every medicine you take, including nonprescription pain relievers.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Probenecid differs from pharmacy to pharmacy

Probenecid is an older generic that not every pharmacy keeps on the shelf, so one may quote from stock while another orders it in. Quotes depend on which maker the pharmacy buys from and whether the drug is on its flat-price generic list.

The usual gout dose is two tablets a day, so a month’s supply is a modest count and the dispensing fee is a large share of each fill; a ninety-day supply spreads that fee. A short course with an antibiotic is a different quantity again, so the quote reflects exactly what is written.

Ways to pay less for Probenecid without insurance

• If the prescription names Benemid, expect a generic; the brand is no longer sold in the US.
• Once your dose and uric acid level are stable, ask the prescriber whether a ninety-day supply suits you, so you pay fewer dispensing fees.
• Ask whether probenecid is on the pharmacy’s flat-price generic list, and compare more than one pharmacy, since stocking differs for a drug filled less often.
• If probenecid does not suit you, ask the prescriber about allopurinol, a generic that lowers uric acid in a different way; do not switch on your own.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Probenecid

1. 1.Which of my pain relievers can I use with probenecid, since the label rules out aspirin and other salicylates?
2. 2.Should I be taking something to make my urine less acidic, and how much water should I drink each day?
3. 3.Do any of my other medicines, such as methotrexate, a sulfa drug or a diabetes pill, need a dose change while I take probenecid?
4. 4.What should I do if I get a gout attack during my first weeks on probenecid?

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