Caffeine Allopurinol

Noninterfering allopurinol, caffeine, cotinine, ephedrine, nicotine, phenylephrine... 

Noninterfering acebutolol, acetazolamide, acetophenetidin, aldosterone, allopurinol, caffeine, cephalothin, chlorothiazide, cotinine, ephedrine, furosemide, hydrochlorothiazide, nicotine, pheniramine, phenylephrine, phenytoin, primidone, quinine, triamcinolone... 

The urinary caffeine test is not based on assays of specific substrates and products of NAT2 ( including other metabolism pathways involving at least xanthine-oxidases), and is affected by diet habits, xanthine-oxidase inhibitors such as allopurinol (Fuchs 1999), or other drugs (Klebovitch 1995). NAT activities are affected by anti-inflammatory drugs. Of note, acetominophen is an inhibitor of NAT2 in vivo (Rothen 1998). 

Fuchs P, Haefeli WE, Ledermann, Wenk M (1999) Xanthine oxidase inhibition by allopurinol affects the reliability of urinary caffeine metabolic ratios as markers for N-acetyltransferase2 and CYP1A2 activities. Eur J Clin Pharmacol 54 869-876... 

Noninterfering acetaminophen, allopurinol, amikacin, amoxapine, amytal, bretylium, caffeine, carbamazepine, carisoprodol, chloramphenicol, chlordiazepoxide, chlorpropamide, clonazepam, codeine, diazepeun, disop30 amide, droperidol, ethinamate, ethinamate, etho-suximide, fluphenazine, flurazepam, furosemide, gentamicin, haloperidol, hydrochlorothiazide, hydro yzine, ibuprofen, kanamycin, lidocaine, loxapine, meperidine, mepho-barbital, meprobamate, methaqualone, methotrexate, morphine, nafcUlin, naloxone, neomycin, perphenazine, phenacetin, phenobarbital, phenytoin, prazepam, primidone, procaine, propoxyphene, reserpine, salicylamide, salicylic acid, secobarbital, spironolactone, theophyUine, thiopental, thioridazine, tobramycin, valproic acid, verapeunil... 

Simultaneous acetaminophen, aldosterone, allopurinol, amitriplyline, caffeine, calcitriol, cephalothin, chlordiazepoxide, chlorothiazide, corticosterone, cortisone, dexamethasone, diazepam, ephedrine, ethinyl estradiol, furosemide, hydrocortisone, ibuprofen, imipra-mine, indomethacin, mechlorethamine, methylprednisone, metolazone, nandrolone, naproxen, phenacetin, phenobarbital, phen3doin, probenecid, progesterone, propranolol, sulfasalazine, testosterone, theophylline, vincristine... 

Allopurinol may invalidate the results of studies using caffeine as a probe drug for determining acetylator status or activity of CYP1A2. 

In 21 healthy subjects, allopurinol 300 mg daily for 8 days altered the levels of urinary caffeine metabolites of a single 200-mg dose of caffeine. In particular, the metabolic ratio used to determine whether people are fast or slow acetylators was substantially changed. Thus, allopurinol may invalidate the results of phenotyping with the urinary caffeine test. In addition, the caffeine metabolite ratio used to express the activity of the cytochrome P450 isoenzyme CYP1A2 was not stable when allopurinol was used. This interaction is of relevance to research rather than clinical practice. 

Evidence appears to be limited to a single case report and the studies in healthy subjects. The interaction only appears to be of moderate importance. Nevertheless, it would seem prudent to check for any signs of theophylline adverse effects (headache, nausea, tremor) during concurrent use, particularly in situations where the metabolism of the theophylline may already be reduced (other drugs or diseases), or where high doses of allopurinol are used. For mention that allopurinol may invalidate the results of phenotyping tests using caffeine, see Caffeine + Allopurinol ,... 

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