N-acetyl-beta-glucosaminidase and beta 2-microglobulin. Their urinary excretion in patients with renal parenchymal disease.

The urinary excretion of N-acetyl-beta-glucosaminidase (NAG) and beta 2-microglobulin (beta 2M) was studied in 43 patients with various forms of renal parenchymal disease. Patients with membranous nephropathy, membranoproliferative glomerulonephritis, focal segmental glomerulosclerosis, obstructive pyelonephritis, nephrosclerosis, and minimal change nephropathy generally had urinary NAG and beta 2M levels more than 3 SDs above those seen in normal subjects. Patients with progressive renal disease averaged higher NAG and beta 2M urinary levels than those with the same renal lesion and stable function. Since elevated urinary levels of NAG and beta 2M suggest renal tubular injury or dysfunction, our observations suggest tubulointerstitial involvement in a wide variety of renal diseases.

Clinical consequences of polymorphic acetylation of basic drugs.

The clinical consequences (therapeutic and toxic) of drug acetylation polymorphism are reviewed for procainamide, hydralazine, phenelzine, isoniazid, and salicylazosulfapyridine. Genetic slow acetylators are more likely than rapid acetylators to experience the following adverse drug reactions: (1) earlier development of procainamide-induced antinuclear antibody; (2) earlier and more frequent development of procainamide-induced systemic lupus erythematosus (SLE); (3) hydralazine-induced SLE; (4) spontaneous SLE; (5) drowsiness and nausea from phenelzine; (6) cyanosis, hemolysis, and transient reticulocytosis from salicylazosulfapyridine; and (7) polyneuropathy after isoniazid therapy. The incidence of isoniazid hepatitis may, however, be more common in rapid than than in slow acetylators. Genetic slow acetylators are also more likely than rapid acetylators to experience greater therapeutic responses from similar doses of the following: phenelzine, hydralazine provided beta blockers are concurrently used, and isoniazid if once weekly therapy is used. Thus, knowledge of the acetylator phenotype of a patient can help determine the relative risk for some drug-related toxic and therapeutic responses.

Polymorphic acetylation procainamide in man.

N-Acetylprocainamide (NAPA) and procainamide plasma and urine concentrations were determined by thin-layer chromatography (TLC) densitometry in people of known acetylator phenotype (dapsone phenotyping) taking procainamide for more than 3 days. The plasma NAPA/procainamide ratio 3 hr after the last dose for fast acetylators (mean plus or minus SD) is 1.8 plus or minus 0.59 (N equal to 8) and for slow acetylators, 0.61 plus or minus 0.09 (N equal to 6) P smaller than 0.001). The renal clearance of NAPA averaged 1.2 times the simultaneously measured endogenous creatinine clearance, whereas procainamide clearance was approximately double the creatinine clearance. There was no difference between slow and rapid acetylators in the renal clearance of either drug or the urine pH, indicating that the difference in plasma NAPA/procainamide ratios between these two groups is due to differences in their rates of acetylation. Therefore, procainamide is probably acetylated by the polymorphic N-acetyltransferase in man. Reflecting the blood level differences, the NAPA/procainamide ratio in urine (collected 99 to 180 min after last dose) was found to be higher in rapid than in slow acetylators. The plasma protein binding of NAa and of procainamide are similar. Since NAPA seems to have an antiarrhythmic potency similar to procainamide, NAPA probably contributes to the antiarrhythmic activity of procainamide therapy, especially in genetic rapid acetylators.

Age and renal clearance of cimetidine.

In 35 patients (ages 20 to 86 yr) receiving cimetidine therapeutically two serum samples and all urine formed in the interim were collected for analysis of cimetidine by high-pressure liquid chromatography and for creatinine. Cimetidine clearance decreased with age. The extrapolated 6-hr serum concentration of cimetidine per unit dose, after intravenous cimetidine, increased with age of the patients. The ratio of cimetidine clearance to creatinine clearance (Rc) averaged 4.8 +/- 2.0, indicating net tubular secretion for cimetidine. Rc seemed to be independent of age and decreased with increasing serum concentration of cimetidine, suggesting that secretion of cimetidine is a saturable process. There was only one case of dementia possibly due to cimetidine (with a drug level of 1.9 microgram/ml 6 hr after a dose) in a group of 13 patients without liver or kidney disease who had cimetidine levels above 1.25 microgram/ml. Thus, high cimetidine levels alone do not always induce dementia.

Plasma levels, protein binding, and elimination data of lidocaine and active metabolites in cardiac patients of various ages.

The serum and urine levels of lidocaine and two active dealkylated metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), were determined by HPLC in 33 cardiac patients receiving lidocaine for more than 1 day. Clinical assessment of nervous system toxicity was carried out at the time of blood drawing. The ratios in serum of MEGX to lidocaine and of GX to lidocaine were 0.36 +/- 0.26 (mean +/- SD) and 0.11 +/- 0.11. Lidocaine and MEGX binding to serum proteins from seven patients 2 days after their myocardial infarctions were 55.4 +/- 5.9% and 14.3 +/- 3.0%. After correction for this difference in protein binding, the MEGX/lidocaine ratio in serum water was 0.68 +/- 0.49. MEGX levels in serum water were 80% or more of the lidocaine levels in 11 of the 33 patients. GX binding was 5 +/- 4%. Even after correction for protein-binding differences, GX levels in serum water were low compared to lidocaine levels. The steady-state serum GX concentration normalized for lidocaine infusion rate declined with age. Of 27 patients without toxicity, six had serum lidocaine levels above 8 micrograms/ml. Five of six patients with toxicity had levels less than 8 micrograms/ml. The renal clearance of lidocaine, MEGX, and GX was less than creatinine clearance in most patients. We conclude that MEGX, but not GX, contributes to the pharmacologic activity of lidocaine therapy in a substantial fraction of patients. We also suggest that the concept of a single value for the upper limit of the therapeutic level of lidocaine in serum is an oversimplification because it does not take into account individual differences in drug-protein binding or accumulation of active metabolites.

Prevalence of high (3S)-3-hydroxyquinidine/quinidine ratios in serum, and clearance of quinidine in cardiac patients with age.

In the sera from 42 patients receiving quinidine, (3S)-3-hydroxyquinidine (3-OH), an active metabolite of quinidine, and quinidine were determined by high-pressure liquid chromatography with fluorescence detection. These results were added to those of 25 other patients reported previously. The 3-OH/quinidine ratio averaged 0.34 +/- 0.17 (SD) with a range of 0.10 to 0.90. Eleven patients (16%) had ratios above 0.50. After adjusting for protein binding differences between the 2 compounds, these 16% had 3-OH concentrations in serum water greater than that of quinidine. An additional 7 patients (10%) of the total) had levels of this metabolite in serum water slightly less than that of quinidine. A histogram showing the frequency distribution of 3-OH/quinidine in serum indicates extensive skewing with possibly a bimodal distribution with the antimode at 0.50. Thus, 3-OH may make a significant contribution to the effect of quinidine therapy in a fraction of treated patients. The clearance of quinidine decreased with age, indicating the need for, on the average, higher doses of quinidine in the young.

Aging and renal clearance of procainamide and acetylprocainamide.

Thirty-two patients had blood and urine collected simultaneously for measurement of procainamide, acetylprocainamide, and creatinine. The ratios of drug clearance to creatinine clearance were calculated for each. The procainamide:creatinine clearance ratio averaged 2.9 +/- 1.6 (SD) and fell as age of the patients rose (r = 0.5, p < 0.01). The acetylprocainamide:creatinine clearance ratio averaged 1.7 +/- 0.8 and also fell with age. The combination of decline in overall renal function with age with this decrease in the rate of renal tubular secretion of these drugs led to a progressive age-related rise in the steady-state serum level of procainamide (r = 0.56, p < 0.01) and acetylprocainamide (r = 0.36, p < 0.1) achieved by any dose of procainamide. Thus, the dosage of procainamide must be individualized for both overall renal function (GFR) and the age-related variations in renal tubular secretion that are of most note in children and the elderly.

Stereoselective renal tubular secretion of quinidine and quinine.

Quinidine and quinine are stereoisomers. When given sequentially or simultaneously, the renal clearance of values of quinidine and quinine were measured in seven healthy volunteers and when given simultaneously, to an additional five elderly men. Analytic specificity was provided by an HPLC drug assay. Protein binding was measured by equilibrium dialysis. The quinidine clearance exceeded the quinine clearance in every individual. The mean (+/- SD) ratio of these clearances was 4.2 +/- 1.4 when the drugs were given together and 4.4 +/- 2.3 when they were given separately in the younger subjects and 3.4 +/- 0.5 when given simultaneously to the elderly. Calculating clearance of drug in serum water (unbound drug clearance) revealed a quinidine clearance of 6.1 +/- 2.3 times that of creatinine measured simultaneously, and for quinine it was 1.5 +/- 0.6 times that of creatinine. We conclude that there is stereoselective net renal tubular secretion of quinidine over quinine indicating stereoselectivity of this renal tubular transport process.

Renal injury in patients with rheumatoid arthritis treated with gold.

While severe nephrotoxicity is uncommon during gold therapy of rheumatoid arthritis (RA), the prevalence of mild nephrotoxicity has not been investigated. To study this, levels of leucine aminopeptidase (LAP) and N-acetyl-beta-glucosaminidase (NAG) (nmole/hr/mg urinary creatinine), and beta 2-microglobulin (beta 2M) (microgram/mg urinary creatinine) were measured in urine samples from 33 patients with RA receiving gold and 28 patients with various musculoskeletal diseases not receiving gold. Each patient had a normal urinalysis and blood urea nitrogen or serum creatinine. LAP was above 30 in 55% of RA patients and 7% of controls (p < 0.01). NAG was above 100 in 70% of RA patients and 14% of controls (p < 0.01). In 8 RA patients, NAG was over 200; LAP was over 100 in 4, but in none of the controls. Beta 2M was above 0.32 in 7 of 23 female RA patients and in none of 12 female controls (p = 0.012) and none of the male patients. Patients who excreted high levels of beta 2M also excreted high levels of NAG and LAP. These data show that gold in therapeutic doses affects renal tubular cells, cauing the release of NAG and LAP from lysosomes and brush borders of the cells. This may represent the mildest stage of nephrotoxicity. Elevated beta 2M in the urine of some patients indicate a degree of nephrotoxicity sufficient to cause renal tubular dysfunction.

Microsomal hydroxylation as measured by pentobarbital elimination in patients with idiopathic systemic lupus erythematosus.

A mechanism postulated for drug- or chemical-induced systemic lupus erythematosus (SLE) is that the chemical is covalently bound to nuclear macromolecules increasing the immunogenicity of the macromolecule. This may require metabolic activation by oxidation. There are many similarities between drug-induced and idiopathic SLE. Twelve patients with idiopathic SLE and 12 normal subjects were given 100 mg pentobarbital orally to evaluate their microsomal hydroxylating activity. Plasma pentobarbital concentration was measured by gas-liquid chromatography. Mean plasma pentobarbital half-life was 24 +/- 10 (mean +/- SD) hr in the SLE patients, which is only slightly shorter than the 26 +/- 12 hr in the control subjects. The mean apparent volume of distribution in the patients was 1.28 +/- 0.30 l/kg, which is slightly above the 1.00 +/- 0.37 l/kg in the normal subject (P less than 0.05). Mean metabolic clearance rate in the SLE patients was 0.045 +/- 0.022 l/hr/kg, which is more than the 0.028 +/- 0.008 l/hr/kg in the normal control subjects (P less than 0.02). Since the metabolic clearance rate of a drug is the proper value for evaluating metabolism rate, we conclude that patients with SLE hve an increased elimination rate for drugs or other foreign compounds that are biotransformed by microsomal oxidation and may more rapidly bioactivate chemicals to reactive compounds.

Pubertal changes in net renal tubular secretion of digoxin.

To evaluate the effect of puberty on the net renal tubular secretion of digoxin, we measured the ratio of digoxin clearance to creatinine clearance in 23 patients aged 4 to 21 yr and correlated this ratio with both sexual maturity (Tanner stage) and chronologic age. All subjects were at steady-state levels for digoxin treatment; all had normal serum creatinine values for age as well as normal serum potassium levels. Mean ratio for immature children (n = 14, Tanner 1 through 3.5) was 1.45 +/- 0.66. Mean ratio for mature adolescents (n = 9, Tanner 4 through 5) was 0.95 +/- 0.28. The difference between the two groups was significant (P less than 0.05). When patients were regrouped by age using either 13 or 15 yr as a cutoff, the difference in ratios was no longer statistically significant. Based on 45 subjects (new and from our previous study) aged 2 mo to 80 yr, there was a significant decrease in the clearance ratio with increasing age, but when the 23 subjects aged 4 to 21 yr were analyzed separately, the correlation between ratio and age was not significant. It appears that the decrease in net renal tubular secretion of digoxin from childhood to adulthood correlates better with full sexual maturation at puberty (Tanner 4 through 5) than with chronologic age. This observation may represent a developmental change in pharmacokinetics with broader significance than for digoxin disposition alone.

Alterations in state in apneic pre-term infants receiving theophylline.

The present study is a report on 9 premature infants treated with aminophylline for relief of apnea. With serum theophylline levels of 2 to 10 microgram/ml, all infants experienced significant decrease of apneic episodes in association with increased wakefulness and increased amounts of active (REM) sleep. These effects may occur independently, but it is possible that the alteration of sleep states may be partially responsible for the decrease in apneic episodes in these infants.

Hydromorphone levels and pain control in patients with severe chronic pain.

To better understand the use of narcotic analgesics, the hydromorphone concentration was measured in serum samples from 43 patients with chronic severe pain who were receiving this drug. At the time of blood sampling, pain intensity, mood, and cognitive performance were assessed. There was large individual variation in the dose-drug level relationship. Seven patients with bone or soft tissue pain and drug levels of greater than or equal to 4 ng/ml had good pain control, whereas 10 did not. None of 15 patients with levels less than 4 ng/ml had pain control, despite drug doses similar to those given patients with higher levels. Thus 60% of the patients without control of their pain had hydromorphone levels below the lowest level that produced pain control. No patient with pain from nerve infiltration or compression had good pain control, irrespective of the drug level or dose. Poor mood correlated with high pain intensity and low drug level. Impaired cognitive performance was not related to drug level. Knowing that there is a low concentration of narcotic in the blood of a patient with chronic severe pain who is receiving high drug doses and who shows lack of both efficacy and side effects may reassure health care professionals that further narcotic dosage escalation is appropriate.

Steady-state serum levels of quinidine and active metabolites in cardiac patients with varying degrees of renal function.

The concentrations of quinidine, (3S)-3-hydroxyquinidine (3-OH), and 2'-oxoquinidinone (2'-OXO) in serum samples from 25 patients on long-term quinidine therapy were determined by a high-pressure liquid chromatography assay. Large individual variation in the levels of each of the compounds measured was observed. After correcting for differences in protein binding, the ratio of 3-OH/quinidine in serum water is 0.61 +/- 0.31 (SD) and the ratio of 2'-OXO/quinidine is 0.39 +/- 0.44. Seven of the 25 patients had serum water levels of one of these metabolites similar to or greater than that of quinidine. The quinidine levels, after normalizing for dose, are significantly higher in hemodialysis patients (about twice) than in nonazotemic patients; azotemic patients have mean values intermediate between them. Quinidine, 3-OH, and 2'-OXO are equally potent antiarrhythmic drugs (ED50 = 0.18, 0.17, and 0.21 mmoles/kg, respectively) when tested against chloroform- and hypoxia-induced ventricular fibrillation in mice. O-Desmethylquinidine, a new metabolite detected in urine of quinidine-treated patients, is less active. Quinidine and 2'-OXO are equally potent (ED50 = 0.010 mmoles/kg), while 3-OH seems less potent and more toxic when tested against BaCl2-induced ventricular arrhythmias in rabbits. Thus, these metabolites appear to contribute to the effects of quinidine and may make a significant contribution in some cases.

Cumulation of N-acetylprocainamide, an active metabolite of procainamide, in patients with impaired renal function.

N-Acetylprocainamide (NAPA) accumulated in the plasma of 6 cardiac patients with renal failure taking procainamide chronically for therapy (4 were undergoing hemodialysis) and contributed to the therapeutic and toxic effects of the procainamide. NAPA plasma levels ranged from 14.0 to 28.0 microgram/ml 3 hr after a dose of procainamide which is well above the 3-hr NAPA plasma levels of nonazotemic cardiac patients (range 1.9 to 6.3 microgram/ml; p = 0.002) on larger doses of procainamide. There was almost no decline in NAPA plasma levels on interdialysis days. In one of the patients with renal failure NAPA was still present 15 days (13.8 microgram/ml) and 38 days (0.9 microgram/ml) after procainamide was stopped, indicating a half-life of several days. Measurement of procainamide plasma concentrations by the usual fluorometric or colorimetric methods does not detect NAPA. Since NAPA accumulates in patients with impaired renal function, the concentrations of both this active metabolite and procainamide should be determined in these patients if drug level monitoring is to be helpful.

Active drug metabolites and renal failure.

Drugs that are administered to man may be biotransformed to yield metabolites that are pharmacologically active. These metabolites may accumulate in patients with end-stage renal disease if renal excretion is a major elimination pathway for the metabolite. This is true even if the active metabolite is a minor metabolite of the parent drug as long as the minor metabolite is not further biotransformed but is mainly excreted in the urine. Minor metabolite accumulation may also occur if it is further biotransformed by a pathway that is inhibited in uremia. Some clinical consequences of accumulation of the active drug metabolites of procainamide, meperidine, clofibrate, allopurinol, sulfadiazine and nitrofurantoin in patients with renal failure are discussed. The high incidence of adverse drug reactions seen in renal failure may be explained, in part, by the accumulation of active drug metabolites. Examples of active drug metabolites that do not accumulate in patients with renal failure because of further biotransformations are also included.

Increased urinary enzyme excretion in workers exposed to nephrotoxic chemicals.

Nephrotoxic chemicals are commonly present in the environment, particularly in the workplace. The level of occupational exposure to these chemicals has been so reduced that exposure to these agents now rarely causes clinically evident acute renal disease. A sensitive indicator of renal injury, urinary excretion of N-acetyl-beta-glucosaminidase, was utilized to evaluate persons exposed in the workplace to lead, mercury, or organic solvents, for evidence of renal effects from this exposure. None of the persons had clinically evident renal disease by history, none had hypertension, and all had normal findings on urinalysis. When compared with appropriate control populations, workers exposed to lead, workers exposed to mercury, and two of three groups of workers exposed to organic solvents had significant increases in urinary acetyl glucosaminidase activity. The third group of laboratory workers with low exposure to organic solvents had no increase in urinary acetyl glucosaminidase activity. It is concluded that exposure to environmental nephrotoxins at levels currently considered safe can produce renal effects as manifested by elevations of urinary acetyl glucosaminidase excretion. It is speculated that these renal effects are not always innocuous.

Antiarrhythmic activity of p-hydroxy-N-(2-diethylaminoethyl) benzamide (the p-hydroxy isostere of procainamide) in dogs and mice.

p-Hydroxy-N-(2-diethylaminoethyl)benzamide (2), the p-hydroxy isostere of procainamide (1), shows antiarrhythmic activity against acontine-induced atrial arrhythmia and lowers mean arterial blood pressure after iv infusion in dogs. In isolated canine Purkinje fibers, phenolic 2 in a bath concentration of 20 mug/ml significantly reduced the rate of phase O depolarization, prolonged the repolarization time, and reduced automaticity. These in vitro and the above in vivo activities of phenolic 2 were similar to those observed for procainamide (1). Bioisosters, phenolic 2 and procainamide (1), have almost identical respective 13C NMR chemical shifts indicating that electron densities on the respective carbons are very similar. This may explain their similar antiarrhythmic and hypotensive effects. Phenolic 2 and procainamide (1) therapeutic ratios in ICR male mice (acute LD50/ED50 against chloroform hypoxia induced ventricular fibrillation) are 2.1 and 1.8, respectively. Procainamide analogues with electron-donating groups [OH, NH2, NHC(=O)CH3] on the aromatic ring possess more antiarrhythmic activity in mice than the analogue with an electron-withdrawing group (NO2). This indicates that a shift in electron density toward the amide region in the former analogues, as determined by 13C NMR spectroscopy, is one of the factors influencing antiarrhythmic potency in this series.

Pharmacologically active drug metabolites: therapeutic and toxic activities, plasma and urine data in man, accumulation in renal failure.

Drugs that are administered to man may be biotransformed to yield metabolites that are pharmacologically active. The therapeutic and toxic activities of drug metabolites and the species in which this activity was demonstrated are compiled for the metabolites of 58 drugs. The metabolite to parent drug ratio in the plasma of non-uraemic man and the percentage urinary excretion of the metabolite in non-uraemic man are also tabulated. Those active metabolites with significant pharmacological activity and high plasma levels, both relative to that of the parent drug, will probably contribute substantially to the pharmacological effect ascribed to the parent drug. Active metabolites may accumulate in patients with end stage renal disease if renal excretion is a major elimination pathway for the metabolite. This is true even if the active metabolite is a minor metabolite of the parent drug, as long as the minor metabolite is not further biotransformed and is mainly excreted in the urine. Minor metabolite accumulation may also occur if it is further biotransformed by a pathway inhibited in uraemia. Some clinical examples of the accumulation of active drug metabolites in patients with renal failure are: (a) The abolition of premature ventricular contractions and prevention of paroxysmal atrial tachycardia in some cardiac patients with poor renal function treated with procainamide are associated with high levels of N-acetylprocainamide. (b) The severe irritability and twitching seen in a uraemic patient treated with pethidine (meperidine) are associated with high levels of norpethidine. (c) The severe muscle weakness and tenderness seen in patients with renal failure receiving clofibrate are associated with excessive accumulation of the free acid metabolite of clofibrate. (d) Patients with severe renal insufficiency taking allopurinol appear to experience a higher incidence of side reactions, possibly due to the accumulation of oxipurinol. (e) Accumulation of free and acetylated sulphonamides in patients with renal failure is associated with an increase in toxic side-effects (severe nausea and vomiting, evanescent macular rash). (f) Peripheral neuritis seen after nitrofurantoin therapy in patients with impaired renal function is thought to be due to accumulation of a toxic metabolite. The high incidence of adverse drug reactions seen in patients with renal failure may for some drugs be explained in part, as the above examples illustrate, by the accumulation of active drug metabolites. Monitoring plasma levels of drugs can be an important guide to therapy. However, if a drug has an active metabolite, determination of parent drug alone may cause misleading interpretations of blood level measurements. The plasma level of the active metabolite should also be determined and its time-action characteristics taken into account in any clinical decisions based on drug level monitoring.

Alteration of drug-protein binding in renal disease.

The protein binding of acidic drugs but not basic drugs is decreased in serum from patients with poor renal function. This decreased binding is due to the retention of compounds that displace drugs from their binding sites on albumin. Phenytoin and valproic acid are the 2 drugs that require a change in the values for therapeutic levels to allow for this decreased binding.