Buprenorphine and naloxone co-administration in opiate-dependent patients stabilized on sublingual buprenorphine

Buprenorphine and naloxone sublingual (s.l.) dose formulations may decrease parenteral buprenorphine abuse. We evaluated pharmacologic interactions between 8 mg s.l. buprenorphine combined with 0, 4, or 8 mg of naloxone in nine opiate-dependent volunteers stabilized on 8 mg s.l. buprenorphine for 7 days. Combined naloxone and buprenorphine did not diminish buprenorphine's effects on opiate withdrawal nor alter buprenorphine bioavailability. Opiate addicts stabilized on buprenorphine showed no evidence of precipitated opiate withdrawal after s.l. buprenorphine-naloxone combinations. Buprenorphine and naloxone bioavailability was approximately 40 and 10%, respectively. Intravenous buprenorphine and naloxone produced subjective effects similar to those of s.l. buprenorphine and did not precipitate opiate withdrawal.

Buprenorphine pharmacokinetics: relative bioavailability of sublingual tablet and liquid formulations

Buprenorphine is an effective new treatment for opiate dependence. This study compared the bioavailability of buprenorphine from a tablet to that from a reference solution. Six men experienced with, but not dependent on, opiates (DSM-III-R) were each administered 7.7 mg of buprenorphine in liquid form and 8 mg in tablet form 1 week apart in a balanced crossover design. Plasma levels were measured by electron capture capillary gas chromatography (GC), and concentration-time curves were constructed. Pharmacokinetic data were analyzed by analysis of variance. The bioavailability from the tablet was approximately 50% that from the liquid and was not affected by saliva pH. Lower bioavailability from the tablet may be due to slow dissolution.

Wound tissue oxygen tension predicts the risk of wound infection in surgical patients

OBJECTIVE

To test the hypothesis that subcutaneous wound oxygen tension (PsqO2) has a predictive relation to the development of wound infection in surgical patients.

DESIGN

A noninterventional, prospective study.

SETTING

A university department of surgery.

PATIENTS

One hundred thirty operative general surgical patients at notable risk of infection as predicted by an anticipated Study on the Effect of Nosocomial Infection Control (SENIC) score of 1 or greater.

OUTCOME MEASURES

PsqO2 was measured perioperatively. Its relation to the subsequent incidence of surgical wound infection was then determined and compared with the SENIC score as a criterion standard.

RESULTS

Although the SENIC score and PsqO2 are inversely correlated, PsqO2 is the stronger predictor of infection. Low PsqO2 identified patients at risk and concentrated them in a cohort that was about half the size of that identified by the SENIC score.

CONCLUSIONS

Subcutaneous perfusion and oxygenation are important components of immunity to wound infections. The SENIC score identifies systemic physiological variables that are important to the development of wound infection. Nevertheless, PsqO2 is the more powerful predictor of wound infection. Moreover, PsqO2 can be manipulated by available clinical means, and thus may direct interventions to prevent infection.

Bioavailability of sublingual buprenorphine

Buprenorphine administered sublingually is a promising treatment for opiate dependence. Utilizing a new, sensitive, and specific gas chromatographic electron-capture detector assay, the absolute bioavailability of sublingual buprenorphine was determined in six healthy volunteers by comparing plasma concentrations after 3- and 5-minute exposures to 2 mg sublingual and 1 mg intravenous buprenorphine. The amount of unabsorbed buprenorphine in saliva was measured after 2-, 4-, and 10-minute exposures to 2 mg sublingual buprenorphine in 12 participants. Pharmacokinetic parameters were analyzed by analysis of variance; bioequivalence was evaluated by the Schuirmann two-sided test. The 3- and 5-minute sublingual exposures each allowed 29 +/- 10% bioavailability (area under the plasma concentration-time curve unextrapolated) and were bioequivalent. Buprenorphine recovered from saliva after 2-, 4-, and 10-minute exposures was, on average, 52% to 55% of dose. Increased saliva pH was correlated with decreased recovery from saliva. Study results indicate that bioavailability of sublingual buprenorphine is approximately 30%. Sublingual exposure times between 3 and 5 minutes produce equivalent results. Buprenorphine remaining in saliva causes an almost twofold overestimation of bioavailability.

Relationship between skin fluorescence and blood flow in normal and in chronically ischemic subjects dosed with fluorescein

To elucidate parameters diagnostic of chronic ischemia, the fluorescence of skin on the foot, leg, arm, and forehead of six chronically ischemic patients and six normal subjects injected with fluorescein was measured serially using a surface-measurement fluorometer (dermofluorometer). Simultaneously collected plasma samples were assayed spectrofluorometrically for unmetabolized fluorescein. The time courses of plasma fluorescein content and dermofluorometer readings were jointly analyzed by combining a standard pharmacokinetic model, a model predicting skin site from plasma concentrations of fluorescein, and a model predicting the dermofluorometer response to those skin concentrations. Fluorescein plasma clearance (0.22 +/- 0.06 versus 0.46 +/- 0.20 L/h/kg) in ischemic patients was only half, and half-life was double (2.4 +/- 1.0 versus 1.3 +/- 0.3 h) those in normal subjects, with volume of distribution (Vdss = 0.46 L/kg) being similar. Despite the ischemia diagnosis for all patients involving claudication of the lower extremities, patients could be distinguished statistically from normal subjects on the basis of fluorescence readings taken on the arm, but not those using the foot or leg. The rate constant describing flux of fluorescein from the arm skin site in patients was only half that in normal subjects, and the peak reading on the arm occurred at 42 +/- 14 min after fluorescein injection in patients, but at only 15 +/- 6 min in normal subjects. Lack of discrimination between subject groups via leg and foot readings may be due to several physiologic and/or experimental factors, including the need to take skin surface readings much earlier than previously recognized.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue oxygen tension and other indicators of blood loss or organ perfusion during graded hemorrhage

Currently employed clinical indicators of perfusion provide inadequate warning of developing hazards caused by marginal perfusion in certain vital organs or "peripheral" tissues that are pivotal to postsurgical wound healing. In this study, mean arterial blood pressure, cardiac output, and transcutaneous and subcutaneous oxygen tensions (PtcO2 and PsqO2) were investigated during serial hemorrhage, as indicators of the degree of both hypovolemia and perfusion to specific tissues. Blood was removed in stages (10%, 20%, 30%, 40%, 55%, 60%, and 65% of original volume) from anesthetized dogs. Injections of variously radiolabeled microspheres allowed assessment of blood flow at each stage of hemorrhage in bone, brain, colon, heart, kidney, liver, muscle, pancreas, skin, small intestine, spleen, stomach, and subcutaneous tissue. PsqO2 was correlated more highly with blood volume lost than was PtcO2. Furthermore PsqO2 was more sensitive to blood loss than was either cardiac output or PtcO2 and, also during the early loss (0% to 40%), was more sensitive than mean arterial pressure. Some organs (e.g., pancreas) appeared to lose considerable blood flow with only small loss of blood volume, but their blood flow then stabilized at a low level despite further hemorrhage. Other organs, notably the kidney, appeared to be relatively unaffected by substantial loss of blood volume (20% to 40%), after which, however, their blood flow quite abruptly became sensitive to further hypovolemia. This explains why blood flow-related performance of the kidney (e.g., urine volume) may not adequately predict a developing hazard or peripheral perfusion. Some indicators were found to be better indexes of blood flow in some organs than in others (e.g., cardiac output and PsqO2 correlated more closely with skin, spleen, and intestinal flows [and one another] than with vital organ flows).

Pharmacokinetic interactions between theophylline and other medication (Part II)

Part I of this article, which appeared in the previous issue of the Journal, covered the effects or lack of effects on theophylline clearance of sympathomimetics, corticosteroids, antihistamines and other antiallergy drugs, antimicrobial agents, phenytoin, carbamazepine, barbiturates, antacids and activated charcoal. In Part II, this discussion is extended to the effects of other agents. Overall summaries, both textual and tabular, appear in Part I.

Development of a new controlled-release formulation of chlorpheniramine maleate using in vitro/in vivo correlations

Development of a controlled-released formulation of chlorpheniramine maleate is described, using in vitro/in vivo correlates, according to a process that has been termed "biorelevant dissolution". The process begins with simulations using several possible input rates combined with known disposition parameters of chlorpheniramine maleate. Based on desired plasma concentrations, an input rate is selected for further development which consists of a combination of clinical bioequivalence studies and further in vitro testing and simulations. The method is designed to reduce the requirements for trial and error clinical bioequivalence testing of a new controlled-release formulation.

Pharmacokinetic interactions between theophylline and other medication (Part I)

Many drugs have been found to increase or decrease the clearance of theophylline, probably by interaction with one or more of the variants of the cytochrome P450 drug-metabolising system. Theophylline may be particularly susceptible to alteration of its clearance because of the particular form(s) of the P450 system involved, because its metabolism is saturable, and/or because 90% of its elimination is via metabolism. Its clearance has been found to be decreased (typically by around 25%, but often by far more) by erythromycin, troleandomycin (triacetyloleandomycin), roxithromycin, enoxacin, ciprofloxacin, pefloxacin, norfloxacin, ofloxacin, fluoroquinolone T-3262, pipemidic acid, cimetidine, etintidine, propranolol, verapamil, diltiazem, nifedipine, furosemide (frusemide), at least some anovulent agents, viloxazine, allopurinol, ticlopidine, idrocilamide, thiabendazole, disulfiram, influenza- and BCG-vaccination, interferon, and caffeine (half-life increase). In contrast, theophylline clearance (clearance/bioavailability) was found to be increased by isoprenaline (isoproterenol), terbutaline, some corticosteroids, phenytoin, phenobarbital, activated charcoal, felodipine moricizine, benzodiazepines and sulfinpyrazone - typically by about 25%, but sometimes by as much as 80% or more. For several of these concomitant medications, however, only some of the published studies can substantiate an influence, which may highlight the sensitivity of some interactions to particular experimental and/or clinical conditions, e.g. with terbutaline, erythromycin, ciprofloxacin, norfloxacin, ofloxacin, phenobarbital, cimetidine, verapamil, diltiazem, nifedipine, anovulents, allopurinol and influenza vaccination. Moreover, reports both of inhibition and of induction of theophylline clearance by each of rifampicin and isoniazid have appeared. Nevertheless, under investigation many medications have not been found to perceptibly influence theophylline disposition kinetics, e.g. ephedrine, orciprenaline (metaproterenol), prednisone, prednisolone, temelastine, terfenadine, mequitazine, picumast, repirinast, josamycin, midecamycin, miocamycin, spiramycin, amoxicillin, ampicillin, cefalexin, cefaclor, ceftibuten, cotrimoxazole (trimethoprim plus sulfamethoxazole), tetracycline, doxycycline, lomefloxacin, fluoroquinolones NY-198 and AM-833, nalidixic acid, lincomycin, metronidazole, certain antacids, ranitidine, roxatidine, pirenzepine, rioprostil, metoclopramide, metoprolol, atenolol, nadolol, medroxyprogesterone, dextropropoxyphene (propoxyphene), piroxicam, ozagrel, mebendazole and ascorbic acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Lack of correlation of clinical breast examination with high-risk histopathology

PURPOSE

Routine breast examination frequently finds differences in palpable density and palpable nodularity, but it is not known if these differences correlate with the presence of high-risk histopathology.

PATIENTS AND METHODS

To test for a relationship between clinical breast examination and histopathology, we devised separate, 4-point scales of clinical density and nodularity and validated these scales by repeat examinations 4 or more months apart in 199 separate breasts (the scale was the same or within 1 point on repeat examination 87% of the time for density and 90% for nodularity). We then used these two clinical scales to compare density and nodularity to histopathology of breast tissue at the margins of segmental resections in 60 women undergoing breast-conserving treatment of primary breast cancer. In cases such as these, a large sample of "normal" tissue is intentionally removed when the wide excision is done to obtain negative margins. Histopathology at the margins was graded according to the consensus panel of the American College of Pathology; as might be expected in women with previous cancer, some higher-risk histopathology was found in 37% of cases. A relationship was sought using Spearman's rank correlation coefficient.

RESULTS

Neither clinical breast density (rho = 0.16) nor clinical breast nodularity (rho = 0.01) related to the presence of high-risk histopathology in the underlying tissue. Interestingly, breast nodularity increased with age (rho = 0.28), and clinical density and nodularity were inversely related (rho = -0.28).

CONCLUSION

We conclude that neither clinical breast density nor nodularity correlates with histopathology and that it is unlikely that a larger study would find a clinically useful correlation. Therefore, a clinical examination should not be used to decide that high-risk histopathology is likely to be present in an individual woman's breast.

A comparison of the influence of famotidine and cimetidine on phenytoin elimination and hepatic blood flow

The H2-receptor antagonist cimetidine has been reported to decrease the hepatic clearance of numerous drugs by inhibiting cytochrome P-450 metabolism, decreasing liver blood flow or both. In this open-label, randomized crossover study we determined whether therapeutic doses of famotidine, a newer H2-receptor antagonist, has similar effects. Ten healthy subjects received single doses of both phenytoin 100 mg orally and indocyanine green intravenously without other treatment, and then again during treatment with famotidine or cimetidine. After a drug-free period, this sequence was repeated with the alternate H2-receptor antagonist. Cimetidine decreased the plasma clearance of phenytoin by 16% +/- 14% (mean +/- s.d.), but was not found to have a significant influence on phenytoin volume of distribution or terminal elimination rate constant nor on blood clearance of indocyanine green. Famotidine was not found to alter either phenytoin or indocyanine green kinetics.

Effect of cimetidine or ranitidine administration on nifedipine pharmacokinetics and pharmacodynamics

The effect of cimetidine or ranitidine administration on responses to single and multiple doses of nifedipine were studied in 11 subjects who received cimetidine (300 mg q.i.d.) and 12 who received ranitidine (150 mg b.i.d.) in combination with nifedipine. After single doses of nifedipine, cimetidine decreased apparent oral clearance (dose/AUC) from 66 +/- 32 L/hr to 33 +/- 14 L/hr (p less than 0.01); elimination half-life increased from 4.0 +/- 2.2 to 4.9 +/- 2.9 hours (p less than 0.07). Increases in heart rate were greater (26 +/- 13 vs 13 +/- 11 beats/min standing; 19 +/- 11 vs 9 +/- 9 beats/min supine) and lasted longer than after nifedipine alone. Hypotensive effects were similar (10 +/- 7 mm Hg decrease vs 9 +/- 9 mm Hg). During nifedipine multiple-dose administration, cimetidine decreased the apparent oral clearance from 76 +/- 39 to 43 +/- 20 L/hr (p less than 0.01). Blood pressure responses were not altered by cimetidine but heart rate increased more (18 +/- 9 vs 9 +/- 9 beats/min supine; 18 +/- 13 vs 13 +/- 14 beats/min standing). Ranitidine coadministration did not alter nifedipine elimination or dynamic responses. During administration of nifedipine alone, the ratio of oral clearances (multiple to single doses) was 1.1 +/- 0.5. Thus (1) cimetidine but not ranitidine alters responses to nifedipine and (2) nifedipine kinetics do not differ between single- vs multiple-dose conditions.

Pentamidine pharmacokinetics in patients with AIDS with impaired renal function

In patients with normal renal function, pentamidine elimination half-life and plasma clearance (mean +/- SD) were 6.22 +/- 1.17 hr and 411 +/- 55 liters/hr, respectively. With creatinine clearances from 35 to 145 ml/min, neither the elimination half-life (P = .47) nor the plasma clearance (P = .40) was correlated with renal function. Plasma concentrations in patients receiving dialysis ranged between 5.9 and 582 ng/ml and appeared not to be significantly affected by dialysis. The number of prior doses and the elimination half-life estimated from the terminal slope were correlated (r = .81, P = .025), and the results suggested that the current assay technology is still not sensitive enough to detect true elimination half-life. Trough plasma concentrations ranged between 4.3 and 67.5 ng/ml (28.4 +/- 26.6 ng/ml) in patients who had received prior doses of pentamidine, a result suggesting that drug accumulation occurs with multiple dosing. The data suggest that dosage adjustments are not necessary with creatinine clearances of greater than 35 ml/min. Because multiple dosing leads to increased trough concentrations and drug accumulation, lower dose regimens may still be efficacious, yet associated with reduced toxicity.

Effects of formulation and food on the absorption of hydrochlorothiazide and triamterene or amiloride from combination diuretic products

The absorption of three combination formulations of hydrochlorothiazide and either triamterene or amiloride was studied over a 5-year period in seven separate investigations under varying conditions of food and fasting. The most widely prescribed combination, containing 25 mg of hydrochlorothiazide and 50 mg of triamterene, demonstrated impaired absorption in the fasting state that was partially corrected by the addition of a breakfast high in fat. The increase in the fat content of the food appeared to correlate directly with the amount of both drugs absorbed from this formulation. The second formulation studied, a new combination formulation of 50 mg of hydrochlorothiazide and 75 mg of triamterene, demonstrated acceptable absorption in the fasting state that was not altered by the concurrent administration of a high-fat breakfast. The absorption of the third formulation, a combination of 50 mg hydrochlorothiazide and 5 mg amiloride, was acceptable in the fasting state and demonstrated a slight reduction in the absorption of the amiloride component when administered concurrently with a high-fat meal. The clinical and biopharmaceutic implications of these observations are discussed.

A theophylline dosage regimen which reduces round-the-clock variations in plasma concentrations resulting from diurnal pharmacokinetic variation

Slower drug absorption at night can leave residual drug from an evening dose of a sustained-release product remaining to be absorbed at the time of the next morning's dose, thereby giving higher plasma concentrations of the drug during the day than the night. When a capsule product releasing theophylline over 12 h after a morning dose was given repetitively at 8 a.m. and 8 p.m. for 4 days, daytime plasma concentrations from 4 h to 8 h after the dose were about 40% greater than corresponding night-time concentrations, and the mean steady-state concentration during the night-time interval was only 81% of that during the daytime interval. Altering the regimen to one capsule at 12 noon and one at 10 p.m. eliminated all significant differences between a.m. and corresponding p.m. plasma concentrations of theophylline and between the mean steady-state concentrations for each of the interdose intervals within a day.

Use of a specific and sensitive assay to determine pentamidine pharmacokinetics in patients with AIDS

The first-dose pharmacokinetics of pentamidine were studied in patients with AIDS. Pentamidine isethionate (4 mg/kg) was administered intramuscularly or intravenously to two groups of six patients each. Serial plasma and urine concentrations were measured by high-performance liquid chromatography, which is accurate and precise (sensitivity limits, 2.29 ng/ml in plasma and 229 ng/ml in urine). The mean peak concentrations in plasma after intramuscular and intravenous administration were 209 ng/ml and 612 ng/ml, respectively. Plasma concentrations, which declined biexponentially, were detectable throughout the 24-hr dosing interval and fell to less than 25 ng/ml after 8 hr. The mean plasma clearance, elimination half-life, apparent volume of distribution, and apparent volume at steady state for intramuscularly treated patients were 305 liters/hr, 9.36 hr, 924 liters, and 2,724 liters, respectively; these parameters for intravenously treated patients were 248 liters/hr, 6.40 hr, 140 liters, and 821 liters, respectively. Renal clearance of pentamidine was 5.0% of the plasma clearance for intramuscularly treated patients and 2.5% for intravenously treated patients. We found significant differences in the pharmacokinetic parameters between intramuscularly and intravenously treated patients.

Absorption and disposition of two combination formulations of hydrochlorothiazide and triamterene: influence of age and renal function

In this study we compared the absorption and disposition of two commonly used combination formulations of hydrochlorothiazide and triamterene (Dyazide and Maxzide) in 48 patients with essential hypertension after dosing with each formulation to steady state. Interdose AUC and urinary recovery of hydrochlorothiazide, triamterene, and the major metabolite of triamterene, hydroxytriamterene sulfate (adjusted for dose), documented marked impairment in the absorption of hydrochlorothiazide (approximately two third as bioavailable) and triamterene (about half as bioavailable) from Dyazide in comparison to Maxzide. The study also demonstrated a reduction in the clearance of triamterene, hydrochlorothiazide, and hydroxytriamterene sulfate with increasing age. Linear correlation analyses suggested that this effect was a result of the reduction in renal function that occurs with increasing age.

The impact of neglecting nonlinear plasma-protein binding on disopyramide bioavailability studies

Disopyramide has nonlinear protein binding and thus the relationship between the extent of its bioavailability and AUC, the area under the plasma concentration-time curve, is nonlinear and absorption rate-dependent. The unbound species follows linear pharmacokinetics. A solution of disopyramide, the innovator's product, and two generic formulations were found to be statistically indistinguishable in their bioavailability of disopyramide, whether comparison was based upon AUC or area under the plasma unbound concentration-time curve (AUCu). The AUC and AUCu gave similar results because of truly similar bioavailability, coupled with sufficiently similar release rates, among the four preparations chosen for study. The concentration dependence of disopyramide protein binding and the time course of unbound plasma concentrations were fit by models which then allowed prediction of AUC under various biopharmaceutical scenarios. Nonlinear binding of disopyramide to plasma proteins renders AUC an insensitive parameter for the discrimination of products with different extents of bioavailability; immediate-release products allowing bioavailabilities of 75 or 125% relative to the solution can generate AUCs 86 and 112%, respectively, of that from the solution. Nonlinear binding, furthermore, leads to a tendency for AUC to overestimate the bioavailability of slower release products in single-dose studies; if AUC were the index of bioavailability, products permitting the same bioavailability as the solution but releasing over 12 hr could appear to allow 114% relative bioavailability. Moreover, in some situations the bias arising from the insensitivity of AUC to product differences can be reinforced by the dependence of AUC on release rate; an apparent relative bioavailability of 80% can be achieved by a 12-hr release product allowing a true relative bioavailability of a mere 58%. While multiple-dose studies appear largely to avoid the tendency to overestimate low bioavailability in slow-release products, in these studies AUC appears to be even more insensitive in resolving discrepancies between products. Assay technology now available makes AUCu a feasible and more reliable index of bioavailability than AUC when plasma protein binding of drugs is nonlinear.

Absence of a significant pharmacokinetic interaction between hydrochlorothiazide and triamterene when coadministered

Hydrochlorothiazide, triamterene, and hydroxytriamterene sulfate were monitored in the plasma and urine of 24 healthy young men taking single doses of a liquid preparation containing both hydrochlorothiazide and triamterene, liquid preparations containing either of these drugs alone, and a combination tablet recently formulated with a dose ratio of hydrochlorothiazide : triamterene (1 : 1.5) found to give optimal potassium-sparing effect. In contradiction to a recent publication, no interaction between the drugs affecting the bioavailability or renal clearance of either could be demonstrated. The previous report of drug-drug interaction probably arose from formulation-related problems with bioavailability from the two capsule and two tablet products which had been studied. A well-formulated hydrochlorothiazide-triamterene combination tablet promotes plasma concentrations and urinary excretion of hydrochlorothiazide, triamterene, and hydroxytriamterene sulfate which are virtually identical to those seen after either a combination liquid dosage form or simple liquid forms containing only one of the two drugs.

Pharmacokinetic-pharmacodynamic analysis of unbound disopyramide directly measured in serial plasma samples in man

The pharmacokinetics and pharmacodynamics of the antiarrhythmic drug, disopyramide, were investigated in 12 volunteers who took 300 mg doses of 3 different capsule preparations and an aqueous oral solution of the drug at 1-week intervals. Concentrations of drug unbound to plasma proteins were measured by a sensitive immunoenzyme assay after ultrafiltration of plasma samples taken serially after dosing. QT interval was measured on serial ECG recordings with correction for changes in heart rate. Unbound concentrations of disopyramide were modelled by an open one-compartment pharmacokinetic model with a zero-order absorption rate and a lag time. There was no significant difference in parameter estimates between the four preparations, except for the lag time, which was significantly shorter for the solution preparation. The saturable protein binding of disopyramide was described by a hyperbolic model including a specific binding site and additional nonspecific binding. The pharmacodynamic relationship between unbound drug concentration and QT prolongation was fit by a simple linear model. This fit was better using unbound concentration of the drug than using total concentrations.

Bioequivalence study of a new tablet formulation of triamterene and hydrochlorothiazide

A three-treatment, single-dose, crossover bioequivalence study was conducted in healthy volunteers to compare urinary drug recovery following administration of hydrochlorothiazide tablets, the currently marketed capsule formulation of triamterene and hydrochlorothiazide (Dyazide), and a new tablet preparation of these active ingredients (Maxzide). No significant differences were observed in the urinary recovery of hydrochlorothiazide after the administration of hydrochlorothiazide tablets and Maxzide tablets. However, only about one-half as much hydrochlorothiazide was recovered following the administration of Dyazide capsules. Similarly, the urinary recovery of triamterene and the sulfate ester of hydroxy-triamterene after administration of Dyazide capsules was approximately one-half the levels observed after giving the new tablet formulation. The clinical consequences of the limited bioavailability of the active ingredients of Dyazide are discussed.

Digital cutaneous fluorometry: correlation between blood flow and fluorescence

Central to the use of fluorescein in vascular diagnosis is the requirement that the intensity of evoked fluorescence be proportional to blood flow. With the introduction of the digital dermofluorometer, a device that quantitates cutaneous fluorescence, establishment of this relationship has become possible. After experimentally producing measured reductions in the distal aortic flow of eight rabbits, the ratio of fluorescence in the flow-restricted and unrestricted areas was obtained by measuring hind- and forelimb fluorescence. At any time between 20 and 60 minutes following a bolus injection of sodium fluorescein (1 mg/kg body weight), there was a significant linear relationship (p less than 0.05, r greater than 0.75) between residual aortic flow and the ratio of hind-/forelimb fluorescence. Simultaneously obtained plasma fluorescein concentrations decayed rapidly by first-order kinetics with a half-life of 12.5 minutes, regardless of the degree of distal aortic occlusion. The time course of the rise and fall of cutaneous fluorescence was slower than that of the plasma fluorescein concentration, proving that interstitial rather than intravascular fluorescein was responsible for the measured fluorescence. We conclude that the intensity of tissue fluorescence is linearly related to blood flow and that conclusions regarding perfusion may be drawn from relative fluorescence at any time between 20 and 60 minutes following a bolus injection of fluorescein. Furthermore, the passage of fluorescein into the interstitium is dependent on a time-limited diffusion process, which along with flow, establishes the time to peak and the absolute amplitude of the tissue fluorescence curve.

Naproxen pharmacokinetics in the elderly

While naproxen pharmacokinetics appear to be altered in the presence of both diminished renal and hepatic function, the degree to which naproxen disposition might be influenced in the elderly by concurrent alteration in these functions is not obvious. Total plasma clearance/bioavailability (CL/F) of naproxen after a single 375 mg oral dose was found to be less in a group of 10 healthy men between 66 and 81 years of age than in 10 healthy men between 22 and 39 years (0.318 +/- 0.078, 0.416 +/- 0.061 l/h). At steady state (375 mg, 12 hourly), however, CL/F was statistically indistinguishable between the two groups. The fraction of naproxen unbound to plasma protein was doubled in elderly subjects, both at peak and trough drug concentrations. The lowered protein binding tended to obscure a 50% decrement in the intrinsic clearance of naproxen in the elderly as estimated by unbound clearance/bioavailability (213 +/- 64, 396 +/- 155 l/h). As a result, mean steady-state plasma concentrations of naproxen were indistinguishable between the elderly and young (64.2 +/- 8.5, 58.2 +/- 8.1 mg/l) but the elderly generated twice the mean steady-state unbound plasma drug concentration (0.157 +/- 0.039, 0.0859 +/- 0.0212 mg/l). Since it is the unbound drug concentration which appears in general to relate more closely to pharmacological and toxic effect, it may be advisable to reduce naproxen doses by half in the elderly, pending plasma drug concentration-response studies in this age group. If a similar perturbation with age occurs in benoxaprofen protein binding as was observed with naproxen, benoxaprofen intrinsic clearance in the elderly might be only one quarter of that in younger individuals; a factor which may contribute to the toxicity of this drug in the elderly.

Pharmacokinetic drug interactions with theophylline

Since up to 90% of a theophylline dose is biotransformed, drugs influencing microsomal enzyme systems in the liver may affect the elimination of theophylline. Other integrated mechanisms (e.g. hepatic uptake) may also be altered by concurrent administration of other drugs. Whatever the mechanism, the interaction may be sufficient to necessitate adjustment of the theophylline dosage, preferably guided by plasma theophylline determinations. Comedication with phenobarbitone may require an increase of the theophylline dose by about 30% due to increased clearance resulting from enzyme induction. Similarly, with phenytoin and carbamazepine a dose increase of about 40 to 50% may be required. In the case of rifampicin, isoniazid or sulphinpyrazone comedication, an increase of the theophylline dose by about 20 to 25% may be needed. On the other hand, other drugs decrease theophylline clearance, making a reduction in the dose of concurrent theophylline advisable: with usual doses of erythromycin, propranolol and isoprenaline (isoproterenol), a reduction of about 25% is needed; with cimetidine and oral contraceptives by about 30% or more; and with triacetyloleandomycin (troleandomycin) by about 50%. In high doses, the xanthine oxidase inhibitor allopurinol can also retard theophylline elimination, and a reduction of the theophylline dose by about 20% may be advisable. Conflicting results have been reported on the influence of frusemide (furosemide) and influenza vaccines, while data regarding the effect of corticosteroids, benzodiazepines and verapamil on theophylline kinetics are not yet conclusive. Many drugs, however, appear not to significantly affect theophylline clearance. Some are from the same therapeutic group as the drugs mentioned above and offer clinical alternatives for coadministration with theophylline. Examples of drugs not found to have a significant effect on theophylline pharmacokinetics are ranitidine, josamycin, midecamycin, amoxycillin, tetracycline, cephalexin, cefaclor, orciprenaline, metoprolol, antacids, medroxyprogesterone acetate, metoclopramide and metronidazole. Most of the drugs discussed in this review appear not to affect the volume of distribution of theophylline significantly.

Naproxen disposition in patients with alcoholic cirrhosis

Chronic liver disease is known to alter the absorption and disposition of many drugs. To assess the influence of chronic alcoholic liver disease on the disposition of naproxen, we administered the drug both as a single dose and to steady state to 10 individuals with alcoholic cirrhosis and to 10 healthy controls. Plasma and serum samples collected after naproxen dosing were assayed for both total and (following equilibrium dialysis) unbound drug concentration. Clearance calculated based on both total and unbound naproxen concentration revealed no change in total plasma clearance of the drug at steady state but a marked reduction of approximately 60% in clearance based on unbound drug. Naproxen volume of distribution changed only minimally. Because clearance based on unbound drug concentration at a given dosing rate determines the plasma or blood free drug concentration, this concentration may increase significantly in patients with alcoholic liver disease given usual doses of naproxen. Unbound drug concentration is thought to determine the pharmacologic effect of a drug. We therefore recommend that naproxen dosing be reduced by at least half in patients with chronic alcoholic liver disease. In the absence of data to the contrary, this recommendation can be extended to individuals with other forms of hepatic disease.

Effects of probenecid on ketoprofen kinetics

When six normal men took probenecid with ketoprofen in a two-treatment crossover study, steady-state plasma concentrations of ketoprofen and ketoprofen conjugates rose, but plasma protein binding of ketoprofen and urinary excretion of ketoprofen conjugates decreased. Probenecid decreased protein binding of ketoprofen by 28 +/- 7%, total ketoprofen clearance by 67 +/- 11%, clearance of unbound ketoprofen by 74 +/- 10%, clearance of unbound ketoprofen by conjugation by 91 +/- 5%, and renal clearance of ketoprofen conjugates by 93 +/- 4%. An apparent decrease (22 +/- 29%) in unbound ketoprofen clearance by mechanisms other than conjugation might have been established in a study of more than six subjects. Probenecid, which reaches plasma concentrations that approach 100 times those of ketoprofen or its conjugates, appears to inhibit both the conjugation of ketoprofen and the renal excretion of ketoprofen conjugates. An alternative explanation to inhibition of conjugation involves cumulation and subsequent hydrolysis of ketoprofen conjugates as a result of the renal action of probenecid. In addition to the advantages of obtaining simultaneous uricosuric and anti-inflammatory effects, there may be clinical kinetic advantages of administration of probenecid with ketoprofen, because the large interdose concentration swings of ketoprofen are then substantially reduced.

Improved liquid-chromatography of aspirin, salicylate, and salicyluric acid in plasma, with a modification for determining aspirin metabolites in urine

Detailed performance specifications are given for a specific and sensitive liquid-chromatographic assay for aspirin, salicylic acid, and salicyluric acid in plasma. The sensitivity of this method for aspirin (50 micrograms/L) is 10-fold that of previous methods, so that concentrations of aspirin in plasma can now be followed for about four or five half-lives after the peak plasma concentration arising from a single 650-mg dose. In addition, this assay is as sensitive for salicylic and salicyluric acid in plasma as any hitherto. A modification permits measurement of gentisic acid, salicylic acid, and salicyluric acid in urine; further modifications allow indirect measurement of conjugated gentisate and salicylate in urine.

Improved liquid-chromatography of aspirin, salicylate, and salicyluric acid in plasma, with a modification for determining aspirin metabolites in urine

Detailed performance specifications are given for a specific and sensitive liquid-chromatographic assay for aspirin, salicylic acid, and salicyluric acid in plasma. The sensitivity of this method for aspirin (50 micrograms/L) is 10-fold that of previous methods, so that concentrations of aspirin in plasma can now be followed for about four or five half-lives after the peak plasma concentration arising from a single 650-mg dose. In addition, this assay is as sensitive for salicylic and salicyluric acid in plasma as any hitherto. A modification permits measurement of gentisic acid, salicylic acid, and salicyluric acid in urine; further modifications allow indirect measurement of conjugated gentisate and salicylate in urine.

A method for estimating within-individual variability in clearance and in volume of distribution from standard bioavailability studies

Bioavailability studies are commonly undertaken, and most, because they involve subjects taking repeated doses of a drug, contain information on intraindividual variability in pharmacokinetics. However, because in such studies bioavailability itself is unknown, it is difficult to resolve which pharmacokinetic parameters vary within individuals. A mathematical model is presented which permits estimation of variability in clearance and in volume of distribution. When applied to pooled data arising from five theophylline bioavailability studies, this model has given statistical evidence that clearance of theophylline is inherently more variable within individuals (coefficient of variation, 13%) than volume of distribution (8%). As a result, use of the measurement AUC-beta rather than AUC as a more precise index of bioavailability is justified in studies where beta is measured with reasonable precision. The model could be applied to estimation of within-batch within-person variability in bioavailability.

Renal and biliary elimination of vecuronium (ORG NC 45) and pancuronium in rats

The urinary excretion of ORG NC 45 (Vecuronium) and of pancuronium was studied in unanesthetized rats and the biliary excretion was studied in anesthetized rats. Urine and bile were analyzed for unchanged drug by a new and specific mass spectrometric assay. Pancuronium was eliminated primarily in the urine (85% +/- 6% of the dose in 12 hours), but little ORG NC 45 appeared in the urine (3.5% +/- 1.1% in 12 hours). Biliary excretion accounted for 46% +/- 4% of the ORG NC 45 dose in 7 hours, but only 7.5% +/- 5.3% of an injected dose of pancuronium appeared in the bile. Thus, it appears that ORG NC 45 (a monoquaternary ammonium compound) has a higher biliary clearance than pancuronium (a bisquaternary ammonium compound). The different biodisposition of these two compounds may be due to the greater lipophilicity and concomitant enhanced permeability into the hepatocyte of ORG NC 45. We conclude that in the rat elimination of pancuronium is primarily via the kidney whereas elimination of ORG NC 45 is dependent on nonrenal mechanisms.

Pharmacokinetics of Org NC45 (norcuron) in patients with and without renal failure

To determine the influence of renal failure on the pharmacokinetics and neuromuscular blockade of Org NC 45 (Norcuron), a new monoquaternary homologue of pancuronium, 13 patients under halothane and nitrous oxide anesthesia were studied. Org NC 45 was administered by 2-min infusion in doses of 0.28 mg kg-1 (normal renal function group, n = 4) and 0.14 mg kg-1 (renal failure group, n = 5). Four additional patients with normal renal function were given Org NC 45 0.14 mg kg-1 to determine the onset, duration and recovery rate of neuromuscular blockade. The serum concentration of Org NC 45 was determined by normal-phase high performance liquid chromatography (sensitivity 50 ng ml-1), and a two-compartment open pharmacokinetic model was fitted to resulting data. Estimates of distribution half-life (T 1/2 alpha), elimination half-life (T 1/2 beta), volume of distribution at steady state (Vss) and clearance of Org NC 45 did not differ significantly between patients with normal renal function and those with renal failure. The onset, duration and recovery rate times of the neuromuscular blockade by Org NC 45 0.14 mg kg-1 in patients with normal renal function and those with renal failure did not differ significantly.

Ketoprofen-aspirin interactions

To assess an interaction between ketoprofen and aspirin we gave both drugs orally, to steady state, to healthy men. Although ketoprofen did not alter salicylate absorption and disposition, we observed that concurrent administration of aspirin decreased ketoprofen protein binding and increased its plasma clearance. Salicylate also appeared to reduce metabolic ketoprofen conversion to conjugates and their renal elimination. The data suggested that salicylate also enhanced the metabolic conversion of ketoprofen to nonconjugate metabolites (p = 0.091). Our findings indicate that the drug-drug interaction between aspirin and ketoprofen is complex.

Ketoprofen pharmacokinetics and bioavailability based on an improved sensitive and specific assay

A commercial capsule containing 50 mg of ketoprofen (Orudis), a simple capsule containing 50 mg of ketoprofen alone and 50 mg of ketoprofen in an aqueous solution were given as separate doses in a randomized sequence to 12 normal adult males. The areas under the resulting plasma concentration-time curves (AUC) were remarkably consistent for each volunteer. The bioavailability from the commercial capsule relative to that from the solution was 99.7% +/- 10.5% and that from the simple capsule was 102% +/- 10%. After 6 of the volunteers had taken the commercial capsule 6 hourly for thirteen doses, their AUC extrapolated to infinity was significantly higher (by 22%) than that after the single dose indicating, contrary to previous reports, accumulation upon multiple dosing. The interdose AUC after the thirteenth dose was, however, statistically indistinguishable from the AUC-to-infinity after the single dose as might be expected from linear kinetics. The ketoprofen solution generated peak plasma concentrations in only one-third the time (21 +/- 7 min) required for the capsules (commercial, 72 +/- 45; simple, 61 +/- 39 min). Despite plasma concentrations being tracked over a 200-fold range, log linearity was not established within 12 h in any of the 42 profiles obtained. A two-compartment open model was fitted to the solution data giving excellent prediction of the time-to-peak and clearance (Cl/F = 5.2 +/- 1.1l/h) as determined by eye and by log-trapezoidal rule, respectively.

Measurement of excretion characteristics of theophylline and its major metabolites

Analysis of urinary excretion after administration of 320 mg of theophylline to six normal volunteers appears to indicate the occurrence of capacity limited formation of most of the theophylline metabolites and non-linear renal excretion of theophylline. The renal clearance is elevated at high concentrations where the metabolic clearance is reduced. Even though the individual process of elimination is non-linear, the compensating relationship appears to yield a constant total elimination clearance. The implication of these results in chronic therapy and dose adjustment is discussed.

Negligible excretion of unchanged ketoprofen, naproxen, and probenecid in urine

On the average, 0.6% of a dose of ketoprofen or naproxen or 1.2% of a dose of probenecid was found in the urine of normal male volunteers assayed immediately after its collection. Between approximately 60 and 85% of the dose of these drugs can be excreted in the urine as conjugates, which rapidly hydrolyze at body temperature, at room temperature, and even during frozen storage, thereby regenerating the parent drug. Since urine collections involved sample retention in the bladder at 37 degrees for collection intervals as long as 2--3 hr, the given percentages excreted unchanged probably are overestimates. It is possible that no unchanged ketoprofen, naproxen, or probenecid is excreted in urine. This study contrasts with previous reports of up to 50% of a dose of ketoprofen and 15--17% of doses of naproxen and probenecid being excreted in urine as the parent compound. Those reports probably reflect primarily the duration of frozen sample storage between collection and assay along with the urine collection schedules employed the speed of the clinical procedures, and the analytical procedures used. Attention should be given to potential conjugate hydrolysis whenever the pharmacokinetics of carboxylic acids are studied.

Evaluation of the absorption from 15 commercial theophylline products indicating deficiencies in currently applied bioavailability criteria

The bioavailability of theophylline from alcoholic and aqueous oral solutions was compared to that from an intravenous dose in 12 normal adults. The alcoholic elixir surprisingly gave rise to a significantly greater (114 +/- 14%, mean +/- SD) amount absorbed than did the intravenous dose. The aqueous solution (99 +/- 8%) and intravenous dose were statisticlly indistinguishable in this respect, and, furthermore, the extent of absorption from a 300-mg dose of the aqueous solution was 99 +/- 10% of that from a 500-mg dose, and not statistically different. The aqueous solution was thus employed in three subsequent studies as a standard with which to compare 13 different types of theophylline tablets, all marketed in the United States. Of the 13 tablets, eight showed bioavailability statistically distinguishable from that of the standard. Nevertheless, for only two tablets could it be claimed with 95% confidence level that the bioavailability was less than 95%. For none can it be stated at this confidence level that the bioavailability is less than 90%. Bioavailability studies should include criteria of clinical significance in addition to criteria of statistical significance. Contrary to the usual rationale behind choice of a bioavailability standard, nine of the 12 uncoated tablets appeared to allow more rapid absorption of theophylline than did the standard oral solution, an aqueous syrup. Increasing the dose of syrup decreased the rate of theophylline absorption. Orally administered drug solutions may have properties more absorption rate limiting than the disintegration of many brands of tablet.

Gastrointestinal absorption of quinidine from some solutions and commercial tablets

The gastrointestinal absorption of quinidine from three commercially available tablet products has been compared to that from a quinidine sulfate solution previously found to have 70% of the systematic availability of an intravenous dose. Quinidine gluconate solution was included in the study to compare the absorption characteristics of the two quinidine salts. The tablets were given in a counterbalanced sequence preceded by one quinidine solution and followed by the other in a crossover design. The three tablets proved to be equivalent to one another with respect to extent and rate of absorption. The absorption properties of the two solutions were indistinguishable. The tablets were equivalent to the solutions in extent but not in rate of absorption.

Evaluation of the absorption from some commercial enteric-release theophylline products

In a single-dose bioavailability study, Wales, Robinson, Columbia, and Choledyl (Warner/Chilcott) enteric-coated tablets all allowed a bioavailability of theophylline (99% +/- 25%, 102% +/- 23%, 103% +/- 18%, and 98% +/- 15%; mean +/- SD, n = 12) statistically indistinguishable from that of the standard uncoated tablet (Searle 200 mg aminophylline). Only the Wales and Choledyl tablets (7.6, 4.2 hr) could be shown (p < 0.5) to generate a peak plasma theophylline concentration later than the standard (1.4 hr). All tablet brands demonstrated a significant lag time before appearance of theophylline in the plasma, and both Wales and Choledyl tablets also had a (tpeak-tlag) statistically different from that of the standard. Despite misleading indications from the mean plasma profile (plasma concentrations at each sampling time averaged over all subjects), plasma data from the individual participants and in vitro dissolution data show that, while release of theophylline from the Wales tablet might be inordinately slow, this is not a sustained-release preparation. Of the enteric-coated tablets only the Columbia product allowed significant levels in the first sample after dosage. Five of the 18 Columbia doses gave rise to 40-99% of the peak concentration in the 1-hr sample. In vitro, it takes 39 +/- 14 min for 40% of the theophylline content of Columbia tablets to dissolve in simulated intestinal fluid. Suprisingly rapid delivery of an enteric-coated tablet to the duodenum would appear to be required to allow a significant percentage of theophylline to be dissolved and absorbed before 1 hr. None of 12 Columbia tablets tested in vitro, however, allowed dissolution of more than 1.2% of their theophylline content during 1 hr immersion in simulated gastric fluid. Since once in intestinal fluid Columbia tablets appear to dissolve more rapidly than the other enteric products, it is not clear whether the five Columbia tablets in question had imperfections or wheter, in fact, this tablet brand more closely than the others represents the ideal of immediate release once in the duodenum. Plasma samples should be taken as early as 15 min after dosage when evaluating the bioavailability of enteric release products.

Evaluation of the absorption from some commercial sustained-release theophylline products

Absorption of theophylline from three commerical products labeled as sustained release was compared to the absorption from a standard uncoated tablet (Searle 200-mg aminophylline tablet) in a single-dose study. Aminodur tablets (Cooper) and Slophyllin Gyrocap capsules (Dooner) had bioavailability (100.2% +/- 19.8% and 98.5% +/- 13.8%) statistically indistinguishable from that of the standard but showed significantly slower absorption (peak times of 10.4 +/- 2.8 and 4.36 +/- 1.35 hr) and lower peak plasma concentrations (13.9 +/- 4.5 and 22.6 +/- 3.5 micrograms/ml/g dose) than the standard (tpeak, 1.52 +/- 0.45 hr; Cpeak, 28.1 +/- 6.2 micrograms/ml/g dose). The time of the plasma concentration peak (2.47 +/- 1.38 hr) after a dose of Tedral S.A. (Warner/Chilcott) was not statistically different from that after the standard, but both the peak concentration (16.0 +/- 3.9 micrograms/ml/g dose) and availability (76.0 +/- 18.4%) were. Multiple-dose projections from single-dose data indicate that of the three test products only Aminodur maintains reasonably constant interdose plasma levels during 12 hoursly dosing. With an 8 hourly dosing schedule Gyrocaps also might be satisfactory. Reasonable predictions of the plasma concentrations arising from Aminodur doses have been made using a single-compartment body model and assuming input from an outer followed by an inner layer of the tablet.

Convenient and sensitive high-performance liquid chromatography assay for ketoprofen, naproxen and other allied drugs in plasma or urine

A new high-performance liquid chromatography technique enables convenient and rapid assay of ketoprofen and naproxen in biological samples at a sensitivity (10 and 2 ng/ml, respectively in plasma; 20 and 50 ng/ml in urine) far greater than previously available. Superior sensitivity is attributable to the buffered neutral eluent employed, which yields improved separation from material of biological origin. There is no interference from the major ketoprofen and naproxen metabolites tested and excellent reproducibility and accuracy can be maintained. Moreover, the same system can be used to assay probenecid and also shows promise of applicability to ibuprofen, fenoprofen and other members of the aryl-alkanoic acid class of non-steroidal anti-inflammatory agents.

Evaluation of a modified high-performance liquid chromatography assay for acebutolol and its major metabolite

Extensive modification of an existing high-performance liquid chromatography assay for acebutolol and its major metabolite has markedly improved chromatographic stability eliminating the previous need for frequent adjustment of the eluent composition to accommodate continuous loss of column retention. The eluents now used and avoidance of the requirement for elevated column temperature may be significant factors in the ability to maintain column life over 8 months of continuous use with little decrease in retention. As a result of the improved chromatographic stability full advantage can now be taken of automatic injection devices for the unattended processing of large numbers of samples. A significant modification of the work-up of blood samples has improved precision of the assay in whole blood. Nevertheless, it is recommended that plasma samples rather than whole blood be analyzed, since the plasma assay is faster and still more precise.

Quinidine pharmacokinetics in man: choice of a disposition model and absolute bioavailability studies

Parameters describing disposition and absolute oral bioavailability of quinidine were determined in ten normal male volunteers using a specific assay. Various models were compared for their ability to describe the experimental data. An intravenous quinidine gluconate and an oral quinidine sulfate solution were administered (3.74 mg/kg quinidine base). In three subjects the intravenous and oral studies were repeated. One-, two-, and three-compartment models with zero and first-order input were fitted to the plasma concentrations. The selection of the best model was made by the Akaike information criterion and by eye. After intravenous administration, plasma concentration-time curves could be adequately described by a two-compartment model. Mean disposition constants (+/- SD) were obtained from individualized fits (V1: 0.398 +/- 0.336 LITER/KG, Vdarea: 2.53 +/- 0.72 liter/kg, alpha: 0.316 +/- 0.294 min -1, beta: 0.00204 +/- 0.00262 min -1, k2: 0.0305 +/- 0.0101 min -1). A clearance of 4.9 +/- 1.5 ml/min/kg was observed. After oral administration, three-compartment models were needed to describe the observed data in some cases. Absorption was in most cases best described by a zero-order rather than by a first-order process. The time to peak concentration varied from 23 to 121 min, the lag time was always less than 3 min, and the mean elimination rate constant was 0.00171 min -1. The mean oral bioavailability of quinidine was 0.70 +/- 0.17.