Pharmacokinetics of tolmetin with and without concomitant administration of antacid in man

Clinically significant drug interactions with antacids: an update

One may consider that drug-drug interactions (DDIs) associated with antacids is an obsolete topic because they are prescribed less frequently by medical professionals due to the advent of drugs that more effectively suppress gastric acidity (i.e. histamine H(2)-receptor antagonists [H2RAs] and proton pump inhibitors [PPIs]). Nevertheless, the use of antacids by ambulant patients may be ever increasing, because they are freely available as over-the-counter (OTC) drugs. Antacids consisting of weak basic substances coupled with polyvalent cations may alter the rate and/or the extent of absorption of concomitantly administered drugs via different mechanisms. Polyvalent cations in antacid formulations may form insoluble chelate complexes with drugs and substantially reduce their bioavailability. Clinical studies demonstrated that two classes of antibacterials (tetracyclines and fluoroquinolones) are susceptible to clinically relevant DDIs with antacids through this mechanism. Countermeasures against this type of DDI include spacing out the dosing interval - taking antacid either 4 hours before or 2 hours after administration of these antibacterials. Bisphosphonates may be susceptible to DDIs with antacids by the same mechanism, as described in the prescription information of most bisphosphonates, but no quantitative data about the DDIs are available. For drugs with solubility critically dependent on pH, neutralization of gastric fluid by antacids may alter the dissolution of these drugs and the rate and/or extent of their absorption. However, the magnitude of DDIs elicited by antacids through this mechanism is less than that produced by H2RAs or PPIs; therefore, the clinical relevance of such DDIs is often obscure. Magnesium ions contained in some antacid formulas may increase gastric emptying, thereby accelerating the rate of absorption of some drugs. However, the clinical relevance of this is unclear in most cases because the difference in plasma drug concentration observed after dosing shortly disappears. Recent reports have indicated that some of the molecular-targeting agents such as the tyrosine kinase inhibitors dasatinib and imatinib, and the thrombopoietin receptor agonist eltrombopag may be susceptible to DDIs with antacids. Finally, the recent trend of developing OTC drugs as combination formulations of an antacid and an H2RA is a concern because these drugs will increase the risk of DDIs by dual mechanisms, i.e. a gastric pH-dependent mechanism by H2RAs and a cation-mediated chelation mechanism by antacids.

Stepwise determination of multicompartment disposition and absorption parameters from extravascular concentration-time data. Application to mesoridazine, flurbiprofen, flunarizine, labetalol, and diazepam

When disposition is monoexponential, extravascular concentration-time (C, t) data yield both disposition and absorption parameters, the latter via the Wagner-Nelson method or deconvolution which are equivalent. Classically, when disposition is multiexponential, disposition parameters are obtained from intravenous administration and absorption data are obtained from extravascular C, t data via the Loo-Riegelman or Exact Loo-Riegelman methods or via deconvolution. Thus, in multiexponential disposition one assumes no intrasubject variation in disposition, a hypothesis that has not been proven for most drugs. Based on the classical two- and three-compartment open models with central compartment elimination, and using postabsorptive extravascular C, t data only, we have developed four equations to estimate k10 when disposition is biexponential and two other equations to estimate k10 when disposition is triexponential. The other disposition rate constants are readily obtained without intravenous data. We have analyzed extravascular data of flurbiprofen (12 sets), mesoridazine (20 sets), flunarizine (5 sets), labetalol (9 sets), and diazepam (4 sets). In the case of diazepam intravenous C, t data were also available for analysis. After disposition parameters had been estimated from the extravascular data the Exact Loo-Riegelman method with the Proost modification was applied to the absorptive extravascular data to obtain AT/VP as a function of time. These latter data for each subject and each drug studied were found to be fitted by a function indicating either simple first-order absorption, two consecutive first-order processes, or zero-order absorption. After absorption and disposition parameters had been estimated, for each set of extravascular data analyzed, a reconstruction trend line through the original C, t data was made. The new methods allow testing of the hypothesis of constancy of disposition with any given drug. There is also a need for new methods of analysis since the majority of drugs have no marketed intravenous formulation, hence the classical methods cannot be applied.

Effects of concurrent sucralfate administration on pharmacokinetics of naproxen

Sucralfate has been reported to protect the gastroduodenal mucosa against a variety of agents and is known to adsorb bile salts. Since gastrointestinal side effects can seriously compromise the efficacy of nonsteroidal anti-inflammatory drug therapy, and since it seems reasonable to assume that sucralfate may adsorb nonsteroidal anti-inflammatory drugs, the influence of sucralfate on the pharmacokinetic parameters of naproxen was assessed in 12 healthy volunteers. To do so, the pharmacokinetic profile of naproxen, administered alone or with sucralfate, singly or repeatedly (twice daily for five days), was compared. No significant difference was observed with any pharmacokinetic parameter between the single administration of naproxen alone or with sucralfate. However, a significantly lower maximum plasma concentration was attained with the repeated administration of naproxen in combination with sucralfate, compared with the repeated administration of naproxen alone. When single- and multiple-dose administration were compared, significant differences were observed in the maximum plasma concentration and the cumulative area under the curve. These results suggest an accumulation of naproxen after five days' administration. This accumulation, however, is not altered by the administration of sucralfate. The results of this study suggest that when naproxen is administered with sucralfate, only a delay in naproxen's absorption may occur, confirmed by a lower maximum plasma concentration, a longer time to reach the maximum plasma concentration, a similar elimination half-life, and equivalence in bioavailability. The clinical importance of such a delay has yet to be proved; however, it is unlikely that the clinical efficacy of naproxen will be altered, since the amount of drug absorbed remains the same.

High-performance liquid chromatographic determination of tolmetin, tolmetin glucuronide and its isomeric conjugates in plasma and urine

A rapid and sensitive analytical procedure is described for the simultaneous measurement of tolmetin (T), tolmetin glucuronide (1 beta-TG) and the isomers of tolmetin glucuronide in plasma and urine. A reversed-phase liquid chromatographic system is used with an ion-pairing mobile phase of methanol-tetrabutylammonium hydrogensulfate buffered to pH 4.5 and kept at a constant temperature of 50 degrees C. Detection is by UV at 313 nm. Plasma (0.5 ml) and urine (0.1 ml) are collected in pre-cooled containers and immediately adjusted to pH 3.0 to minimize TG isomerization and hydrolysis. Samples are then deproteinated with acetonitrile, the supernatant is evaporated to dryness and reconstituted in an acetate buffer (pH 4.5), and 50 microliters are injected onto the system. Using zomepirac as the internal standard, the measurable, linear concentration ranges are 0.05-50 micrograms/ml for T in plasma and 0.025-50 micrograms/ml for T in urine. Chromatographic peaks representing T,1 beta-TG and three isomers of TG were identified, all with retention times less than 10 min. The need for special handling of biological samples is discussed.

Effect of food and various antacids on the absorption of tenoxicam

1 Twelve healthy volunteers received a single oral dose of tenoxicam 20 mg on six occasions separated by 3 weeks. 2 The six occasions were: fasted overnight; postprandial; fasting and 15 ml aluminium hydroxide gel; postprandial and 15 ml aluminium hydroxide gel; fasting and 15 ml aluminium and magnesium hydroxide gel; postprandial and 15 ml aluminium and magnesium hydroxide gel. 3 Twenty plasma samples were collected over 15 days following dosing with tenoxicam. 4 The following kinetic parameters for plasma tenoxicam were compared: peak concentrations, time taken to reach peak concentrations, area under the plasma concentration-time curve (AUC) and half-life of elimination. 5 Food lengthened the time taken to reach peak tenoxicam concentrations (5.82 +/- 4.6 vs 1.84 +/- 1.0 h in the fasting state; P less than 0.02) and marginally reduced the peak concentrations achieved. AUC was not affected by any of the different regimens. 6 These effects of food on tenoxicam bioavailability are unlikely to be of clinical significance during chronic dosing with the drug.

Single dose pharmacokinetics of ketoprofen, indomethacin, and naproxen taken alone or with sucralfate

The effects of sucralfate on the rate and extent of absorption of ketoprofen, indomethacin, and naproxen were investigated in healthy volunteers. Six volunteers each received sucralfate (2 g) half an hour before a ketoprofen (50 mg) capsule, and, on another occasion, a ketoprofen (50 mg) capsule alone according to a 2 X 2 Latin square pattern of administration. The same design was used for studies with indomethacin (50 mg) capsules and naproxen (500 mg) tablets. Sucralfate decreased significantly (p less than 0.05) the maximum plasma concentrations (Cmax) of ketoprofen, indomethacin, and naproxen. Although the time necessary to attain Cmax (tmax) for the three drugs tended to increase, only for indomethacin was this increase significant. Sucralfate decreased significantly the rate of absorption (ka) of naproxen and indomethacin, but not that of ketoprofen; it had no significant effect on the elimination half-life and area under the plasma concentration as a function of time curves (AUC0----infinity) of the three drugs. Sucralfate thus decreases the Cmax and increases the tmax of ketoprofen, indomethacin, and naproxen without affecting their bioavailabilities.

Bioavailability studies with etodolac in dogs and man

The effects of formulation, particle size, coadministration of food, antacids, or antiulcer agents on the bioavailability of etodolac (ULTRADOL, 1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid), a novel non-steroidal anti-inflammatory agent, have been evaluated in dogs and man. The effects of dosage regimen and/or repetitive dosing on bioavailability were also determined. In man, capsule and tablet dosage forms containing micronized etodolac were shown to have a bioavailability (AUC) equal to that of the reference etodolac solution. Etodolac from tablets and capsules was rapidly absorbed since only minor decreases in Cmax and increases in tmax were observed compared to the etodolac solution. In a comparison of regular and micronized etodolac dosage forms, both in dogs and man, similar findings, i.e. no change in AUC but small parallel changes in Cmax and tmax, were noted. Administration of etodolac with food had no effect on etodolac bioavailability in dogs but tended to cause a delay in its absorption. Coadministration of an antacid, magaldrate, or the antiulcer agent, sucralfate, had no effect on the bioavailability of etodolac in dogs, although with the latter, a significant reduction in Cmax was noted. In man, etodolac may be administered as a single bolus dose or in divided (b.i.d.) doses without any loss in bioavailability. With either regimen, on repeat administration for 7 days, no etodolac accumulation was noted.

Comparison of tolmetin kinetics in rheumatoid arthritis and matched healthy controls

We could find no significant differences in the kinetics of tolmetin when comparing five rheumatoid arthritis patients with moderate disease activity with a carefully matched group of normal healthy volunteers. Further, there were no discernible clinically significant differences in the kinetics of tolmetin when comparing a single dose to one week of therapy. These results, although limited by the small number of subjects involved and the large interpatient variability, suggest that it may be possible to extrapolate pharmacokinetic data from normals to patients with moderately active disease.

Clinical use of tolmetin sodium in patients with ankylosing spondylitis: a review

The efficacy and safety of tolmetin sodium in the management of ankylosing spondylitis are presented in a review of published and unpublished data. In both open and controlled clinical studies, tolmetin was superior to placebo and equal to indomethacin in its capacity to relieve pain, inflammation, and other symptoms of ankylosing spondylitis (AS). Objective and subjective assessments showed that both tolmetin sodium and indomethacin provided significant therapeutic benefits to patients with AS. In AS, the two drugs showed similar adverse reaction profiles. Adverse reactions with both drugs were minimal and predominantly affected the gastrointestinal tract; in most cases these symptoms cleared spontaneously without discontinuing the drugs.

Bioavailability of ketoprofen in man with and without concomitant administration of aluminium phosphate

The purpose of this study was to determine whether a concomitant single dose of antacid (aluminium phosphate), or multiple doses of this antacid, administered prior to and with ketoprofen would alter the bioavailability of this non steroidal anti-inflammatory agent. The possible effects of aluminium phosphate were evaluated following administration of ketoprofen alone (Phase I), co-administration of antacid and ketoprofen (Phase II), and antacid for four days before administration of ketoprofen with co-administration on the day of the study (Phase III). There were no significant differences between treatment means for peak plasma concentration, time to peak plasma concentration, and area under the plasma concentration-time curve. The observed differences were due only to individual effects. The results indicate a lack of interaction between ketoprofen and the antacid aluminium phosphate (Phosphalugel).

Pharmacokinetic factors influencing variability in human drug response

It is well recognised that the clinical response to drug administration varies widely between individuals and that most of this variability is pharmacokinetic in origin. In general, variability arises because of inter-individual differences in rates of drug absorption, drug distribution and elimination, either by metabolism or excretion. Variability of drug response is also a consequence of a variety of drug interactions which may influence pharmacokinetic parameters. Among the many factors which are responsible for the variation in human drug response, age is relatively important. As a consequence of impaired metabolism and excretion the inter-individual variation in the kinetic of many drugs is much greater in the elderly. Also the degree of plasma-protein binding, in turn, influences the distribution, action, metabolism and renal excretion of drugs. Thus changes in plasma protein binding of drugs, e.g. in diseased states, may give rise to altered pharmacokinetic and possibly altered drug response. The above factors influencing variability in drug response are discussed with particular reference to examples of non-steroidal antiinflammatory drugs used in the treatment of rheumatic diseases.

Piroxicam pharmacokinetics in man: aspirin and antacid interaction studies

Pharmacokinetic studies with piroxicam, a nonsteroidal antiinflammatory agent, have been carried out following the administration of single and multiple oral doses. A plasma half-life of approximately 45 hours is observed, permitting the use of single daily doses in therapy. Enterohepatic recirculation of drug is suggested by the presence of multiple peaks in plasma concentration curves. Piroxicam is highly bound to serum proteins. The absorption and disposition of piroxicam are unaffected by the concomitant administration of aspirin and antiacids. Salicylate plasma levels are similarly unaffected by piroxicam administration.