Influence of food and fluid ingestion on aspirin bioavailability

Rapid identification of potential nonsteroidal anti-inflammatory drug overdose-induced liver toxicity and prediction of follow-up exposure: Integrating bioanalytical and population pharmacokinetic assay

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most frequently used drugs that can cause liver toxicity. The aim of this study was to integrate bioanalytical and population pharmacokinetic (PopPK) assay to rapidly screen and quantify the concentrations of NSAIDs in plasma and monitor clinical safety. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous quantification of acetaminophen (APAP), flurbiprofen (FLB), aspirin (ASP), and ibuprofen (IBP), four commonly used NSAIDs. The PopPK model of the signature toxicant was analyzed based on the published literature. The LC-MS/MS method was successfully validated and applied to determine NSAID concentrations in patient plasma samples. APAP, ASP, and IBP data were best fitted using a one-compartment model, and FLB data were best fitted using a two-compartment model. Bootstrapping and visual predictive checks suggested that a robust and reliable pharmacokinetic model was developed. A fast, simple, and sensitive LC-MS/MS method was developed and validated for determining APAP, FLB, ASP, and IBP in human plasma. Combined with the PopPK model, this method was applied to rapidly analyze the concentrations of NSAIDs in clinical samples from patients presenting to the emergency department with acute liver dysfunction and monitored NSAIDs clinical safety.

Bioavailability of aspirin in fasted and fed states of a novel pharmaceutical lipid aspirin complex formulation

Dyspeptic symptoms are common with aspirin and clinicians frequently recommend that it be taken with food to reduce these side effects. However, food can interfere with absorption, especially with enteric-coated aspirin formulations. We evaluated whether food interferes with the bioavailability of a new, pharmaceutical lipid-aspirin complex (PL-ASA) liquid-filled capsule formulation. In this randomized, open label, crossover study, 20 healthy volunteers fasted for ≥ 10 h and then randomized as either "fasted", receiving 650 mg of PL-ASA, or as "fed", with a standard high-fat meal and 650 mg of PL-ASA 30 min later. After a washout of 7 days, participants crossed over to the other arm. The primary outcome was comparison of PK parameters of the stable aspirin metabolite salicylic acid (SA) between fasted and fed states. Mean age of participants was 36.8 years and 55% were male. The ratios for the fed to fasted states of the primary SA PK parameters of AUC_0-t and AUC_0-∞ were 88.7% and 88.8% respectively, with 90% confidence intervals between 80 and 125%, which is consistent with FDA bioequivalence guidance. Mean peak SA concentration was about 22% lower and occurred about 1.5 h later in the fed state. Food had a modest effect on peak SA levels and the time required to reach them after PL-ASA administration, but did not impact the extent of exposure (AUC) compared with intake in a fasted state. These data demonstrate that PL-ASA may be co-administered with food without significant impact on aspirin bioavailability.Clinical Trial Registration:http://www.clinicaltrials.gov Unique Identifier: NCT01244100.

Effect of aspirin intake at bedtime versus on awakening on circadian rhythm of platelet reactivity

The risk of acute cardiovascular events is highest during morning hours, and platelet activity peaks during morning hours. The effect of timing of aspirin intake on circadian rhythm and morning peak of platelet reactivity is not known. It was our objective to evaluate the effect of timing of aspirin intake on circadian rhythm and morning peak of platelet reactivity. A randomised open-label cross-over trial in healthy subjects (n=14) was conducted. Participants used acetylsalicylic acid (80 mg) on awakening or at bedtime for two periods of two weeks, separated by a four-week wash-out period. At the end of both periods blood was drawn every 3 hours to measure COX-1-dependent (VerifyNow- Aspirin; Serum Thromboxane B2 [STxB2]) and COX-1-independent (flow cytometry surface CD62p expression; microaggregation) platelet activity. VerifyNow platelet reactivity over the whole day was similar with intake on awakening and at bedtime (mean difference: –9 [95 % confidence interval (CI) –21 to 4]). However, the morning increase in COX-1-dependent platelet activity was reduced by intake of aspirin at bedtime compared with on awakening (mean difference VerifyNow: –23 Aspirin Reaction Units [CI –50 to 4]; STxB2: –1.7 ng/ml [CI –2.7 to –0.8]). COX-1-independent assays were not affected by aspirin intake or its timing. Low-dose aspirin taken at bedtime compared with intake on awakening reduces COX-1-dependent platelet reactivity during morning hours in healthy subjects. Future clinical trials are required to investigate whether simply switching to aspirin intake at bedtime reduces the risk of cardiovascular events during the high risk morning hours.

Aspirin as a COX inhibitor and anti-inflammatory drug in human skeletal muscle

Although aspirin is one of the most common anti-inflammatory drugs in the world, the effect of aspirin on human skeletal muscle inflammation is almost completely unknown. This study examined the potential effects and related time course of an orally consumed aspirin dose on the inflammatory prostaglandin E₂ (PGE₂)/cyclooxygenase (COX) pathway in human skeletal muscle. Skeletal muscle biopsies were taken from the vastus lateralis of 10 healthy adults (5 male and 5 female, 25 ± 2 yr old) before (Pre) and 2, 4, and 24 h after (Post) a standard dose (975mg) of aspirin and partitioned for analysis of 1) in vivo PGE₂ levels in resting skeletal muscle and 2) ex vivo skeletal muscle PGE₂ production when stimulated with the COX substrate arachidonic acid (5 μM). PGE₂ levels in vivo and PGE₂ production ex vivo were generally unchanged at each time point after aspirin consumption. However, most individuals clearly showed suppression of PGE₂, but at varying time points after aspirin consumption. When the maximum suppression after aspirin consumption was examined for each individual, independent of time, PGE₂ levels in vivo (184 ± 17 and 104 ± 23pg/g wet wt at Pre and Post, respectively) and PGE₂ production ex vivo (2.74 ± 0.17 and 2.09 ± 0.11pg·mg wet wt^-1·min^-1 at Pre and Post, respectively) were reduced ( P < 0.05) by 44% and 24%, respectively. These results provide evidence that orally consumed aspirin can inhibit the COX pathway and reduce the inflammatory mediator PGE₂ in human skeletal muscle. Findings from this study highlight the need to expand our knowledge regarding the potential role for aspirin regulation of the deleterious influence of inflammation on skeletal muscle health in aging and exercising individuals. NEW & NOTEWORTHY This study demonstrated that orally consumed aspirin can target the prostaglandin/cyclooxygenase pathway in human skeletal muscle. This pathway has been shown to regulate skeletal muscle metabolism and inflammation in aging and exercising individuals. Given the prevalence of aspirin consumption, these findings may have implications for skeletal muscle health in a large segment of the population.

Simultaneous determination of eight B-vitamins in rat intestinal perfusate to identify effects of osmotic pressures on absorptions

A rapid and accurate HPLC-DAD method was developed and validated to simultaneously determine eight B-vitamins (VBs, namely thiamine, riboflavin, niacinamide, calcium pantothenic, pyridoxine, biotin, folic acid and cyanocobalamin) and phenolsulfonphthalein in rat intestinal perfusate. Chromatographic separation was achieved using an Inertsil ODS-3 column (250 × 4.6 mm i.d., 5 μm) at a temperature of 40°C. Gradient elution mode was applied at the flow rate of 1.0 mL/min with the mobile phase of acetonitrile-30 mm K₂ HPO₄ (pH 5.80). The method was successfully applied to identify the effects of osmotic pressures on the absorption of the VBs. The absorption profiles of single and mixed VBs were also compared. Histological section technology was applied to observe the microstructure of small bowel mucosa after perfusion. The results indicated that each compound possessed a better absorption profile under isotonic conditions than under hypotonic or hypertonic conditions for single or mixed solutions. Compared with single VBs, better absorptions in mixed VBs were observed. Pathological tissue slice test suggested that hypotonic and hypertonic solutions changed or damaged the microstructure of mucosa to varying degrees. Taken together, the investigations indicated that multi-VBs administered orally under isotonic condition could generate fast and complete absorption profiles for VBs.

Effects of food on pharmacokinetics of immediate release oral formulations of aspirin, dipyrone, paracetamol and NSAIDs - a systematic review

Aims

It is common to advise that analgesics, and especially non-steroidal anti-inflammatory drugs (NSAIDs), be taken with food to reduce unwanted gastrointestinal adverse effects. The efficacy of single dose analgesics depends on producing high, early, plasma concentrations; food may interfere with this. This review sought evidence from single dose pharmacokinetic studies on the extent and timing of peak plasma concentrations of analgesic drugs in the fed and fasting states.

Methods

A systematic review of comparisons of oral analgesics in fed and fasting states published to October 2014 reporting kinetic parameters of bioavailability, time to maximum plasma concentration (t_max), and its extent (C_max) was conducted. Delayed-release formulations were not included.

Results

Bioavailability was not different between fasted and fed states. Food typically delayed absorption for all drugs where the fasting t_max was less than 4 h. For the common analgesics (aspirin, diclofenac, ibuprofen, paracetamol) fed t_max was 1.30 to 2.80 times longer than fasted t_max. C_max was typically reduced, with greater reduction seen with more rapid absorption (fed C_max only 44–85% of the fasted C_max for aspirin, diclofenac, ibuprofen and paracetamol).

Conclusion

There is evidence that high, early plasma concentrations produces better early pain relief, better overall pain relief, longer lasting pain relief and lower rates of remedication. Taking analgesics with food may make them less effective, resulting in greater population exposure. It may be time to rethink research priorities and advice to professionals, patients and the public.

Effect of water intake on pharmacokinetics of lansoprazole from fast disintegrating tablet in human subjects

Lansoprazole fast disintegrating tablet (LFDT) has been developed as a multiple unit formulation to increase the QOL of patients, i.e., easy intake without water. However, there is a possibility that patients intake LFDT in accordance with clarithromycin and amoxicillin with water. To study the effect of water on the absorption of lansoprazole (LPZ), the study was carried out using human volunteers. After selected by phenotype of LPZ metabolism, extensive metabolizers (EMs) of LPZ were used in this study. Twelve healthy male EMs intook LFDT containing 30 mg LPZ with 150 mL of water and without-water, i.e., with saliva, to study the pharmacokinetics of LPZ from the gastrointestinal tract by a cross-over manner with one-week washout period under fasted condition in the morning. The mean AUC(0-24s) were 2004.4+/-973.6 ng.h/mL in without-water experiment and 2018.5+/-1159.6 ng.h/mL in the case of with-water experiment. Mean C(maxs) were 851.9+/-450.8 ng/mL in without-water experiment and 830.8+/-456.8 ng/mL in with-water experiment, respectively. ANOVA was applied to the log-transformed AUC(0-24) and C(max) values. The 90% two sided confidence intervals for log-transformed AUC(0-24) was 0.78-1.22 and that for log-transformed C(max) was 0.67-1.37, respectively. By comparing these pharmacokinetic parameters, we may state that there was no significant difference between the two administration modes.

[Variance of bioavailability of pharmaceutical preparations and analysis of factors affecting it]

Phenytoin (pulverized powder), mefenamic acid (capsule), and sulpiride (film-coated tablet) are currently available on the Japanese market. For absorption of these drugs from their pharmaceutical preparations, they must disintegrate and dissolve during passage through the gastrointestinal tract. The bioavailability of these drugs differ among different pharmaceutical preparations and even for the same preparation. This led to a review of the influence of the features of pharmaceutical preparations and the physicochemical properties of film coating materials as well as the physiologic factors affecting drug bioavailability. The influence of coadministered drugs and concomitant intake of beverages and food on the bioavailability of drugs from pharmaceutical preparations is also described.

A mechanistic approach to understanding the factors affecting drug absorption: a review of fundamentals

This article provides an overview of the patient-specific and drug-specific variables that can affect drug absorption following oral product administration. The oral absorption of any chemical entity reflects a complex spectrum of events. Factors influencing product bioavailability include drug solubility, permeability, and the rate of in vivo dissolution. In this regard, the Biopharmaceutics Classification System has proven to be an important tool for predicting compounds likely to be associated with bioavailability problems. It also helps in identifying those factors that may alter the rate and extent of drug absorption. Product bioavailability can also be markedly influenced by patient attributes such as the integrity of the gastrointestinal tract, physiological status, site of drug absorption, membrane transporters, presystemic drug metabolism (intrinsic variables), and extrinsic variables such as the effect of food or concomitant medication. Through an awareness of a drug's physicochemical properties and the physiological processes affecting drug absorption, the skilled pharmaceutical scientist can develop formulations that will maximize product availability. By appreciating the potential impact of patient physiological status, phenotype, age, gender, and lifestyle, dosing regimens can be tailored to better meet the needs of the individual patient.

Incomplete thromboxane inhibition with 100 mg of intravenous acetylsalicylic acid in patients with acute ST elevation myocardial infarction: a placebo-controlled pilot trial

BACKGROUND

Acetylsalicylic acid (ASA) is now a standard treatment of acute myocardial infarction (AMI). ASA inhibits thromboxane A(2) (TXA(2)) production by blocking the constitutive cyclooxygenase (COX)-1 enzyme, but only to a small degree the inducible COX-2. COX-2 is induced by increased concentrations of cytokines, which is related to an enhanced inflammatory response. Previously, we have found a complete inhibition of TXA(2) synthesis in healthy volunteers after intravenous administration of 50 mg of ASA. We measured in a randomized, placebo-controlled pilot trial the effect of 100 mg of ASA injected intravenously on TXA(2) synthesis in AMI patients treated with streptokinase.

METHODS AND RESULTS

Nineteen patients with AMI treated with streptokinase were randomized to 100 mg of ASA or placebo injected intravenously. Se-TXB(2) and bleeding time were measured before and after drug administration. One hundred and eighty minutes after intravenous ASA administration, treatment with oral ASA was initiated. We found a significant decrease in serum concentrations of TXB(2) after 30, 60 and 180 min following ASA injection compared to placebo, but in none of the patients was complete inhibition of TXA(2) production achieved. No significant change in bleeding time could be demonstrated.

CONCLUSION

Intravenous ASA in a dosage of 100 mg did not completely prevent TXA(2) production in AMI patients treated with streptokinase. This may be due to synthesis of TXA(2) by the inducible COX-2 enzyme and/or to a transcellular metabolism in platelets of prostanoids generated by endothelial cells.

Methotrexate disposition following concomitant administration of ketoprofen, piroxicam and flurbiprofen in patients with rheumatoid arthritis

The effects of three non-steroidal anti-inflammatory drugs (NSAIDs) on the pharmacokinetics of methotrexate were studied in 10 patients with rheumatoid arthritis. Ketoprofen (3 mg kg-1 day-1), flurbiprofen (3 mg kg-1 day-1), piroxicam (20 mg day-1), or a non-NSAID control (paracetamol/acetaminophen) were administered to patients for at least 6 days (13 days in the case of piroxicam to establish steady state) in a randomized crossover design prior to receiving a weekly oral dose of methotrexate. In the non-NSAID control portion of the study, MTX oral clearance (CLo) was 11.0 +/- 3.9 l h-1, renal clearance (CLR) was 7.9 +/- 2.8 l h-1, percent excreted unchanged was 72 +2- 19% and fraction unbound (fu) was 0.54 +/- 0.11. Values of oral clearance, renal clearance, fraction unbound and percentage excreted unchanged of methotrexate varied no more than 12.2% from non-NSAID control during concomitant administration of ketoprofen, flurbiprofen or piroxicam and were not statistically different from non-NSAID control. In contrast to other NSAIDs such as ibuprofen and salicylates, ketoprofen, flurbiprofen or piroxicam in clinically relevant doses do not appear to affect methotrexate disposition and may be used safely in combination with methotrexate.

The effects of a salicylate, ibuprofen, and naproxen on the disposition of methotrexate in patients with rheumatoid arthritis

We have studied the pharmacokinetics of methotrexate in patients with rheumatoid arthritis concurrently treated with choline magnesium trisalicylate, ibuprofen, naproxen, or a non-NSAID analgesic (control treatment). The apparent systemic clearance of methotrexate was significantly reduced by all three treatments. Trisalicylate and ibuprofen both significantly reduced methotrexate renal clearance, but only the trisalicylate significantly displaced methotrexate from protein, increasing the fraction unbound by 28%. These data show that NSAIDs can affect the disposition of methotrexate, possibly increasing the potential for toxicity and necessitating dosage adjustments. However, large inter-subject variability precludes specific dosage recommendations.

Influence of antacid administrations on aspirin absorption in patients with chronic renal failure on maintenance hemodialysis

In order to investigate the possible interaction between oral aspirin and antacids in uremic patients on chronic hemodialysis, we administered to 5 uremic patients: (1) aspirin alone; (2) aluminum-magnesium hydroxide with aspirin; (3) aluminum-magnesium hydroxide followed (two hours) by aspirin; (4) calcium carbonate simultaneously with aspirin; and (5) calcium carbonate followed (two hours) by aspirin. In all the occasions, aspirin was given two hours after a standard lunch. Both antacid preparations induced comparable changes in aspirin mean peak plasma concentration (Cmax), if given simultaneously with aspirin, whereas no difference was found in other pharmacokinetic parameters. When antacids were followed (two hours) by aspirin, both Cmax and time of maximum concentration (Tmax) were significantly altered in respect to the value with aspirin alone. No changes in the time course of post aspirin serum thromboxane B2 were detected when aspirin and antacids were administered simultaneously, but the inhibition of serum thromboxane B2 was delayed when antacids were followed (two hours) by aspirin. These results indicate that the administration of antacids to uremic patients interferes with absorption of oral aspirin. This interference can be minimized if aspirin and antacids are given simultaneously.

Aspirin in cardiovascular disease

Although other mechanisms may be contributory, the antithrombotic properties of aspirin derive predominantly from its platelet-inhibitory effects. These are mediated via irreversible acetylation of platelet cyclo-oxygenase with subsequent blockade of platelet thromboxane synthesis. Long term administration of doses of aspirin as low as 20mg daily depresses platelet thromboxane formation by more than 90%; however, higher doses appear to be necessary to prevent thromboxane-dependent platelet activation in vivo. While there is evidence of biochemical selectivity with low doses of aspirin, significant reduction of the platelet-inhibitory eicosenoid, prostacyclin, occurs even at dosages ranging from 20 to 40mg daily. The ability of aspirin to prevent the occurrence or recurrence of vaso-occlusion has been extensively investigated. In the secondary prevention of myocardial infarction 7 placebo-controlled trials involving more than 15,000 patients have been completed. The dose of aspirin varied from 300 to 1500mg daily. Although none of the individual trials produced statistically significant reductions in total or coronary mortality, taken together the results are highly suggestive of a beneficial effect of aspirin. Similarly, 2 recent studies in patients with unstable angina demonstrated a protective effect of aspirin against acute myocardial infarction and death. While each study employed widely different doses of aspirin (324mg and 1250mg daily) similar reductions in mortality were reported. The effects of aspirin on the prevention of coronary artery bypass graft occlusion have been evaluated in 9 trials. Aspirin in doses of 100 to 975mg daily was shown to be of benefit in preventing early (less than 6 months) graft occlusion, particularly when therapy was started within 24 hours of operation. In patients with prosthetic vascular grafts of the lower limbs, aspirin has been shown to reduce platelet deposition, however further controlled trials will be required to establish the patient population most likely to benefit and, as in all these studies, the optimum dose of aspirin to employ. In patients with prosthetic heart valves it is clear that aspirin alone is insufficient to prevent thromboembolic complications and when administered as an adjunct to anticoagulant therapy it is associated with a high incidence of bleeding. In contrast, there is convincing evidence from several studies for the efficacy of aspirin in doses of 990 to 1300mg daily in the prevention of stroke and death in patients with transient ischaemic attacks.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of food on ciramadol bioavailability in normal subjects

Eleven healthy volunteers completed a study to compare the relative bioavailability to orally administered ciramadol in a fasting versus postprandial state. A single oral dose of 30 mg of ciramadol was administered on two separate occasions, 2 weeks apart, in a randomized crossover study. A mono- or biexponential pharmacokinetic equation with first-order absorption was applied to analyse the serum data for each subject. Significant differences were found in peak time (tmax) and absorption time (tabs) whereas the mean AUCs for the two modes of administration were not significantly different. The relative bioavailability (F) of the drug when administered in the postprandial state with respect to the fasting state was 96 per cent. It is thus concluded that ingestion of food has no effect on the extent of absorption of ciramadol; however, food may alter its rate of absorption.

Structural identifiability of "first-pass" models

This paper considers the structural identifiability of two compartmental models classically used to describe the pharmacokinetics of drugs orally administered and transformed into a metabolite with a first-pass effect at the hepatic level. The simplest model proves not to be globally identifiable even when plasma and urinary measurements of the drug and metabolite concentrations are made. It admits two sets of admissible solutions, so that a priori knowledge must be introduced to distinguish them. The more complex model appears globally identifiable when blood and urine measurements are made.

Bioavailability of mefenamic acid: influence of food and water intake

The influence of food and water intake on mefenamic acid (N-2,3-xylylanthranilic acid) bioavailability from commercial capsules of high bioavailability was studied in four healthy male volunteers. The drug was administered as a single oral dose of 250 mg, under fasting or nonfasting conditions, and a 4 X 4 Latin-square design was used. Eight blood samples were collected over a 24-h period following drug administration, and the drug plasma concentrations were determined by HPLC. The bioavailability of mefenamic acid from capsules was markedly influenced in the fasting subjects by the water but not by the food intake. A good correlation was found between the bioavailability and amount of water ingested with the drug in the fasting subjects. The area under the plasma concentration-time curve (AUC0-infinity) of mefenamic acid was highest when the capsule was taken with 50 mL of water or immediately after a meal. Increasing the amount of water from 50 to 500 mL in the fasting subjects caused a significant reduction in AUC0-infinity.

A pharmacokinetic approach to the establishment of biopharmaceutic characteristics of different acetylsalicylic acid formulations in man

Eleven acetylsalicylic acid (ASA) formulations were administered to 26 healthy volunteers in a cross-over design. The properties of the preparations differed from conventional, effervescent, buffered to buccal. The objectives of this study were: Consideration of the general aspects of a biopharmaceutical study: which parameter for which biopharmaceutic characteristic? Measurement of the kinetic parameters of ASA: first-pass effect, mean residence time, mean appearance time, total body clearance, apparent volume of distribution, half-lives, etc. Comparison of the formulations. Most of the formulations yield mean residence times for ASA of 0.3-1.0 h, which do not differ significantly (p greater than 0.05). For most of the products the first-pass effect is about 40 per cent; the average values of the apparent volume of distribution and whole body clearance, corrected for the first-pass effect, are about 201 and 650 ml min-1, respectively. Peak levels are reached slowly for the buccal formulations, and rapidly for the buffered products. It is difficult, especially for ASA, to characterize the gastro-intestinal absorption with pharmacokinetic model parameters, because the first-pass effect is large and often elimination of ASA is faster than absorption. The model-independent approach has the special advantages of calculating reliable pharmacokinetic parameters, and creating theoretical possibilities to characterize the absorption patterns of the different formulations in a quantitative way. No significant differences in the values of the parameters are found between most of the formulations. The ASA first-pass effect is reasonably constant and buccal application has no advantage. Enteric coating of the outer layer of ASA formulations causes inconsistent absorption and may be categorized under 'artificial mistakes'.

Preparation and analysis of deuterium-labeled aspirin: application to pharmacokinetic studies

Inhibition of endogenous prostacyclin and thromboxane biosynthesis by aspirin is critically dose-dependent in humans. Gastrointestinal and hepatic hydrolysis may limit systemic availability of aspirin, especially in low doses, perhaps contributing to the biochemical selectivity of aspirin. Existing analytical methods do not permit determination of systemic bioavailability when low (less than 100 mg) doses of aspirin are administered. Deuterium-labeled aspirin (2-acetoxy[3,4,5,6-2H4]benzoic acid) was synthesized from salicylic acid by catalytic exchange and subsequent acetylation. Analysis of the compounds as benzyl esters by GC-MS followed extractive alkylation from plasma. Heptadeuterated compounds were used as internal standards. Simultaneous administration of tetradeuterated aspirin intravenously with native aspirin orally to anesthetized dogs permitted kinetic studies of both aspirin and salicylic acid. The sensitivity of the method is superior to published methods using HPLC and, thus, more applicable to studies of low dose aspirin. Pulse administration of stable isotope-labeled aspirin permits detailed and repeated studies of dose-related aspirin pharmacokinetics in humans.

Interactions affecting drug absorption

The influence of drug-drug and drug-food interactions affecting the absorption of orally administered medication is reviewed. Drug-drug interactions can be classified in terms of indirect effects by one drug on gastrointestinal tract physiology influencing the absorption of other drugs, or direct interactions involving altered pH, adsorption, absorption, or chelation. Most, but not all, drug-drug interactions result in reduced or delayed systemic drug availability. Drug-food interactions may result in reduced, delayed, or increased systemic drug availability. The absorption of only a small number of drugs is unaffected by concomitant food intake. The degree of interaction and whether it positively or negatively affects drug absorption depends on a number of factors including the physical and chemical nature of the drug, the formulation, the type of meal, and the time interval between eating and dosing. Mechanisms of drug-food interactions are not well characterised. They clearly involve both direct and indirect factors in a similar fashion to drug-drug interactions, but indirect factors probably predominate. Reduced or delayed drug absorption is generally attributed, at least in part, to delayed stomach-emptying due to food. Increased absorption may also result from delayed stomach-emptying facilitating greater drug dissolution before it passes from the stomach into the small intestine. Increased bioavailability of some drugs, e.g. propranolol, metoprolol and labetalol, may be related to reduced presystemic clearance. The potential clinical implications of drug-drug and drug-food interactions must be taken into account with oral medications in order to minimise variations in systemic drug availability and hence in clinical efficacy.

Drug metabolite concentration-time profiles: influence of route of drug administration

In order to assess the contribution of an active metabolite to the overall pharmacological response following drug administration it is necessary to characterise the metabolite concentration-time profile. The influence of route of drug administration on metabolite kinetics has been investigated by computer simulation. Comparisons between simulated profiles and published concentration-time data have been carried out. A route dependence in metabolite concentration-time curves is readily apparent provided the metabolite kinetics are formation rate limited and the hepatic clearance of drug is greater than 25 l/h (medium to highly cleared). Oral drug administration produces a triphasic metabolite concentration-time profile whereas only two phases are discernable after intravenous drug administration. The magnitude of the difference in maximum metabolite concentration is directly proportional to the hepatic clearance of drug due to first-pass metabolite production. The route dependence in the shape of the metabolite concentration-time curves is most dramatic when the absorption and distribution of drug and the elimination of metabolite is rapid. A reduction in the rate of either of these processes alters the shape of the metabolite concentration-time profile such that the consequence of first-pass metabolite formation may be reduced.

Platelet aggregation and plasma levels of acetylsalicylic acid in stroke patients on long-term treatment with an enteric-coated aspirin formulation

Enteric-coated formulations of acetylsalicylic acid (ASA) should be advantageous in prophylaxis after stroke because they cause fewer gastrointestinal side effects. However, the absorption of unchanged ASA and the effectiveness of these formulations have been questioned, which prompted the present investigation. Fourteen elderly stroke patients on long-term medication with enteric-coated ASA 1.5 g daily and four patients on placebo were studied. When tested with arachidonic acid platelet aggregation was completely inhibited in all ASA subjects whereas it was normal in the controls. Plasma samples, drawn every 1/2 h for 6 h after tablet intake, were analyzed by HPLC. The presence of ASA was short lasting with a mean peak concentration of 55 mumol/l reached after 2-3.5 h. Salicylic acid (SA) appeared later, having a mean peak value of 591 mumol/l after 2.5-6 h. Thus, absorption of ASA as well as inhibition of platelet aggregation were confirmed during long-term medication with enteric-coated ASA.

Pharmacokinetics of aspirin and salicylate in elderly subjects and in patients with alcoholic liver disease

Plasma aspirin, salicylate and salicyluric acid concentrations were monitored in young, elderly and alcoholic subjects after ingestion of a single 1.2 g dose of soluble aspirin. The plasma aspirin, salicylate and unbound salicylate concentration-time profiles varied considerably between individual subjects. Most of the pharmacokinetic parameters derived from these profiles were not significantly different between young subjects, elderly subjects and subjects with alcoholic liver disease. Individual plasma albumin concentrations provided a better index of the unbound plasma salicylate clearances and salicylate plasma protein binding than the age of the subject or the presence of alcoholic liver disease. Highest unbound plasma salicylate concentrations were found in subjects with the lowest plasma albumin concentrations.

Influence of food on aspirin absorption from tablets and buffered solutions

After a standard meal, 12 normal volunteers received three aspirin dosage forms in a single-dose, complete crossover study. The three dosage forms were an unbuffered tablet, an effervescent solution with 16 meq of buffer, and an effervescent solution with 34 meq of buffer. Plasma and urine aspirin, salicylic acid, and salicyluric acid were measured for 10 hr. Significant differences in the absorption kinetics of aspirin were observed, with aspirin from the two solutions being absorbed faster than from the tablet. Urine pH and renal clearance for all three acid compounds were influenced by the buffer during the first 2 hr only. Area under the curve (AUC) and urine accumulation comparisons suggest that 15-20% more aspirin reaches the general circulation after the tablet, but that the total salicylate absorbed is not different. Comparison with an earlier study indicates the solution with 34 meq of buffer is virtually unaffected by the presence of the meal while the solution with 16 meq buffer and the tablet are more slowly absorbed in the nonfasted state.

Systemic availability of acetylsalicylic acid in normal men and women and its effect on in vitro platelet aggregability

The systemic availability of acetylsalicylic acid (ASA) after oral ingestion of 1 g in an effervescent formulation was 16.3 +/- 2.0% and 16.9 +/- 3.2% of the ingested dose in normal women and men, respectively. The average plasma half-life of ASA in each sex was also identical at 18.5 +/- 1.4 and 18.1 +/- 1.2 min, respectively. The inhibitory effect of ASA on collagen-induced platelet aggregation in vitro on blood from both sexes was studied. The IC50 was 23.9 +/- 2.9 micrograms/ml in females and 22.5 +/- 2.7 micrograms/ml in males, which did not differ significantly. The inhibition by salicylic acid (SA) of the antiaggregatory effect of ASA was similar in both sexes with increases in IC50 to 33.5 +/- 5.1 micrograms/ml in females (p less than 0.02) and to 29.5 +/- 3.8 micrograms/ml in males (p less than 0.05). It is concluded that the observed sex-difference in the antithrombotic effect of ASA cannot be explained neither by differences between females and males in the pharmacokinetic properties of ASA after oral ingestion, nor by differences in the in vitro effect of ASA on the platelet aggregation induced by collagen.

Aspirin: plasma concentration and effects

The antithrombotic effect of acetylsalicylic acid is intimately linked to its reactivity. The labile acetyl moiety irreversibly acetylates not only cyclo-oxygenase, but other biological components. The presence off ubiquitous esterases leads to the rapid disappearance of ASA from the body. The pharmacokinetics of ASA is affected by the dosage form used and the presence of food. Despite the absence of a definable relationship between plasma ASA levels and response, recent data would suggest a dose of about 0.5 mg/kg/day adequately suppresses platelet aggregation without affecting prostacyclin formation.

Systemic availability of acetylsalicylic acid in human subjects after oral ingestion of three different formulations

Systemic availability of acetylsalicylic acid (ASA) in normal human subjects after oral ingestion of 1 g in three different formulations was determined by using high-pressure liquid chromatography for ASA assay. For an effervescent, a plain and a sustained release preparation systemic availabilities expressed in percent of the ingested dose were 16.9 +/- 3.2, 8.6 +/- 1.2 and 2.6 +/- 0.4%, respectively. All subjects had clearly measureable amounts of ASA in plasma after oral intake of a sustained release preparation with an average peak concentration of 15 mumol/l. Peak concentration after an effervescent and plain formulation was on the average 80 and 40 mumol/l, respectively. Half-life of ASA in plasma was 18.1 +/- 1.2 min. for the effervescent and 28.7 +/- 5.3 min. for the plain preparation, while the elimination phase was too ill defined for the sustained release formulation. Average plasma half-life of salicylic acid (SA) was similar after the three different administration forms with values between 3.0 and 3.7 hrs. Further, no difference in SA distribution volumes or amounts of SA absorbed was found. The present study demonstrates that oral ingestion of ASA in effervescent, plain and sustained release formulations gives rise to significant amounts of ASA in plasma. Concentrations found indicate that long-term antithrombotic therapy with ASA in a sustained release formulation may be possible.

Salicylamide pharmacokinetics in healthy males: dietary effect

The effect of diet on the absorption, metabolism, and elimination of salicylamide (SAM), in man was studied in five healthy male volunteers. In a three-way cross-over study, 300 mg SAM capsules were administered under fasting, carbohydrate, and lipid diet conditions. Total urinary salicylates, salicylamide glucuronide (SAMG), and salicylamide sulphate (SAMS) were determined at different time intervals. Diet was found to have no significant effect on the extent of SAM absorption or on its apparent elimination half-life. A significant increase (P less than 0.001) in the fraction excreted as SAMS in the lipid diet trial compared to the fasting or carbohydrate trials is observed. In the lipid diet trial, the ratio (R) of the cumulative urinary SAMS/SAMG was found to be 15-3 times the ratio obtained under fasting or carbohydrate diet conditions. The equilibrium solubilities of SAM under physiologic conditions in water (W), simulated intestinal fluid (M), and corn oil (O) were 4.08, and 4.81, and 12.5 mg ml-1, respectively. The equilibrium apparent distribution coefficients KO/W, KO/M, and KM/W were 3.1, 2.6 and 1.18, respectively. The increase in R is probably due to a decrease in free SAM concentration at the absorption site (intestinal mucosa) in the presence of lipids. A model for drug distribution in the gastrointestinal tract during lipid digestion is proposed and discussed.

Influence of food and fluid volume on chlorothiazide bioavailability: comparison of plasma and urinary excretion methods

The bioavailability of chlorothiazide from oral tablets was examined under fasting and nonfasting conditions in healthy male volunteers. Bioavailability was determined from urinary excretion data and plasma chlorothiazide concentrations. Two fasting treatments and one nonfasting treatment yielded similar plasma chlorothiazide profiles, characterized by sharply ascending and descending segments until 12-13 hr postdosing, followed by a prolonged period with variable and erratic chlorothiazide levels. A triexponential function that adequately described mean data from each treatment could not be applied to individual plasma curves because of their variable nature. Chlorothiazide absorption was not influenced by different accompanying water volumes in fasted individuals but was doubled when tablets were administered immediately after a standard meal. Urinary excretion of chlorothiazide correlated well with plasma drug concentrations; 48-hr urinary recovery accounted for 24.7% of a 500-mg dose in nonfasted subjects compared to 12.3 and 14.9% in fasted subjects receiving the drug with 20 and 250 ml of water, respectively. Observed relationships between chlorothiazide dosage and absorption efficiency are consistent with previous suggestions that chlorothiazide absorption from the GI tract is saturable and site specific.

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.

Excretion of salicylic acid into tears following oral administration of aspirin

The concentration of salicylic acid in human tears has been measured by using reverse-phase, high-pressure liquid chromatography. Pharmacokinetic profiles in tears and in plasma have been obtained following oral administration of 650, 1300, and 1950 mg of aspirin in normal subjects. Salicylate excretion in tears is dose-dependent and is proportional to the plasma concentration. Tear and plasma salicylate levels for rheumatology patients on salicylates are also included.

Clinical pharmacokinetics of salicylates: a re-assessment

1 Aspirin is partly hydrolyzed to salicylic acid during absorption. Absorbed aspirin is rapidly hydrolyzed systemically. Salicylic acid elimination kinetics are dependent on drug concentration due to the limited capacity of two major biotransformation pathways: formation of salicyluric acid and of salicylphenolic glucuronide. 2 The time courses of the various pharmacological effects of single doses of aspirin are not directly coincident with the plasma concentrations of either aspirin or salicylic acid but there is reasonably good evidence that the pharmacological effects are related to the concentration of aspirin, salicylic acid, or both. 3 Steady-state plasma salicylate concentrations increase more than proportionally with increasing daily dose; the time required to reach steady state increases with increasing daily dose. Dosage intervals of 8 or even 12 h are usually sufficient to maintain plasma salicylate concentrations in the anti-inflammatory concentration range. Monitoring of plasma salicylate concentrations in this range is facilitated by the relatively small drug concentration fluctuations during a dosing interval at steady-state. 4 Limited data suggest that the pharmacological activity of salicylate is produced by free (unbound) drug. As the plasma protein binding of salicylic acid is concentration-dependent and subject to pronounced interindividual differences, it is preferable, at least in principle, to monitor free rather than total concentrations of salicylate in plasma. Although salicylate concentration in saliva reflects the free rather than total salicylate concentration in plasma or serum, use of saliva for indirect monitoring of plasma salicylate concentrations seems to be impractical for technical reasons.