Effect of food and an antacid on quinidine bioavailability

Factors and dosage formulations affecting the solubility and bioavailability of P-glycoprotein substrate drugs

Introduction: Expression of P-glycoprotein (P-gp) increases toward the distal small intestine, implying that the duodenum is the preferential absorption site for P-gp substrate drugs. Oral bioavailability of poorly soluble P-gp substrate drugs is low and varied but increases with high-fat meals that supply lipoidal components and bile in the duodenum.Areas covered: Absorption properties of P-gp substrate drugs along with factors and oral dosage formulations affecting their solubility and bioavailability were reviewed with PubMed literature searches. An overview is provided from the viewpoint of the 'spring-and-parachute approach' that generates supersaturation of poorly soluble P-gp substrate drugs.Expert opinion: The oral bioavailability of P-gp substrate drugs is difficult to predict because of their low solubility, preferential absorption sites, and overlapping substrate specificities with CYP3A4, along with the scattered intestinal P-gp expression/function. To attain high and steady oral bioavailability of poorly soluble P-gp substrate drugs, physicochemical modification of drugs to improve solubility, or oral dosage formulations that generate long-lasting supersaturation in the duodenum, is preferred. In particular, supersaturable lipid-based drug delivery systems that can increase passive diffusion and/or lymphatic absorption are effective and applicable to many poorly soluble P-gp substrate drugs.

Permeability of blood-brain barrier in macaque model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson disease

Brain bioavailability of drugs developed to address central nervous system diseases is classically documented through cerebrospinal fluid collected in normal animals, i.e., through an approximation as there are fundamental differences between cerebrospinal fluid and tissue contents. The fact that disease might affect brain availability of drugs is almost never considered at this stage although several conditions are associated with blood-brain barrier damage. Building upon our expertise in Parkinson's disease translational research, the present study addressed this gap comparing plasma and cerebrospinal fluid bioavailability of l-3,4-dihydroxyphenylalanine, carbamazepine, quinidine, lovastatin, and simvastatin, in healthy and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated macaques, the gold standard model of Parkinson's disease. The drugs were selected based upon their differential transport across the blood-brain barrier. Interestingly, brain bioavailability of quinidine was decreased while others were unaffected. Pharmacokinetics and pharmacodynamics experiments of drugs addressing Parkinson's disease might thus be performed in healthy animals unless the drugs are known to interact with the organic cation transporter.

Food-drug interactions

Interactions between food and drugs may inadvertently reduce or increase the drug effect. The majority of clinically relevant food-drug interactions are caused by food-induced changes in the bioavailability of the drug. Since the bioavailability and clinical effect of most drugs are correlated, the bioavailability is an important pharmacokinetic effect parameter. However, in order to evaluate the clinical relevance of a food-drug interaction, the impact of food intake on the clinical effect of the drug has to be quantified as well. As a result of quality review in healthcare systems, healthcare providers are increasingly required to develop methods for identifying and preventing adverse food-drug interactions. In this review of original literature, we have tried to provide both pharmacokinetic and clinical effect parameters of clinically relevant food-drug interactions. The most important interactions are those associated with a high risk of treatment failure arising from a significantly reduced bioavailability in the fed state. Such interactions are frequently caused by chelation with components in food (as occurs with alendronic acid, clodronic acid, didanosine, etidronic acid, penicillamine and tetracycline) or dairy products (ciprofloxacin and norfloxacin), or by other direct interactions between the drug and certain food components (avitriptan, indinavir, itraconazole solution, levodopa, melphalan, mercaptopurine and perindopril). In addition, the physiological response to food intake, in particular gastric acid secretion, may reduce the bioavailability of certain drugs (ampicillin, azithromycin capsules, didanosine, erythromycin stearate or enteric coated, and isoniazid). For other drugs, concomitant food intake may result in an increase in drug bioavailability either because of a food-induced increase in drug solubility (albendazole, atovaquone, griseofulvin, isotretinoin, lovastatin, mefloquine, saquinavir and tacrolimus) or because of the secretion of gastric acid (itraconazole capsules) or bile (griseofulvin and halofantrine) in response to food intake. For most drugs, such an increase results in a desired increase in drug effect, but in others it may result in serious toxicity (halofantrine).

Effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of quinidine in healthy volunteers

A study was conducted to examine the effect of grapefruit juice on the disposition of quinidine sulfate and changes of QT intervals after oral administration to twelve healthy male volunteers. Participants received two oral doses of quinidine sulfate tablets (400 mg) with 240 mL of water or grapefruit juice, each separated by a 1-week washout period. Plasma samples for analysis of quinidine and its major metabolite, 3-hydroxyquinidine, were collected for a 24-hour period and analyzed by a high-performance liquid chromatography method. For pharmacodynamic data, the electrocardiograms (ECGs) were performed for 12 hours, and the recordings were marked for ECG interval at all blood collection time periods. There was no significant difference in pharmacokinetic parameters of quinidine when administered with grapefruit juice or water, except for time to maximum concentration (tmax), which was 1.6 hours after administration with water and 3.3 hours after administration with grapefruit juice. Administration with grapefruit juice also resulted in a 33% decrease in the area under the concentration-time curve (AUC) of 3-hydroxyquinidine compared with water, but did not increase the AUC of quinidine or change the ratio of AUC of 3-hydroxyquinidine to the AUC of quinidine. Pharmacodynamic parameters, including changes in the rate-corrected QT (QTc) interval, closely paralleled the pharmacokinetic data, in that administration with grapefruit juice led to delayed maximal effect on QTc and reduction in maximal effect. Administration with grapefruit juice therefore delays the absorption of quinidine and inhibits the metabolism of quinidine to 3-hydroxyquinidine.

Effect of drug formulation and feeding on the pharmacokinetics of orally administered quinidine in the horse

Quinidine is the drug of choice for the treatment of cardiac arrhythmias in horses. The plasma concentrations vs. time profiles following oral administration of two formulations of quinidine sulphate, an oral solution and an oral suspension paste, were evaluated in nine horses. They received multiple administrations of the oral solution under fed and non-fed conditions and of the paste under non-fed conditions. A loading dose of 20 mg.kg-1 and a maintenance dose of 10 mg.kg-1 quinidine with dosing interval of 6 h were used. The relative bioavailability of the oral solution under fed conditions in comparison to the solution under non-fed conditions was 75.0 +/- 10.2% for the loading dose and 97.18 +/- 31.66% after the fourth dose. For the paste formulation the relative bioavailability values are not reported, as steady-state levels were not reached. There was a large variation in plasma quinidine levels when the paste formulation was administered. Feeding conditions had a significant influence on the Cmax values after administration of the loading dose. The Tmax values were not affected by food intake. It was concluded that an oral solution has to be preferred because of the variable drug bioavailability from the paste formulation and the poor acceptability of the paste by the horse.

Effects of food and sucralfate on the pharmacokinetics of naproxen and ketoprofen in humans

Compliance to nonsteroidal anti-inflammatory drug therapy can be compromised by gastrointestinal side effects. To overcome this problem, food, antacid, or sucralfate are often co-administered with nonsteroidal anti-inflammatory drugs. Three studies were conducted on three groups of 12 volunteers in order to determine the influence of food or sucralfate on the pharmacokinetics of naproxen and ketoprofen. In a crossover experimental design, the first group received a single dose (50 mg) of ketoprofen with and without sucralfate (2 g). The second group received single (100 mg) and multiple (100 mg twice daily for 5 days) doses of enteric-coated ketoprofen with and without food. The third group received single (500 mg) and multiple (500 mg twice daily) doses of naproxen with and without sucralfate. Multiple blood samples were drawn and analyzed by high-pressure liquid chromatography. Short- and long-term pharmacokinetic parameters were determined. Results in group 1 showed that neither ketoprofen bioavailability nor maximal plasma concentration and time to reach maximal concentration were affected by the administration of sucralfate. However, in group 2 absorption of ketoprofen was markedly affected by food. In the presence of food, maximal plasma concentration decreased from 10.7 to 6.3 micrograms/ml after single-dose administration and 12.1 to 8.0 micrograms/ml after multiple-dose administration. The time to reach maximal plasma concentration was also modified by food, increasing from 2.8 to 7.1 hours after single-dose and 2.8 to 7.6 hours after multiple-dose administration. Food caused a significant decrease in the bioavailability of ketoprofen (over 40 percent) following both single-dose (23.8 versus 13.1 micrograms.hour/ml) and multiple-dose (29.3 versus 16.8 micrograms.hour/ml) administration. Results obtained in group 3 showed that sucralfate reduced the absorption rate constant of naproxen, from 1.7 to 1.2 hours-1 and from 1.5 to 0.7 hour-1 following single- and multiple-dose administration, respectively. However, bioavailability of naproxen was not affected by sucralfate administration. Overall, these studies have shown that sucralfate does not alter the pharmacokinetics of naproxen and ketoprofen; the amount of drug absorbed remains constant. However, plasma concentrations of ketoprofen after single- and multiple-dose administration were greatly affected by food, with a decrease of greater than 40 percent in bioavailability.

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.

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.