Enhancement of drug absorption by antacids. An unrecognised drug interaction

The Impact of Diet and Exercise on Drug Responses

It is well known that lifestyle changes can alter several physiological functions in the human body. For exercise and diet, these effects are used sensibly in basic therapies, as in cardiovascular diseases. However, the physiological changes induced by exercise and a modified diet also have the capacity to influence the efficacy and toxicity of several drugs, mainly by affecting different pharmacokinetic mechanisms. This pharmacological plasticity is not clinically relevant in all cases but might play an important role in altering the effects of very common drugs, particularly drugs with a narrow therapeutic window. Therefore, with this review, we provide insights into possible food–drug and exercise–drug interactions to sharpen awareness of the potential occurrence of such effects.

Low Serum Naproxen Concentrations Are Associated with Minimal Pain Relief: A Preliminary Study in Women with Dysmenorrhea

OBJECTIVE

Incomplete pain relief after administration of nonsteroidal anti-inflammatory drugs (NSAIDs) is common, but it is unknown whether malabsorption or heightened metabolism contributes to NSAID resistance. To explain the etiology of NSAID resistance, we evaluated naproxen absorption and metabolism in relation to pain relief in a pilot study of women with dysmenorrhea.

METHODS

During menses, participants completed before and after naproxen ingestion pain assessments. Analgesic effectiveness was calculated as a percent change in pain rating before and after naproxen administration. To evaluate the impact of malabsorption, the correlation between analgesic effectiveness and serum naproxen was analyzed. To identify whether hypermetabolism contributes to NSAID resistance, we also analyzed the metabolite O-desmethylnaproxen.

RESULTS

Serum naproxen and O-desmethylnaproxen concentrations of the dysmenorrheic cohort (N = 23, 126 ± 10 µg/mL, 381 ± 56 ng/mL) and healthy controls (N = 12, 135 ± 8 µg/mL, 355 ± 58 ng/mL) were not significantly different (P > 0.05), suggesting that menstrual pain does not affect drug absorption and metabolism. However, nine dysmenorrhea participants had levels of analgesic effectiveness <30%. Among dysmenorrheic women, analgesic effectiveness was correlated with serum naproxen (r = 0.49, P = 0.019) and O-desmethylnaproxen (r = 0.45, P = 0.032) concentrations. After controlling for other gynecological diagnoses, a multivariate model analysis confirmed that lower serum naproxen concentrations were associated with reduced pain relief (P  = 0.038).

CONCLUSIONS

Our preliminary findings suggest that poor drug absorption contributes to ineffective pain relief in dysmenorrheic women. Future studies should explore whether malabsorption contributes to NSAID resistance for other pain conditions.

Pharmacokinetic analysis of the FAK scaffold inhibitor C4 in dogs

Inhibition of focal adhesion kinase-vascular endothelial growth factor receptor 3 complex by C4 was previously shown to reduce tumor growth alone and synergistically with other chemotherapeutic agents in animal tumor models. Single and multiple dose IV and oral dosing studies were performed in dogs to determine C4 pharmacokinetics. C4 was administered to 4 dogs at 1.25 or 2.50 mg/kg IV, or 7.50 mg/kg oral gavage. Single- (IV and oral) and multiple- (IV) dose pharmacokinetic samples were collected on days 1 and 3 at pre-dose and 0.5, 1, 2, 4, 8, 24, 120, 144, and 168 h post-dose. C4 concentrations were determined using liquid chromatography with tandem mass spectral detection with a limit of quantitation of 2.50 pg/mL. Pharmacokinetics of C4 was characterized by a 3-compartment model with linear distributional and elimination clearances using Phoenix 64 WinNonlin 6.3. Mean C4 plasma concentration-time profiles revealed a triexponential decline following either IV or oral administration, independent of dose with no accumulation. For the 2.5 mg/kg dose, the median half-life was ~21 h. Median C max and area under the curve (AUC0-24) were similar for days 1 and 3. Oral bioavailability for formulations of PBS, TPGS, Maalox(®), and Pepcid(®) was greatest with TPGS (45 %), followed by Maalox(®) (42 %), Pepcid(®) (37 %), and PBS (30 %). The pharmacokinetic study revealed that C4 has linear pharmacokinetics and does not accumulate following multiple-dose administration. Characterization of C4 pharmacokinetics provides a better understanding of the novel targeted agent, which will help facilitate further development of C4.

Drug interactions with oral antidiabetic agents: pharmacokinetic mechanisms and clinical implications

There is a growing epidemic of type 2 diabetes (T2DM), and it is associated with various comorbidities. Patients with T2DM are usually treated with multiple drugs, and are therefore at an increased risk of harmful drug-drug interactions (DDIs). Several potentially life-threatening DDIs concerning oral antidiabetic drugs have been identified. This has mostly been initiated by case reports but, more recently, the understanding of their mechanisms has greatly increased. In this article, we review the pharmacokinetic DDIs concerning oral antidiabetics, including metformin, sulfonylureas, meglitinide analogs, thiazolidinediones and dipeptidyl peptidase-4 inhibitors, and the underlying mechanistic basis that can help to predict and prevent DDIs. In particular, the roles of membrane transporters and cytochrome P450 (CYP) enzymes in these DDIs are discussed.

Chronic kidney disease: pharmacological considerations for the dentist

BACKGROUND

Patients with chronic kidney disease (CKD) represent a challenge for the dentist seeking to prescribe medications. Understanding the medical management of renal insufficiency and the pharmacokinetics of common dental drugs will aid clinicians in safely treating these patients.

TYPES OF STUDIES REVIEWED

The authors reviewed the literature concerning the medical and pharmacological management of CKD. They reviewed the pharmacokinetic effects of drugs described in case reports and research articles and obtained from them recommendations regarding the use of drugs and adjustment of dosages.

CLINICAL IMPLICATIONS

Because CKD is progressive, patients have varying levels of renal function but do not yet have end-stage renal disease. Some drugs that dentists prescribe commonly may worsen a patient's renal function, lead to drug toxicity or both. Managing the care of patients and prescribing medications tailored to their needs begin with a recognition of the patient with renal disease at risk of developing adverse effects. Clinicians can identify these patients from information obtained in their medical histories and from the drugs they may be taking.

CONCLUSIONS

To treat patients with kidney disease, clinicians must recognize those at risk, have knowledge of the pharmacokinetic changes that occur and recognize that adjustment of drug dosages often is needed.

Pharmacology of morphine in obese patients: clinical implications

Morphine is an analgesic drug used to treat acute and chronic pain. Obesity is frequently associated with pain of various origins (e.g. arthritis, fibromyalgia, cancer), which increases the need for analgesic drugs. Obesity changes drug pharmacokinetics, and for certain drugs, specific modalities of prescription have been proposed for obese patients. However, scant data are available regarding the pharmacokinetics and pharmacodynamics of morphine in obesity. Prescription of morphine depends on pain relief but the occurrence of respiratory adverse effects correlates with obesity, and is not currently taken into account. Variations in the volume of distribution, elimination half-life and oral clearance of morphine, as well as recent advances in the respective roles of drug-metabolizing enzymes, catechol-O-methyltransferase and the mu opioid receptor in morphine pharmacokinetics and pharmacodynamics, may contribute to differences between obese and non-obese patients. In addition, drug-drug interactions may alter the disposition of morphine and its glucuronide metabolites, which may either increase the risk of adverse effects or reduce drug efficacy.

Drug–drug interactions in oncology: Why are they important and can they be minimized?

Adverse drug-drug interactions are a major cause of morbidity and mortality. Cancer patients are at particularly high risk of such interactions because they commonly receive multiple medications, including cytotoxic chemotherapy, hormonal agents and supportive care drugs. In addition, the majority of cancer patients are elderly, and so require medications for co-morbid conditions such as cardiovascular, gastrointestinal, and rheumatological diseases. Furthermore, the age-related decline in hepatic and renal function reduces their ability to metabolize and clear drugs and so increases the potential for toxicity. Not all drug-drug interactions can be predicted, and those that are predictable are not always avoidable. However, increased awareness of the potential for these interactions will allow healthcare providers to minimize the risk by choosing appropriate drugs and also by monitoring for signs of interaction. This review considers the basic principles of drug-drug interactions, and presents specific examples that are relevant to oncology.

Drug dosing in chronic kidney disease

Patients with chronic kidney disease (CKD) are at high risk for adverse drug reactions and drug-drug interactions. Drug dosing in these patients often proves to be a difficult task. Renal dysfunction-induced changes in human pathophysiology regularly results may alter medication pharmacodynamics and handling. Several pharmacokinetic parameters are adversely affected by CKD, secondary to a reduced oral absorption and glomerular filtration; altered tubular secretion; and reabsorption and changes in intestinal, hepatic, and renal metabolism. In general, drug dosing can be accomplished by multiple methods; however, the most common recommendations are often to reduce the dose or expand the dosing interval, or use both methods simultaneously. Some medications need to be avoided all together in CKD either because of lack of efficacy or increased risk of toxicity. Nevertheless, specific recommendations are available for dosing of certain medications and are an important resource, because most are based on clinical or pharmacokinetic trials.

The influence of excipients on the diffusion of ibuprofen and paracetamol in gastric mucus

The aim of this study was to examine the diffusion of commonly administered analgesics, ibuprofen and paracetamol, through gastric mucus. As ibuprofen and paracetamol are often formulated with alkalising excipients, or are commonly co-administered with antacids that have been demonstrated to alter their absorption, diffusion was also studied in the presence of a range of soluble and insoluble antacids or buffering agents. The effect of pH, which has been demonstrated to modify the properties of mucus, was also studied. Mucus was a significant barrier to diffusion for both drugs, compared to an unstirred aqueous layer with diffusion rates significantly lower in the presence of a mucus barrier for both drugs; ibuprofen diffusion also demonstrated a significant increase in the lag time. Paracetamol diffusion was not significantly affected by addition of any antacid, whereas ibuprofen rates were affected and the diffusion lag time for ibuprofen was significantly reduced in all cases. Isolated increases in pH increased the rate and reduced the lag time for ibuprofen diffusion. It was shown that mucus acts as a passive barrier in the case of paracetamol diffusion, and an interactive barrier to ibuprofen diffusion. Changes in mucus viscosity at different pH values may be responsible for the observed changes in ibuprofen diffusion rate.

Enteral Drug Absorption in Patients with Short Small Bowel

Drug therapy may become difficult when a significant amount of the small intestine is resected, as happens in patients with a short small bowel. Drug absorption from the gastrointestinal tract is altered in these patients; however, this effect is variable in patients and differs with each drug. Literature regarding clinical outcomes of normal or alternative administration routes in patients with a short small bowel is limited. We explored what is written about the normal absorption of commonly used drugs and what difference the resection of different but substantial parts of the small intestine makes. Changes in the gastrointestinal tract after resection of >50% of the small intestine causes malabsorption of macronutrients and micronutrients, and may alter the drug absorption process. The metabolic activity of the abundantly present intestinal lactobacilli can also affect the enteral drug absorption in patients with short small bowel as this results in the production of lactic acid, gaseous CO(2), ethanol and an increased bile acid deconjugation. Accelerated intestinal luminal transit time causes a reduction in absorption of certain antimicrobial agents, digoxin, hydrochlorothiazide, ciclosporin, cimetidine, mesalazine (5-aminosalicylic acid), oral contraceptives and levothyroxine. Gastric hypersecretion and lack of sufficient contact time with the intestinal mucosa in patients with short small bowel leads to insufficient absorption of drugs such as omeprazole. Successful treatment with warfarin, tricyclic antidepressants, metronidazole, fluconazole, procainamide, sotalol and pindolol are reported in several studies. Many different factors cause this variability in drug absorption in such patients. Monitoring the serum drug concentration in these patients may ease dealing with the management problems.

Clinically significant drug interactions with cholinesterase inhibitors: a guide for neurologists

Cholinesterase inhibitors are the only pharmacological class indicated for the treatment of mild to moderate Alzheimer's disease. These drugs are also being used off label to treat severe cases of Alzheimer's disease or vascular dementia and other disorders. The widespread use of cholinesterase inhibitors raises the possibility of their use in combination regimens, with the subsequent risk of deleterious drug-drug interactions in high-risk populations. The purpose of this review is to present the possible sources of pharmacokinetic or pharmacodynamic drug-drug interactions involving cholinesterase inhibitors. The four cholinesterase inhibitors (tacrine, donepezil, rivastigmine and galantamine) that are currently available have different pharmacological properties that expose patients to the risk of several types of drug interactions of nonequivalent clinical relevance. The principal proven clinically relevant drug interactions involve tacrine and drugs metabolised by the cytochrome P450 (CYP) 1A2 enzyme, as well as tacrine or donepezil and antipsychotics (which results in the appearance of parkinsonian symptoms). The bioavailability of galantamine is increased by coadministration with paroxetine, ketoconazole and erythromycin. It is of interest to note that because rivastigmine is metabolised by esterases rather than CYP enzymes, unlike the other cholinesterase inhibitors, it is unlikely to be involved in pharmacokinetic drug-drug interactions. Care must be taken to reduce the risk of inducing central (excitation, agitation) or peripheral (e.g. bradycardia, loss of consciousness, digestive disorders) hypercholinergic effects via drug interactions with cholinesterase inhibitors. A review of the literature does not reveal any alarming data but does highlight the need for prudent prescription, particularly when cholinesterase inhibitors are given in combination with psychotropics or antiarrhythmics. Possible interactions involving other often coprescribed antidementia agents (e.g. memantine, antioxidants, cognitive enhancers) remain an open area requiring particularly prudent use.

Review article: over-the-counter drugs and the gastrointestinal tract

An increasing number of drugs are becoming available over-the-counter, empowering patients to treat them- selves. Although drugs presently available over-the-counter are generally safe, there are issues of safety and possible delays in diagnosis of serious conditions. Therefore it is vital that patients are made aware of the indications and limitations of over-the-counter drugs through improved communication and education. Pharmacists and drug companies will have an increasingly important role in giving information and advice to patients. This review looks at the present and future of over-the-counter medication, highlighting the safety aspects.

Altered pharmacokinetics of halofantrine by an antacid, magnesium carbonate

This study investigated the in vitro adsorption of halofantrine (Hf) by some antacids. Magnesium carbonate showed the highest adsorptive effect, the extent of adsorption being up to 83%. Only 4% of Hf adsorbed by the antacid could be eluted with 0.1 M HCl while no detectable elution occurred with water. Other antacids investigated were magnesium trisilicate and aluminium hydroxide and these had Hf-adsorption capacities of 23 and 43%, respectively. The effect of magnesium carbonate on the bioavailability of Hf was evaluated in seven healthy volunteers. The subjects were administered with 500 mg oral dose of Hf-HCl or the same dose of the drug in combination with 1 g of magnesium carbonate, in a crossover fashion. Blood samples were collected at predetermined time intervals and were analysed for Hf and its major metabolite, desbutylhalofantrine (Hfm), using high-performance liquid chromatography method. The results showed that magnesium carbonate significantly prolonged (P<0.05) the time to reach maximum plasma concentration (Tmax) of Hf. Also the maximum plasma concentrations (Cmax) of Hf and Hfm were significantly reduced (P<0.05). Furthermore, there was a reduction in the area under the curve (AUC) values of Hf and this was as high as 56% (range 1-56%). Results of this study suggest that it may not be advisable to concomitantly administer Hf with an antacid like magnesium carbonate.

The effect of pH on the in-vitro dissolution of three second-generation sulphonylurea preparations: mechanism of antacid-sulphonylurea interaction

Simultaneously administered magnesium hydroxide or sodium bicarbonate can increase the rate and extent of absorption of non-micronized glibenclamide and glipizide. To clarify the mechanism of this interaction we have studied the effect of pH on the dissolution of two different formulations of glibenclamide (micronized and non-micronized) and one formulation of glipizide. One tablet of each sulphonylurea preparation was placed in a dissolution chamber containing continuously mixed dissolution medium at pH 2, pH 6 or pH 9; 5 mL of the medium was replaced every 2 min. The amount of glibenclamide dissolved from the non-micronized formulation within 2 h, was 1.2, 4.5 and 76% at pH 2, pH 6 and pH 9, respectively (P < 0.01), whereas 21, 29 and 100% was dissolved from the micronized formulation (P < 0.01). The amount of glipizide dissolved within 2 h at pH 2, pH 6 and pH 9 was 3.9, 24 and 92%, respectively (P < 0.01). We conclude that the elevated pH of the gastric contents is the most likely explanation for the interactions previously demonstrated between antacids and sulphonylureas after their concomitant ingestion.