Author: W. Gerber, J. D. Steyn, A. F. Kotzé, J. Hamman
Simultaneous oral intake of herbs, supplements, foods and drugs with other drug(s) may result in pharmacokinetic or pharmacodynamic interactions with the latter, pharmacokinetic interactions include the improvement of the bioavailability of a drug (i.e., by enhancing absorption and/or inhibiting metabolism) or prolongation of a drugs plasma level within its therapeutic window (i.e., by decreasing excretion), whereas beneficial pharmacodynamic interactions include additive or synergistic effects, Mechanisms by which pharmacokinetic interactions can cause beneficial effects include enhancement of membrane permeation (e.g., structural changes in the epithelial cell membranes or opening of tight junctions), modulation of carrier proteins (e.g., inhibition of efflux transporters and stimulation of uptake transporters) and inhibition of metabolic enzymes, delivering drugs that are poorly bioavailable in therapeutic levels via alternative routes of administration than parenteral injection, bioavailability, efflux inhibition, pharmacokinetic interactions, tight junction modulation, enzyme inhibition, patients are taking food, herbs, supplements and/or over-the-counter health products together with their prescribed medications, concomitant use of these products may lead to food-drug, herb-drug, supplement-drug and/or drug-drug interactions, Pharmacodynamic interactions mainly involve diverse reactions at receptor sites resulting in antagonistic or synergistic effects as well as causing changes in physiological environments, while pharmacokinetic interactions affect the absorption, distribution, metabolism and excretion of the co-administered agent (e.g., food component, herb, supplement, health product ingredient) and/or co-administered drug, drugs present with poor oral bioavailability include low solubility, extensive pre-systemic metabolism, poor membrane permeability and active efflux transportation, Deliberate inhibition of pre-systemic metabolism or efflux can achieve improved bioavailability and prolonged half-lives of poorly bioavailable drugs with consequently less frequent dosing and a lower total required dose (i.e., inhibition of P-glycoprotein [P-gp], cytochrome P450 [CYP450] and organic anion transporters, in vitro drug absorption enhancing effects of Aloe Vera Gel gel and whole leaf materials were first shown across intestinal epithelial cell (Caco-2) monolayers, which was attributed to opening of tight junctions between adjacent epithelial cells as indicated by a reduction in trans-epithelial electrical resistance. Other publications also reported the ability of aloe materials to increase intestinal membrane permeation of various drugs in vitro, aloe materials were incorporated into solid oral dosage forms (i.e., dual phase spherical bead system), Aloe vera liquid preparations could increase the bioavailability of vitamins in humans when co-administered, Aloe Vera Gel gel could also increase the buccal absorption of the anti-retroviral drug, didanosine, by as much as 11-fold, mechanism responsible for the absorption enhancing effects may be because of increased residence time due to muco-adhesive abilities of aloe gel or that the polysaccharides in aloe are able to weaken the epithelial barrier by dismantling intercellular junctions, aloe vera potential modulation of cimetidine efflux, Aloe vera gel shown to improve ketoprofen diffusion across dermatomed skin, Aloe vera gel polysaccharides inhibit indinavir metabolism in an in vitro LS180 cell model, dietary supplement is defined as oral ingested product that is intended to supplement a persons diet and is not necessarily considered food (e.g., vitamins, minerals, herbs, amino acids), Understanding dietary supplement-drug interactions is especially important as a relatively large number (about 25%) of individuals that make use of dietary supplements on a regular basis, take it with one or more prescription drugs, pharmacokinetic interactions are discussed within the broad categories of food-drug, herb-drug, dietary supplement-drug and drug-drug interactions, Inhibition of efflux transporters and metabolism enzymes by co-administered compounds may lead to increased bioavailability of drugs with poor pharmacokinetic properties. Some of these interactions can potentially be coordinated by including functional excipients (i.e., compound that causes beneficial interaction) with the drug in a dosage form. This technique may even be used to lower the quantity of active drug required per administered dose due to increased bioavailability,
