What is "fasting" drug administration? On the role of gastric motility in drug absorption

Drug, meal and formulation interactions influencing drug absorption after oral administration. Clinical implications

Drug-drug, drug-formulation and drug-meal interactions are of clinical concern for orally administered drugs that possess a narrow therapeutic index. This review presents the current status of information regarding interactions which may influence the gastrointestinal (GI) absorption of orally administered drugs. Absorption interactions have been classified on the basis of rate-limiting processes. These processes are put in the context of drug and formulation physicochemical properties and oral input influences on variable GI physiology. Interaction categorisation makes use of a biopharmaceutical classification system based on drug aqueous solubility and membrane permeability and their contributions towards absorption variability. Overlaying this classification it is important to be aware of the effect that the magnitudes of drug dosage and volume of fluid administration can have on interactions involving a solubility rate limits. GI regional differences in membrane permeability are fundamental to the rational development of extended release dosage forms as well as to predicting interaction effects on absorption from immediate release dosage forms. The effect of meals on the regional-dependent intestinal elimination of drugs and their involvement in drug absorption interactions is also discussed. Although the clinical significance of such interactions is certainly dependent on the narrowness of the drug therapeutic index, clinical aspects of absorption delays and therapeutic failures resulting from various interactions are also important.

Influence of food and body weight on the pharmacokinetics of penticainide

The pharmacokinetics of penticainide, a class Ic antiarrhythmic drug, was studied in 16 healthy adults (eight males and eight females) after a single 300-mg oral dose in fasting conditions and with a standard meal. Penticainide concentrations in plasma and urine were measured by hplc. The pharmacokinetic parameters of penticainide including Cmax, tmax, AUC and t1/2 were not significantly altered in the presence of food. AUC values (mean +/- sd) were 50.68 +/- 10.8 mg.h.l-1 and 49.52 +/- 9.87 mg.h.l-1 in the absence and presence of food, respectively. However, a significant difference was observed between males and females in both fasting and fed conditions with a higher value of the apparent oral clearance in the second group. The values of apparent oral clearance, expressed in weight-normalized units were 1.33 +/- 0.35 ml.mn-1.kg-1 (male) and 1.93 +/- 0.34 ml.mn-1.kg-1 (female) in fast conditions (P < 0.01) and 1.38 +/- 0.28 ml.mn-1.kg-1 (male) and 1.93 +/- 0.49 ml.mn-1.kg-1 (female) in fed conditions (P < 0.02), respectively. The pharmacokinetics of penticainide is not modified by the presence of food, but an influence of body weight may be considered.

Variability in absorption lag time of pyridoxal phosphate under fasting and pre- and post-meal conditions

Inter-individual variations in the absorption lag time of pyridoxal phosphate were determined after administration of an enteric-coated tablet (EC) or a plain capsule (PC) to 113 healthy volunteers under fasting, pre-meal, and post-meal conditions. The absorption lag time of pyridoxal phosphate was assessed from the urinary excretion of 4-pyridoxic acid after administration of EC and PC. Significantly larger lag times after administration of both formulations were observed under post-meal conditions than under pre-meal conditions (0.477 +/- 0.315 h versus 0.081 +/- 0.086 h for PC and 1.995 +/- 1.345 h versus 1.064 +/- 1.327 h for EC), indicating that the mean gastric emptying rates of both a solution and a tablet were delayed after food intake. The lag time for PC showed little inter-individual variation with (0-1.2 h) or without food (0-0.25 h), whereas that for EC showed markedly large inter-individual variation, from 0.25 to 2.63 h (median, 1.5 h) in the fasting condition, from 0.25 to > 5.5 h (median 0.25 h) under pre-meal conditions, and from 0.25 to > 5.5 h (median 1.25 h) under post-meal conditions. The effect of food on the gastric emptying rate of a solution appears to be almost uniform, whereas that for a tablet is so unpredictable that a reliable absorption rate for an enteric-coated tablet cannot be expected, particularly under pre- and post-meal conditions.

Pharmacokinetic studies in healthy volunteers in the context of in vitro/in vivo correlations

A multitude of in vivo variables can influence systemic drug absorption after intake of an oral formulation. For the measurement of consistent in vivo parameters within and between pharmacokinetic studies it is of primary importance that such variables be recognized. Consequently, as many variables as possible should be eliminated or controlled by proper study designs to prevent (or minimize) their disturbance of in vitro/in vivo correlations. The possible influences of some important variables are elaborated and discussed in this paper. The influences of food can be anticipated and controlled against the background of gastrointestinal physiology with and without food and its interplay with the dosage form. Food, and also posture and exercise, may influence splanchnic-hepatic blood flow which may substantially affect the absorption of drugs with a high first-pass metabolism. The influence of the discussed variables may be modified by the dosage form of a particular drug. Single dose studies are appropriate for studying immediate release formulations and in the development of controlled release formulations. Multiple dose studies are preferred for the formal validation of controlled release formulations.