The effect of phentolamine on basal and pethidine-induced inhibition of gastric emptying in healthy volunteers

Pharmacokinetic considerations in gastrointestinal motor disorders

Although it has been recognised that alterations in gastrointestinal motility, whether induced by physiological or pathological processes, have significant effects on the pharmacokinetics of orally administered drugs, this subject has received inappropriately little attention. Studies relating to this topic have focused on healthy volunteers and animals and have largely been confined to the effects of single drug doses. There is limited information about the effects of disease on pharmacokinetics under steady-state conditions. Changes in gastrointestinal motility may affect the pharmacokinetics of orally administered drugs by altering the rate of delivery, bioavailability or mucosal absorption of the drug. In general the rate of absorption and time taken to achieve maximal plasma concentrations for well absorbed drugs may be modified by changes in gastrointestinal motility, but overall bioavailability is not usually affected. In these cases the therapeutic and clinical effects of the alteration in pharmacokinetics will, therefore, depend on which parameters are important for the action of the drug. For poorly absorbed drugs both the rate of absorption and bioavailability are likely to be altered by changes in gastrointestinal motility. However, the complex effects of food and disease, as well as the properties and formulation of any drug (solubility, ease of dispersion, delayed release formulation) often make the prediction of the magnitude, or even the direction, of any effect difficult to predict. Drugs with direct effects on gastrointestinal motility may influence their own patterns of absorption. In patients with gastrointestinal motility disorders, drugs administered in a controlled release formulation, or those with poor bioavailability, are most likely to have a poorly predictable therapeutic effect. Care should be taken to ensure that the formulation of the drug, its timing of administration in relation to meals and the use of coadministered drugs optimise, or at least ensure consistent absorption.

Inter- and intrasubject variability of gastric emptying in healthy volunteers measured by scintigraphy and paracetamol absorption

1. Inter- and intrasubject variability in the gastric emptying of semisolids and liquids was measured by scintigraphic emptying of radionuclide-labelled semisolid and from paracetamol absorption in ten healthy volunteers of both sexes. 2. The intrasubject variability was not statistically significant for any of scintigraphic or paracetamol absorption parameters. 3. The intersubject variation was significant for all scintigraphic and paracetamol absorption parameters. 4. In women, the gastric emptying rate of semisolid decreased linearly during the menstrual cycle. 5. The lag period and paracetamol absorption parameters were unrelated to the day of the menstrual cycle day. 6. There was no statistically significant relationship between scintigraphic and paracetamol absorption parameters.

The effect of phentolamine on basal and pethidine-induced inhibition of gastric emptying in healthy volunteers

1. The effect of phentolamine 5 mg i.v. on basal and pethidine-induced inhibition of gastric emptying of semisolid TC-99m labelled Chelex-100 resin/oatmeal was studied in ten healthy volunteers. 2. Each volunteer acted as his/her own control. 3. Basal gastric emptying remained unchanged after administration of phentolamine. 4. Administration of phentolamine reversed the pethidine-induced inhibition of gastric emptying.