Age-dependent pulmonary first-pass elimination of propranolol in rats

Challenges and innovations of drug delivery in older age

Both drug delivery performance and various age-related physical, mental and physiological changes can affect drug effectiveness and safety in elderly patients. The many drug delivery systems developed over the years include recent novel transdermal, nasal, pulmonary and orally disintegrating tablets that provide consistent, precise, timely and more targeted drug delivery. Certain drug delivery systems may be associated with suboptimal outcomes in the elderly because of the nature of drug present, a lack of appreciation of the impact of age-related changes in drug absorption, distribution and clearance, the limited availability of pharmacokinetic, safety and clinical data. Polypharmacy, patient morbidity and poor adherence can also contribute to sub-optimal drug delivery systems outcomes in the elderly. The development of drug delivery systems for the elderly is a poorly realised opportunity, with each system having specific advantages and limitations. A key challenge is to provide the innovation that best meets the specific physiological, psychological and multiple drug requirements of individual elderly patients.

Age-dependent changes in first-pass metabolism of acetaminophen in rats

The contribution of gastrointestinal tract (GIT), liver, and lung towards the first-pass metabolism of acetaminophen was examined using 3-week-old, 10-week-old and 1-year-old rats after administration of 30 mg kg-1 doses by intra-arterial, intravenous, intraperitoneal, and oral routes. Plasma concentrations of acetaminophen and its two major metabolites, acetaminophen glucuronide and acetaminophen sulfate, were measured for about 5h after drug administration. Total oral extraction of acetaminophen was extensive in 10-week-old and 1-year-old rats (Eo = 0.46) and the major contribution to the overall first-pass metabolism was due to the GIT (Eg = 0.50-0.53). Oral extraction in 3-week-old rats was minimal (Eo = 0.10) and there did not appear to be an extraction by the GIT (Eg = 0.00). These results suggest that the ability of GIT to metabolize acetaminophen to glucuronide and sulfate is undeveloped in the infant rats. No changes in the contribution of different organs to the first-pass metabolism of acetaminophen was observed 10 weeks after birth. Pharmacokinetic parameters for acetaminophen in infant rats (3-week-old) and 10-week-old rats were similar after drug administration by the intra-arterial and intravenous routes.

Propofol: assay and regional mass balance in the sheep

1. Pharmacokinetic data for propofol, a new intravenous anaesthetic agent, indicate that there may be extensive extrahepatic clearance. This was investigated during intravenous infusions of propofol in adult merino ewes with chronic intravascular cannulae using a newly developed simple and rapid assay for propofol in blood and other biological samples. 2. The assay was based on organic solvent extraction of pH 4.5 buffered blood, urine or tissue homogenate, followed by reverse-phase h.p.l.c. with fluorescence detection. 3. A mean total body clearance of propofol of 3.15 l/min, (SD 0.87 l/min; n = 8) was found, consistent with a high hepatic extraction ratio (overall mean 0.87, SD 0.19; n = 8) and clearance (overall mean 1.12, SD 0.25 l/min; n = 7). The difference between total and hepatic clearances consisted principally of pulmonary clearance, but its extent was variable. 4. Other regional pharmacokinetic data were consistent with propofol distribution into muscle and brain tissues and propofol 'production' by the kidney, probably from a propofol metabolite formed elsewhere. 5. If these data are confirmed in humans then clinical pharmacokinetic data so far derived from peripheral venous blood sampling will require re-evaluation.