Influence of food intake on presystemic clearance of drugs

Many drugs have a low degree of oral bioavailability even though their gastrointestinal absorption is complete. This is because they undergo extensive presystemic metabolic transformation during the first passage of the drug through the gastrointestinal mucosa and the liver. In addition to effects on the absorption of some drugs, food intake has been found to influence the bioavailability of drugs with extensive presystemic metabolic clearance. Extensive presystemic clearance occurs commonly with compounds that are lipophilic bases, e.g. propranolol and amitriptyline, but rarely if ever with lipophilic acids, e.g. salicylic acid and penicillin, except for esters of such acids, e.g. acetylsalicylic acid (aspirin) and pivampicillin. While presystemic clearance of (esterified) acidic drugs is unaffected by food, concurrent food intake markedly reduces presystemic clearance, and thus enhances bioavailability, of several lipophilic bases. Among these are propranolol, metoprolol, labetalol, dixyrazine and hydralazine, which are presystemically metabolised by hydroxylation, glucuronidation and acetylation enzymes systems. In contrast, the bioavailability of lipophilic bases which undergo presystemic dealkylation (amitriptyline, codeine, dextropropoxyphene, prazosin, zimelidine) is unaffected by concurrent food intake. Food intake reduces presystemic clearance of hydralazine and propranolol when these drugs are administered in conventional rapid-release tablets but not when they are given in slow-release formulations. Likewise, coadministration of hydralazine reduces presystemic clearance of rapid-release but not slow-release propranolol. These and other observations favour the view that food may reduce presystemic clearance of (certain) lipophilic basic drugs via transient, complex effects on splanchnic-hepatic blood flow and/or shunt processes, and that the extent of this effect is influenced by the rate of drug delivery to the liver. In addition, these findings refute the notion that the reduced presystemic clearance results from (long-lasting) hepatic enzyme inhibition by some nutrient. On the other hand, repeated intake of specific nutrients (protein) and food contaminants (benzpyrene) can enhance presystemic drug clearance by enzyme induction. Thus, food may exert a dual effect on presystemic drug clearance. A complete evaluation of the influence of food on presystemic drug clearance necessitates bioavailability studies carried out following both single and repeated meals, including different kinds of food prepared by various cooking methods. The influence of food on the presystemic clearance of drugs is most likely to be clinically relevant with drugs having narrow therapeutic margins and/or steep dose-response curves.

Chronic erosive gastritis resulting in cachexia

Nine patients are reported who presented with severe weight loss of up to 13.6 kg (30 lb) as a result of chronic erosive gastritis. In many the cachexia was sufficient to prompt a search for malignancy but no other lesion was found. The importance of the radiological pursuit of this diagnosis is emphasised. Illustrative case histories are presented.

Head injury in the Pacific Northwest

This report describes 451 consecutive patients admitted to a regional trauma center with head injury over 1 year's time. Our results replicate findings from other hospital- and population-based studies of head trauma. Males exceeded females by 3 to 1; the most frequent age of patients was between 15 and 24 years; and motor vehicles were the most common cause of injuries. Mortality was related inversely to Glasgow coma scale (GCS) scores and directly to age. This study also points out two current problems in head trauma research. One is the difficulty in using the GCS in a community with highly sophisticated emergency medical services. In 38% of the patients, one or more GCS components could not be assessed directly. In 17% of cases, GCS scores could not be confidently assigned. This was principally because endotracheal tubes were in place before arrival at the hospital, precluding determination of the verbal response. A second problem is the influence of chronic pre-existing central nervous system conditions on head outcome. Twenty-nine per cent of our patients had one or more such conditions at the time of their injury. Minimal estimates of prevalence ranged from 1% (mental retardation) to 18% (alcoholism).

Successful substitution of rectal metronidazole administration for intravenous use

Wound infection and isolation of anaerobic organisms before and after intravenous and rectal administration of metronidazole were studied in 24 505 surgical patients. In the 6303 patients who underwent "risk" surgery (bowel, biliary, gynaecological, or otolaryngological surgery) introduction of intravenous metronidazole was associated with a striking fall in wound infection and wound anaerobe isolation rates; and the changes were maintained when the majority of metronidazole used was in suppository form. In the 18 202 patients who underwent "clean" surgery (e.g., orthopaedic, ophthalmic, and plastic surgery) metronidazole use was associated with a small formulation-independent change in infection rate without change in anaerobe isolation rates. Without compromising clinical care the use of intravenous metronidazole can be limited to a minority of patients with special needs.

Cimetidine-procainamide pharmacokinetic interaction in man: evidence of competition for tubular secretion of basic drugs

The hypothesis that basic drugs can compete for active tubular secretion by the kidney was tested in six healthy volunteers by comparing the single dose pharmacokinetics of oral procainamide before and during a daily dose of cimetidine. The area under the procainamide plasma concentration-time curve was increased by cimetidine by an average of 35% from 27.0 +/- 0.3 micrograms/ml X h to 36.5 +/- 3.4 micrograms/ml X h. The elimination half-life increased from an harmonic mean of 2.92 to 3.68 h. The renal clearance of procainamide was reduced by cimetidine from 347 +/- 46 ml/min to 196 +/- 11 ml/min. All these results were statistically significant (p less than 0.016). The area under the plasma concentration-time curve for n-acetylprocainamide was increased by a mean of 25% by cimetidine due to a significant (p less than 0.016) reduction in renal clearance from 258 +/- 60 ml/min to 197 +/- 59 ml/min. The data suggests that cimetidine inhibits the tubular secretion of both procainamide and n-acetylprocainamide, and, if so, represents the first documented evidence for this type of drug interaction in man. The clinical implications from this study necessitate dosage adjustments of procainamide in patients being concomitantly treated with cimetidine. The interaction is pertinent not only for basic drugs that are cleared by the kidney, but also for metabolites of basic drugs and endogenous substances which require active transport into the lumen of the proximal tubule of the kidney for their elimination.

Low oral bioavailability of dihydroergotamine and first-pass extraction in patients with orthostatic hypotension

The relative importance of the effect of absorption and first-pass extraction in bioavailability and clinical effectiveness of oraldihydroergotamine (DHE) was examined in six subjects with orthostatic hypotension. Maximum increases in systolic blood pressure of standing subjects occurred within 15 min of intravenous administration (10 micrograms/kg); after 30 min pressure declined linearly with respect to time over the ensuing 3 hr. Plasma DHE concentrations declined biexponentially with respect to time. Mean plasma half-life was 2.15 hr and plasma clearance averaged 862 ml/min. There was no rise in "standing" systolic blood pressure on oral administration (200 to 600 micrograms/kg). Peak plasma concentrations ranged from less than 0.1 to 2 ng/ml. Apparent oral absorption for DHE ranged from 19.5% to 53.3% while systemic bioavailability varied from less than 0.1% to 1.5%. when glyceryl trinitrate was taken orally with DHE, the bioavailability of the latter increased between 56% and 370% over the 0.1% to 1.5% without any apparent alteration in DHE absorption. Standing systolic blood pressure increased 27% (P less than 0.05) 2 hr after the same doses of DHE with glyceryl trinitrate. These findings suggest that the extent of first-pass extraction by the liver is the prime determinant of DHE bioavailability after oral administration and that factors that alter gastrointestinal and portal vein flow to the liver affect its bioavailability.

Toxicity of Saskatoon serviceberry to cattle

Saskatoon serviceberry (Amelanchier alnifolia) twigs were administered to cattle in feed rations and by intraruminal dosing to determine the toxicity of the cyanogenic shrub. When chopped twigs were fed as 75% of the diet, cattle exhibited restlessness, shivering, loss of weight, scours and shortness of breath. Low level dosing experiments indicated a rapid turnover of hydrogen cyanide in the rumen. When potential doses were increased to 5 mg hydrogen cyanide/kg (body weight) progressive stages of poisoning developed rapidly, rumen hydrogen cyanide levels were elevated for at least three hours and the increase in heart rate correlated with the rise in blood hydrogen cyanide concentration.

Assessment of variability among diets of individual deer with the aid of canonical analysis

Canonical analysis was compared with dissimilarity indices for evaluating the food niche of mule deer. Significant differences were found among individual deer primarily in their predilection for shrubs and secondarily in their selection of forbs or grasses. Patterns of selection changed with plant communities, reflecting changing availabilities and possibly associative affects of individual food items. Diets also changed from winter to spring particularly in the relative contribution of forbs. Canonical analysis proved useful for identifying changes in the food niche since, as a multivariate technique, it evaluated complete diets and obviated univariate analysis of each dietary component.