The effect of desmethylimipramine on the absorption of alcohol and paracetamol

First pass metabolism of ethanol is strikingly influenced by the speed of gastric emptying

BACKGROUND

Ethanol undergoes a first pass metabolism (FPM) in the stomach and liver. Gastric FPM of ethanol primarily depends on the activity of gastric alcohol dehydrogenase (ADH). In addition, the speed of gastric emptying (GE) may modulate both gastric and hepatic FPM of ethanol.

AIMS

To study the effect of modulation of GE on FPM of ethanol in the stomach and liver.

METHODS

Sixteen volunteers (eight men and eight women) received ethanol (0.225 g/kg body weight) orally and intravenously, and the areas under the ethanol concentration time curves were determined to calculate FPM of ethanol. In seven of these subjects, FPM of ethanol was measured after the intravenous administration of 10 mg metoclopramide (MCP) and 20 mg N-butylscopolamine (NBS) in separate experiments to either accelerate or delay GE. GE was monitored sonographically by integration of the antral area of the stomach every five minutes for 90 minutes after oral ethanol intake. In addition, gastric biopsy specimens were taken to determine ADH activity and phenotype, as well as to evaluate gastric histology. Blood was also drawn for ADH genotyping.

RESULTS

GE time was significantly delayed by the administration of NBS as compared with controls (p<0.0001) and as compared with the administration of MCP (p<0.0001). This was associated with a significantly enhanced FPM of ethanol with NBS compared with MCP (p = 0.0004). A significant correlation was noted between GE time and FPM of ethanol (r = 0.43, p = 0.0407). Gastric ADH activity did not significantly correlate with FPM of ethanol.

CONCLUSION

FPM of ethanol is strikingly modulated by the speed of GE. Delayed GE increases the time of exposure of ethanol to gastric ADH and may therefore increase gastric FPM of ethanol. In addition, hepatic FPM of ethanol may also be enhanced as the result of slower absorption of ethanol from the small intestine. Thus a knowledge of GE time is a major prerequisite for studying FPM of ethanol in humans.

The effect of pirenzepine on gastric emptying and salivary flow rate: constraints on the use of saliva paracetamol concentrations for the determination of paracetamol pharmacokinetics

1. The effects of pirenzepine on gastric emptying, salivary flow and saliva paracetamol concentrations were investigated in healthy volunteers. 2. Pirenzepine significantly reduced the area under the saliva flow-time curves (7.29 +/- 3.30 g min-1 h without pirenzepine; 4.19 +/- 2.59 g min-1 h with pirenzepine, P less than 0.01). Pirenzepine had no significant effect on plasma paracetamol Cmax (17.5 +/- 7.8 micrograms ml-1 without pirenzepine; 12.6 +/- 7.7 micrograms ml-1 with pirenzepine), plasma tmax (0.2 h (0.2-0.8 h) without pirenzepine; (0.2 h 0.2-0.8 h) with pirenzepine) and plasma AUC(0.6 h) (32.3 +/- 7.2 micrograms ml-1 h without pirenzepine; 30.3 +/- 6.5 micrograms ml-1 h with pirenzepine). 3. Mean ratios of saliva:plasma paracetamol AUC (1.06 +/- 0.24 without pirenzepine; 1.84 +/- 0.48 with pirenzepine, P less than 0.001) and saliva:plasma paracetamol Cmax (1.7 +/- 1.0 without pirenzepine; 6.5 +/- 2.7 with pirenzepine, P less than 0.01) were significantly increased by pirenzepine pretreatment, but there was a poor correlation between the percentage change in the area under the saliva flow-time curve and the percentage change in saliva paracetamol AUC (r = 0.47, P = 0.21). 4. The findings suggest that a) pirenzepine is a more selective antagonist of the muscarinic receptors in salivary glands than those in gastric smooth muscle and b) caution is required when using saliva paracetamol concentrations to determine the pharmacokinetics of the drug in the presence of other agents which may influence salivary flow rate.

Psychopharmacology in patients with hepatic and gastrointestinal disease

Psychotropic drugs often need to be prescribed to patients who also have pre-existing gastrointestinal (GI) and/or hepatic disease. This paper addresses the effect of GI and hepatic disease on the pharmacokinetics of psychotropic drugs, the effect of psychotropic drugs on pre-existing GI and hepatic diseases, the adverse GI and hepatic effects of psychotropic medications, the effects of GI medications on mental status, and the potential drug interactions between commonly prescribed GI medications and psychotropic drugs. Drug selection and dosage modification based on these considerations should allow safe and effective psychotropic treatment for patients with pre-existing GI and/or hepatic disease.

Hydrocephalus after cerebellar infarction

Images

Epidural anaesthesia does not delay early postoperative gastric emptying in man

The effect of epidural anaesthesia on early postoperative gastric emptying was measured in seven patients, after minor surgery on the extremities. Gastric emptying, estimated indirectly by the rise in serum paracetamol following oral administration of the drug, was not delayed following epidural anaesthesia. It was furthermore demonstrated that gastric emptying was normal or nearly normal when diazepam 15 mg was given orally to the same patients 2 weeks later.

General anaesthesia with halothane and drug absorption. The effect of general anaesthesia with halothane and diazepam on postoperative gastric emptying in man

The effect of general anaesthesia with halothane on postoperative absorption of paracetamol was measured in seven patients, after minor surgery on the extremities. Gastric emptying, estimated indirectly by the rise in serum paracetamol following oral administration of the drug, was significantly delayed after general anaesthesia with halothane compared with gastric emptying when general anaesthesia with halothane was not administered. It was furthermore demonstrated that absorption of paracetamol and therefore gastric emptying were normal or nearly normal when diazepam 15 mg was given orally to the same patients 2 weeks later.

Observations on the relation between alcohol absorption and the rate of gastric emptying

Alcohol (ethanol) is absorbed slowly from the stomach and rapidly from the small intestine, and the rate of its absorption depends on the rate of gastric emptying. When gastric emptying is fast, the absorption of alcohol is fast. When gastric emptying is slow the absorption of alcohol is delayed and peak blood alcohol concentrations are reduced. Alterations of the gastric emptying rate, which may have a physiologic, pharmacologic or pathologic cause, markedly influence the rate of alcohol absorption. The gastric emptying rate makes an important contribution to inter- and intraindividual variations in the rate of alcohol absorption and therefore the timing and magnitude of the acute intoxicating effect of an oral dose of alcohol.

The effect on paracetamol absorption of stimulation and blockade of beta-adrenoceptors

1 The effect of drugs acting on beta-adrenoceptors on the absorption and excretion of paracetamol was studied in 26 volunteers and nine patients with mild hypertension, each subject acting as his/her own control. 2 Isoprenaline given 30 min before paracetamol significantly slowed absorption, the effect being dose related, and blocked by prior administration of propranolol. 3 When isoprenaline was given immediately before the paracetamol, absorption was not altered, although a cardiovascular response was seen. 4 Oral salbutamol also delayed paracetamol absorption. 5 Propranolol given alone increased the rate of paracetamol absorption. 6 These results with the changes in the rate of gastric emptying produced by these agents.

Antidepressant drugs and ethanol: behavioral and pharmacokinetic interactions in mice

The interactions between ethanol and antidepressant drugs (both tricyclics and newer non-tricyclics) were studied in mice. The ability of these drugs to enhance the sedative effects of ethanol at two different doses (3.2 and 4.0 g/kg) was measured. The percentage of mice losing the righting-reflex was used for the lower dose, and the duration of ethanol-induced sleep was used at the higher dose. The relative order of potency was amitriptyline greater than or equal to imipramine > maprotiline = mianserin > desipramine greater than or equal to chlorimipramine > iprindole greater than or equal to alaproclate > norzimelidine greater than or equal to zimelidine. Amitriptyline (60 mg/kg) caused death in all mice when combined with 4.0 g/kg ethanol. Clinically established antidepressants which enhanced ethanol sedation only at doses considerably above therapeutic levels were zimelidine and iprindole. The relative potency of the antidepressants to enhance ethanol sedation is correlated with their inherent sedative properties which are in turn related to their ability to block central 5-HT, alpha-NA, muscarinic and H1-receptors. Amitriptyline (20 mg/kg) was found to increase ethanol plasma levels to 202, 167 and 132% of control values at 30, 60 and 90 min after ethanol administration, respectively. Desipramine, mianserin and alaproclate also increased ethanol plasma levels initially, but to a lesser extent. These findings suggest that in addition to their sedative effect, several antidepressants, particularly amitriptyline, are likely to interact with ethanol by increasing its concentration in plasma.

Alcohol absorption, gastric emptying and a breathalyser

1 The value of a portable breathlyser (Alcometer AE-M2) in the assessment of gastric emptying after alcohol ingestion was investigated by comparing breath and venous blood alcohol concentrations with simultaneous scintigraphic measurements of gastric emptying rate. 2 Alcohol absorption, as determined by the area under the venous blood alcohol concentration-time curve during the first 30 min, correlated with gastric emptying during the same period, implying dependence of the rate of alcohol absorption on gastric emptying rate. 3 There was no correlation between breath and venous alcohol concentrations during the first 15 min after alcohol ingestion, but a significant correlation was observed thereafter. 4 Breath alcohol measurements may be sufficient to detect gross alterations in gastric emptying but measurements of venous blood alcohol are likely to be more reliable.