Prospective Study of Liver Function following Repeat Halothane and Enflurane

Pharmacokinetics of obese adults: Not only an increase in weight

Obesity is a pathophysiological state defined by a body mass index > 30 kg/m2 and characterized by an adipose tissue accumulation leading to an important weight increased. Several pathologies named comorbidities such as cardiovascular disease, type 2 diabetes and cancer make obesity the fifth cause of death in the world. Physiological changes impact the four main phases of pharmacokinetics of some drugs and leads to an inappropriate drug-dose. For absorption, the gastrointestinal transit is accelerated, and the gastric empty time is shortened, that can reduce the solubilization and absorption of some oral drugs. The drug distribution is probably the most impacted by the obesity-related changes because the fat mass (FM) increases at the expense of the lean body weight (LBW), leading to an important increase of the volume of distribution for lipophilic drugs and a low or moderately increase of this parameter for hydrophilic drugs. This modification of the distribution may require drug-dose adjustments. By various mechanisms, the metabolism and elimination of drugs are impacted by obesity and should be considered as similar or lower than that non-obese patients. To better understand the necessary drug-dose adjustments in obese patients, a narrative review of the literature was conducted to highlight the main elements to consider in the therapeutic management of adult obese patients.

Comparative tolerability profiles of the inhaled anaesthetics

Improved understanding of the structure/activity relationship of inhaled anaesthetics has resulted in the synthesis of fluorinated compounds which are more potent and less toxic than their unfluorinated antecedents. The toxic effects of inhaled anaesthetics on the liver and kidney are complex but, in general, are related to the extent to which individual inhaled agents are metabolised. Halothane hepatotoxicity is a rare, idiosyncratic reaction which typically occurs in obese women having more than one exposure to the drug within a short time interval. All currently available volatile anaesthetic drugs have depressant effects on the cardiovascular and respiratory systems; arrhythmias are more likely with halothane than with the fluorinated ethers. Cerebral blood flow tends to increase during inhalation anaesthesia, especially with halothane and in the presence of hypercarbia; isoflurane may be given sparingly during neurosurgical procedures whilst monitoring its end-tidal concentration. Although the volatile agents tend to cause uterine relaxation they may be given safely in low concentration to avoid awareness during Caesarean section. In general, young children require rather higher concentrations of volatile agents than adults and seem to be less susceptible to organ toxicity. Two relatively new volatile agents, sevoflurane and desflurane, offer some advantages over isoflurane but neither is an "ideal drug'. Sevoflurane interacts with soda-lime to produce a series of degradation products, the most important of which is compound A. Production is greatest during low-flow, closed circuit anaesthesia using high inspired concentrations of the drug. Compound A has nephrotoxic potential in rats but the clinical significance of the interaction between sevoflurane and soda-lime is unclear. Nitrous oxide when given for prolonged periods may cause irreversible bone marrow depression.

Hepatitis following treatments with famotidine and then cimetidine

OBJECTIVE

To report a case of hepatitis induced by two histamine (H2)-receptor blockers, famotidine and cimetidine.

CASE SUMMARY

A 51-year-old obese woman with a duodenal ulcer developed symptomatic, famotidine-induced hepatitis. Other causes for hepatitis were ruled out. Famotidine was discontinued and the patient took omeprazole for a month without incident. Cimetidine therapy was then initiated and shortly thereafter, the patient developed another episode of symptomatic hepatitis that resolved upon drug discontinuation. Two abdominal ultrasound examinations six months apart and an abdominal computed tomography scan obtained later showed what appeared to be a stable, fatty liver.

DISCUSSION

This appears to be the first reported case of clinical hepatitis related to famotidine and the first reported case where clinical hepatitis followed the administration of two different H2-receptor blockers. The fatty liver probably was secondary to obesity and incidental to the hepatitis episodes.

CONCLUSIONS

Famotidine can cause clinical hepatitis, and drug-induced hepatitis can occur after the administration of two different H2-receptor blockers.

Obesity as a risk factor in drug-induced organ injury. III. Increased liver and kidney injury by furosemide in the obese overfed rat

Effects of the diuretic drug furosemide were examined in obese animals to evaluate the hypothesis that organ damage by reactive drug metabolites may be potentiated by this disease. Obese overfed Sprague-Dawley rats that were treated ip with 450 mg/kg furosemide on the basis of total body mass suffered a 58% mortality rate over 24 h. This contrasted with 0% mortality in animals of normal body mass. On the basis of median histopathology scores, organ necrosis was judged to be greater in the liver (2+) and kidneys (1+) of obese rats than in the liver (1+) and kidneys (less than 1+) of normal controls (p less than 0.05). Obese animals demonstrated a fourfold rise in fat mass over controls. The low solubility of furosemide in lipid makes it probable that aggravated drug toxicity in obese rats dosed to total body mass resulted in part from elevated furosemide concentrations in lean body mass. In a subsequent study designed to minimize this possibility, furosemide was administered on the basis of fat-free body mass to equalize initial drug exposure in obese and control rats. Even with this downward dosage adjustment, obese animals suffered increased hepatic necrosis (median score of 2+ versus 0 in treated controls), greater impairment of renal function (plasma creatinine concentration of 2.41 mg/dl versus 0.96 mg/dl in treated controls), and more extensive enzymuria (enzyme excretion 175-300% more elevated than in treated controls). In conclusion, obese rats appear to be at increased risk of furosemide-induced liver and kidney injury due to at least two factors: (1) increased exposure of target organs in lean body mass to furosemide when the dosing of this poorly lipophilic drug was based on total body mass, and (2) increased susceptibility of target organs in lean body mass to furosemide injury when dosing was adjusted downward to reflect fat-free body mass and to equalize initial drug exposure.

Obesity as a risk factor for drug-induced organ injury. VI. Increased hepatic P450 concentration and microsomal ethanol oxidizing activity in the obese overfed rat

The obese overfed rat effectively models many of the pharmacological changes in human obesity. Recent data show that the obese rat is unusually susceptible to liver damage by several metabolically activated drugs that may be more toxic in obese humans. Results of the present study suggest a specific molecular locus for this interaction. In obese rats, P450 content of liver and the microsomal concentration of P450 were elevated 88% and 31%, respectively, over nonobese controls. Increases in microsomal ethanol oxidation were of identical magnitude. The ethanol-inducible form of P450 that is responsible for microsomal ethanol oxidation, P450IIE1, bioactivates several drugs that are shown to cause increased injury in obese rats. Collectively, these findings indicate that specific forms of P450 may become up-regulated in obesity, increasing the risk of a biochemically defined spectrum of drug-induced organ injuries.

Prolonged anaesthesia with isoflurane and halothane. Effects on hepatic function

Hepatic function was assessed pre-operatively and on the first and sixth postoperative days in 40 healthy patients who underwent prolonged maxillofacial surgery with isoflurane or halothane anaesthesia. No major changes were observed in hepatic enzymes or bilirubin. One-stage prothrombin time and Factor VII concentrations decreased on the first postoperative day and this change was more pronounced in the halothane group. The results support the use of isoflurane rather than halothane for prolonged anaesthesia in respect of the synthesising function of the liver.

Hepatotoxicity and death following two enflurane anaesthetics

A 67-year-old woman died with massive fatty change in the liver 41 hours after her second enflurane anaesthetic in 28 days. The clinical features of five previously reported similar deaths are summarised. Possible mechanisms of the hepatotoxicity are reviewed briefly.

Serum fluoride levels in morbidly obese patients: enflurane compared with isoflurane anaesthesia

Obese patients are known to metabolise anaesthetic agents more than patients of normal weight. The extent of this was investigated by the measurement of serum fluoride concentrations in 10 morbidly obese patients undergoing gastroplasty. Five were allocated to receive enflurane and five to receive isoflurane supplemented anaesthesia. The mean peak serum fluoride concentrations after enflurane anaesthesia were greater (22.7 mumol/litre, SE 2.9) than after isoflurane anaesthesia (6.5 mumol/litre, SE 0.6). The mechanisms and implications of this finding are discussed.