The increasing problem of multidrug-resistant Gram-negative bacteria causing severe infections and the shortage of new antibiotics to combat them has led to the re-evaluation of polymyxins. These antibiotics were discovered from different species of Bacillus polymyxa in 1947; only two of them, polymyxin B and E (colistin), have been used in clinical practice. Their effectiveness in the treatment of infections due to susceptible Gram-negative bacteria, including Pseudomonas aeruginosa and Acinetobacter baumannii, has not been generally questioned. However, their use was abandoned, except in patients with cystic fibrosis, because of concerns related to toxicity. We reviewed old and recent evidence regarding polymyxin-induced toxicity by searching Pubmed (from 1950 until May 2005). It was reported in the old literature that the use of polymyxins was associated with considerable toxicity, mainly nephrotoxicity and neurotoxicity, including neuromuscular blockade. However, recent studies showed that the incidence of nephrotoxicity is less common and severe compared to the old studies. In addition, neurotoxic effects of polymyxins are usually mild and resolve after prompt discontinuation of the antibiotics. Furthermore, cases of neuromuscular blockade and apnea have not been reported in the recent literature. New evidence shows that polymyxins have less toxicity than previously reported. The avoidance of concurrent administration of nephrotoxic and/or neurotoxic drugs, careful dosing, as well as more meticulous management of fluid and electrolyte abnormalities and use of critical care services may be some of the reasons for the discrepancy between data reported in the old and recent literature.

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Toxicity of polymyxins: a systematic review of the evidence from old and recent studies

Metabolic error of muscle metabolism after recovery from malignant hyperthermia

The liver is the major site of biotransformation for most opioids. Thus, the disposition of these drugs may be affected in patients with liver insufficiency. The major metabolic pathway for most opioids is oxidation. The exceptions are morphine and buprenorphine, which primarily undergo glucuronidation, and remifentanil, which is cleared by ester hydrolysis. Oxidation of opioids is reduced in patients with hepatic cirrhosis, resulting in decreased drug clearance [for pethidine (meperidine), dextropropoxyphene, pentazocine, tramadol and alfentanil] and/or increased oral bioavailability caused by a reduced first-pass metabolism (for pethidine, dextropropoxyphene, pentazocine and dihydrocodeine). Although glucuronidation is thought to be less affected in liver cirrhosis, and clearance of morphine was found to be decreased and oral bioavailability increased. The consequence of reduced drug metabolism is the risk of accumulation in the body, especially with repeated administration. Lower doses or longer administration intervals should be used to remedy this risk. Special risks are known for pethidine, with the potential for the accumulation of norpethidine, a metabolite that can cause seizures, and for dextropropoxyphene, for which several cases of hepatotoxicity have been reported. On the other hand, the analgesic activity of codeine and tilidine depends on transformation into the active metabolites, morphine and nortilidine, respectively. If metabolism is decreased in patients with chronic liver disease, the analgesic action of these drugs may be compromised. Finally, the disposition of a few opioids, such as fentanyl, sufentanil and remifentanil, appears to be unaffected in liver disease.

Pharmacokinetics of opioids in liver disease.

Commonly used antibacterial agents may be associated with various neurotoxic reactions. Central nervous system toxicities include seizure disorders, encephalopathy, bulging fontanelles, and neuropsychiatric symptoms. These abnormalities have been associated with the use of the penicillins, cephalosporins, sulfonamides, tetracyclines, chloramphenicol, colistin, aminoglycosides, metronidazole, isoniazid, rifampin, ethionamide, cycloserine, and dapsone. Cranial nerve toxicities, such as myopia, optic neuritis, deafness, vertigo, and tinnitus, have been associated with the use of erythromycin, sulfonamides, tetracyclines, chloramphenicol, colistin, aminoglycosides, vancomycin, isoniazid, and ethambutol. Peripheral nerve symptoms consisting of paresthesias, motor weakness, or sensory impairment have been associated with the use of the penicillins, sulfonamides, chloramphenicol, colistin, metronidazole, isoniazid, ethionamide, and dapsone. Neuromuscular blockade has been associated with the use of the tetracyclines, polymyxins, lincomycin, clindamycin, and aminoglycosides. Management generally consists of supportive therapy and immediate discontinuation of therapy with the offending drug.

The neurotoxicity of antibacterial agents.

The major factors controlling intraocular pressure during surgery are the dynamic balance between aqueous humour production in the ciliary body and its elimination via the canal of Schlemm; the autoregulation and chemical control of choridal blood volume; the extraocular muscle tone and vitreous humour volume. Prior to surgical incision of the anterior chamber in open intraocular procedures, a low-normal intraocular pressure is mandatory to avoid the hazards of iris or lens prolapse and vitreous loss associated with sudden decompression. In general, the central nervous system depressant drugs, hypnotics, narcotics, major tranquillizers, volatile anaesthetic agents are associated with a reduction in intraocular pressure, with the exception of ketamine and possibly trichloroethylene.

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Intraocular pressure--physiology and implications for anaesthetic management.

Acute Transient Sialadenopathy during Induction of Anesthesia

Action of succinylcholine on extraocuur muscles and intraocular pressure

WITHIN the last 25 years, with improved methods of examination and treatment and better understanding of the functional alterations, it has become possible to diagnose and treat arterial disease before ischemic tissue is irreparably damaged. Two fundamental lesions of the aorta or its main branches are amenable to surgical correction: aneurysm and occlusive disease. We will consider briefly some aspects of the epidemiology and pathophysiology of arterial disease and at greater length the anesthetic and surgical problems associated with the more commonly treated lesions.

Phiroze B. Sabawala

Papers

Acute Transient Sialadenopathy during Induction of Anesthesia

Action of succinylcholine on extraocuur muscles and intraocular pressure

Surgery of the aorta and its branches.

The action of some antibiotics on the human intercostal nerve-muscle complex.

Action of volatile anesthetics on human muscle preparations.