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Imipenem is given in combination with cilastatin, a specific inhibitor of the renal enzyme dehydropeptidase-1 that inactivates imipenem. Imipenem has been widely replaced by meropenem. Imipenem has an extremely wide spectrum of activity, including most aerobic and anaerobic Gram-negative, including those expressing extended-spectrum beta-lactamases (ESBLs), and Gram-positive bacteria (but not MRSA). It has no activity against Stenotrophomonas maltophilia, which emerges in some patients treated with imipenem. Acquired resistance is relatively common in Pseudomonas aeruginosa and is starting to emerge in some of the Enterobacteriaceae, including Enterobacter spp., Citrobacter spp. and Proteus spp.
Like potassium, magnesium is one of the major cations of the body responsible for neurotransmission and neuromuscular excitability. Regulation of magnesium balance is mainly by the kidneys.
Hypomagnesaemia may result from failure to supply adequate intake, from excess NG drainage or suctioning or in acute pancreatitis. It is usually accompanied by a loss of potassium. The patient may become confused and irritable, with muscle twitching.
Hypomagnesaemia should also be suspected in association with other fluid and electrolyte disturbances when the patient develops unexpected neurological features or cardiac arrhythmias.
Magnesium sulphate has long been the mainstay of treatment for pre-eclampsia/eclampsia in America, but the practice in the UK until recently has been to use more specific anticonvulsant and antihypertensive agents. A large international collaborative trial shows a lower risk of recurrent convulsions in eclamptic mothers given magnesium sulphate compared with those given diazepam or phenytoin.
Octreotide is an analogue of somatostatin. It is used to provide relief from symptoms associated with carcinoid tumours and acromegaly. It may also be used for the prevention of complications following pancreatic surgery. For patients undergoing pancreatic surgery, the peri- and post-operative administration of octreotide reduces the incidence of typical post-operative complications (e.g. pancreatic fistula, abscess and subsequent sepsis, post-operative acute pancreatitis). Octreotide exerts an inhibiting effect on gallbladder motility, bile acid secretion and bile flow, and there is an acknowledged association with the development of gallstones in prolonged usage.
Ketamine is a non-competitive antagonist of N-methyl-D-aspartate (NMDA) receptors and also binds to mu and kappa opioid receptors. It is licensed as an anaesthetic agent for diagnostic and surgical procedures and is best suited to shorter procedures. It has a role in the ICU as a co-analgesic, with opioid-sparing properties. It has good analgesic properties in subanaesthetic doses. Use of midazolam or another benzodiazepine as an adjunct to ketamine reduces the incidence of emergence reactions.
Ketamine has also been used for treatment of patients with severe asthma, as it has bronchodilating properties, probably deriving from two different mechanisms – firstly, via a central effect inducing catecholamine release, thereby stimulating beta-2 (β2)-adrenergic receptors, and secondly, by inhibition of vagal pathways to produce an anticholinergic effect acting directly on bronchial smooth muscle. Ketamine is metabolized in the liver to an active metabolite – norketamine. This has a potency of around one-third that of ketamine.
Fentanyl is 100 times as potent as morphine. Its onset of action is within 1–2 minutes after IV injection and a peak effect within 4–5 minutes. The duration of action after a single bolus is 20 minutes. The context-sensitive half-life following IV infusion is prolonged because of its large volume of distribution.
Acetazolamide is a carbonic anhydrase inhibitor normally used to reduce intraocular pressure in glaucoma. Metabolic alkalosis may be partially corrected by the use of acetazolamide. The most common cause of metabolic alkalosis on the ICU is usually the result of furosemide administration.
Labetalol is a combined α- and β-adrenoceptor antagonist. The proportion of β-blockade to α-blockade when given orally is 3:1, and 7:1 when given IV. It lowers the blood pressure by blocking α-adrenoceptors in arterioles and thereby reduces the peripheral resistance. Concurrent β-blockade protects the heart from reflex sympathetic drive, normally induced by peripheral vasodilatation.
This glycopeptide antibiotic, like vancomycin, has bactericidal activity against both aerobic and anaerobic Gram-positive bacteria: Staphylococcus aureus, including MRSA, Streptococcus spp., Listeria spp. and Clostridium spp. It is only bacteriostatic for most Enterococcus spp. It does not cause ‘red man’ syndrome through histamine release and is less nephrotoxic than vancomycin. However, due to the variation between patients, effective therapeutic levels for severe infections may not be reached for a number of days using the most commonly recommended dosage schedules. Serum monitoring of pre-dose levels can be undertaken, particularly for severe infections.
In the UK resistance is well recognized in enterococci and coagulase-negative staphylococci and, more worryingly, is now emerging in S. aureus.