Monday, December 17, 2007

Corticosteroids for bacterial meningitis

editorial Greenwood BM. NEJM 2007; 357:2507-08 (editorial) and (same issue)

Mai NTH et al. Dexamethasone in Vietnamese adolescents and adults with bacterial meningitis pp. 2431-2440


Scarborough M et al. Corticosteroids for bacterial meningitis in adults in subSaharan Africa pp. 2441-2450.

The prologue is that meta-analysis in industrialized countries showed that dexamethasone given to children with Hemophilus B type b meningitis before antibiotics reduces sequelae, especially hearing loss (McIntyre PB et al. Jama 1997; 278:925-931. Studies in adults in ind. countries also show a benefit (NEJM 2002; Lancet Inf Dis 2004). A trial of 598 children in Malawi, about one third of whom were infected with the HIV virus, showed "convincing evidence of lack of benefit." Most African pediatricians have accepted the result (Lancet 2002). The study above (Scarborough et al.) of adults age greater than 16 with acute bacterial meningitis given dexamethasone 16 mg bid for four days with ceftriaxone showed no benefit of dexamethasone on any endpoint. In contrast, the study by Mai et al. in Vietnam of 435 persons odler than 14 with .4 mg/kg dexamethasone for 4 days of placebo before ceftriaxone, showed benefits in some analyses on death, hearing loss in treated group (if TB patients are excluded). Notable was the strikingly higher mortality in Africa v. Vietnam (54 v. 11%) possibly due to HIV infection, or a different infection (Str pn in Malawi S. suis in Vietnam). A South American study showed no benefit of dexamethasone, but benefit of glycerol (Clin Infect Dis 2007, author Peltola et al.). Editorial concludes the focus should be on vaccines although dexamethasone might be used in the developed world.

Friday, December 07, 2007

Serotonin syndrome and its differential diagnosis and treatment

Boyer EW, Shannon M. Current Concepts. The Serotonin Syndrome. NEJM 2005; 352:1111-20.

General notes
1. The serotonin syndrome (SS) is not an idiopathic drug reaction but a predictable consequence of excess serotonergic drug stimulation of the CNS and peipheral receptors.

2. It has a spectrum of findings ranging from barely perceptible to lethal.

The classical triad is mental status changes, autonomic hyperactivity and neuromuscular abnormalities. Symptoms can include tremor, diarrhea, delirium, rigidity, shivering, mydriasis, tachycardia, hypertension, and hyperthermia. Inadvertent increase in the dose of a causative drug can provoke a dramatic deterioration.

Drugs and drug combinations include MAOI's, TCA's, SSRI's, opiates, OTC cough suppressants, antibiotics, weight reduction drugs, antiemetics, antimigraine drugs, drugs of abuse, herbal products, drugs that inhibit CYP2D6 and CYP3A4 systems, PAST use of fluoxetine (within 6 weeks), or illegal drug ecstasy. Most cases occur within minutes to hours after initiating a new medicine or increasing a dose. It does not resolve if offending drugs are still given.

Clinical notes: lower extremity hyprereflexia and clonus is much worse than the upper extremity. Horizontal ocular clonus  and opsolclonus may occur. Mutism is not infrequent.  Startle is increased, and repetitive head rotaton may occur. Patients may degenerate into frank shock. Diagnosis: Clonus (inducible, spontaneous or ocular) is the most important finding. The differential includes anticholinergic poisoning, malignant hyperthermia, and NMS which all are differentiated on clinical/historical grounds.

Anticholinergic patients have normal reflexes and "toxidrome" of mydriasis, agitated delirium, dry oral mucosa, hot dry skin, urine retention, absent bowel sounds (always present in SS). Malignant hyperthermia has increasing end tidal CO2 levels, ypertonicity, hyperthermia, and metabolic acidosis, within minutes of exposure to inhalational anesthesia. Skin exam shows mottling, cyanosis juxtaposed to bright red flushing. The skeletal muscles are rigid, and there is areflexia. NMS is an idiopathic reaction to DA agonists with slow onset, bradykinesia, lead pipe rigiditym hyperthermia, fluctuating consciousness and autonomic instability that evolves over hours to days (whereas SS has rapid onset and hyperkinesia).

Management involves removing offending drug, supportive care, control of ANS instability, and occassionally benzodiazepines. Moderately ill patients should aggressively correct CV and respiratory problems and receive 5H2a antagonists. Severely hyperthermic patients (41) should also be sedated, paralyzed and intubated. Benzodiazepines may be life saving. Physical restraints are not advised. The antidote is usually cyproheptadine, giving 12-32 mg over a 24 hour period (initial dose of 12 mg then 2 mg q 2 hours prn, given po, crushed in a Dobhoff). I-m thorazine can be used. Hypertension and tachycardia can be treated with short acting drugs such as esmolol and nitroprusside. Hyperthermia should be treated with nondepolarizing drugs such as vecuronium, NOT succinylcholine. Antipyretics are not indicated since fever is due to muscle activity and the hypothalamic set point is working OK. Propanolol is not indicated as it can cause hypotension and shock, and abolish reflex tachycardia. BCT and dantrolene are not useful (unlike NMS and malignant hyperthermia).

Cyproheptadine can be sedating but that is OK. Chlorpromazine can cause hypotension which is irrelevant.

Sunday, December 02, 2007

Therapy for nerve agent poisoning

Newmark, J. Therapy for nerve agent poisoning. Arch Neurol 2004; 61:649-652

Nerve agents include tabun (GA), sarin (GB), soman (GD), cyclosarin (GF) and VX. All evaporate and are gone within 24 hours, except VX which is oily and the only one which is persistent. VX is the most lethal substance known to man. The drugs were weaponized in Nazi Germany, used by Iraq against Iran in the Iraq-Iran war, and used in 2 subway attacks in Japan in 1994-5.

Clinical scenario-- in a shopping mall, you hear a "pop" and see smoke, your vision dims and nose runs severely. People may collapse, breathing heavily or seizing, with constricted pupils.

The mechanism is similar to organophosphate pesticides, although they are much less fat soluble and therefore more toxic. Theyinhibit AchE, acetylcholinesterase, producing a cholinergic crisis. Most exposures occur through the vapor route and act within seconds to minutes. The initial symptoms are miosis and rhinorhhea and salivation. Later, brochorrhea and bronchospasm occur. They are absorbed at the alveoli, and although they are not important clinically, the gold standard of diagnosis is RBC AChE. Circulating toxin first affects the GIT causing cramping, pain, nausea and defecation. It will affect the heart variably with unpredictable effects on BP and HR. They cause massive overstimulation of peripheral neuromuscular synapses witha progression from fasciculation to twitching that may be misinterpreted as a seizure. When ATP is depleted (a late finding) the patient will eventually have flaccid paralysis. Rapid CND cholinergic stimulation will cause LOC, seizures, inhibition of medullary respiratory center with central apnea. Death is due to respiratory failure (combined) due to bronchospasm, bronchorhhea, inadequate function of respiratorymuscles, and central apnea.

Liquid exposure has a longer slower onset and offset than vapor. Skin decontamination may not suffice if not done immediately, as nerve agent may be trapped subcutaneously and continue to penetrate.

Patients recovered frommild poisoning have a neurobehavioral syndrome including HA, personalitychange, depression, and higher order problemswith memory and reading. It may resemblePTSD or postanoxic encephalopathy. Chronic effects are few, with one report of a PN and a few of vestibular problems.

Ventilatory support can be lifesaving even for someone in full arrest, if an antidote is given. Treatment has not changed since 1945 and includes an anticholinergic drug to counteract crisis, an oxime to reactivate inhibited AChE, and an AED to prevent seizures. In the field,atropine is used with i-m autoinjectorswith an initial therapy of 2,4,or 6 mg with retreatment every 5-10 minutes as needed. 0.5 or 1.0 mg ampules are available for children. In the hospital it may be given intravenously. Atropine binds to muscarinicreceptorsbut not nicotinic receptors, so twitching and dyscoordination will continue. The respiratory problems are life threatening and atropine saves lives,per the Iranian experience.

The fielded oxime is 2-pralidoximm chloride (2 PAM). The i-m dose is 600 mg per autoinjector. The upper limit is 2000 mg/hr due to the risk of sudden elevation of blood pressure. Oximes reactivate catalytic cholinesterase and simultaenously split nerve agent or organophosphate insectisides into harmless, rapidly metabolized fragments. After nerve agent binds AChE , the resultant complex spontaneously loses a side chain ("aging") rendering the remaining enzyme-inhibitor complex unable to be reactivated by oxime. Most nerve agents age slowly and the reaction can be ignores (sarin over hours, VX over days to weeks) but soman over two minutes. Once the complex has aged, the oximes are useless although not harmful to the patient.

The MARK 1 set (Meridian Medical Technologies, Columbia, MS) has a 2 mg atropine and 600 mg 2-PAM autoinjectors and is already approved by the FDA for the general use.

Standard AED's (antiepileptic drugs) are not useful for seizures due to nerve agents. Only benzodiazepines are effective. The military uses diazepam 10mg autoinjectors. Midazolam is the most effective, given i-v, in terms of speed of actions, low dose required, and broad spectrum. Epilepsy does not develop and chonic AED's are not advised.

The fourth drug available is pyridostigmine bromide, which may be useful if soldiers are concerned about a rapidly aging poison (soman) . Pyridostigmine will sequester a percentage of the patients excess AChE and render it unavailable to be irreversibly inhibited by a a nerve agent. Therefore a lethal dose becomes survivable with antidotes.

Care must be provided inthe field, not in the hospital (too late). Additional information is available at the chemical casualty division website at or the Army Medical Research Institute of Chemical Defense at (410) 436-3276.

Multiple auras: clinical significanceand pathophysiology

Widdiss-Walsh P, Kotagel P et al. Multiple auras: clinical significance and pathophysiology. Neurology 2007; 69:755-761.

Ninety percent of those with two aura types and 100 % of those with three aura types have right hemisphere localization of their seizures. Some examples were rising epigastric sensation with a simultaneous unpleasant odor or visual field distortion. Multiple auras previously are considered commoner in in patients "alien tissue" (v. mesial temporal sclerosis).