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wikitox:2.1.7.1.3.1_biguanides [2019/07/05 20:08]
andrew
wikitox:2.1.7.1.3.1_biguanides [2019/07/05 20:09] (current)
andrew
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-===== CLINICAL EFFECTS ===== 
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-==== Metabolic effects ==== 
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-A profound lactic acidosis is the most consistent reported finding in overdose. The pH is often less than 7.0 and high concentrations of lactate are observed. In some cases ketones are also high and account for some of the acidosis. The serum bicarbonate is low and there is usually a large [[:​wikitox:​anion_gap_acidosis|anion gap]]. Hyperkalaemia is often associated with the lactic acidosis and is presumably secondary to cellular shifts resulting from the acidosis. Hypoglycaemia (Bingle et al, 1970) has occasionally been reported but is very uncommon. Biguanides impair gluconeogenesis and this case presented quite late after a prolonged period of fasting. The metabolic acidosis initially increases the respiratory rate (Kussmaul'​s respiration) leading to a compensatory respiratory alkalosis. If this cannot be maintained due to respiratory disease or increasing sedation then the pH will fall rapidly. 
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-==== Cardiac effects ==== 
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-Hypotension and tachycardia are common, as is reduced cardiac output. These may progress to cardiogenic shock. Patients may be dehydrated secondary to impaired consciousness and/or vomiting. All of these may contribute to the lactic acidosis (by reducing tissue perfusion) and should be corrected if possible. Myocardial infarction has occurred secondary to profound acidosis. 
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-==== Central nervous system effects ==== 
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-Nausea and vomiting are common in the early stages; delirium, sedation, coma, and seizures may all occur secondary to the acidosis. 
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-==== Other effects ==== 
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-Hypothermia,​ acute renal failure, pulmonary oedema, pneumonia may all complicate the episode, particularly in delayed presentations. 
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-===== INVESTIGATIONS ===== 
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-==== Blood concentrations ==== 
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-These are unhelpful in management. There is not a good correlation between blood concentrations of biguanides and outcome. In many of the series of acidosis occurring in chronic therapeutic use, the majority of patients have had undetectable concentrations at the time of presentation. 
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-==== Biochemistry ==== 
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-Electrolytes,​ glucose, renal function, anion gap and lactate should all be measured at regular intervals (say 2-4 hourly) and more frequently if there are particular concerns (e.g., hyperkalaemia). 
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-==== ECG ==== 
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-A baseline ECG should be performed. Continuous ECG monitoring is advisable in patients with severe acidosis as complications secondary to either acidosis or hyperkalaemia may occur. 
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-===== DIFFERENTIAL DIAGNOSIS ===== 
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-The differential diagnosis is of any agent that causes profound acidosis and CNS effects and would include [[:​wikitox:​2.2.5.2.2_ethylene_glycol|ethylene glycol]], [[:​wikitox:​2.1.1.4_salicylates|salicylate]],​ [[:​wikitox:​2.2.5.2.5_methanol|methanol]],​ isoniazid, alcoholic and diabetic ketoacidosis. Lactic acidosis secondary to decreased tissue perfusion from toxicological (e.g. carbon monoxide, [[:​wikitox:​2.2.9.1.2_cyanide|cyanide]]) or non-toxicological (sepsis or cardiogenic shock) causes also must be considered. 
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-===== DIFFERENCES IN TOXICITY WITHIN THIS DRUG CLASS ===== 
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-Lactic acidosis in therapeutic use is far more common with phenformin than metformin and phenformin has been removed from the market in most countries. There are insufficient data to determine if such differences are also true in overdose. 
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-===== DETERMINATION OF SEVERITY ===== 
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-The following are associated with a less favourable outcome (mortality and morbidity): 
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-  * Elderly (age >60) 
-  * Complicating medical conditions (e.g. ischaemic heart disease, respiratory disease) 
-  * Renal failure 
-  * Hypotension (shock) 
-  * Diabetes 
-  * Low pH on presentation (pH<7.0) 
-  * Low bicarbonate on presentation (HCO3 < 6.0 mmol/L) 
-  * High lactate ( > 17 mmol/L) 
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-However, none of these is a particularly good predictor of outcome. 
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-===== TREATMENT ===== 
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-==== Supportive ==== 
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-All patients with significant acidosis should be admitted to intensive care. [[:​wikitox:​3.4.8_fluid_resuscitation|Intravenous fluids]] should be given and it may be useful to closely monitor fluid balance with a central line as either over or under hydration may worsen the acidosis or cardiac function. Ventilation must be maintained and if the respiratory rate is falling then the patient should be ventilated. 
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-==== GI Decontamination ==== 
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-Oral [[:​wikitox:​3.2.2.2.3_activated_charcoal|activated charcoal]] should be given to all patients who present within 1 hour of ingestion as these drugs are quite slowly absorbed. There is unlikely to be any benefit from [[:​wikitox:​3.2.2.2.3.1_repeated_doses_of_activated_charcoal|repeated doses of activated charcoal]]. Generous fluid replacement to counteract the volume depletion associated with gastrointestinal decontamination is particularly important in overdose with drugs that lead to hypotension. 
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-==== Treatment of specific complications ==== 
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-**Acidosis** 
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-Maintaining adequate tissue perfusion, oxygenation and glucose delivery and maximising compensatory hyperventilation are all important factors in the treatment of significant acidosis. The use of specific antidotes (including bicarbonate) to correct acidosis is controversial and may provide no additional benefit. We would recommend routine use of glucose and insulin, very slow and low doses of sodium bicarbonate if the pH is less than 6.9 - 7.0, and dichloroacetate if it is available. 
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-==== Antidotes ==== 
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-**Bicarbonate** \\ Bicarbonate rapidly corrects acidaemia. Unfortunately,​ it is likely that it temporarily worsens intracellular and CNS acidosis by liberating carbon dioxide which crosses lipid membranes much more efficiently than bicarbonate where it is converted to carbonic acid. Also, rapid alkalinisation decreases oxygen delivery due to inhibition of oxygen dissociation from haemoglobin and reduces ionised calcium. All these factors mean that cardiac output and tissue perfusion may fall which may paradoxically increase lactate production and worsen the acidosis (McGuinness & Talbert, 1993). Neither animal studies nor case series support the use of rapid high doses of sodium bicarbonate,​ although this is the most common treatment administered. (Ryder, 1987) \\  \\ **Dichloroacetate** \\ Dichloroacetate stimulates pyruvate dehydrogenase,​ decreases glycolysis (thus decreasing lactate formation) and increases lactate oxidation to pyruvate (Stacpoole //et al//, 1992). Some, but not all, animal models of biguanide poisoning have shown benefit from the use of dichloroacetate (Ryder, 1987). A large randomised trial of dichloroacetate in lactic acidosis, mostly due to shock and/or sepsis, demonstrated that dichloroacetate was effective in reducing the degree of acidosis but in these patients had no effect on outcome (Stacpoole //et al//, 1992). However, in biguanide poisoning the lactic acidosis is probably the primary event, rather than secondary to severe organ failure or sepsis, and reversal of the acidosis may provide more benefit. \\  \\ Dose: 50 mg/kg as a 10% solution infused over 30 minutes repeated 2 hours later. The drug is unlikely to be available except as part of a study protocol. \\  \\ **Glucose & Insulin** \\ It has been postulated that administration of glucose and insulin stimulates pyruvate dehydrogenase. Glucose and insulin will also be useful treatment for patients that have some contributory ketoacidosis. Many patients with lactic acidosis have a larger [[:​wikitox:​anion_gap_acidosis|anion gap]] than can be accounted for by lactic acid. Two authors have reviewed the outcomes of patients reported in the literature to have been treated with glucose and insulin (Misbin, 1977; Luft //et al//, 1979). Surprisingly,​ while Misbin'​s conclusion was that the patients treated with glucose and insulin had much better reported survival, Luft //et a//l found that all treatments reported had similar survival rates. While these were much better than those reported with no treatment their conclusion was that this probably indicated publication bias for positive treatment outcomes. However, it is unlikely to cause any harm and may provide benefit. \\  \\ Typical doses have been 2 to 5 units of insulin per hour. Sufficient glucose should be given to maintain blood glucose; often this has required quite low doses (1 to 3 grams of glucose/​hour - 10 to 30 mL of 10% glucose/​hour). \\  \\ **Tromethamine (THAM, Trometamol)** \\ This proton acceptor has been used to correct biguanide induced lactic acidosis in a few case reports but there is little reason to favour it over either low doses of bicarbonate or dichloroacetate (Ryder, 1987). 
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-==== Elimination enhancement ==== 
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-As these drugs are renally excreted, it is important to maintain a good urine output to facilitate renal clearance. Clearance is enhanced in acidic urine. So any effort to further increase renal clearance is likely to contribute to the metabolic acidosis and is thus contraindicated. \\  \\ **Haemodialysis** \\ The clearance of metformin may be enhanced by [[:​wikitox:​3.2.3.1.1_haemodialysis|haemodialysis]],​ the other biguanides have larger volumes of distribution and will be less effectively cleared. Haemodialysis against a bicarbonate buffer may also partially correct acid-base and electrolyte abnormalities (Chalopin //et al//, 1984). There are no clear-cut indications for haemodialysis in this situation but clearly it would be favoured by the presence of renal failure and/or significant electrolyte disturbances. CVVH may be considered though may not be as effective (Arroyo //et al//, 2010). 
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-===== LATE COMPLICATIONS,​ PROGNOSIS - FOLLOW UP ===== 
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-Mortality in reported series of phenformin induced lactic acidosis is up to 50%. Long term sequelae do not appear to have been reported but it would be surprising if the hypotension,​ severe acidosis, and cerebral oedema that may occur with this poisoning did not sometimes result in long term neuropsychiatric deficits. Patients should be followed up at least once after the acute illness has resolved. Other issues that may be dealt with are whether the patient has contraindications to the further use of biguanides. 
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-===== RESOURCES ===== 
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-See PowerPoint presentation by Dr Rama Rao, New York Poisons Information Centre on hypoglycaemics . 
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-===== REFERENCES ===== 
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-[[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=6378583&​dopt=Abstract|Asmal AC, Marble A. ]]Oral hypoglycemics. An update. //​Drugs// ​ 1984; 28: 62-78. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=5472759&​dopt=Abstract|Bingle JP. Storey GW. Winter JM. ]]Fatal self-poisoning with phenformin. //Br Med J//  1970; 3: 752. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=6691764&​dopt=Abstract|Chalopin JM, Tanter Y, Besancenot JF, Cabanne JF, Rifle G. ]]Treatment of metformin-associated lactic acidosis with closed recirculation bicarbonate-buffered haemodialysis. //Arch Int Med//  1984; 144: 203-205. \\ Hardman JG, Gilman AG, Limbird LE. Goodman and Gilman'​s The pharmacological basis of therapeutics 9th ed. 1996. McGraw Hill, New York. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=8853933&​dopt=Abstract|Harrower AD. ]]Pharmacokinetics of oral antihyperglycaemic agents in patients with renal insufficiency. //Clin Pharmacokinet// ​ 1996; 31(2):​111-9. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=6345342&​dopt=Abstract|Jefferys DB, Volans GN. ]]Self-poisoning in diabetic patients. //Hum Toxicol// ​ 1983; 2:345-348. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=344119&​dopt=Abstract|Luft D, Scmulling RM, Eggstein M.]] Lactic acidosis in biguanide treated diabetics. //​Diabetologia// ​ 1978; 14:75-87. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=1760902&​dopt=Abstract|Marchetti P, Giannarelli R, di Carlo A, Navalesi R. ]]Pharmacokinetic optimisation of oral hypoglycaemic therapy. //Clin Pharmacokinet// ​ 1991; 21(4):​308-17. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=2656043&​dopt=Abstract|Marchetti P, Navalesi R.]] Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update. //Clin Pharmacokinet// ​ 1989; 16(2):​100-28. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=8251683&​dopt=Abstract|McGuinness ME, Talbert RL]]. Phenformin induced lactic acidosis: A forgotten adverse drug reaction. //Ann Pharmacother// ​ 1993;27: 1183-87. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=9441244&​dopt=Abstract|Misbin RI. ]]Phenformin-associated lactic acidosis: Pathogenesis and treatment. //Ann Intern Med//  1977;87: 591-595. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=8240727&​dopt=Abstract|Moore DF, Wood DF, Volans GN.]] Features, prevention and management of acute overdose due to antidiabetic drugs. //Drug Safety// ​ 1993; 9: 218-229. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=6397981&​dopt=Abstract|Paterson KR, Paice BJ, Lawson DH. ]]Undesired effects of biguanide therapy. //Adv Drug React Acute Poisoning Rev//  1984; 3(3):​173-82. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=2833297&​dopt=Abstract|Ryder REJ. ]]The danger of high dose sodium bicarbonate in biguanide-induced lactic acidosis: the theory, the practice and alternative therapies. //Br J Clin Pract// ​ 1987;41: 730-737 \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=7741982&​dopt=Abstract|Scheen AJ, Lefebvre PJ. ]]Antihyperglycaemic agents. Drug interactions of clinical importance. //Drug Safety// ​ 1995; 12(1):​32-45. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=8743335&​dopt=Abstract|Scheen AJ. .]] Clinical pharmacokinetics of metformin. //Clin Pharmacokinet// ​ 1996; 30: 359-371. \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=3065405&​dopt=Abstract|Seger D. .]] Toxic emergencies of endocrine and metabolic therapeutic agents. //J Emerg Med//  1988; 6(6):527-37 \\ [[http://​www.ncbi.nlm.nih.gov/​entrez/​query.fcgi?​cmd=Retrieve&​db=PubMed&​list_uids=1435883&​dopt=Abstract|Stacpoole PW, Wright EC, Baumgartner TG, et al.]] A controlled clinical trial of dichloroacetate for treatment of lactic acidosis in adults. //N Engl J Med//  1992; 327: 1564-9. \\ 6- Dec- 2014 
  
  
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