6.1 Antidiabetic Agents, Metformin Lactic Acidosis, and Thyroid Hormone

Insulin Secretagogues: Sulfonylureas and Meglitinides

Sulfonylureas (glipizide, glyburide, glimepiride, chlorpropamide) bind the SUR1 subunit of the pancreatic beta cell ATP-sensitive potassium channel, closing it. The membrane depolarizes, voltage-gated calcium channels open, and insulin is released regardless of the blood glucose. Meglitinides (repaglinide, nateglinide) act at the same channel with a shorter duration.

Why the Hypoglycemia Is Dangerous

1. Delayed onset. Hypoglycemia commonly appears 8 to 18 hours after ingestion, and later with extended-release products or in kidney impairment.
2. Recurrence after dextrose. A dextrose bolus raises glucose, which then stimulates further insulin release from drug-primed beta cells, so the patient crashes again.
3. Duration. Effects last 24 hours or more, especially with glyburide and chlorpropamide.
4. One tablet can harm a toddler, which is why any credible pediatric exposure is referred and observed for at least 24 hours with serial glucose measurement.

Management

Metformin

Metformin is a biguanide that reduces hepatic gluconeogenesis and increases peripheral glucose uptake. It does not stimulate insulin release, so hypoglycemia is uncommon unless the patient is fasting, has liver disease, or took another agent.

Metformin-Associated Lactic Acidosis

By inhibiting mitochondrial complex I and hepatic pyruvate carboxylase, metformin blocks the conversion of lactate to glucose and shifts metabolism toward anaerobic glycolysis. The result is a severe anion gap lactic acidosis.

• Risk factors: kidney impairment (the drug is renally cleared), acute illness, dehydration, sepsis, heart failure, alcohol use, and massive intentional overdose.
• Presentation: vomiting, abdominal pain, hyperventilation, hypotension, hypothermia, and altered mental status with lactate that can exceed 15 to 25 mmol/L. Mortality rises steeply with pH below 7.1.
• Management: volume resuscitation, treatment of the precipitating illness, and early extracorporeal treatment. EXTRIP recommends ECTR when lactate exceeds 20 mmol/L, when pH is 7.0 or less, or when standard supportive measures fail, and suggests it for lactate of 15 to 20 mmol/L or pH of 7.0 to 7.1. Shock, impaired kidney function, liver failure, or decreased consciousness lower the threshold for starting it. Bicarbonate-buffered intermittent hemodialysis is preferred, and treatment continues until lactate is below 3 mmol/L and pH is above 7.35.

Exogenous Insulin

Deliberate or accidental insulin overdose, including injection of long-acting analogues, produces hypoglycemia lasting far beyond the usual therapeutic duration because a subcutaneous depot continues to absorb.

• Management: continuous concentrated dextrose infusion (D10 peripherally, D20 or higher centrally) titrated to glucose of about 100 to 150 mg/dL, frequent bedside checks, oral intake when safe, and repletion of potassium, magnesium, and phosphate, which shift intracellularly.
• Octreotide does not work, because the problem is injected insulin rather than pancreatic secretion.
• Observation is prolonged: 24 hours or more for long-acting analogues, and local excision of an injection site is a historical measure that is rarely used.

Other Diabetes Medications

Thyroid Hormone

Levothyroxine (T4) and liothyronine (T3) increase the transcription of genes governing metabolic rate, and they up-regulate beta-adrenergic responsiveness. Two pharmacologic facts explain the clinical course.

1. Conversion and distribution take time. T4 must be deiodinated to T3, and the half-life of T4 is about 7 days, so effects appear over days rather than hours.
2. Acute single ingestions are usually benign. Children who swallow even large numbers of levothyroxine tablets most often remain asymptomatic. When symptoms occur they appear 2 to 7 days later and are mild: tachycardia, irritability, tremor, diarrhea, sweating, and insomnia.

Practical Approach

Counseling point: because the latency is days, follow-up calls for a thyroid hormone ingestion extend well beyond the usual 24-hour window.

Corticosteroids and Sex Hormones

The topic list also names steroids among the hormones. Acute ingestions are among the most reassuring calls a specialist handles.

• Corticosteroids (prednisone, dexamethasone, hydrocortisone): a single acute overdose causes little beyond transient hyperglycemia, gastrointestinal upset, or insomnia. Toxicity comes from chronic use (adrenal suppression, Cushingoid effects) and from abrupt withdrawal after long-term therapy, which can precipitate adrenal crisis.
• Oral contraceptives and estrogens: exploratory ingestions by children cause at most nausea, vomiting, and occasionally minor withdrawal vaginal bleeding in young girls days later; home observation is standard.
• Anabolic steroids and testosterone: acute ingestion has low toxicity; chronic misuse causes erythrocytosis, hepatotoxicity, and cardiovascular effects.

Poison Center Case: One Tablet, Twenty-Four Hours

A grandmother calls because her 2-year-old grandson (12 kg) was found with her open pill organizer. One glyburide 5 mg tablet is missing. He is playing normally and his bedside glucose at the emergency department is 96 mg/dL four hours later. The physician asks whether the child can go home, since he is asymptomatic and euglycemic.

Specialist guidance. The CSPI explains that a normal glucose at 4 hours is expected and reassures no one: sulfonylurea hypoglycemia commonly begins 8 to 18 hours after ingestion. The recommendation is admission for at least 24 hours with hourly then two-hourly glucose checks, oral feeding, no prophylactic dextrose, and octreotide 1 to 1.25 mcg/kg available at the bedside to give with dextrose at the first documented hypoglycemic episode. Discharge is appropriate only after the child has gone at least 24 hours without hypoglycemia, counting from the last octreotide dose if any was given.