M06.14.001 Alcohols

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Learning Objectives

By the end of this session, the learner will be able to describe the metabolic pathways of common alcohols, identify the toxic metabolites responsible for metabolic acidosis, and recognize the clinical features of Fetal Alcohol Syndrome (FAS) and Disulfiram-like reactions.

1. Metabolism of Alcohols

All alcohols follow a similar two-step oxidation pathway in the liver. The toxicity of methanol and ethylene glycol is not due to the alcohols themselves, but their acidic metabolites.

Step Enzyme Inhibitor (Pharmacotherapy)
Step 1 Alcohol Dehydrogenase Fomepizole (Antidote for Methanol/Ethylene Glycol)
Step 2 Aldehyde Dehydrogenase Disulfiram (Used in Alcoholism to cause aversion)

2. Comparison of Alcohol Toxicities

All alcohols cause CNS depression and a High Anion Gap Metabolic Acidosis, but they differ in their “target organ” damage.

Alcohol Toxic Metabolite Clinical Hallmark
Ethanol Acetaldehyde Nausea, flushing, hangover symptoms.
Methanol Formic Acid Retinal damage / Blindness.
Ethylene Glycol Oxalic Acid Nephrotoxicity (Calcium oxalate crystals in urine).

 

3. Fetal Alcohol Syndrome (FAS)

Ethanol is a potent teratogen. FAS is characterized by a specific triad of findings:

Category Specific Findings
Facial Features Smooth philtrum, thin upper lip, small palpebral fissures.
CNS Dysfunction Microcephaly, intellectual disability, and behavioral problems.
Growth Pre- and postnatal growth restriction.

4. Disulfiram-like Reactions

Some drugs inhibit aldehyde dehydrogenase as a side effect. If alcohol is consumed while taking these, Acetaldehyde accumulates, causing severe illness (flushing, nausea, tachycardia).

High-Yield Medications to Remember:

  • Metronidazole (Antibiotic)
  • Griseofulvin (Antifungal)
  • First-generation Sulfonylureas (e.g., Chlorpropamide)
  • Certain Cephalosporins (e.g., Cefotetan)

Clinical Pearls:

  • Fomepizole Mechanism: It has a higher affinity for Alcohol Dehydrogenase than Methanol/Ethylene Glycol, preventing their conversion into toxic acids.
  • Ethylene Glycol Diagnosis: Look for “envelope-shaped” calcium oxalate crystals in the urinalysis.

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