Insulin Glargine and Insulin Lispro

Mechanism

Pharmacological Class and Group

Recombinant polypeptide hormones: Ultra-long-acting basal insulin (Glargine) and Ultra-rapid-acting prandial insulin (Lispro).

Mechanism of Action

Insulin activates a highly conserved metabolic cascade in target cells (myocytes, adipocytes, hepatocytes). Modifications to the native sequence deliberately alter the temporal profile of its absorption:

• Insulin Glargine: Addition of two arginines at the C-terminal end of the B chain and substitution of asparagine in position A21 with glycine. This shifts the molecular isoelectric point from a neutral pH of 5.4 to a slightly acidic pH of 6.7. When injected into the subcutaneous cellular tissue (pH 7.4), it precipitates in the form of insoluble microcrystals that slowly and sustainably release insulin monomers into the capillary circulation.
• Insulin Lispro: Inversion of the order of the amino acids lysine and proline in positions B28 and B29 of the B chain. This abrogates the natural self-complexation and the intrinsic tendency to form stable hexamers, promoting immediate dissociation into ultra-rapidly absorbed monomers after subcutaneous injection.

Insulin Receptor Signaling

1. Binding to the Insulin Receptor (IR): Glycosylated transmembrane receptor of the receptor tyrosine kinase family, composed of two extracellular alpha subunits and two intracellular beta subunits.

2. Autophosphorylation and Kinase Activation: Ligand binding promotes autophosphorylation of key tyrosine residues in the cytoplasmic kinase domain of the beta subunit. This induces the binding and phosphorylation of Insulin Receptor Substrates (IRS-1, IRS-2).

3. Phosphatidylinositol 3-Kinase (PI3K) / Akt Pathway (Major Metabolic Pathway): IRS-1 recruits PI3K, which phosphorylates membrane lipids to form PIP3. PIP3 recruits the PDK1 kinase, which activates protein kinase B (Akt/PKB) by phosphorylation. Akt activated:

• Phosphorylates and inactivates AS160, promoting the fusion of vesicles carrying GLUT4 to the cell membrane.
• Phosphorylates and inactivates Glycogen Synthase Kinase-3 (GSK-3), which activates glycogen synthesis.
• Inhibits mitochondrial PEPCK expression by terminally blocking hepatic gluconeogenesis.

4. MAPK / Ras-Raf-MEK-ERK Pathway (Main Mitogenic Pathway): Controls the transcription of genes for cell division, somatic growth and local angiogenesis.

Pharmacokinetics

High Resolution Pharmacokinetics

Indicators and dose

Clinical Indications and Off-Label Uses

• Type 1 Diabetes Mellitus: Mandatory exogenous hormone replacement for life, typically in a basal-bolus regimen combining Glargine and Lispro.
• Type 2 Diabetes Mellitus: For the control of hyperglycemia when oral and non-invasive incretin therapy is ineffective or formally contraindicated (for example, in advanced organ failure).
• Gestational Diabetes: Preferred gold standard for optimizing perinatal metabolic goals.
• Diabetic Ketoacidosis (DKA) and Hyperglycemic Hyperosmolar State (HHS): Priority intravenous use of short-acting regular insulin to correct acidemia and dehydration.
• Severe hyperkalemia (acute clinical use): Administration of insulin infusion together with hypertonic dextrose to shift extracellular potassium to the intracellular space by active stimulation of the capillary sodium-potassium ATPase pump.

Dosage and Clinical Adjustment

Dosing is strictly individualized according to the patient's glycated hemoglobin goals, lifestyle, caloric intake, and glucose self-monitoring.

Guideline Starting Guidelines:

• Type 1 Diabetes Mellitus: Total daily requirement estimated between 0.4 and 1.0 IU/kg/day. It is usually divided into 40-50% as basal-acting insulin (Glargine) administered once a day, and the remaining 50-60% divided into boluses of rapid insulin (Lispro) before each main meal, calculated according to carbohydrate count and correction factor.
• Type 2 Diabetes Mellitus: Addition of basal dose of Insulin Glargine typically starting with 10 IU per day or 0.1 to 0.2 IU/kg/day subcutaneously at night, titrating 2 IU every 3 days until normal fasting blood glucose is reached (< 100-110 mg/dL).

Adjustment in Kidney and Liver Failure:

The kidney purifies 30-40% of systemic insulin and the liver 50-60%. In advanced renal failure (eGFR < 30 mL/min/1.73 m²) and Child-Pugh C cirrhosis, the plasma elimination half-life of exogenous insulin is notably prolonged. Widespread dose reductions of 25-50% are required to prevent severe hypoglycemia.

Security

Absolute and Relative Contraindications

Absolute Contraindications

• Active episode of hypoglycemia: Additional exogenous administration may aggravate neuroglycopenia and cause seizures, coma, or death.
• Documented severe systemic hypersensitivity.

Relative Contraindications

• Patients with severe uncorrected hypokalemia (initiation of therapy can exacerbate the fall in serum potassium, inducing lethal ventricular arrhythmias).

Adverse Effects (ADR) and Specific Toxicity

• Very common (>10%): Hypoglycemia (it is the most common and potentially fatal undesirable effect of the treatment).
• Common (1%-10%): Local reactions at the injection site (pain, erythema), general weight gain, local lipohypertrophy (due to the direct lipogenic effect of concentrated insulin at the site of repeated injections, mitigated by systematic rotation of the placement area).
• Rare (0.01%-0.1%): Generalized insulin edema (transient fluid retention secondary to rapid correction of chronic hyperglycemia), anti-insulin antibodies, IgE-mediated immediate hypersensitivity reactions.

Clinical Alert: Classification of Severe Hypoglycemia and Neuroglycopenia

Autonomic symptoms (tremors, palpitations, diaphoresis, anxiety) usually trigger at serum glucose values < 54 mg/dL. If blood glucose drops below 50 mg/dL acutely, symptoms of neuroglycopenia appear (temporospatial disorientation, mental confusion, erratic behavior, diplopia, progressive lethargy, generalized seizures, and hypoglycemic coma).

Treatment in the conscious patient is the rule of 15 g of rapidly absorbed carbohydrates; In the unconscious patient or without an intravenous route available, the first-line treatment of choice is the injection of 1 mg of glucagon intramuscularly or subcutaneously, or infusion of 10% or 50% dextrose solution intravenously.

Drug Interactions of Clinical Relevance

• Drugs that enhance the hypoglycemic effect: ACE inhibitors, beta-adrenergic blockers, high-dose salicylates, ethyl alcohol (directly inhibits oxidative lactic metabolism and basal hepatic reserve gluconeogenesis).
• Drugs that attenuate insulin efficacy (hyperglycemia inducers): Systemic corticosteroids, loop diuretics, growth hormone, excessive replacement thyroid hormones, high-dose hormonal contraceptives.

Safety in Pregnancy and Breastfeeding

• Pregnancy: Compatible. Both insulins (Glargine and Lispro) have been shown to be safe and are the mainstay of treatment in pregnancy (they do not cross the placental barrier in measurable concentrations).
• Breastfeeding: Compatible. Insulin is digested safely in the infant's digestive tract; improves the maternal lactogenesis profile by normalizing mammary oxidative metabolism.