Humulin I (Isophane) (Insulin Human (Rdna))

Humulin I (Isophane) is indicated for the treatment of diabetes mellitus when basal insulin coverage is required.

• Type 1 diabetes mellitus in adults and children.
• Type 2 diabetes mellitus as part of a basal insulin regimen.
• Adjunct therapy when oral antidiabetic agents are insufficient.
• Use in patients requiring a long‑acting insulin to maintain fasting glucose control.
• May be combined with rapid‑acting insulin for flexible dosing.

• Humulin I (Isophane) contains protamine‑crystallized human insulin that forms a subcutaneous depot, releasing insulin slowly over time. The insulin molecules bind to insulin receptors on muscle and adipose tissue, activating the receptor’s tyrosine kinase activity, which promotes translocation of GLUT‑4 transporters and enhances glucose uptake. In the liver, receptor activation suppresses gluconeogenesis, thereby lowering circulating glucose concentrations and improves overall metabolic control.

Adverse reactions reported with Humulin I (Isophane) are generally related to its insulin activity and formulation components.

Common

• Hypoglycemia, especially if meals are missed or dosing is excessive.
• Injection site reactions such as redness, swelling, or itching.
• Lipodystrophy at the injection site.
• Weight gain associated with improved glycemic control.
• Transient blurred vision due to rapid glucose changes.
• Nausea or abdominal discomfort after injection.
• Mild headache or dizziness during dose adjustments.

Serious

• Severe hypoglycemia with neuroglycopenic symptoms.
• Allergic reactions including urticaria, angioedema, or anaphylaxis.
• Lipohypertrophy leading to erratic insulin absorption.
• Edema or heart failure exacerbation in susceptible patients.
• Hypersensitivity leading to serum sickness‑like reaction.

When prescribing Humulin I (Isophane), clinicians should consider several precautions to minimize risks and ensure safe use.

• Assess renal and hepatic function before initiating therapy, as impairment may alter insulin clearance.
• Monitor blood glucose closely during periods of illness, stress, or changes in physical activity.
• Adjust dose in pregnant or lactating women, recognizing altered insulin requirements.
• Use caution in patients with a history of severe hypoglycemia or unawareness of symptoms.
• Inspect injection sites regularly for lipodystrophy or infection.
• Evaluate cardiovascular status in patients with heart failure, as fluid retention may worsen symptoms.

Humulin I (Isophane) may interact with other medicines that affect glucose metabolism or insulin action.

Avoid

• Concurrent use of other rapid‑acting insulins without dose adjustment, which can cause severe hypoglycemia.
• Combination with sulfonylureas or meglitinides without careful monitoring, increasing hypoglycemia risk.
• Concurrent use of meglitinides with overlapping action profiles may cause additive hypoglycemia.

Use with caution

• Beta‑blockers, which may mask hypoglycemia symptoms.
• Corticosteroids, which can raise blood glucose and require insulin dose increase.
• Diuretics, especially thiazides, that may affect potassium levels and glucose control.
• ACE inhibitors or ARBs, which may potentiate insulin’s antihyperglycemic effect.
• Thyroid hormones, which can accelerate insulin metabolism and alter glycemic control.