Insulin Formulations

This set of flashcards covers key terms and concepts related to insulin formulations, their action profiles, and delivery methods.

Insulin Self-Association

The process where insulin forms dimers and hexamers, affecting its solubility and action.

Protamine

A substance that complexes with insulin to delay its release, resulting in intermediate-acting formulations like NPH insulin.

Insulin Analogues

Bioengineered forms of insulin that have different amino acid sequences compared to endogenous human insulin, influencing their solubility and duration of action.

Excipients

Substances used in insulin formulations to modulate solubility and stabilize insulin.

Basal Insulin

Long-acting insulin used for background insulin requirements, typically administered once daily.

Bolus Insulin

Rapid-acting insulin used to manage blood glucose spikes during meals.

NPH Insulin

Neutral Protamine Hagedorn insulin, an intermediate-acting insulin formulation.

Recombinant Human Insulin

Insulin produced using recombinant DNA technology, chemically identical to native human insulin.

Insulin Glargine

A long-acting insulin analogue that provides a steady level of insulin with a lower risk of hypoglycemia.

Closed-loop systems

Automated insulin delivery systems that integrate a glucose monitor with insulin delivery.

Afrezza®

A rapid-acting, inhaled insulin formulation developed for convenience in blood glucose management.

Insulin detemir

A long-acting insulin analogue that binds to albumin, prolonging its action.

Insulin lispro

A rapid-acting insulin analogue that is absorbed quickly due to modifications in its amino acid sequence.

Hexamer

A form of insulin consisting of six monomers, influencing its solubility and absorption rate.

Insulin Aspart

A rapid-acting insulin analogue that reduces the tendency for self-association, enabling faster action.

Inhaled Insulin

A delivery method for insulin using a device to inhale insulin powder, designed for faster absorption.

GIPET®

A technology aimed at enhancing oral insulin delivery that was discontinued due to commercial viability issues.

"Why are different insulin release profiles needed in diabetes treatment?"

"Because insulin therapy needs to mimic normal physiology: a steady basal background level plus extra insulin spikes around meals."

"What is the difference between basal and bolus insulin therapy?"

"Basal insulin provides a steady background level; while bolus insulin gives rapid coverage for post-meal glucose spikes."

"What are the three formulation levels that can be used to alter insulin action?"

"The insulin molecule itself; excipients in the formulation; and the delivery device."

"What is native human insulin structurally?"

"A 51-amino-acid protein made of A and B chains; with a molecular weight of about 5808 Da."

"Why can insulin not be given effectively by simple passive absorption across intact membranes?"

"Because it is a relatively large protein and cannot readily cross intact biological barriers like the gut wall or skin."

"In what forms can insulin self-associate?"

"Monomers; dimers; and hexamers."

"What is insulin self-association?"

"The reversible process by which insulin monomers join to form dimers and then hexamers."

"How does insulin self-association affect solubility?"

"Monomers are more soluble; while dimers and hexamers are less soluble."

"How does insulin solubility affect onset and duration of action?"

"More soluble insulin is faster acting and shorter lasting; less soluble insulin is slower acting and longer lasting."

"What happens to insulin association as insulin concentration increases?"

"The equilibrium shifts toward more dimers and hexamers."

"Besides concentration; what else affects insulin self-association/dissociation?"

"Excipients."

"Why are monomer-rich insulin formulations generally used for bolus insulin?"

"Because they are absorbed faster and therefore act rapidly."

"Why are hexamer- or aggregate-promoting formulations generally used for basal insulin?"

"Because they slow absorption and prolong insulin action."

"What was animal insulin

and where was it obtained from?"

"Why has animal insulin largely been replaced?"

"It has been superseded by recombinant human insulin."

"What is recombinant human insulin?"

"Insulin that is structurally identical to endogenous human insulin but produced in a bioreactor using recombinant DNA technology."

"What major advantage does recombinant DNA technology offer for insulin products?"

"It allows production of both native human insulin and modified insulin analogues."

"What is the difference between an insulin solution and an insulin suspension?"

"In a solution the insulin is dissolved; in a suspension it is present as suspended particles."

"How do insulin solutions typically behave pharmacokinetically?"

"They have a rapid onset and shorter duration of action."

"How do insulin suspensions typically behave pharmacokinetically?"

"They have a slower onset and longer duration of action."

"Why do suspensions have a slower onset than solutions?"

"Because the insulin must first dissolve from suspended particles before absorption."

"What visual clue often suggests an insulin product is a solution?"

"It is usually clear and colourless."

"What visual clue often suggests an insulin product is a suspension?"

"It is usually white and cloudy."

"What role do excipients play in insulin formulations?"

"They modulate insulin solubility; stability; and self-association; thereby affecting release rate."

"Which excipients are commonly used as antimicrobial preservatives in insulin formulations?"

"Phenol and m-cresol."

"What effect do zinc and phenolic compounds have on insulin?"

"They promote self-association of insulin into hexamers."

"Why does zinc tend to prolong insulin action?"

"Because it stabilises hexamers; reducing solubility and slowing absorption."

"Why can phenol and m-cresol matter beyond preservation?"

"They also influence insulin hexamer formation and conformation."

"What does NPH stand for?"

"Neutral Protamine Hagedorn."

"What is the mechanism of NPH insulin?"

"Protamine complexes with insulin through ionic interactions to form aggregates in a suspension."

"Why does NPH insulin have an intermediate duration of action?"

"Because insulin must be released from the insulin-protamine complex before absorption."

"What is the general principle behind insulin analogues?"

"They are bioengineered insulin molecules with structural modifications that alter solubility and time-action profile."

"What kinds of modifications are made in insulin analogues?"

"Amino acid substitutions or attachment of long-chain hydrocarbon/lipid groups."

"What is the aim of rapid-acting insulin analogues?"

"To destabilise dimers and hexamers so monomers are favoured."

"What is the aim of long-acting insulin analogues?"

"To reduce solubility or create reservoirs/depot systems that prolong release."

"What modification is made in insulin lispro?"

"ProB28 and LysB29 are switched."

"How does insulin lispro act faster than human insulin?"

"The amino acid switch destabilises dimers and hexamers; favouring monomers."

"What is the brand name commonly associated with insulin lispro?"

"Humalog."

"What modification is made in insulin aspart?"

"ProB28 is replaced with Asp."

"How does insulin aspart become faster acting?"

"The substitution destabilises dimers and hexamers; favouring monomers."

"What are brand names associated with insulin aspart?"

"NovoRapid and Fiasp."

"What modifications are made in insulin glulisine?"

"AsnB3 is replaced by Lys; and LysB29 is replaced by Glu."

"How does insulin glulisine achieve faster action?"

"It decreases hexamer formation; stabilises monomers; and enhances solubility."

"What is a brand name associated with insulin glulisine?"

"Apidra."

"What common pharmacokinetic feature do lispro; aspart; and glulisine share?"

"They are rapid/faster-acting because they favour monomeric insulin."

"What modification is made in insulin degludec?"

"ThrB30 is removed and a hexadecandioyl group is attached via a glutamic acid spacer at LysB29."

"How does insulin degludec prolong action?"

"After injection; hexamers link into long multi-hexamer chains in the subcutaneous depot."

"What must happen before insulin degludec monomers are released?"

"Zinc must slowly diffuse away; allowing hexamers to disassemble and release monomers."

"What is a brand name associated with insulin degludec?"

"Tresiba."

"What modification is made in insulin detemir?"

"ThrB30 is removed and myristic acid is attached at LysB29."

"How does insulin detemir prolong action?"

"The fatty acid chain promotes binding to albumin; forming a circulating and local reservoir."

"What is a brand name associated with insulin detemir?"

"Levemir."

"What modifications are made in insulin glargine?"

"AsnA21 is replaced by Gly; and Arg residues are added at B31 and B32."

"How does insulin glargine prolong action?"

"It is less soluble at physiological pH; so after injection it forms microprecipitates that slowly dissolve."

"Why is insulin glargine formulated in an acidic solution?"

"To keep it soluble before injection; once injected into physiological pH; it precipitates."

"What are brand names associated with insulin glargine?"

"Lantus and Toujeo."

"Which insulin analogues in this lecture are rapid acting?"

"Lispro; aspart; and glulisine."

"Which insulin analogues in this lecture are long acting?"

"Degludec; detemir; and glargine."

"What is the key mechanistic difference between rapid-acting and long-acting insulin analogues?"

"Rapid-acting analogues increase solubility/monomer formation; long-acting analogues decrease solubility or form depots/reservoirs."

"What broad relationship links onset and duration of insulin action?"

"Faster onset usually corresponds to shorter duration; slower onset usually corresponds to longer duration."

"Why is insulin delivery device design especially important?"

"Because insulin must cross impermeable biological barriers and often requires self-administration."

"What is the most common route of insulin administration?"

"Subcutaneous injection."

"What is an insulin pen?"

"A user-friendly; prefilled or refillable injection device designed for simple subcutaneous insulin dosing."

"What is an insulin pump?"

"A wearable device that continuously infuses insulin into subcutaneous tissue at programmed rates."

"What advantage do insulin pumps offer over simple intermittent injections?"

"They can provide more continuous and adjustable insulin delivery."

"What is a closed-loop insulin delivery system?"

"A system combining a glucose monitor and insulin pump in a feedback loop to automate insulin delivery."

"Why are closed-loop systems sometimes called an artificial pancreas?"

"Because they attempt to mimic the body’s natural glucose-responsive insulin regulation."

"What is the main limitation of a standalone pump without glucose sensing?"

"It does not automatically respond to changing glucose levels in real time."

"What was Exubera?"

"An inhaled insulin product developed by Pfizer using spray-dried recombinant human insulin."

"What was the particle size used in Exubera?"

"About 3 µm."

"What were some problems with Exubera?"

"Poor user acceptability; bulky device; dosing in mg instead of units; low bioavailability; cost-effectiveness issues; and poor sales."

"Did Exubera fail because it was ineffective?"

"No; it worked; but it was not therapeutically superior and had major usability and commercial problems."

"What was an important pharmacokinetic drawback of Exubera?"

"Only about 10% bioavailability."

"What is Afrezza?"

"A rapid-acting inhaled bolus insulin product marketed in the USA."

"How is insulin formulated in Afrezza?"

"Recombinant human insulin is adsorbed onto self-assembled fumaryl diketopiperazine (FDKP) particles."

"What particle size is used in Afrezza?"

"About 2.0–2.5 µm."

"What practical improvements did Afrezza make over Exubera?"

"A much smaller inhaler and dosing expressed in insulin units."

"What routes of insulin delivery beyond injections are discussed in the lecture?"

"Inhalation; oral delivery approaches; transdermal systems; and microneedle-based systems."

"Why is oral insulin delivery difficult?"

"Because insulin is degraded in the GI tract and has poor permeability across intestinal barriers."

"What is the overall summary principle linking insulin formulation and insulin action?"

"Formulation strategies alter insulin solubility; self-association; and release; which determines onset and duration of action."