Emma (Insulin formulation) Flashcards
History of insulin
- Insulin is found in every creature with a backbone. The central core of the molecule shows a few species differences.
- bovine insulin is only three amino acids variant to human insulin
- Porcine insulin has only one amino acid different to human insulin (preferred option but some groups cannot have pig products)
- Banting and best in 1921 isolated insulin the clinical use and began the first insulin injections in Canada
- When the process was scaled up the potency of extract diminished
- A precipitate that was discarded was where the potent material was and this discovery led to process to isoelectric precipitation with standardised purity and potency.
- Marketed in 1923 after being tested
- In 1982 the first human insulin was marketed
- In 1996 the rapid-acting insulin analog became available
Recombinant insulin
rDNA human insulin obtained in 1978 from combination of A and. chains individually expressed in E coli.
This replaced the need for animal insulin although they are still available (Patients that have grown up on bovine insulin find it very hard to change to human insulin so older patients may still be using bovine insulin instead. Once they change to human they can no longer feel a hypo coming on so need to be comfortable with continuous monitoring).
Key technologies included:
- rapid chemical synthesis of DNA
- use of RP-HPLC for purification of DNA fragments and detection and characterisation of expressed proteins
Main groups of insulin
Animal- porcine (pig) or bovine (cow). Some evidence exists that some patients may lose their sense of falling blood sugar of use human insulin.
Human – not from humans but synthetically matched to human insulin
Analogues – chemical structure of human insulin has been changes to make the insulin to work quicker or last longer
Zinc complex
6 insulin molecules associated with 2 zinc ions to form a hexamer
Insulin
Hexamer insulin molecules bound to 2 zinc ions. Stable but not biologically active at insulin receptors as they are too big. Minimal diffusion into capillaries.
Dimer insulin molecules- biologically active at receptors but less stable than hexamer. Limited diffusion into capillaries.
Monomer insulin molecules- biologically active at receptors but not stable. Rapid diffusion into capillaries.
The speed of hexamer dissociation determines the observed pharmacokinetic and pharmacodynamics profiles of an insulin preparation.
Different states of association of insulin
Naturally occurring insulin in the beta cells self associated into dimers. Three dimers combine with 2 zinc ions to form a hexameric complex (an adaptation for maximal storage capacity within beta cell).
Insulin from these hexamers (previously released by exocytosis from the beta cells) is converted to biologically active monomers which enters the blood stream and act on the insulin receptors at the target tissue.
The formulation and release issue
Soluble human insulin consists of hexameters, which dissociate into dimers and monomers at the injection site.
There is a black face between injection of hexamers and the availability of biologically active dimers and monomers at target tissues- therefore soluble human insulin should be given 30 mins before a mean which can be hard to work out.
Compare to human physiology, insulin peak after s.c. injection of regular insulin is too late and not high enough.
The short acting insulin analogues were developed to overcome the flaws in the pharmacokinetics of human regular insulin.
NPH insulin- intermediate acting
- 1936 promise zinc insulin described.
- 1946 Neutral Protamine Hagedorn (NPH) introduced- a neutral (no charge) insulin with prolonged action.
- NPH insulin’s provided as a crystalline suspension of insulin with protamine and zinc, resulting in an onset of action in 1 to 3 hours, duration of action up to 24hrs, and peak action from 6-8 hours (prolonged action time as it takes a while for the crystals to breakdown).
- Due to the added crystals, NPH insulin is typically cloudy when compared to other forms of insulin and has a neutral pH.
- Available as Novolin N and Humulin N. Can be mixed with regular insulin.
Lente insulins- long acting
Formulations made available in 1953.
Zinc used as delaying agent. The duration of action is proportional to the size of the crystals from zinc complexes.
Hypurin Bovine Lente is available in the UK as a zinc suspension.
Modified insulins- ultra long acting
Insulin glargine (Lantus-Aventis)
- One amino acid has been replaced by two amino acids at the end of the B chain. This modification makes it more soluble at an acidic pH, but much less soluble at the neural pH that is found in the body
- Acidic solution which micro precipitates after s.c. injection due to reduced solubility at physiological pH
- Crystals dissolve slowly to release insulin glargine with full activity after 4-5- hours and sustained to 24 hours (no significant peak)
Insulin detemir (Levemir)
- One amino acid omitted from the end of the B chain and replaced with a fatty acid. Insulin detemir does not form a precipitate upon injection. Instead, detemir’s action is extended because its altered form makes it stick to itself in the subcutaneous depot (injection site), so it is slowly absorbed.
- Once the detemir molecules dissociate from each other, they readily enter the blood circulation, but there the added fatty acid binds to albumin.
Modified insulins- rapid acting
Lispro insulin (Humalog)
- Onset in 10-15 mins
- Avoids need to carefully plan time of injection prior to a meal (much easier)
- Peak at 30-90 minutes with duration of 3-5 hours
- Lysine and proline residues are ‘switched’ on C-terminal of the B chain (does not form hexamers and dimers only monomers so faster acting)
- Other similarly modified insulins are Aspart and Glulisine
- Modification of the residues prevents dimers (and hexamers) forming so the injection contains only monomers
- These modified insulins can still bind to the receptor
Pump insulins
- Pump insulins are also known as Continuous Subcutaneous Insulin Infusion (CSII).
- The first prototype was a backpack designed in 1963. The first wearable device was developed in 1973.
- Currently CSII are small pumps worn around the waist that infuse a constant trickle of insulin.
- There were a number of issues with the development as the insulin aggregated in the lines, buffered insulin formulations were then tried and new tubing materials developed.
- In the end it was found that the use of less aggregating insulins (e.g. lispro) which breakdown quickly was the solution.
- Risks/disadvantages
- Skin infection
- Ketoacidosis if flow is interrupted (there is no depot in the reserve)
- The pump site must be moved every 2-3- days
Automated insulin delivery device- artificial pancreas
Medtronic’s MiniMed 670G hybrid closed loop system is the first FDA-approved device that is intended to automatically monitor glucose and provide appropriate basal insulin doses.
‘Artificial human pancreas’ which naturally supplies a low, continuous rate of insulin. It
- adjusts insulin levels with little or no input from the user by measuring glucose levels every 5 minutes and automatically administering or withholding insulin
- includes a sensor that attaches to the body to measure the glucose levels under the skin, an insulin pump strapped to the body, and an infusion patch connected to the pump with a catheter that delivers insulin.
While the device automatically adjusts insulin levels, users need to manually request insulin doses to counter carbohydrate (meal) consumption.
Alternatives to injection of insulin- inhaled insulin
- Dry powder formulation of recombinant human insulin which is absorbed through the lung alveoli
- Extensive studies have shown a similar kinetic profile to fast acting injected insulin
Exubera-Pfizer was marketed for a short period of time (2006-2007) then removed.
Afrezza-Sanofi withdrew from a $925 million marketing agreement with MannKind (2014-16).
These were both removed due to poor sales volume. The price of inhaled insulin is much greater than that of injected insulin. The patient also still needs basal injections at night time so it does not completely remove the need for injection.
Alternatives to injection of insulin- Buccal
Buccal insulin (Oralin-Generex)
- uses RapidMist technology to deliver insulin to buccal mucosa
- the technology enables alternative delivery of both small and large molecules through an oral spray providing convenience, metered dosing, and the elimination of injections
- mixture of insulin, surfactants and lipids
- high velocity, fine particle aerosol resulting in increased deposition on mucosa with thin membranes and superficial blood vessels. This leads to rapid uptake
