Insulins
Insulins are synthetic polypeptide hormones. They:
- Have a similar mechanism of action and pharmacodynamics of endogenous insulin
- One unit of insulin is defined as the amount required to make a previously healthy 2kg rabbit hypoglycaemic
Types of Insulin
Different insulins are categorised by their time of onset, peak, and duration, and are classified as either:
- Fast acting
- Intermediate acting
- Long acting
Fast Acting
Fast acting insulins are used for controlling BSL spikes post meals, and for control of hyperglycaemia. Administered subcutaneously they have have an:
- Onset of 5-15 minutes
- Peak at 1-2 hours
- Last 4-6 hours.
Fast acting insulins include:
- Insulin Aspart (Novorapid)
- Insulin Lispro (Humalog)
Intermediate Acting
Intermediate acting insulins are used for control of BSL between meals as a pseudo-basal bolus. Administered subcutaneously they have an:
- Onset of 1-2 hours
- Peak at 4-6 hours
- Last >12 hours
Intermediate acting insulins include:
- NPH
- Protophane
Long Acting
Long acting insulins are used for creating a baseline insulin level. Administered subcutaneously they have an:
- Onset of 1-1.5 hours
- Peak at 5 hours
- Last 24 hours
Long-acting insulins include:
- Insulin glargine (Lantus)
- Insulin detemir (Levemir)
Pharmacokinetics of Exogenous Insulin Preparations
| Property | Drug |
|---|---|
| Class | Synthetic polypeptide hormones |
| Uses | Diabetes, hyperglycaemia, hyperkalaemia, β-blocker toxicity, Ca2+-blocker toxicity |
| Presentation | Clear colourless solution typically at 100 IU.ml-1 |
| Route of Administration | SC, IM, IV |
| Absorption | Variable, as described above. Insulin is complexed with different substances (e.g. protamine, zinc), which alter its rate of absorption |
| Distribution | Minimal protein binding and minimal redistribution out of ECF - VD 0.075L.kg-1 |
| Metabolism | Glutathione insulin transhydrogenase. Metabolism is constant - duration of action is entirely due to different rates of subcutaneous absorption. |
| Elimination | Renal of inactive metabolites |
References
- Diabetes Education Online. Types of Insulin. UCSF. Accessed January 2016.
- Graph of insulin activity profiles from: Diabetes Education Online. Types of Insulin. UCSF. Accessed January 2016.
- Mudaliar S, Mohideen P, Deutsch R, Ciaraldi TP, Armstrong D, Kim B, Sha X, Henry RR. Intravenous glargine and regular insulin have similar effects on endogenous glucose output and peripheral activation/deactivation kinetic profiles. Diabetes Care. 2002 Sep;25(9):1597-602.
- Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.