The lente types of Semilente, Lente and Ultralente are also called zinc suspension insulins.
The Merck Manual defines semilente insulin as a short-acting, slightly slower than R/neutral and Analog insulins, insulin containing zinc microcrystals in an acetate buffer. This insulin is known by two other names: Prompt Zinc and Prompt Lente; this to distinguish it from the Lente and Ultralente insulins which are also part of the zinc suspension group, but whose onsets are slower and whose durations are longer.
Semilente's time activity profile is very much like that of R/neutral. It beginsworking within 45 minutes, peaks in 2-4 hours and has a 4-6 hour duration. Unlike R/neutral, it is "cloudy", not clear, and is not soluble, therefore unable to be used intervenously. This type of insulin was once as available as R/neutral; many people preferred it over R/neutral for bolus insulin. It has now almost disappeared entirely from the market. We know semilente best as one of the two lente-types which comprise Lente insulin; Ultralente is the other.