Hormonal counterregulation, symptom awareness, and neurophysiological function in type 1 diabetes during insulin-induced hypoglycaemia

Hypoglycaemia induced by exogenous insulin--'human' and animal insulin compared

AIMS

A systematic review of the literature was carried out to examine whether published evidence suggests a difference in the frequency and awareness of hypoglycaemia induced by 'human' and animal insulin.

METHODS

The review identified randomized controlled trials and studies of other designs including observational comparisons, case series and case reports in which the use of 'human' insulin was compared to animal insulin in people with diabetes. These were identified from bibliographic databases and hand-searches of key journals. The main outcome measures were frequency, severity, awareness and symptoms of insulin induced hypoglycaemia.

RESULTS

Fifty-two randomized controlled trials, 37 of double-blind design, were identified which included one or more of the relevant outcome measures. Of these, 21 specifically investigated hypoglycaemic frequency and awareness as primary outcomes (six in people with previously reported reduced hypoglycaemic awareness). The remainder of the identified trials reported hypoglycaemic outcomes as a secondary or incidental outcome during comparative investigations of efficacy or immunogenicity. Seven of the double-blind studies reported differences in frequency of hypoglycaemia or awareness of symptoms, although none of the studies which selected subjects on the basis of previously reported impaired awareness demonstrated significant differences between insulin species. Four of the unblinded trials reported differences in hypoglycaemia. This reached statistical significance in two of the studies. A further 56 studies of other designs and case reports were considered. In addition to the 10 case reports describing individuals with impaired hypoglycaemic awareness, nine studies reported differences in the incidence and manifestation of hypoglycaemia during 'human' insulin treatment. Notably, none of the four population time trend studies found any relationship between the increasing use of 'human' insulin and hospital admission for hypoglycaemia or unexplained death among those with diabetes. The largest case series could find no support for the hypothesis that an influence of treatment with 'human' insulin on hypoglycaemia had contributed to any of the 50 deaths investigated. When all types of studies considered are ranked in order of rigour (according to the accepted 'hierarchy of evidence'), it is the least rigorous which lend most support to the notion that treatment with 'human' insulin has an effect on the frequency, severity or symptoms of hypoglycaemia.

CONCLUSIONS

Evidence does not support the contention that treatment with 'human' insulin per se affects the frequency, severity or symptoms of hypoglycaemia. However, a number of studies, mainly those of less rigorous design, describe an effect when people are transferred from animal insulin to 'human' insulin. It is not possible to state how common this is or whether the phenomenon is specific to 'human' insulin or an effect resulting from stricter glycaemic control (perhaps compounded, in some cases, by neurological complications in long-standing diabetes). This remaining uncertainty makes it essential that insulin from animal sources continues to be available so that clinicians and patients may retain this choice of treatment.

Human insulin and hypoglycaemia: a literature survey

Thirty-nine clinical studies and 12 epidemiological reports comparing human insulin and porcine insulin were reviewed. Twenty-five studies (encompassing 338 subjects) showed identical symptoms and physiological response to acute hypoglycaemia overall. Fifteen studies (encompassing more than 1253 patients) showed identical incidence of hypoglycaemia overall and similar symptoms with the two types of insulin. Twelve studies showed identical incidence of hypoglycaemia overall with the two types of insulin. Thus, the overwhelming evidence from a large number of studies including a large number of patients suggests that: (1) human and porcine insulin do not provoke different hormonal responses to hypoglycaemia; (2) they do not cause different symptoms of hypoglycaemia; (3) the incidence of severe hypoglycaemia with human insulin does not differ from that of porcine insulin.

Recovery of hypoglycaemia-associated compromised cerebral function after a short interval of euglycaemia in insulin-dependent diabetic patients

To test the hypothesis that compromised cerebral function, induced by recurrent hypoglycaemic episodes, may recover after a short interval of euglycaemia, we examined electrophysiological activity and symptom awareness during two sequential euglycaemic-hypoglycaemic clamp studies in 11 insulin-dependent diabetic patients without any signs of peripheral or autonomic neuropathy. Neurophysiological testing and evaluation of hypoglycaemic symptoms were performed at stable glycaemic plateaus of 5.6, 3.3, 2.2, and 1.7 mmol/l. The first clamp study was preceded by 3 short-term hypoglycaemic episodes, whereas the second clamp study followed a 2 day interval of strict euglycaemia. The latter caused a recovery of electrophysiological activity, which was demonstrated by recovery of delays of the middle latency auditory evoked potentials (latency shift of the P(a) component, MANOVA, P < 0.01). Reversal of hypoglycaemic symptom unawareness involved the overall symptom perception (MANOVA, P < 0.04), as well as the autonomic symptoms of heart pounding (P < 0.05) and sweating (P < 0.05). We conclude that the previously reported impaired cerebral function, occurring as a consequence of repetitive hypoglycaemic episodes, may recover after a single euglycaemic interval.

Changing from porcine to human insulin

The development of hypoglycaemia unawareness is associated with long duration of diabetes, improved glycaemic control, alcohol intake and recurrent hypoglycaemia. However, current evidence suggests that neither frequency of severe episodes nor mortality from hypoglycaemia are increased following a change from animal to human insulin. Nevertheless, a small number of patients continue to report an alteration in the nature of hypoglycaemic warning symptoms following a change in insulin species. This is possibly a consequence of a reduced catecholamine response to lowering blood glucose levels or to species differences in the effect of insulin on central nervous system function. In practical terms, it seems sensible to warn patients that the nature of the symptoms associated with hypoglycaemia might alter following conversion from porcine to human insulin. At the time of the changeover, patients should be encouraged to perform frequent blood glucose measurements. Also, the usual insulin dose should be reduced by 10% at the start of human insulin treatment. Other aspects of insulin treatment including injection technique, meal timing, exercise, etc. should be discussed. For patients who are convinced that loss of warning of hypoglycaemia occurred after conversion from porcine to human insulin, a change back to animal insulin would be preferred to relaxing glycaemic control in the first instance. Pressure should be brought to bear on the pharmaceutical industry to maintain the availability of animal insulins for the small number of patients who have experienced problems with human insulin.