Association of Metformin With the Development of Age-Related Macular Degeneration

Importance

Age-related macular degeneration (AMD) is a leading cause of blindness with no treatment available for early stages. Retrospective studies have shown an association between metformin and reduced risk of AMD.

Objective

To investigate the association between metformin use and age-related macular degeneration (AMD).

Design, Setting, and Participants

The Diabetes Prevention Program Outcomes Study is a cross-sectional follow-up phase of a large multicenter randomized clinical trial, Diabetes Prevention Program (1996-2001), to investigate the association of treatment with metformin or an intensive lifestyle modification vs placebo with preventing the onset of type 2 diabetes in a population at high risk for developing diabetes. Participants with retinal imaging at a follow-up visit 16 years posttrial (2017-2019) were included. Analysis took place between October 2019 and May 2022.

Interventions

Participants were randomly distributed between 3 interventional arms: lifestyle, metformin, and placebo.

Main Outcomes and Measures

Prevalence of AMD in the treatment arms.

Results

Of 1592 participants, 514 (32.3%) were in the lifestyle arm, 549 (34.5%) were in the metformin arm, and 529 (33.2%) were in the placebo arm. All 3 arms were balanced for baseline characteristics including age (mean [SD] age at randomization, 49 [9] years), sex (1128 [71%] male), race and ethnicity (784 [49%] White), smoking habits, body mass index, and education level. AMD was identified in 479 participants (30.1%); 229 (14.4%) had early AMD, 218 (13.7%) had intermediate AMD, and 32 (2.0%) had advanced AMD. There was no significant difference in the presence of AMD between the 3 groups: 152 (29.6%) in the lifestyle arm, 165 (30.2%) in the metformin arm, and 162 (30.7%) in the placebo arm. There was also no difference in the distribution of early, intermediate, and advanced AMD between the intervention groups. Mean duration of metformin use was similar for those with and without AMD (mean [SD], 8.0 [9.3] vs 8.5 [9.3] years; P = .69). In the multivariate models, history of smoking was associated with increased risks of AMD (odds ratio, 1.30; 95% CI, 1.05-1.61; P = .02).

Conclusions and Relevance

These data suggest neither metformin nor lifestyle changes initiated for diabetes prevention were associated with the risk of any AMD, with similar results for AMD severity. Duration of metformin use was also not associated with AMD. This analysis does not address the association of metformin with incidence or progression of AMD.

[Hypercapnia and mixed acidosis as the only sign of malignant hyperthermia (MH)?]

CASE REPORT

A 34-year-old male (190 cm/100 kg) was scheduled for surgery of the nasal septum. He had had uneventful anaesthesia for appendicectomy 14 years earlier: following 600 mg thiopentone, 180 mg suxamethonium and up to 2 vol.% halothane for 20 min had been used and no symptoms of malignant hyperthermia (MH) were recorded. Following oral premedication with 2 mg flunitrazepam at 7.00 a.m. anaesthesia was induced with a priming dose of atracurium at 8.45 a.m. followed by 0.2 mg fentanyl, 500 mg thiopentone, and 100 mg suxamethonium. Endotracheal intubation was accomplished easily, and the patient was ventilated manually in a semi-closed circle system until spontaneous ventilation resumed. Enflurane (1.5% for 5 min, 1.0% for 10 min, and 0.8% until the diagnosis of MH was suspected) was given in 33% O2/66% N2O. Seventy minutes after induction it was noted that the spontaneous respiratory rate and minute volume had risen continuously from 10/min and 6 l/min, respectively, to 20/min and 12 l/min. Attempts at deepening anaesthesia with repeated doses of fentanyl up to a total dose of 0.95 mg failed to reduce the hyperventilation. In spite of a high fresh gas flow of 6 l/min and assisted manual ventilation, the FIO2 started to fall from 0.34 to 0.28 at 10:20 a.m. The O2/N2O ratio was changed to 1:1, but the FIO2 remained at 0.3. MH was suspected, enflurane was discontinued, and an arterial blood gas analysis was done (Table 2). When marked acidosis and hypercarbia were found, dantrolene 2.5 mg/kg was given, the operation was terminated, and the patient's trachea was extubated and he was monitored closely in the intensive care unit for 24 h. Vital signs were stable (Table 3) and no further complications were observed. The patient did not mention pain or uneasiness postoperatively. About 6 months later, a muscle biopsy was done according to the European MH Protocol and the patient was found to be MHEh.

DISCUSSION

In this case five main reasons for the hypercarbia and mixed acidosis must be considered (Table 1). Firstly, hypoventilation does not seem to be reasonable as the patient was ventilated with 8 to 12 l/min, which is within the range of 80-120 ml/kg.min. Secondly, we can exclude shock and hypoperfusion because the patient had a normal blood pressure and heart rate (within 65-90 beats/min), his fingertips and skin were well perfused, his body temperature was 37 degrees C, and there was no sign of muscle rigidity. Thirdly, a defect of the CO2 absorber as well as CO2 admixture to the N2O and O2 ventilation gases can cause hypercarbia. We use two absorbers in sequence of which one is changed every day, and found neither a change in colour of the indicator nor an abnormally raised temperature of the absorbers. A postoperative check of the ventilator showed no defect in the O2/N2O supply and a correctly functioning anaesthesia apparatus. A malfunction of both CO2 absorbers resulting in intraoperative hypercarbia could not explain a postoperative mixed acidosis lasting for more than 6 h. Anaesthesias performed at the same time using soda lime from the same canisters were totally uneventful.

CONCLUSION

It is concluded that the hypercarbia and mixed acidosis were caused by hypermetabolism. A thorough postoperative examination by an internist did not reveal any thyroid, pulmonary, endocrine, or circulatory reason for our intra- and postoperative findings. Iatrogenic factors like superficial anaesthesia or systemic side effects of adrenaline admixture to local anaesthetics can cause hypermetabolism without striking clinical signs, but they do not cause mixed acidosis lasting longer than 6 h (Table 2). The most suitable explanation in this case is an abortive form of MH. Even patients who are MHS positive on muscle biopsy do not necessarily go through an MH crisis every time they have stress or undergo anaesthesia. The diagnosis of a fulminant MH crisis is a clinical one. Therefore, we are aware that there is no direct scientific ev

[Oleic acid-induced interstitial lung edema in the dog: comparison of PEEP with high-frequency jet superimposed ZEEP ventilation]

Oleic acid (0.12 ml/kg) was used to induce pulmonary edema in 10 mongrel dogs. To treat the consequent hypoxaemia we used either positive end expiratory pressure (PEEP) ventilation (n = 5) or zero end expiratory pressure ventilation (ZEEP) plus additional high frequency jet support (n = 5). Hypoxaemia, which paralleled the dramatic increase in lung water, was significantly improved (aADO2) by PEEP but not by ZEEP plus jet. Also venous admixture was significantly lowered by PEEP only. Cardiac output and pulmonary arterial pressure in the two groups were not significantly different. This demonstrates that ZEEP plus jet is not superior to PEEP in the case of oleic acid induced edema, though we obtained good clinical results with the former system in the treatment of atelectasis. In addition, histological evaluation of the dog lungs showed emphysematous lung injury by the jet system, which indicates that such a jet system should be used with caution.

[Choice of anaesthesia technique in thoracic endoscopic sympathectomy (author's transl)]

Thoracic endoscopic sympathectomy (TES) is a short surgical procedure used for the treatment of palmar and axillary hyperhidrosis. It involves pneumothorax, the lateral and head up position, and necessitates minimal chest excursions during breathing, so that a special type of anaesthesia is required. In 13 patients two different methods were compared and blood gas analysis as well as circulatory parameters were studied. We therefore propose an anaesthetic method using controlled mechanical ventilation; relaxation; intravenous anaesthesia; at least 1 1 fluid replacement; and careful monitoring.

[Acute poisoning with tricylic antidepressants and treatment with physostigmine salicylate (author's transl)]

Three cases of self poisoning with tricyclic antidepressants (TAD) are reported, one of them with a potentially lethal dose. All three cases were treated with physostigmine salicylate (PS) and in two cases there was complete reversal of coma within a few minutes. In striking contrast to the reported high incidence of cardiac arrhythmias no cardiac complications were observed in any of the cases. Therefore we think that the use of PS should be considered when treating cases of TAD poisoning.

[Severe accidental acrolein intoxication in the home (author's transl)]

In a private household overheated fat-containing food emitted vapours which caused severe intoxication in a previously healthy man. The resulting pulmonary changes presented a grave threat to the patient's life for several days. The origin and properties of the vapours led to the conclusion that acrolein was their major toxic component.