There's more inside the tablet

Several years ago I was invited to be the medical officer for a geological expedition to the Arctic. The attractions of the beauty and grandeur of the high Arctic in summer are somewhat diminished by swarms of mosquitoes, which are notable for their size and ferocity. Even the locals find the attentions of the cuculid hordes hard to bear, with the caribou preferring to rest on patches of snow, where the lower air temperature discourages the biters. There was at that time unfounded speculation that B vitamins acted as systemic insect repellants,12 possibly because of the aroma of yeast excreted via the sweat. It therefore seemed a good idea to conduct a randomised clinical trial of the effect of daily vitamin B supplements on the number of mosquito bites. For convenience, I used a dark green multivitamin capsule, which we routinely gave to our patients with endstage renal failure.

I thought that the trial was perfect: using a safe intervention to prevent a distressing problem. However, my geologist colleagues were deeply suspicious from the start, perhaps because they were not keen on the idea of me counting their bites every day, or perhaps because randomisation had placed me in the control group. However, I persuaded them to participate and on the first night in mosquito country half the scientists took a vitamin capsule without ill effect. The following morning, however, I was woken by generalised uproar and howls of distress. The early risers had left their tents to relieve themselves, only to be shocked by the sight of fluorescent green urine.

The pea green urine was due partly to the colouring in the capsule. I thought this was interesting as, of course, I had not observed this colourful effect in the anuric dialysis patients, but my colleagues were convinced that they had barely escaped with their lives. Informed consent, such as it was, was immediately withdrawn. The trial collapsed and faith in the medical profession was restored only when one of the geologists fell several hundred feet down a snow field and I was able to help retrieve his bag of precious specimens (and render first aid).

Did I learn anything from this experience? Firstly, there is a great deal more inside a tablet or capsule than appears on the label. These colorants and other excipients may be biologically active.3 Secondly, even the most straightforward clinical trial may encounter unexpected problems and therefore requires stringent safety monitoring. Thirdly, if my dialysis patients could not excrete the colorant from the capsules, what became of it? Did it contribute to the patients' sallow skin and funny smell, which we had assumed to be due to anaemia and uraemia, but which we never see nowadays. Finally, what about the mosquito bites? I learnt that some individuals suffer disproportionately, being bitten more often or reacting more violently than their equally unwashed companions. I also learnt that tobacco smoke was far more effective than any of the then available insect repellants, but I suppose I am not allowed to say that.