As part of a study on the interaction between diuretics and renal prostaglandins, four healthy medical students receiving indomethacin for 8 days were also given triamterene for 3 days. Whereas renal function was initially normal in all four subjects, creatinine clearance decreased in two by 62% and 72% after concomitant administration of the two drugs, and was only restored to normal after 4 weeks. In control periods when triamterene or indomethacin was given alone renal function was preserved in all subjects. Urinary prostaglandin E2 was stimulated by triamterene and inhibited by indomethacin in all four subjects; both changes were more marked in the two sensitive subjects. Thus prostaglandin inhibition by indomethacin may unmask triamterene toxicity and contribute to the pathogenesis of the renal failure observed in sensitive subjects. As alternative therapy is readily available, avoidance of this potentially nephrotoxic association is recommended.

1. The influence of four diuretics on renal prostaglandins was investigated in a study designed in two parts (A and B): A, 24 normal subjects on a constant sodium intake received frusemide (80 mg daily), or hydrochlorothiazide (100 mg), or triamterene (200 mg) or spironolactone (300 mg); B, the same subjects were pretreated for 3 days with indomethacin (150 mg daily), which was continued during the 3 day administration of the respective diuretics and during a 2 day post-diuretic period. 2. In study A, only triamterene provoked a rise in urinary prostaglandins E2 and F2 alpha (+ 474 +/- SEM 92%, P less than 0.01, and + 192 +/- 7%, P less than 0.01). In study B, prostaglandins were significantly inhibited in all subjects. After indomethacin, the natriuretic effect of frusemide and spironolactone was reduced by 80 +/- 12% (P less than 0.01) and 54 +/- 11% (P less than 0.001), whereas the natriuresis induced by hydrochlorothiazide and triamterene was unchanged. No correlation was found between urinary PGE2 and F2 alpha and natriuresis. 3. When triamterene was associated with indomethacin, two subjects developed reversible acute renal failure. 4. Plasma renin activity and urinary aldosterone were stimulated by the four diuretics in study A, but their response was blunted in study B. Urinary antidiuretic hormone was not modified by diuretics but was suppressed by indomethacin. 5. Diflunisal, a structurally unrelated nonsteroidal anti-inflammatory drug, given to 12 of the subjects provoked similar interactions with frusemide, hydrochlorothiazide and spironolactone. 6. The results suggest that prostaglandins contribute to the natriuretic effects of frusemide and spironolactone, but not to those of hydrochlorothiazide and triamterene.

Twenty-four hour ambulatory blood pressure and heart rate profiles of 24 patients with diabetes were monitored in order to assess the effect of autonomic neuropathy on 24-h haemodynamic profiles. Eighteen patients had abnormal cardiovascular reflexes. Mean arterial pressure rose at night in six of the patients with autonomic neuropathy and fell by less than or equal to 5 mmHg in seven. In the remaining five patients with autonomic neuropathy and in the six diabetic patients with normal cardiovascular reflexes, the fall in nocturnal mean arterial pressure was comparable to that of 11 non-diabetic patients with essential hypertension. Median 24-h mean arterial pressure was similar in all four groups of diabetic patients. Prevalence of autonomic symptoms was not related to the change in blood pressure in those with autonomic neuropathy. Twenty-seven months after monitoring, three fatal and five severe non-fatal cardiovascular or renal events had occurred in four of the six patients with a rise in nocturnal blood pressure, compared with one non-fatal event in those with a small fall and no severe events in those with a pronounced fall (p = 0.02). Blood pressure rises at night in certain diabetic patients with abnormal cardiovascular reflexes and the nocturnal rise appears to be associated with a poor prognosis.

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