title: Studies on the mechanism of trimethoprim-induced hyperkalemia.
abstract: We examined the effects of trimethoprim (TMP) on metabolic parameters and renal ATPases in rats after a 90 minute infusion (9.6 mg/hr/kg body wt, i.v.) and after 14 days (20 mg/kg body wt/day, i.p.). After one dose of TMP, plasma electrolytes, arterial pH and aldosterone levels were normal, but a natriuresis, bicarbonaturia, and decreased urinary potassium excretion occurred. Na-K-ATPase activity in microdissected segments from these animals was decreased by 36 +/- 0.9% in proximal convoluted tubule (PCT) (P < 0.005); decreases of 50 +/- 2.1% and 40 +/- 1.1% were seen in cortical and medullary collecting tubules (CCT and MCT), respectively (P < 0.005). Na-K-ATPase activity was unaffected in medullary thick ascending limb (MTAL). H-ATPase (in PCT and collecting duct) and H-K-ATPase (in CCT and MCT)-activities were not changed. Following chronic TMP administration, plasma potassium increased as compared to control (5.16 +/- 0.05 mEq/liter vs. 3.97 +/- 0.05 mEq/liter, P < 0.05), however, acid-base status and plasma aldosterone levels were normal. Na-K-ATPase activity was decreased by 45 +/- 2.6% in PCT (P < 0.005), 73 +/- 2.0% in CCT (P < 0.001), and 53 +/- 2.5% in MCT (P < 0.005). Na-K-ATPase, activity in MTAL and H-K-ATPase activity in CCT and MCT were unchanged. H-ATPase activity in PCT and MTAL was normal, but in the collecting tubule (CCT and MCT) it was decreased by approximately 25% (P < 0.05). TMP inhibited Na-K-ATPase activity in a dose-dependent fashion in PCT, CCT, and MCT when tubules from normal animals were incubated in vitro with the drug; TMP in vitro did not affect H-ATPase or H-K-ATPase activity. These results suggest that TMP-induced hyperkalemia may result from decreased urinary potassium excretion caused by inhibition of distal Na-K-ATPase, in the face of intact H-K-ATPase activity.
authors.affiliation: Department of Physiology, Texas Tech University Health Sciences Center, Lubbock, USA.
authors.forename: S
authors.initials: S
authors.lastname: Eiam-Ong
authors.forename: N A
authors.initials: NA
authors.lastname: Kurtzman
authors.forename: S
authors.initials: S
authors.lastname: Sabatini
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D000890:Anti-Infective Agents / Q000008:administration & dosage / Q000633:toxicity*; D006947:Hyperkalemia / Q000139:chemically induced*; D007262:Infusions, Intravenous; D007274:Injections, Intraperitoneal; D007668:Kidney / Q000187:drug effects / Q000503:physiopathology; D008297:Male; D051381:Rats; D014295:Trimethoprim / Q000008:administration & dosage / Q000633:toxicity*
chemical_list: D000890:Anti-Infective Agents; D014295:Trimethoprim; D000251:Adenosine Triphosphatases