ates in a patient taking digoxin, toxicity may occur. Therefore a change in renal function may be an indication for serum digoxin assay. In summary, the serum digoxin assay may be of value in certain conditions, but the physician should use the test appropriately and be aware of its limitations: 1. Although some arrhythmias are characteristic of digitalis toxicity, none is pathognomonic;19 hence the most important procedure is to determine whether the arrhythmia resolves with cessation of use of the drug. 2. Patients with coexistent metabolic, electrolyte or pulmonary disturbance may have serum digoxin values in the normal range, yet may experience digitalis toxicity because of increased sensitivity to cardiac glycosides. 3. True digoxin resistance may occur in patients with atrial fibrillation or hy-

perthyroidism, and in children. Apparent digoxin resistance may occur with poor patient compliance, low bioavailability and drug-associated malabsorption. A. DODEK, MD, FRCP[C], FACC, FACP

St. Paul's Hospital Vancouver, BC

References I. wITHERING W: An account of foxglove and some of its medical uses; with practical remarks on dropsy, and other diseases. Med Classics 2: 305, 1937 2. SMITH TW: Digitalis toxicity: epidemiology and clinical use of serum concentration measurements. Am J Med 58: 470, 1975 3. INGELFINOER JA, GOLDMAN P: The serum digitalis concentration - does it diagnose digitalis toxicity? N Engi J Med 294: 867, 1976 4. MARCUS Fl: Current concepts of digoxin therapy. Mod Concepts Cardlovase Dis 45: 77, 1976 5. HAYEs CJ, BUTLER VP .js, GERSONY WM: Serum digoxin studies in infants and children. Pediatrics 52: 561. 1973 6. GOLDMAN 5, PRoasT P, SELZER A, et al: Inefficacy of "therapeutic" serum levels of digoxin in controlling the ventricular rate in atrial fibrillation. Am I Cardiol 35: 651, 1975

7. BELLEs GA, HOOD WB, SMITH TW, et al: Correlation of serum magnesium levels and

cardiac digitalis intoxication. Am I Cardiol 33: 225, 1974 8. MORRISON J, KiLus' T: Hypoxemia and digitalis toxicity In patients with chronic lung disease (abstr). Circulation 44 (suppi LI): 11-41, 1971 9. DOHERTY JE, PERKINS WH: Digoxin metabolism in hypo- and hyperthyroidism: studies with tritiated digoxin in thyroid disease. Ann Intern Med 64: 489, 1966 10. MORRISON J, KiLui' T: Serum digitalis and arrhythmia in patients undergoing cardiopulmonary bypass. Circulation 47: 341, 1973 11. BLISS HA, FISHMAN WC, SMITH PM: Effect of alterations of blood pH on digitalis toxicity. I Lab Clin Med 62: 53, 1963 12. EDMONDS YE, HOWARD PL, TRAINER TD: Measurement of digitoxin and digoxin. N Engi I Med 286: 1266, 1972 13. KOCH-WESER J, DUNME DW, GREENBLATT DJ: Influence of serum digoxin concentration measurements on frequency of digitoxicity. Clin Pharmacol Ther 16: 284. 1974 14. OGILvIE RI, RUEDY I: An educational program in digitalis therapy. JAMA 222: 50, 1972 15. LINDENDAUM

16. 17. 18. 19.

I,

MELLOW

MH,

BLACKSTONE

MO, et al: Variation in biologic availability of digoxm from four preparations. N Engi I Med 285: 1344, 1971 HEIZER WD, SMITH TW, GOLDFINGER SE: Absorption of digoxin in patients with rnalabsorption syndromes. Ibid, p 257 BROWN DD, Jusn. HP: Decreased bloavailability of digoxin due to antacids and kaolinpectin. N Engi I Med 295: 1034, 1976 MARCUS Fl: Digitalis pharmacokinetics and metabolism. Am I Med 58: 452, 1975 BINNION PF: The plasma-digoxin controversy. Lancet 1; 535, 1972

Unanswered questions about prazosin hydrochloride Another new antihypertensive agent toms and signs disappeared. Three days has been marketed in Canada pra- after treatment was resumed acute arzosin hydrochloride (Minipress) - and thritis of the right wrist developed; this the general practitioner may wonder episode of arthritis also resolved when about its place in the management of treatment with prazosin was disconuncomplicated essential hypertension. tinued. According to the Manitoba Drug InNo data have been published that formation Bulletin1 prazosin "is not the can answer satisfactorily the important drug of choice with which to initiate practical questions regarding treatment antihypertensive treatment"; the pre- with prazosin. What is the time referred. agent is a diuretic. Which agent quired for the full effect of prazosin to should be added if a second one is appear when this drug is used alone needed is more debatable but most ex- and when it is combined with a diurperts favour a /3-blocker such as pro- etic, a /3-blocker or a sympathoplegic? pranolol or a sympatholytic agent such What is the dose of prazosin required as methyldopa. The effectiveness of initially when the patient is taking a these agents is well documented, their full dose of chlorthalidone, clonidine side effects are well known and easily or propranolol? Is the reported case detectable, and their full effects do not of polyarthritis an isolated incident or is this complication going to occur with take long to appear. In general, peripheral vasodilators the same incidence as lupus erythemacause more problems for the prescrib- tosus in patients taking hydralazine? Is ing physician and the patient than other it possible that certain patients will types of antihypertensives: hydralazine metabolize prazosin very slowly, so may cause headaches, palpitations and, that plasma concentrations will be unin patients with coronary artery dis- expectedly high, as is the case for ease, angina; it may also induce a hydralazine in "slow acetylators"? lupus-erythematosus-like syndrome. PraIt is possible, though not yet demzosin has produced syncope after the onstrated, that prazosin may have a first dose, though this occurred with place in lieu of hydralazine in the higher doses than are now recom- management of certain patients with mended in Canada.3 Cairns and Jordan3 severe hypertension whose disease is reported acute febrile polyarthritis in resistant to the classic combinations of a 32-year-old man who had taken pra- well known agents. It is in these pazosin for 10 weeks. Acute arthritis of tients, usually treated by a specialist, the right elbow and both knees was ac- that controlled trials should be done companied by a large effusion in the to compare hydralazine and prazosin right elbow joint: when treatment with for their maximal efficacy and for the prazosin was discontinued the symp- speed of onset of their antihypertensive .6 CMA JOURNAL/NOVEMBER 5, 1977/VOL. 117

effect. These findings should then be weighed against the frequency and magnitude of side effects of each vasodilator. It is difficult to think of a good reason for initiating therapy with prazosin in a patient with newly diagnosed hypertension or for substituting it for better known agents that are controlling moderate or severe hypertension. PIERRE BIRON, MD Department of pharmacology Universit6 de MontrEal MontrEal, J'Q

References 1. Manitoba Drug Standards and Therapeutics Committee: Prazosin (Minipress-Pfizer). Drug Inf Bull 18: 1, 1977 2. Prazosin (Minipress) for hypertension. Med Lett Drugs Ther 19: 1, 1977 3. CAIRNS SA, JORDAN SC: Prazosin treatment complicated by acute febrile polyarthritis. Br Med 1 2: 1424, 1976

BOOKS continued from page 992 CURRENT CONCEPTS IN THE MANAGEMENT OF CHRONIC PAIN. Edited by PIerre 1. LeRoy, Magdy I. Boulos and Joan Goloskov. 192 pp. IlIust. Stratton Intercontinental Medical Book Corporation; Longman Canada Limited, Don Mills, 1977. $19.50. ISBN 0-88372-091-4 ETHICAL ISSUES IN SEX THERAPY AND RESEARCH. Reproductive Biology Research Foundation Conference. Edited by William H. Masters, Virginia E. Johnson and Robert C. Kolodny. 227 pp. Little, Brown and Company (Inc.), Boston, 1977. $12.50. ISBN 0-316-549-835 HEALTH AND DISEASE IN TRIBAL SOCIETIES. Ciba Foundation Symposium 49 (new serIes). 344 pp. II lust. Elsevier-Excerpta Medics-North-Holland, Amsterdam; Excerpta Medica, Amsterdam, 1977. $29. ISBN 0-444-15271-7

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