How safe are folic acid supplements?

Periconceptual use of folic acid supplements by women is effective in preventing neural tube defects in the fetus. Folic acid supplements also may prevent atherosclerosis and some malignant neoplasms. Nevertheless, safety concerns have delayed recommendations to increase folic acid consumption by the general population. Among the potential safety issues of folic acid supplementation are (1) difficulty identifying cobalamin deficiency, precipitation of neurologic complications of cobalamin deficiency, and lowering of cobalamin levels; (2) folate neurotoxicity; (3) antagonism of drugs that inhibit folate metabolism; (4) reduced zinc absorption; (5) association with malignant neoplasms; (6) hypersensitivity reactions; and (7) increased susceptibility to malaria. The data that suggest that folic acid supplements are unsafe are weak and consist predominantly of case series and reports. Nevertheless, greater difficulty diagnosing cobalamin deficiency due to "masking" of hematologic abnormalities by folic acid is a potential risk. Strict vegetarians need to be informed that they are at risk of cobalamin deficiency. Physicians need to be aware that routine hematologic indexes have a low sensitivity for cobalamin deficiency, especially in patients who are receiving folic acid supplements. Because no high-quality data exclude specific adverse effects, physicians should be vigilant in identifying detrimental effects when patients increase their consumption of folic acid.

Aging and heparin-related bleeding

BACKGROUND

Many studies have suggested that elderly patients are at increased risk of bleeding during heparin therapy.

OBJECTIVE

To establish whether the risk of bleeding in the elderly results from concomitant risk factors or is associated with the aging process itself.

METHODS

One hundred ninety-nine patients who presented with proximal deep vein thrombosis were treated with a standard intravenous heparin protocol in a double-blind, randomized, prospective study. Bleeding complications were monitored. Activated partial thromboplastin times and heparin levels were assessed 4 to 6 hours after a standard intravenous heparin bolus and infusion. Heparin doses and heparin levels were also assessed after stable therapeutic heparin infusion rates were established.

RESULTS

There was an increase in total and major bleeding complications with aging (P < .05) that was not accounted for by standard risk factors for bleeding. Aging was associated with an increase in heparin levels (r = .239, P = .003) and a tendency for an increase in activated partial thromboplastin time (r = .134, P = .07) after standard heparin doses. Aging was also associated with lower heparin dose requirements (r = .267, P = .003) after therapeutic activated partial thromboplastin times were achieved.

CONCLUSION

Aging is a risk for heparin-related bleeding that may be explicable by age-related changes in the pharmacologic characteristics of heparin.

Ferrous sulfate does not reduce serum levels of famotidine or cimetidine after concurrent ingestion

A series of randomized crossover studies were performed to determine whether there was a reduction in serum levels of cimetidine and famotidine when coingested with ferrous sulfate (300 mg). Coingestion of a ferrous sulfate tablet with cimetidine (300 mg) was associated with little reduction in serum cimetidine area under the curve (AUC) (mean versus mean, 20.8 versus 23.4 mumol.hr/L; mean percentage difference, -11%; 95% confidence interval [CI] of percentage difference, -26% to 4.2%) or peak concentration (Cmax) (mean versus mean, 5.1 versus 6.1 mumol/L; mean percentage difference, -16%; CI of percentage difference, -36% to 4%). Similarly, ferrous sulfate solution coingested with cimetidine caused little change in cimetidine AUC (mean versus mean, 19.9 versus 23.0 mumol.hr/L; mean percentage difference, -13%; CI of percentage difference, -34% to 7%) or Cmax (mean versus mean, 5.0 versus 5.0 mumol/L; mean percentage difference, 1%; CI of percentage difference, -18% to 20%). Concurrent ingestion of famotidine (40 mg) with a ferrous sulfate tablet did not result in significant reductions in serum famotidine AUC (mean versus mean, 1.78 versus 1.99 mumol.hr/L; mean percentage difference, -10%; CI of percentage difference, -34% to 13%) or Cmax (mean versus mean, 0.31 versus 0.32 mumol/L; mean percentage difference, -3%; CI of percentage difference, -27% to 22%). The formation of famotidine:iron(III) complexes was shown in methanol but was not observed in an aqueous buffer at pH 6.5. Ranitidine did not bind iron in an aqueous buffer and only weakly bound iron in methanol. Coingestion of ferrous sulfate with either cimetidine or famotidine does not cause a clinically relevant reduction in serum histamine H2-receptor blocker levels and, on the basis of in vitro binding experiments, iron is unlikely to interact with ranitidine.

Reduced renal fractional excretion of lithium in cystic fibrosis

We hypothesized that patients with cystic fibrosis would have abnormal lithium handling because the genetic defect in cystic fibrosis encodes an ion channel which causes a generalized electrolyte transport disorder in epithelial membranes. Eight patients with cystic fibrosis and eight age-sex matched healthy subjects ingested 600 mg lithium carbonate and had urine and serum lithium levels assessed 24 h later. Compared with healthy subjects, the patients with cystic fibrosis had higher serum lithium levels (0.071 +/- 0.038 vs 0.113 +/- 0.055 mmol l-1, P = 0.03) and had lower fractional renal excretion of lithium (27.5 +/- 14.8 vs 18.8 +/- 9.3%, P = 0.03). Caution should be used in prescribing standard doses of lithium to patients with cystic fibrosis until more definitive data are available.

Increased use of cardiovascular medications in seniors prescribed non-ASA non-steroidal anti-inflammatory drugs

The objective of this study was to determine the relationship between the prescribing of non-ASA non-steroidal anti-inflammatory drugs (NANSAID) and the prescribing of select cardiovascular (CV) medications. We performed a retrospective, cross-sectional analysis of the prescribed use of these medications between December 1, 1990 and June 30, 1991 by Albertans 65 years of age and older utilizing data from the publically-funded drug benefit plan. Variables examined were: the number of individuals prescribed NANSAID and CV medications; mean daily dose for these medications; calculated relative dose; the proportion of NANSAID users prescribed CV medications compared to non-users; and the relative proportions of users of specific NANSAID prescribed CV medication. We found that 33.4% and 19.6% of Albertan seniors were prescribed CV medications and NANSAID, respectively. NANSAID users were twice as likely to be prescribed CV medications as compared to non-users. Intermediate/high dose NANSAID users were more likely to be prescribed a CV medication as compared to low-dose users. The risk of being prescribed a CV medication was highest for indomethacin and users of multiple NANSAID, while ibuprofen users had the lowest risk. We conclude that NANSAID users are more likely to be also prescribed CV medications. Subjects who consume a lower dose of NANSAID are less likely to be prescribed CV medications. For different NANSAID, there is a spectrum of risk.

Self-measurement of blood pressure: issues related to the training of patients. Canadian Coalition for High Blood Pressure Prevention and Control

For effective self-measurement of blood pressure, patients need to be able to obtain accurate and reproducible measurements. Criteria for measuring blood pressure have been well developed in research studies, and through the use of standardized training programs it has been established that nonmedically trained individuals can obtain valid measurements. These recommendations for blood pressure measurement were adapted to the self-measurement situation. Either manual sphygmomanometers or automated electronic devices can be used effectively. Although automated devices may be easier to use, the health care practitioner should ensure that any such device has been demonstrated to be accurate and reliable before its adoption. There are no reported programs available for training individuals in the use of self-measurement. A check-list has been developed for use by health care practitioners. It is estimated that proper training will usually take more than 20 mins. Since many health care practitioners do not use the recommended blood pressure measurement technique, there is also a need to develop programs to 'train the trainers'. Finally, individuals undertaking regular self-measurement should have their technique and the calibration of their instruments checked at regular intervals (six to 12 months).

Self-measurement of blood pressure: assessment of equipment. Canadian Coalition for High Blood Pressure Prevention and Control

Equipment for the self-measurement of blood pressure is readily available to consumers. These devices use one or more surrogate (indirect) measures of pressure to estimate systolic and diastolic blood pressure. Manual auscultatory devices using stethoscope and sphygmomanometer have been adapted for home use, but a variety of automated devices based on auscultation, oscillometry, and other techniques are available and may be more suitable for individuals who have limited vision, hearing or dexterity. Despite the existence of voluntary evaluation protocols and mandatory manufacturing standards, blood pressure readings from some automatic devices may not be accurate. Some devices are packaged with insufficient information to ensure proper use, and most individuals need some form of guidance in their use and calibration testing. If self-measurement of blood pressure is to be of benefit, the health care professional must recommend only those devices that are accurate and suitable to the patient or client. The Canadian Coalition for High Blood Pressure Prevention and Control will endeavour to develop a regular means by which health care professionals can keep informed of available devices for blood pressure self-measurement.

Self-measurement of blood pressure: benefits, risks and interpretation of readings. The Canadian Coalition for High Blood Pressure Prevention and Control

The literature on the benefits and risks of self-measurement of blood pressure and interpretation of the readings was reviewed. Self-measurement of blood pressure is useful in selected patients with high blood pressure, can be used to monitor blood pressure closely outside health care facilities, and can determine whether patients have white coat hypertension. The involvement of patients in their own blood pressure management is increased and self measurement may result in more rapid achievement of target blood pressure readings, improvement in adherence to antihypertensive therapy and decreased health care utilization. However, some patients may not be suited to monitor their own blood pressure and some may experience an increase in anxiety regarding their health. With careful training and selection of patients, most can accurately assess their blood pressure. Self-measured readings are generally lower than readings in a physician's clinic (or office) and this must be accounted for in assessing response to therapy and usual levels of blood pressure. Self-measured readings are a valuable supplement to clinic readings in many patients.

Self-measurement of blood pressure: recommendations of the Canadian Coalition for High Blood Pressure Prevention and Control

OBJECTIVE

To provide health care professionals with guidelines on the use of blood pressure self-measurement.

METHODS

Recommendations were devised after consideration of expert reviews and guidelines, personal files, international standards documents, personal communication with investigators and the results of a MEDLINE search (1966-94) using the term 'blood pressure determination'.

BENEFITS, HARMS, COSTS

Self-measurement of blood pressure can be used to detect white coat hypertension, monitor changes in blood pressure closely, more rapidly achieve desired blood pressure goals, increase adherence to antihypertensive therapy and improve patient self-reliance. However, self-measured blood pressure readings may be misleading because there is insufficient normative, prognostic and outcome data and because some patients may not take accurate measurements. The use of self-measurement of blood pressure has a relatively small direct cost and may result in an overall reduction in treatment costs.

RECOMMENDATIONS

Self-measured blood pressure readings can be a valuable supplement to clinic (or office) blood pressure readings. However, self-measurement is appropriate neither for patients who are physically or mentally incapable of accurate assessment and interpretation of readings nor for those who do not want to participate. Patients who self-monitor blood pressure require careful training in blood pressure measurement and instruction on the recording and interpretation of blood pressure readings. Advice to patients using monitoring equipment must take into account the needs and abilities of the patient. Although only a few electronic devices for the self-measurement of blood pressure have met recommended performance standards, their use may be more appropriate for some patients and the training requirements fewer than if manual devices are used.

VALIDATION

The guidelines of several expert groups were examined in the preparation of these recommendations. The recommendations were presented at the World Conference on Hypertension Control in 1995 and were reviewed by the parent societies of the Canadian Coalition for High Blood Pressure Prevention and Control.

Methyldopa kinetics before and after ingestion of methyldopa for eight weeks

Methyldopa urine and plasma levels and urine metabolite levels were assessed following intravenous (IV) and oral (PO) methyldopa before, and after ingestion of methyldopa (500 mg) daily for eight weeks. There was no increase in (estimated) methyldopa absorption (8.4%) or renal clearance (PO 13.9%, IV 2.33%) after the eight weeks of methyldopa ingestion. However, the initial methyldopa absorption and renal clearance values in this study were higher than that in previous studies. There was an inverse relation between the initial methyldopa absorption and the change in absorption (r - 0.605) and between the initial methyldopa renal clearance and the change in renal clearance (PO r -0.874, IV r -0.891). Overall, this study did not confirm our previous studies showing induction of methyldopa absorption and renal clearance, possibly due to prior up regulation of transporter function. Consistent with methyldopa inducing drug transporters, those with low initial absorption and renal clearance values had the greatest increases.

Prevention and control of high blood pressure: challenges and opportunities

Cardiovascular disease is still the leading cause of death in developed countries and is becoming more common in the developing world. The reduction in incidence of many cardiovascular diseases in the last few decades may be attributed in part to extensive programs to reduce and manage risk factors such as hypertension. Nevertheless, untreated, uncontrolled and undiagnosed hypertension remains a significant concern. Many nations have adopted policies and programs for hypertension control. An international sharing of knowledge and experience could lead to improvements in the prevention and treatment of hypertension and to lower rates of cardiovascular disease. In keeping with Canada's leadership in hypertension and cardiovascular disease prevention, Ottawa will host the World Conference on Hypertension Control from June 21 to 24, 1995. This conference will give participants the opportunity to review current programs and develop improved strategies for hypertension control and cardiovascular disease reduction.

Pharmacokinetics and presystemic gut metabolism of methyldopa in healthy human subjects

This study examined the pharmacokinetics and metabolism of methyldopa after giving single 250-mg oral and intravenous doses to 16 healthy human volunteers. A 48-hour washout period was allowed between oral and intravenous treatments. Blood and urine samples were collected; methyldopa was assayed in blood and urine, and its metabolites (methyldopa sulfate, alpha-methyldopamine, and alpha-methyldopamine sulfate) were assayed in urine. Pharmacokinetic parameters were recorded as follows: half-life was 2.0 +/- 0.7 hours; total body and renal clearance were 268 +/- 72 and 107 +/- 35 mL/min, respectively; and volume of distribution at steady-state was 33 +/- 11 L. The absolute bioavailability of the drug was 42 +/- 16%. The measurable metabolites in urine after oral and intravenous administration accounted for 27% and 17% of the dose, respectively. Methyldopa sulfate was the most abundant metabolite recorded; its quantity was higher after oral than after intravenous administration, 20.1 +/- 5.7% versus 6.7 +/- 5.3% of the dose (P < .05), suggesting significant presystemic gut metabolism. First-pass gut metabolism for methyldopa was estimated to be 17.6 +/- 6.9% of the dose given.

Prediction of reduction in predialysis concentrations due to interdialysis weight gain

There is little quantitative information about the influence of weight change before and during hemodialysis on the concentration of proteins, lipoproteins, lipids, enzymes and other dialysis-resistant compounds in blood. We studied the concentration of 12 such compounds before and at the end of high-flux hemodialyses, 1.5 h after the start and 1, 2 and 3 h postdialysis and have developed formulae for roughly predicting the near steady-state 2-3 h postdialysis concentration. For hemoglobin, albumin, total protein and total cholesterol, the relationship of mean change in concentration to weight loss in groups was linear, and the % increase in concentration correlation correlated with % weight reduction (r = 0.64-0.81 and p = 0.002-0.0002). Correlations with ultrafiltration rate were comparable. By 3 h postdialysis values were relatively stable; the average fall in concentration for theses 4 compounds was 25% from end dialysis. The simplest formula we found which roughly predicts the % increase in concentration from predialysis to 3 h postdialysis is to multiply the % loss in body weight in kg during dialysis by 3.3. More accurate formulae were developed using combined and specific regression equations relating % weight loss during dialysis to % concentration rise. Mean values for alkaline phosphatase, triglycerides, lipoprotein (a), high-density lipoprotein cholesterol, calcium, apolipoprotein B, bilirubin and aspartate aminotransferase also rose appreciably during dialysis with significant increases for the first five. With major interdialytic weight gain, the reduction in predialysis concentrations of hemoglobin and cholesterol may be enough to inappropriately modify treatment decisions about anemia (e.g. erythropoietin) or hypercholesterolemia, and to cause false concern about the concentration of albumin for nutrition and prognosis. Major weight gain may also contribute to concentration changes in numerous other compounds resistant to dialysis.

Dehydration during fasting increases serum lipids and lipoproteins

The study was an open, prospective, randomized cross-over design to determine if dehydration during fasting increases lipid concentrations. Fifteen healthy subjects participated, 1 of whom did not complete the study. The subjects fasted once with no fluid replacement and once with salt and water supplementation. Following both fasts, blood was drawn for lipid assessments. Compared to fasting with fluid and salt replacement, fasting with no fluids was associated with higher (mean, 95% confidence interval) total serum cholesterol (8.1%, 4.3-11.9%), HDL cholesterol (7.5%, 1.8-13.1%), LDL cholesterol (10.5%, 2.2-18.8%), apolipoprotein A-1 (8.9%, 5.0-12.8%), and apolipoprotein B (10.5%, 5.2-15.8%). The change in serum triglycerides was not statistically significant (12.4%,-0.5-25.3%). There was a greater reduction in body weight during fasting with fluid restriction compared to fasting with salt and water supplementation (1.8%, 1.3-2.2%). Fasting with fluid restriction results in significantly higher lipid levels and, therefore, variation in hydration of patients could contribute to fluctuation in lipid levels of patients. Care should be taken to ensure that patients are in a standard state of hydration during assessment of lipid levels. We recommend: 1) that patients fast no longer than 12 h, and 2) that, during fasting, patients avoid unnecessary physical activity, avoid hot dry environments, ensure a liberal intake of water, and avoid diuretic substances such as caffeine.

Errors in assessment of blood pressure: blood pressure measuring technique

This article reviews the recommended techniques for accurate and reproducible blood pressure measurements. The scientific basis underlying current recommendations for blood pressure measurement is presented. Many of the current recommendations are not followed in ambulatory care clinics and this paper will show how measurement errors in excess of 15 mm Hg or more can occur. Many patients will be misclassified and treated inappropriately when errors in blood pressure measurement of this magnitude are made. Rigorous adherence to proper blood pressure measurement is necessary to evaluate a patient's risk of cardiovascular disease, and to assess the need or efficacy of antihypertensive therapy.

Pitfalls to avoid in the measurement of blood pressure in the elderly

Accurate, reproducible blood pressure readings are more difficult to obtain in the elderly. Elderly patients have more variable blood pressure, show a reduction in blood pressure following meals, and can have postural hypotension, discrepancies in blood pressure between arms, auscultatory gaps and 'pseudohypertension', all of which can mislead clinicians regarding these patients' usual blood pressure. Arrhythmias, particularly atrial fibrillation, make accurate blood pressure determination difficult and are more common in the elderly. Prostatic hypertrophy causing high pressure urinary retention is suggested as a common and reversible cause of hypertension in older men. Proper measurement of blood pressure in elderly patients demands additional thought and action, all of which are necessary for accurate cardiovascular risk assessment and proper therapeutic decisions. Increasing the number of visits and the number of carefully taken blood pressure readings per visit will result in a more accurate assessment of blood pressure in older patients.

Errors in assessment of blood pressure: sphygmomanometers and blood pressure cuffs

This article reviews the current recommendations on equipment when blood pressure is measured by sphygmomanometer. The scientific rationale underlying the current recommendations for selection and maintenance of blood pressure measuring equipment is presented. The errors that can occur when the recommendations are not followed are quantified whenever the data are available. Inadequate assessment and maintenance of equipment often lead to the use of faulty equipment, and as a result errors in the assessment of patients' blood pressure are likely to be common. If followed, the current guidelines for use and maintenance of equipment would remove most of the problems noted. Physicians must ensure that properly maintained and appropriate equipment is used to measure blood pressure.

Ferrous sulphate does not directly affect pteroylmonoglutamic acid absorption in rats

A variety of compounds which bind to Fe have substantial reductions in absorption when co-administered with Fe compounds. The binding of both Fe2+ and Fe3+ ions to pteroylmonoglutamic acid and the pteroylmonoglutamate dianion was examined in vitro. In dimethylsulphoxide (DMSO) alone, pteroylmonoglutamate formed a 2:1 (pteroylmonoglutamate:Fe3+ ion) complex. However, in DMSO-aqueous Bis-Tris buffer (4:1, v/v; pH 6.0) no evidence of complex formation could be seen. Likewise spectroscopic evidence was obtained for complex formation with Fe2+ ion and pteroylmonoglutamate in DMSO alone but not in the aqueous DMSO buffer. In vivo studies examined the effect of FeSO4 on pteroylmonoglutamic acid absorption in an isolated perfused rat jejunal model of nutrient absorption. The dose of pteroylmonoglutamic acid approximated a human dose of 1 mg for the rat, while the FeSO4 doses were chosen to represent 6.4 mg, 64 mg and 300 mg human doses. There was no significant effect of FeSO4 on pteroylmonoglutamic acid absorption or instability of pteroylmonoglutamic acid in vivo in the presence of FeSO4 in the rat. Although 2:1 binding of pteroylmonoglutamic acid to Fe ions could be demonstrated in DMSO alone, no binding could be demonstrated in DMSO-Bis-Tris buffer (4:1, v/v; pH 6.0). It is unlikely that there will be a significant reduction in pteroylmonoglutamic acid absorption during concurrent ingestion of Fe preparations.

Errors in assessment of blood pressure: patient factors

This article reviews patient-related factors affecting blood pressure measurement and provides the scientific rationale underlying current recommendations for the measurement of blood pressure in the evaluation of hypertension. Information is included on the magnitude of errors that can occur when the recommendations are not followed. A variety of factors relating to the patient's emotions, activity, bodily function and environment cause blood pressure to fluctuate throughout the day such that peak systolic and diastolic blood pressures are often twice as high as trough levels. Many physicians fail to account for these factors when assessing a patient's blood pressure. Errors in the classification and treatment of a patient's blood pressure and the finding of labile blood pressure can occur often when patients are not adequately prepared in advance of the blood pressure measurement.

Prescription of nonsteroidal anti-inflammatory drugs for elderly people in Alberta

OBJECTIVE

To examine the extent prescribed nonsteroidal anti-inflammatory drugs (NSAIDs) are used by elderly people in Alberta as well as the degree of concurrent use of multiple NSAIDs, of peptic ulcer medications and of certain medications known to have clinically significant adverse interactions with NSAIDs.

DESIGN

Retrospective analysis of the Alberta Blue Cross database.

SETTING

Alberta.

PATIENTS

All people 65 years of age and older using the subsidized drug benefit plan for whom prescription claims were submitted for reimbursement between Jan. 1 and June 30, 1991.

OUTCOME MEASURES

Number of people who received one or more prescriptions for NSAIDs, rates of prescribing peptic ulcer medications and drugs with the potential for clinically significant interactions with NSAIDs among NSAID users and non-NSAID users, and rate of prescribing more than one NSAID concurrently.

RESULTS

Of the Albertan population 65 years of age and over 61,601 (26.7%) received at least one prescription for an NSAID during the study period. In decreasing order, the five most commonly prescribed NSAIDs were acetylsalicylic acid, diclofenac, naproxen, indomethacin and ibuprofen. The total cost of NSAID therapy was $5,415,974. Of the people prescribed an NSAID 25.8% were also prescribed a peptic ulcer medication, as compared with 10.5% of the non-NSAID users. There was a significant relation between the increasing number of NSAID prescriptions and the likelihood of receiving a peptic ulcer medication. Those who received a prescription for an NSAID were more likely than non-NSAID users to have been prescribed coumarin anticoagulants, diuretics, angiotensin-converting-enzyme inhibitors, beta-blockers, oral corticosteroids, methotrexate and lithium, all of which are known to have possible adverse interactions with NSAIDs. A total of 2,631 people had two or more prescriptions for NSAIDs filled on the same day.

CONCLUSIONS

NSAIDs are prescribed frequently for elderly people and are associated with an increased likelihood of concurrent prescription of peptic ulcer medication and medications that could have adverse drug interactions with NSAIDs. Additional study is required to evaluate the appropriateness of NSAID use in elderly patients, to determine the degree of actual patient consumption of these medications, to document the true prevalence of clinically significant drug interactions and to formulate educational strategies to reach physicians with this information.

The antianginal efficacy of isosorbide dinitrate therapy is maintained during diuretic treatment

OBJECTIVES

To determine whether the use of a diuretic would maintain the antianginal efficacy of isosorbide dinitrate during 1 week of therapy.

METHODS

During continuous therapy, organic nitrates have a reduction in antianginal effectiveness and cause fluid retention. The study was a randomized, double-blind, placebo-controlled crossover design examining the effect of 1 week of daily treatment with 50 mg hydrochlorothiazide/5 mg amiloride on the antianginal effectiveness of 30 mg isosorbide dinitrate administered every 6 hours. Exercise stress testing was performed before and 3 hours after administration of isosorbide dinitrate at the start and end of the placebo and diuretic treatment phases.

RESULTS

The time to onset of angina (475 +/- 35 versus 490 +/- 29 seconds, difference not significant) and to moderate angina after administration of isosorbide dinitrate (542 +/- 40 versus 566 +/- 37 seconds, difference not significant) were similar at the start and end of the diuretic phase of the study but were reduced at the end of the placebo phase (471 +/- 40 versus 410 +/- 40 seconds, p < 0.05 and 531 +/- 38 versus 466 +/- 39 seconds, p < 0.05, respectively). Total exercise time and time to onset of angina 3 hours after administration of isosorbide dinitrate were longer (p < 0.005) at the end of the diuretic phase compared with the end of the placebo phase. Patients gained weight during the placebo phase and lost weight during the diuretic phase of the study. The change in weight was inversely correlated to the change in total exercise time (r = -0.53, p < 0.05).

CONCLUSIONS

Patients using a diuretic with isosorbide dinitrate maintain an increased anginal threshold and total exercise time compared with placebo. Weight change is inversely related to exercise duration, and this result is consistent with fluid retention restoring cardiac preload during nitrate use. The increased anginal threshold during concurrent isosorbide dinitrate and diuretic use may be attributable to maintenance of the organic nitrate-induced reductions in cardiac preload.

Frusemide causes acute increases in lipid concentrations

In a randomized double-blind placebo controlled parallel study involving fourteen healthy male volunteers, we examined whether the acute reduction in vascular volume associated with frusemide ingestion would haemoconcentrate lipid particles. Three hours after a single 40 mg oral dose of frusemide, there were 9.6-14.4% increases in lipids and lipoproteins which were highly correlated to changes in body weight. Until further studies determine the extent of haemoconcentration in patients being treated long term with frusemide, we recommend that blood be drawn for lipid analysis prior to frusemide ingestion.

Absence of an effect of ferrous sulfate on phenytoin absorption in the rat

A variety of drugs which bind to iron have significant reductions in absorption when co-administered with iron compounds. The chemical structure of phenytoin indicates that there may be possible binding to iron ions. In vitro experiments were performed to determine whether any binding of iron to phenytoin occurred, and in vivo studies examined the effect of ferrous sulfate on phenytoin absorption in an isolated perfused rat jejunal model of drug absorption. The dose of phenytoin was limited by solubility and represents a human dose of 28 mg on a mg/kg basis for the rat assuming the total dose to be in 10 cm bowel in the rat. The ferrous sulfate doses were chosen to represent 28 and 300 mg doses on a similar basis to phenytoin. There was no significant effect of ferrous sulfate on phenytoin absorption or instability of phenytoin in the presence of ferrous sulfate in the rat. In vitro experiments indicated that little or no phenytoin binding to iron occurred. Results from animal model studies using low doses of phenytoin suggest it is unlikely that there will be a significant reduction in phenytoin absorption during concurrent therapy with iron salts.

Ferrous sulfate reduces cimetidine absorption

A variety of drugs that bind to iron have significant reductions in absorption when coadministered with iron compounds. Cimetidine has a structure that would suggest strong binding to iron ions. In vitro experiments were performed to examine a variety of characteristics of the binding of iron to cimetidine. Further studies were conducted to determine the effect of concurrent administration of ferrous sulfate on cimetidine absorption in an in vivo isolated perfused rat jejunal model of drug absorption. The dose of cimetidine was chosen to represent a human dose of 300 mg, while the ferrous sulfate doses were chosen to represent 150- and 300-mg doses. The higher ferrous sulfate dose completely inhibited cimetidine absorption (P < 0.01), while the lower dose of ferrous sulfate caused a 63% reduction in cimetidine absorption (P < 0.05). In vitro iron in its ferrous from rapidly oxidizes to the ferric form. The ferric form of iron binds to cimetidine and may be the cause of the decreased cimetidine absorption. Care should be taken in prescribing iron supplements with cimetidine.

Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism

OBJECTIVE

To determine whether simultaneous ingestion of ferrous sulfate and thyroxine reduces the efficacy of thyroid hormone in patients with primary hypothyroidism.

DESIGN

Uncontrolled clinical trial.

SETTING

Outpatient research clinic of a tertiary care center.

PATIENTS

Fourteen patients with established primary hypothyroidism on stable thyroxine replacement.

INTERVENTION

All patients were instructed to ingest simultaneously, a 300-mg ferrous sulfate tablet and their usual thyroxine dose every day for 12 weeks.

RESULTS

After 12 weeks of ferrous sulfate ingestion with thyroxine, the mean level of serum thyrotropin (thyroid stimulating hormone, TSH) rose from 1.6 +/- 0.4 to 5.4 +/- 2.8 mU/L (P < 0.01), but the free thyroxine index did not change significantly. Subjective evaluation using a clinical score showed that nine patients had an increase in symptoms and signs of hypothyroidism; the mean score for the 14 patients changed from 0 to 1.3 +/- 0.4 (P = 0.011). When iron and thyroxine were mixed together in vitro, a poorly soluble purple complex appeared that indicated the binding of iron to thyroxine.

CONCLUSIONS

Simultaneous ingestion of ferrous sulfate and thyroxine causes a variable reduction in thyroxine efficacy that is clinically significant in some patients. The interaction is probably caused by the binding of iron to thyroxine.

Increases in methyldopa absorption and renal excretion after multiple doses

A retrospective analysis of previous studies examining methyldopa absorption suggested the possibility that the absorption of methyldopa might increase on repeat methyldopa ingestion. A prospective study was undertaken to determine the effect of repeated oral doses of methyldopa on methyldopa absorption. Thirteen healthy subjects ingested single 250 mg methyldopa doses on days 0, 7, 14, 28, 56, and 112; 24 urine samples were collected and analyzed for methyldopa and its major metabolites on each study day and methyldopa plasma levels were measured over 8 hours at days 0 and 56. There were significant increases in the absorption of methyldopa (as estimated by the urinary excretion of methyldopa and the measured metabolites over 24 hours) at day 56 (33.4 +/- 8.9%, P less than .025) compared with day 0 (26.0 +/- 10.8%). There was also a significant increase in renal clearance of unmetabolized methyldopa (62.7 +/- 13.6 vs. 99.3 +/- 29.1 mL/min, P less than .01) and a decrease in the plasma half-life of methyldopa at day 56 (2.22 +/- 0.91 vs. 1.56 +/- 0.68 hr, P less than .05). There was a tendency toward increases in methyldopa absorption at day 7, 14, 28, and 112. Several possible explanations for the changes in methyldopa disposition are discussed.

Renal impairment associated with an acute paracetamol overdose in the absence of hepatotoxicity

This report describes a paracetamol overdose in which renal impairment occurred without biochemical evidence of hepatotoxicity. We are aware of only one similar case. However, it is possible this scenario may be seen more frequently with close biochemical follow-up.

Norfloxacin interaction with antacids and minerals

The urinary excretion of norfloxacin was measured in eight healthy volunteers after its co-administration with a variety of over-the-counter preparations, each containing a different metal ion. Commonly used doses of ferrous sulphate, zinc sulphate, aluminium hydroxide and magnesium hydroxide reduced the 24 h urinary excretion of norfloxacin by 50 to 90%. Bismuth subsalicylate had no significant effect. In vitro experiments demonstrated the formation of complexes between norfloxacin and iron, zinc, aluminium, and magnesium ions, respectively. Many pharmaceuticals contain the same metal ions that caused significant interactions with norfloxacin. The efficacy of norfloxacin treatment may be compromised when it is taken concurrently with preparations containing these metal ions.

Clinical and chemical interactions between iron preparations and ciprofloxacin

1. The effect of ferrous sulphate (300 mg), ferrous gluconate (600 mg), and a combination tablet of iron (10 mg), magnesium (100 mg), zinc (15 mg), calcium (162 mg), copper (2 mg), and manganese (5 mg) (Centrum Forte) co-administration on ciprofloxacin bioavailability was tested in eight healthy subjects. 2. Peak serum ciprofloxacin concentrations and area under the curve (AUC) were significantly reduced when ciprofloxacin was administered with 300 mg ferrous sulphate (3.0 vs 2.0 mg l-1, P less than 0.05 and 12.3 vs 6.7 mg l-1 h, P less than 0.01, respectively). Reductions in peak ciprofloxacin concentrations and AUC also occurred when ciprofloxacin was ingested with 600 mg ferrous gluconate (1.3 mg l-1, P less than 0.01 and 4.1 mg l-1 h, P less than 0.01, respectively) and a Centrum Forte tablet (1.4 mg l-1, P less than 0.01 and 5.4 mg l-1 h, P less than 0.01, respectively). 3. When ferrous ion was mixed with ciprofloxacin, rapid spectral changes occurred (t1/2 = 1.9 min). Additional studies were consistent with oxidation of the ferrous form of iron to its ferric form, which is followed by rapid formation of a Fe(3+)-ciprofloxacin complex. Ciprofloxacin seems to bind to ferric ion in a ratio of 3:1 by interacting with the 4-keto and 3-carboxyl groups on ciprofloxacin. 4. The formation of a ferric ion-ciprofloxacin complex is probably the cause of the reduction in ciprofloxacin bioavailability in the presence of iron.

Iron supplements: a common cause of drug interactions

Iron-drug interactions of clinical significance may occur in many patients and involve a large number of therapies. Concurrent ingestion of iron causes marked decreases in the bioavailability of a number of drugs. The affected drugs, tetracycline, tetracycline derivatives (doxycycline, methacycline and oxytetracycline), penicillamine, methyldopa, levodopa, carbidopa and ciprofloxacin have diverse chemical structures and clinical effects. The major mechanism of these drug interactions is the formation of iron-drug complexes (chelation or binding of iron by the involved drug). A large number of other important and commonly used drugs such as thyroxine, captopril and folic acid have been demonstrated to form stable complexes with iron. There is little known about the effects of concurrent therapy with iron supplements for most of the drugs.

Implementation and evaluation of a community-sponsored smoking cessation contest

BACKGROUND

This article provides a description and evaluation of a community-sponsored smoking cessation contest. Adapted from previous efforts, "Quit to Win" relied solely on community resources and was promoted to the two million residents of San Diego County, California.

METHODS

A large recruitment campaign included print and electronic media. Eight hundred and two smokers participated in the contest. Contest entry forms served as the pretreatment measure, quit cards measured smoking status, and follow-up telephone interviews collected additional data on three groups: joiners, nonjoiners, and comparison subjects.

RESULTS

Thirty-five percent of the participants reported being smoke-free two months after the program. Television was by far the most effective promotional medium, while individuals who received a promotional flyer were somewhat more likely to actually join the contest than those who heard of it through other sources. Self-confidence, outcome expectations, and lighter smoking habit were predictive of contest participation. Of joiners, those with a greater fear of suffering from withdrawal were less likely to quit.

DISCUSSION

The approximate cost per quitter was $17.25 based on the direct budget expenses for the contest. However, this does not include the significant cost of the many donated services. Large smoking cessation contests can be cost-effective while providing direct and indirect benefits to anti-tobacco efforts.

Ferrous sulfate reduces methyldopa absorption: methyldopa: iron complex formation as a likely mechanism

Ferrous sulfate and sodium sulfate reduce methyldopa absorption in humans. This current study was conducted to investigate some of the potential factors by which these compounds could reduce methyldopa absorption. A rat model developed to examine drug absorption was used. Solutions of 14C methyldopa alone and with ferrous sulfate or sodium sulfate were injected in vivo into closed duodenal segments. Ferrous sulfate reduced methyldopa absorption 52.9% (p less than 0.01), while sodium sulfate had no significant effect on methyldopa absorption. In vitro iron in its ferrous form rapidly oxidizes to the ferric form in the presence of methyldopa. The ferric form of iron binds strongly to methyldopa, presumably resulting in the decreased methyldopa absorption. Methyldopa was stable in vivo and in vitro in the presence of ferrous sulfate and sodium sulfate. These studies are consistent with ferrous sulfate reducing methyldopa absorption by the formation of ferric iron: methyldopa complexes.

Clinical assessment of blood pressure

This study was performed to determine the blood pressure measuring techniques and accuracy of sphygmomanometers used by physicians in ambulatory care clinics on the Avalon Peninsula of Newfoundland. Of the 114 participating physicians, no physician completely followed all the recommended BP measuring techniques of the American Heart Association. Almost all physicians supported the patient's arm at heart level to measure BP. Fewer physicians used the following recommended techniques; palpation to initially assess systolic BP (38%), measurement of BP in both arms (23%), an appropriate rate of cuff deflation (18%), measurement of BP in recommended patient positions (10%), the appropriate length of rest (4%) or use of a cuff of appropriate size (3%). Approximately 8% of mercury sphygmomanometers were out of calibration by at least 4 mmHg but none were out by more than 6 mmHg. Forty percent of aneroid sphygmomanometers were out of calibration by at least 4 mmHg and of these 30% were out by 10 mmHg or more. Mercury and aneroid sphygmomanometers were used by 60% of physicians. Aneroid sphygmomanometers were used exclusively by 34% of physicians, while 5% of physicians relied solely on mercury devices. Standardized techniques for BP measurement are not used and inaccurate sphygmomanometers are common; these factors may lead to misclassification of blood pressure and inappropriate treatment of patients.

Sinemet-ferrous sulphate interaction in patients with Parkinson's disease

1. This study examined the effects of administering ferrous sulphate 325 mg with Sinemet (100/25 tablet) on levodopa and carbidopa bioavailability and on signs of Parkinson's disease in nine patients. 2. Ferrous sulphate ingestion with Sinemet resulted in a decrease in levodopa area under the curve (AUC) of 30% (P less than 0.01) and a greater than 75% decrease in carbidopa AUC. Despite a strong relationship between reductions in levodopa AUC and reductions in Sinemet efficacy (r = 0.83, P less than 0.01), the average reduction in Sinemet's efficacy associated with ferrous sulphate did not achieve statistical significance (P = 0.055). 3. Chemical studies indicate that iron forms chemical complexes with carbidopa in a similar manner to levodopa and is a likely mechanism for the drug interactions. 4. AUC when a Sinemet tablet is taken concurrently with a ferrous sulphate tablet appears to be clinically significant in some but not all patients. The clinical significance of repeated ingestion of ferrous sulphate with Sinemet requires further studies.

Accurate, reproducible measurement of blood pressure

The diagnosis of mild hypertension and the treatment of hypertension require accurate measurement of blood pressure. Blood pressure readings are altered by various factors that influence the patient, the techniques used and the accuracy of the sphygmomanometer. The variability of readings can be reduced if informed patients prepare in advance by emptying their bladder and bowel, by avoiding over-the-counter vasoactive drugs the day of measurement and by avoiding exposure to cold, caffeine consumption, smoking and physical exertion within half an hour before measurement. The use of standardized techniques to measure blood pressure will help to avoid large systematic errors. Poor technique can account for differences in readings of more than 15 mm Hg and ultimately misdiagnosis. Most of the recommended procedures are simple and, when routinely incorporated into clinical practice, require little additional time. The equipment must be appropriate and in good condition. Physicians should have a suitable selection of cuff sizes readily available; the use of the correct cuff size is essential to minimize systematic errors in blood pressure measurement. Semiannual calibration of aneroid sphygmomanometers and annual inspection of mercury sphygmomanometers and blood pressure cuffs are recommended. We review the methods recommended for measuring blood pressure and discuss the factors known to produce large differences in blood pressure readings.

The effect of ferrous sulfate and pH on L-dopa absorption

Ferrous sulfate decreases L-dopa bioavailability in humans probably as a result of binding of L-dopa by iron in the gastrointestinal tract. This study was conducted to determine if iron by binding L-dopa decreases L-dopa absorption and to investigate the effect of different pH buffers on intestinal absorption of L-dopa in the presence and absence of ferrous sulfate. A rat model developed to examine drug absorption was used. Control animals had buffered [14C]L-dopa solutions injected into two in vivo closed segments of intestine; a 5-cm duodenal and a 5-cm proximal jejunal segment. These studies were conducted using solutions buffered at pH 5.5, 6.5, 7.5, and 8.5. An identical procedure was followed for experimental animals except ferrous sulfate was injected with the buffered L-dopa solutions. Ferrous sulfate resulted in a reduction in L-dopa absorption in the buffers at all pHs in both the duodenum and jejunum. The average reduction in L-dopa absorption in the presence of iron was 22.6% in the duodenum and 23.9% in the jejunum. There was a tendency for ferrous sulfate to cause a greater reduction in L-dopa absorption as the buffer pH increased. There was also a decrease in L-dopa absorption in the higher pH buffers in the absence of iron. Despite this latter result, in the jejunum there was an increase in the percent reduction in L-dopa absorption associated with ferrous sulfate as pH increased. Although this tendency was not as consistent in the duodenum as the jejunum, the combined results are compatible with the chemical model of increased L-dopa--iron binding as pH increases.

Ferrous sulfate reduces levodopa bioavailability: chelation as a possible mechanism

This study examined the effect of ferrous sulfate, a widely used iron treatment, on levodopa bioavailability in normal subjects. A 250 mg tablet of levodopa was taken with and without a 325 mg tablet of ferrous sulfate by eight normal subjects in a randomized crossover trial. When levodopa was taken with ferrous sulfate there was a 55% decrease in peak levodopa levels (3.6 +/- 2.6 vs 1.6 +/- 0.82 nmol/ml; p less than 0.05) and a 51% decrease in AUC (257 +/- 133 vs 125 +/- 51 nmol.min/ml; p less than 0.01). Persons with the highest peak levodopa levels and AUC after levodopa alone had the greatest reduction in peak levodopa levels and AUC after levodopa ingestion with ferrous sulfate. Iron in its ferrous state is oxidized rapidly to the ferric state in the presence of levodopa at pHs found in the small intestine. In the ferric state, iron binds very strongly to levodopa. Chelation of iron by levodopa is the likely mechanism for this drug interaction. The clinical significance of this interaction is yet to be established.

Spurious stones

One hundred and sixteen (3.5%) of 3,300 specimens submitted by 72 patients as urinary stones were artifacts, i.e. not formed of accepted constituents of urinary calculi. The laboratory diagnostic methods included infrared and wet chemical analysis, and X-ray diffraction. Twenty-eight were of organic origin and some of these were undoubtedly submitted by accident as calculi. Eighty-eight were of mineral origin, mainly quartz and feldspar, and it is believed that the great majority were submitted for secondary gain or for psychiatric reasons. Ten patients each submitted from 2 to 10 artifacts. Five cases studies are presented which illustrate some confounding clinical and laboratory findings. Spurious stones can lead to difficult clinical and laboratory problems.

Human and rat liver phenol sulfotransferase: structure-activity relationships for phenolic substrates

Phenol sulfotransferase (PST) catalyzes the sulfate conjugation of many phenolic drugs. Human liver contains thermostable (TS) and thermolabile forms of PST. Ion exchange chromatography shows that two isozymes of TS PST (peaks I and II) are present in human liver preparations. Rat liver contains four forms of PST that can be separated by ion exchange chromatography. Quantitative structure-activity relationship (QSAR) analysis was used to study phenolic substrates for both human and rat liver PST. Thirty-six substituted phenols were tested as substrates for partially purified human liver TS PST peak I. QSAR analysis resulted in derivation of the following equation: log 1/Km = 0.92 (+/- 0.18)log P - 1.48 (+/- 0.38)MR'4 - 0.64 (+/- 0.41)MR3 + 1.04 (+/- 0.63)MR2 + 0.67(+/- 0.44) sigma- + 4.03 (+/- 0.42). In this equation Km is the Michaelis constant, P is the octanol-water partition coefficient, MR is the molar refractivity of substituents at the 2-, 3-, and 4-positions, and sigma- is the Hammett constant. Values of log 1/Km calculated with this equation were highly correlated with log 1/Km values (r = 0.950) that were observed experimentally. Nine phenols were also tested as substrates for partially purified human liver TS PST peak II. Log 1/Km values for these compounds were significantly correlated for the two isozymes of TS PST (r = 0.992, p less than 0.001). QSAR analysis was also used to derive equations that described the behavior of phenolic substrates for rat liver PST forms I and II. These equations differed substantially from the equation derived for compounds tested with human liver TS PST peak I. Therefore, the characteristics of the active sites of human liver TS PST peak I and rat liver PST forms I and II appear to differ. Application of these equations may make it possible to predict Km values of phenolic substrates for human liver TS PST and for rat liver PST forms I and II.

Human liver phenol sulfotransferase: assay conditions, biochemical properties and partial purification of isozymes of the thermostable form

Phenol sulfotransferase (PST) catalyzes the sulfate conjugation of phenolic and catechol drugs and neurotransmitters. Human platelets and brain contain at least two forms of PST. One form is relatively thermolabile (TL) and catalyzes the sulfate conjugation of monoamines such as dopamine. The other is thermostable (TS) and catalyzes the sulfation of "simple" phenols such as phenol and p-nitrophenol. We found that homogenates of human liver also contain two forms of PST that are similar to brain and platelet TL and TS PST with regard to substrate specificities, thermal stabilities and sensitivities to inhibitors. Optimal conditions were determined for the assay of these two activities in human liver homogenates. The apparent Km of liver homogenate TL PST for dopamine was 27 microM. The apparent Km of the TS form of the enzyme for p-nitrophenol was 0.94 microM. Human liver TS PST also catalyzed the sulfate conjugation of dopamine, but with an apparent Km of 5 mM, over two orders of magnitude higher than that of TL PST. Two different peaks of TS PST activity were separated from the TL activity by ion exchange chromatography of human liver preparations. Both peaks of TS PST activity were partially purified and characterized. Both had similar substrate specificities and inhibitor sensitivities. Km values of TS PST peak I for p-nitrophenol and for 3'-phosphoadenosine-5'-phosphosulfate were 0.91 and 0.86 microM, respectively, while the Km values of TS PST peak II for these two cosubstrates for the reaction were 0.43 and 0.64 microM, respectively. However, the TS PST activity in peak II was significantly more thermolabile than was the activity in peak I. These results are compatible with the conclusion that human liver homogenates contain at least two forms of PST, forms with properties similar to those of TS and TL PST in homogenates of human cerebral cortex and platelets. In addition, human liver contains two isozymes of TS PST.

Catecholamine binding by adrenal medullary protein can interfere with a sensitive radioenzymatic assay for norepinephrine

Norepinephrine (NE) binds extensively to protein that copurifies with phenylethanolamine-N-methyltransferase (PNMT) prepared from bovine adrenal medulla. This binding interferes with a NE assay that employs PNMT to catalyze the transfer of a tritiated methyl group from S-adenosyl-L-methionine to the amine group of NE. It was discovered that the protein binding of endogenous NE is reversed by dialysis at pH 6.0. Preparations of PNMT intended for use in radioenzymatic assays should involve one or more purification steps at pH 6.0.

Sulfate and methyldopa metabolism: metabolite patterns and platelet phenol sulfotransferase activity

Sulfate conjugation catalyzed by phenol sulfotransferase (PST) is the major metabolic pathway for methyldopa. Methyldopa is also O-methylated in a reaction catalyzed by catechol-O-methyltransferase (COMT). Our studies were performed to determine whether sodium sulfate alters methyldopa metabolism. Methyldopa powder, 3.5 mg/kg, was taken with and without sodium sulfate, 13.25 mg/kg, by 24 subjects in a randomized, crossover design. Compared with results obtained when only methyldopa was taken, sodium sulfate taken with methyldopa increased the proportion of drug excreted as methyldopa sulfate expressed as the percentage of all urinary metabolites (66.0% +/- 5.3% and 50.1% +/- 7.5%; means +/- SD). The percentage of free methyldopa excreted also decreased (17.1% +/- 3.7% and 27.3% +/- 5.5%). Platelet PST and red blood cell COMT activities were measured in blood samples from these subjects. When sodium sulfate was taken with methyldopa, there was a significant correlation between platelet PST activities and percentages of metabolites excreted as methyldopa sulfate (r = 0.545; P less than 0.01). This correlation was not significant when methyldopa was taken alone (r = -0.340; P greater than 0.10). There was a significant correlation between red blood cell COMT activities and the proportion of urinary metabolites excreted as 3-O-methyl-alpha-methyldopa when methyldopa was taken alone (r = 0.532; P less than 0.01) but not when it was taken with sodium sulfate (r = 0.153; P greater than 0.20). Our data support the conclusion that variation in sulfate availability may be one factor responsible for individual differences in the metabolism of clinically used doses of methyldopa.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet phenol sulfotransferase and erythrocyte catechol-O-methyltransferase activities: correlation with methyldopa metabolism

Methyldopa is metabolized by sulfate conjugation catalyzed by phenol sulfotransferase (PST), O-methylation catalyzed by catechol-O-methyltransferase (COMT), and decarboxylation catalyzed by aromatic L-amino acid decarboxylase. These experiments were performed to determine whether individual variations in red blood cell (RBC) COMT and platelet PST activities might reflect variations in the metabolism of methyldopa in man. Methyldopa, 3.5 mg/kg, was taken orally by 28 subjects. Blood samples were obtained from these subjects for the assay of platelet PST and RBC COMT activities, and a 24-hr urine sample was collected for the measurement of methyldopa and its major metabolites. Human platelets contain two independently regulated forms of PST. One form is thermolabile (TL), and the other is thermostable (TS). Methyldopa and alpha-methyldopamine are substrates for the TL but not for the TS form of PST. The results of the experiment showed significant correlations between TL platelet PST activity and the proportion of alpha-methyldopamine excreted as a sulfate conjugate, and between RBC COMT activity and the proportion of methyldopa excreted as an O-methyl metabolite. There was no significant correlation, however, between TL platelet PST activity, and the proportion of methyldopa itself excreted as a sulfate conjugate. These results are compatible with the conclusion that differences among subjects in drug metabolizing enzyme activities are one factor responsible for wide individual variations in methyldopa metabolism in man.