Oral therapy for Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome. A controlled trial of trimethoprim-sulfamethoxazole versus trimethoprim-dapsone

Comparison of the in vitro cytotoxicity of hydroxylamine metabolites of sulfamethoxazole and dapsone

The differential incidence of adverse drug reactions (ADR) between trimethoprim-sulfamethoxazole and dapsone might be explained, in part, by differences in the inherent toxicity of the hydroxylamine metabolites of sulfamethoxazole and dapsone. To test this hypothesis, the in vitro cytotoxicities of sulfamethoxazole hydroxylamine, dapsone hydroxylamine, and monoacetyldapsone hydroxylamine were compared using peripheral blood mononuclear cells (PBMC) from healthy volunteers. After 3 hr of exposure to hydroxylamine metabolites, PBMC were washed thoroughly to remove residual hydroxylamine, and viability was assessed 16 hr later by determination of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) conversion. A concentration-dependent toxicity was observed with each hydroxylamine metabolite. While dapsone hydroxylamine and monoacetyldapsone hydroxylamine were not significantly different, both showed significantly greater cytotoxic potency than sulfamethoxazole hydroxylamine (P < 0.05). This differential potency was not a function of differential stability in aqueous medium and was maintained over time. The effects of red blood cells (RBC), impermeable RBC "ghosts," and RBC lysate on hydroxylamine-induced cytotoxicity were determined using a two-compartment dialysis system. Amelioration of hydroxylamine-dependent cytotoxicity occurred when RBC were included in PBMC incubations. This apparent detoxifying effect was markedly greater using RBC lysate in comparison with impermeable "ghosts" (P < 0.05). No difference in detoxification was observed between sulfamethoxazole hydroxylamine and monoacetyldapsone hydroxylamine. Differences in the inherent cytotoxicity of their hydroxylamine metabolites do not appear to explain the differential incidence of ADR between trimethoprim-sulfamethoxazole and dapsone.

Pneumonia in AIDS patients in the critical care unit

Despite advances in prophylaxis and the reduction of mortality and morbidity resulting from highly active antiretroviral therapy, neumocystis pneumonia remains a common problem in HIV-infected patients. There are many possible causes for the continued prevalence of this condition. This article examines the characteristics, and some of the complex causes of P. carinii pneumonia in AIDS patients.

Effects of moderate-dose versus high-dose trimethoprim on serum creatinine and creatinine clearance and adverse reactions

The effects of a 10-day course of moderate-dose (10 mg/kg/day) or high-dose (20 mg/kg/day) trimethoprim therapy on serum creatinine, measured creatinine clearance, urinary creatinine excretion, and serum folate were studied in 20 healthy volunteers. Serum creatinine concentrations increased significantly during trimethoprim therapy, began to decrease near day 10, and returned to baseline during the washout phase at both dosage levels. At the same time, measured creatinine clearance and urine creatinine changed in the opposite direction. No clinical or statistical differences were noted between changes in the moderate- versus the high-dose phases. Serum folate concentration decreases during high-dose trimethoprim therapy were statistically significant. Adverse drug reactions in the two groups were statistically different during the first study period, with the high-dose group having a 75% incidence rate and the moderate-dose group having an 11% incidence rate (P < 0.02). Serum creatinine, measured creatinine clearance, and urinary creatinine excretion demonstrated statistically, but not clinically, significant changes during trimethoprim therapy. In addition, high-dose trimethoprim caused significantly more adverse drug reactions than moderate-dose trimethoprim in normal volunteers.

Hyperkalemia in the elderly: drugs exacerbate impaired potassium homeostasis

OBJECTIVE

To review the pathophysiology underlying the predisposition to hyperkalemia in the elderly; the medications that disrupt potassium balance and promote the development of hyperkalemia in the elderly; the prevention of hyperkalemia in elderly patients treated with potassium-altering medications; and the appropriate management of hyperkalemia when it develops.

METHODS AND MAIN RESULTS

A MEDLINE search of the literature (1966-1996) using the terms hyperkalemia, drugs, elderly, and treatment was conducted and pertinent review articles, textbooks, and personal files were consulted. Elderly subjects appear to be predisposed to the development of hyperkalemia on the basis of both innate disturbances in potassium homeostasis and comorbid disease processes that impair potassium handling. Hyperkalemia in the elderly is most often precipitated by medications that impair cellular uptake or renal disposal of potassium. This electrolyte disorder is best prevented by recognition of at-risk physiology in the aged, avoidance of therapy with certain high-risk medications, and monitoring of plasma potassium concentration and renal function at intervals appropriate for the medication prescribed. Management of hyperkalemia entails identification of the clinical manifestations of severe hyperkalemia, stabilization of cardiac tissue, promotion of cellular potassium uptake, and ultimately removal of potassium from the body.

CONCLUSIONS

Geriatric patients should be considered at risk of developing hyperkalemia, especially when they are prescribed certain medications. Potassium levels should be monitored at appropriate intervals when these patients are treated with potassium-altering medications. Appropriate management of hyperkalemia in the elderly can avoid life-threatening neuromuscular and cardiac complications.

Suppression of pokeweed mitogen-driven human IgM and IgG responses by the hydroxylamine of sulfamethoxazole

OBJECTIVE

To determine the effect(s) of reactive sulfonamide metabolites on antibody production by human lymphocytes.

METHODS

Human peripheral blood cells (PBMCs) were isolated from control volunteers and incubated with the hydroxylamine of sulfamethoxazole (SMX H/A), a reactive metabolite of the most commonly used sulfonamide, in increasing concentrations. PBMCs were then stimulated to produce antibody with pokeweed mitogen. After incubation for 8 days, concentrations of IgG and IgM were determined in supernatant using an ELISA assay.

RESULTS

Production of both IgG and IgM was significantly suppressed by sub-lethal concentrations of SMX H/A in a concentration-dependent fashion (p < 0.05). Suppression was more marked for IgM production (maximal decline to 80% of baseline antibody production) than for IgG production (maximal decline to 57% of baseline antibody production). No suppression was seen when cells were incubated with sulfamethoxazole in concentrations up to 400 microM. This suppression was not related to changes in cell viability; at a concentration of 25 microM of SMX H/A, IgM and IgG concentration were reduced by 47 +/- 8.7% and 73 +/- 7.2%, while cell viability (percentage of live cells) was 93 +/- 5%. Suppression was time-dependent, increasing over the incubation periods to reach a plateau after 2 h of incubation.

CONCLUSION

Sulfonamide reactive metabolites, in concentrations which are achieved during therapy, suppress antibody production by PWM-stimulated human cells. This may explain, in part, the alterations in immunity associated with hypersensitivity reactions to the sulfonamides. This may also have implications for patients receiving sulfonamide therapy and concurrent immunosuppressive therapy.

Pneumocystis carinii pneumonia

Pneumocystis carinii pneumonia (PCP) remains an important complication of AIDS. Advances have been made in establishing the taxonomy of the organism but the life cycle of the organism and pathogenetic mechanisms of disease remain obscure. In HIV patients the incidence of PCP has decreased because of widespread use of prophylaxis and survival of those with PCP has improved with use of adjunctive corticosteroid therapy. Less toxic drug therapies are still needed as well as better noninvasive diagnostic techniques.

Drug treatment of HIV-related opportunistic infections

The AIDS epidemic has led to the emergence of several disease entities which in the pre-AIDS era were rare or seemingly innocuous. Experience of treating these diseases varies. In some instances, such as Pneumocystis carinii pneumonia, there is an abundance of published literature to direct our course of action. However, for many of these newly recognised diseases our treatment experience is limited. Furthermore, in many instances, well controlled trials evaluating treatment modalities in the AIDS population are lacking. We have identified 13 disease entities (P. carinii pneumonia, toxoplasmosis, cryptococcosis, histoplasmosis, Mycobacterium tuberculosis, Mycobacterium avium complex, cytomegalovirus, coccidioidomycosis, isosporiasis, candidosis, Kaposi's sarcoma, herpes simplex virus, and varicella zoster virus) and have reviewed the current literature with regard to their treatment.

Association of hepatic necrosis with trimethoprim sulfonamide administration in 4 dogs

Hepatic necrosis in association with trimethoprim-sulfonamide (TMS) combination therapy was diagnosed in 4 dogs based on history, clinical presentation, and examination of histopathologic specimens collected postmortem. Duration of TMS therapy prior to onset of clinical signs ranged from 4 to 30 days. The dose of TMS ranged from 18 mg/kg to 53 mg/kg bid. Despite supportive medical therapy, all dogs died or were euthanized due to hepatic failure. This report highlights the potential for hepatotoxicity during TMS therapy. Duration of therapy, type of TMS combination, and dose did not appear related to the development of toxicity. The low number of dogs affected suggests an idiosyncratic drug reaction.

Role of viral infections in the induction of adverse drug reactions

A spectrum of adverse drug reactions that are caused by the combined action of drugs and viruses has been described: ampicillin rash in acute infectious mononucleosis; Reye's syndrome; hypersensitivity reactions to sulphonamides in patients with HIV infection; drug-induced agranulocytosis; paracetamol (acetaminophen) hepatotoxicity; aspirin (acetylsalicyclic acid)-induced asthma; Epstein-Barr virus-associated lymphoma and methotrexate; and AIDS-related Kaposi's sarcoma and nitrite use. Changes in pharmacokinetics have been reported for: caffeine, sulfamethoxazole and fluconazole in patients with HIV infection; theophylline, following influenza and influenza vaccination; and recently, dipyrone metabolites in carriers of the hepatitis B virus. In addition increased drug- and drug metabolite-related toxicity has been observed in virally infected cells. Pathogenetic mechanisms for the interaction between drugs and viruses are varied, and include biological mechanisms (often immunological) and changes in drug metabolism. The combined effects of chemical and biological exposure provide a unique model for the study of disease induction.

Comparisons of oxidative metabolism and reductive capacity in sulfonamide-tolerant and -intolerant patients with human immunodeficiency virus

Hypersensitivity reactions to trimethoprim/sulfamethoxazole occur with a high frequency in human immunodeficiency virus (HIV)-infected patients. This study tested whether differences in oxidative metabolism and plasma reductive capacity correlate with sulfonamide intolerance in patients with HIV. Eighteen stable outpatients with HIV were prospectively studied. Nine patients had documented histories of hypersensitivity reactions to trimethoprim/sulfamethoxazole and nine did not. Urinary caffeine metabolite ratios assessed the activity of two oxidative enzymatic pathways: cytochrome P-450 1A2 (demethylation) and 8-hydroxylation. Plasma cyst(e)ine was used as a measure of reductive capacity. The trimethoprim/sulfamethoxazole-intolerant group showed greater rates of 8-hydroxylation, lower rates of demethylation, and lower cyst(e)ine levels. The results of this pilot study extend previous observations of differences in oxidative metabolism and reductive capacity that exist within the population of HIV-infected individuals. In addition, these findings lay the groundwork for future interventional studies that could use agents to inhibit sulfonamide oxidation and increase reductive capacity in sulfonamide-intolerant patients with HIV when rechallenged with trimethoprim/sulfamethoxazole.

Pneumocystis carinii

Improved understanding of Pneumocystis carinii, in particular the widespread use of chemoprophylaxis, has resulted in a declining incidence of infection in patients infected with HIV since the late 1980s. Despite these advances, P. carinii pneumonia continues to represent an important cause of pulmonary disease in HIV-seropositive individuals who do not receive chemoprophylaxis or when breakthrough episodes occur. This article reviews the history, biology, clinical manifestations, prognostic markers, therapy, and chemoprophylaxis of P. carinii pneumonia in HIV-seropositive patients.

N-acetyltransferases: pharmacogenetics and clinical consequences of polymorphic drug metabolism

Since the discovery of polymorphic N-acetylation of drugs nearly 40 years ago, great progress has been made in understanding the molecular genetics of acetylation as well as the clinical consequences of being a rapid or slow acetylator. Inborn errors (several different alleles) at the NAT2 locus are responsible for the traditional acetylator polymorphism. Studies have revealed variant alleles at the NAT1 locus as well. The consequences of pharmacogenetic variation in these enzymes include (i) altered kinetics of specific drug substrates; (ii) drug-drug interactions resulting from altered kinetics; (iii) idiosyncratic adverse drug reactions. The latter have been extensively investigated for the arylamine-containing sulfonamide antimicrobial drugs. Individual differences in multiple metabolic pathways can increase the likelihood of covalent binding of reactive metabolites of the drugs to cell macromolecules with resultant cytotoxicity and immune response to neoantigens. This can result clinically in an idiosyncratic hypersensitivity reaction, manifested by fever, skin rash, and variable toxicity to organs including liver, bone marrow, kidney, lung, heart, and thyroid. Slow acetylation by NAT2 is a risk factor for such reactions to sulfonamides. Given the incidence of these severe adverse drug reactions (much less than 1/1000), slow acetylation cannot be the sole mechanism of predisposition in the population. Differences in rates of production of hydroxylamine metabolites of the drugs by cytochrome P450 (CYP2C9), myeloperoxidase, and thyroid, roxidase, along with an inherited abnormality in detoxification of the hydroxylamines are critically important in determining individual differences in adverse reaction risk. Both NATs, particularly NAT1, also can further metabolize hydroxylamine metabolites to N-acetoxy derivatives. Intensive investigation of patients with these rare adverse reactions using a variety of tools from in vitro cell toxicity assays through molecular genetic analysis will help elucidate mechanisms of predisposition and ultimately lead to diagnostic tools to characterize individual risk and prevent idiosyncratic drug toxicity.

Dapsone- and primaquine-induced methemoglobinemia in HIV-infected individuals

Clinically significant methemoglobinemia can develop as a result of medications. Although dapsone and primaquine are known to produce methemoglobinemia in susceptible individuals, methemoglobinemia has been reported only rarely in the human immunodeficiency virus (HIV) population. We describe five cases of methemoglobinemia caused by either primaquine or dapsone alone or in combination. The initial methemoglobin level ranged from 15.3% in the patient whose methemoglobinemia was caused by primaquine alone to 33.1%. Five patients developed symptomatic methemoglobinemia requiring hospitalization for 1 to 12 days. Two cases resulted from intentional overdoses of dapsone, and three developed within several days of commencing primaquine while dapsone remained present in the bloodstream. The four severe cases required intravenous methylene blue, supplemental oxygen, plus erythrocyte transfusions, whereas the mild case responded to oxygen therapy plus discontinuation of the precipitating drugs. Blood gases and pulse oximetry do not aid in the diagnosis, which requires cooximetry. Our study indicates that dapsone and primaquine alone or in combination can produce clinically significant methemoglobinemia in HIV-infected individuals, either in the setting of an overdose or when primaquine is instituted before dapsone has been cleared from the bloodstream.

AIDS and the lung

Respiratory symptoms are common in HIV-infected persons. The challenge facing clinicians is to determine whether these respiratory symptoms are due to an opportunistic infection or to a chronic process, such as asthma, chronic bronchitis, bronchiectasis, or emphysema. This article reviewed the clinical presentation, diagnosis, and treatment of two important opportunistic infections, PCP and bacterial pneumonia. It also reviewed the current data on obstructive lung diseases as they relate to HIV.

Dapsone in rheumatoid arthritis

Dapsone, a synthetic sulfone with chemical similarities to sulfapyridine, has been used for a number of years to treat leprosy and dermatitis herpetiformis. Recently, a number of prospective, randomized, double-blind trials have shown their success in the management of rheumatoid arthritis, with dapsone being superior to placebo and comparable to chloroquine and hydroxychloroquine. Its mode of anti-inflammatory actions in rheumatoid arthritis is not clearly understood, but modulation of neutrophil activity or inhibition of neutrophil inflammatory product formation or release appear to play a role. The major limiting side effect is hemolytic anemia, which may be mitigated through careful patient selection, conservative drug dosing, close monitoring, and possibly, concurrent administration of antioxidants or cytochrome P450 inhibitors. Methemoglobinemia is another common finding among patients receiving dapsone therapy, but rarely does it result in prominent symptoms other than transient pallor. Less common adverse events to dapsone include the idiosyncratic reactions of leukopenia and agranulocytosis, cutaneous eruptions, peripheral neuropathy, psychosis, toxic hepatitis, cholestatic jaundice, nephrotic syndrome, renal papillary necrosis, severe hypoalbuminemia without proteinuria, an infectious mononucleosis-like syndrome, and minor neurological and gastrointestinal complaints. In this report, two patients with advanced rheumatoid arthritis, who were safely and effectively treated with dapsone after failure with other second-line agents, are described and the literature is reviewed. We suggest that dapsone is an effective second-line agent in the treatment of rheumatoid arthritis.

Hypersensitivity anaphylactoid reaction to pefloxacin in a patient with AIDS

OBJECTIVE

To report a life-threatening anaphylactoid reaction to oral pefloxacin in a patient with AIDS and to review the pertinent literature.

CASE SUMMARY

A 32-year-old woman with AIDS developed an anaphylactoid reaction following a second exposure to oral pefloxacin. This reaction was characterized by severe hypotension, dizziness, itching, and fever.

DISCUSSION

Fluoroquinolones are broad-spectrum antimicrobial agents. They are used frequently in patients with AIDS for numerous indications, including treatment of Mycobacterium avium complex. Pefloxacin, a broad-spectrum fluoroquinolone, was introduced in France in 1985. Since then, many patients with AIDS have been treated with this drug. Several cases of anaphylactoid reactions to ciprofloxacin have been documented in patients with HIV infection. To our knowledge, this is the first reported case of an anaphylactoid reaction to pefloxacin in a patient with AIDS.

CONCLUSIONS

There is a need for continued vigilance in the reporting of adverse drug reactions in patients with AIDS, especially with new drug. Also, care must be taken in introducing drugs, including fluoroquinolones, to this patient population.

Safety of dapsone as Pneumocystis carinii pneumonia prophylaxis in human immunodeficiency virus-infected patients with allergy to trimethoprim/sulfamethoxazole

OBJECTIVE

To assess the safety of dapsone prophylaxis of Pneumocystis carinii pneumonia (PCP) in patients with prior intolerance to trimethoprim/sulfamethoxazole (TMP/SMX).

METHODS

We conducted a retrospective study in the categorical human immunodeficiency virus out-patient program of a university hospital. Patients who had filled prescriptions for dapsone at our pharmacy between January 1991 and April 1994 were evaluated and 75 patients were found eligible for analysis.

RESULTS

The overall incidence of adverse events (AE) in our study cohort was 39%. The most common AEs were anemia (23%) and rash (16%). However, after critical evaluation of each case, only 3 cases of anemia (4%) and 2 cases of rash (3%) were judged to be "likely related" to dapsone. Only 5/75 patients (7%) developed the same intolerance to dapsone as previously experienced on TMP/SMX, and none of these cases was viewed as "likely related" to dapsone. A dapsone regimen of 100 mg qd and a prior episode of PCP were associated with a higher incidence of AEs. Eight cases of PCP occurred in spite of dapsone prophylaxis for an incidence of 7 cases per 1,000 patient-months. Seven of the cases of PCP occurred in patients who were receiving secondary prophylaxis.

CONCLUSIONS

Given the low incidence of AEs judged to be "likely related" to dapsone, this drug is a reasonable choice for PCP prophylaxis in patients with prior AEs to TMP/SMX.

Studies on the mechanism of trimethoprim-induced hyperkalemia

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.

Zidovudine, trimethoprim, and dapsone pharmacokinetic interactions in patients with human immunodeficiency virus infection

Zidovudine is widely prescribed for the treatment of human immunodeficiency virus (HIV) infection. Trimethoprim and dapsone are commonly used in the management of Pneumocystis carinii pneumonia in HIV-infected patients. To examine the pharmacokinetic interactions among these drugs, eight HIV-infected patients (26 to 43 years old) with a mean CD4 count of 524.4 +/- 405.7 cells per mm3 received zidovudine (200 mg), trimethoprim (200 mg), and dapsone (100 mg) as single agents and in two- and three-drug combinations. Blood and urine samples were collected at a specified time and analyzed for zidovudine, zidovudine-glucuronide, trimethoprim, dapsone, and monoacetyl-dapsone concentrations under single-dose and steady-state conditions. Zidovudine did not influence the pharmacokinetic disposition of dapsone or trimethoprim. Dapsone had no effect on the pharmacokinetic disposition of zidovudine. Trimethoprim significantly decreased the renal clearance of zidovudine by 58% (5.0 +/- 1.8 versus 2.1 +/- 0.5 ml/min/kg of body weight [P < 0.05]). There was a concurrent 54% decrease in the mean urinary recovery of zidovudine (11.7 +/- 3.5 versus 5.4 +/- 3.0 [P < 0.05]), and the metabolic ratio was decreased by 78% (0.32 +/- 0.4 versus 0.07 +/- 0.05 [P < 0.05]). The mean area under the concentration-time curve from 0 to 6 h of the zidovudine-glucuronide/ zidovudine ratio was unchanged. We conclude that zidovudine, trimethoprim, and dapsone can be coadministered to patients with AIDS without significant pharmacokinetic interaction. However, in AIDS patients with liver impairment and impaired glucuronidation, doses of zidovudine may need to be decreased.

Effect of standard-dose trimethoprim/sulfamethoxazole on the serum potassium concentration in elderly men

OBJECTIVE

To determine the effect of standard-dose trimethoprim/sulfamethoxazole (TMP/SMX) (TMP 160 mg and SMX 800 mg q12h) on the serum potassium concentration.

DESIGN

Retrospective and concurrent study.

SETTING

A Veterans Affairs Medical Center.

PATIENTS

Fifty-three men hospitalized at the Fargo Veterans Affairs Medical Center. Thirty-three patients who received standard-dose TMP/SMX for 3 or more days comprised the study group. Twenty patients who received oral cephradine or amoxicillin for 3 or more days comprised the control group. Patients who received potassium supplements, potassium-sparing diuretics, angiotensin-converting enzyme inhibitors, nonsteroidal antiinflammatory drugs, beta-blockers, heparin, known nephrotoxic agents, patients with a serum creatinine concentration of more than 177 mumol/L, and patients with baseline hyperkalemia (serum potassium concentration > 5.1 mmol/L) were excluded.

RESULTS

The serum potassium concentration in the study group was 4.22 +/- 0.40 mmol/L and increased by 0.31 +/- 0.38 mmol/L at the end of therapy (p < 0.001). Twenty-six patients in the study group (78.8%) had an increase in the serum potassium concentration during TMP/SMX therapy. Fourteen of these patients had follow-up serum potassium concentrations obtained after completion of therapy. The serum potassium concentration returned to baseline in 10 of these patients. The serum creatinine concentration also increased during therapy. However, the correlation between the increase in the serum potassium concentration and the increase in the serum creatinine concentration was weak (Pearson r = 0.29). The serum potassium in the control group was 4.34 mmol/L and remained essentially unchanged during therapy.

CONCLUSIONS

Therapy with standard-dose TMP/SMX is associated with a slight increase in the serum potassium concentration. Routine monitoring of the serum potassium concentration in patients who are treated with standard-dose TMP/SMX therapy is unnecessary. However, TMP/SMX should be considered as a possible cause of unexplained hyperkalemia in elderly patients receiving TMP/SMX therapy.

Monodrug efficacies of sulfonamides in prophylaxis for Pneumocystis carinii pneumonia

A remarkably high rate of adverse events is associated with the use of trimethoprim-sulfamethoxazole in patients with human immunodeficiency virus type 1 infection. We examined the efficacies of sulfonamides alone in the prevention of Pneumocystis carinii pneumonitis, with the assumption that at least some of the adverse events with the drug combination might be due to trimethoprim. With the immunosuppressed rat model, eight sulfonamides were studied at 100, 10, and 1.0 mg/kg/day (10 rats per dosage and drug). P. carinii infection was prevented in all animals (100%) receiving dosages of as little as 1.0 mg of sulfamethoxazole, sulfamethoxypyridazine, and sulfadimethoxine per kg per day, as little as 10 mg of sulfameter, sulfachlorpyridazine, and sulfaquinoxaline per kg per day; and 100 mg of sulfaguanidine and sulfanilamide per kg per day. These studies suggest that a sulfonamide, such as sulfamethoxazole, might provide effective prophylaxis for P. carinii pneumonitis without trimethoprim.

Inhibition of sulfamethoxazole hydroxylamine formation by fluconazole in human liver microsomes and healthy volunteers

Sulfamethoxazole toxicity is putatively initiated by the formation of a hydroxylamine metabolite by cytochromes P450. If this reaction could be inhibited, toxicity may decrease. We have studied--in vitro and in vivo--fluconazole, ketoconazole, and cimetidine as potentially suitable clinical inhibitors of sulfamethoxazole hydroxylamine formation. Both fluconazole and ketoconazole in human liver microsomal incubations competitively inhibited sulfamethoxazole N-hydroxylation, with the inhibitory constant (Ki) values of 3.5 and 6 micromol/L, respectively. Cimetidine exhibited a mixed type of inhibition of sulfamethoxazole hydroxylamine formation in human liver microsomes, with IC 50 values (the concentration required to decrease hydroxylamine formation by 50%) of 80 and 800 micromol/L, the lower value being observed when cimetidine was preincubated with microsomes and reduced nicotinamide adenine dinucleotide phosphate. In an in vivo study in six healthy volunteers the inhibition of the cytochrome P450-mediated generation of the toxic metabolite in the presence of fluconazole was shown by a 94% decrease in the area under the plasma concentration-time curve of sulfamethoxazole hydroxylamine. In contrast, the recovery of hydroxylamine in urine decreased by only 60%. Total clearance of sulfamethoxazole was decreased by 26% by fluconazole, most likely because of the inhibition of unidentified P450 elimination pathways. There was close agreement between the predicted (87%) and observed inhibition (94%) of sulfamethoxazole hydroxylamine formation in vivo. Similarly, there was close agreement between in vivo and in vitro Ki values--1.6 and 3.5 micron/L, respectively.

Case report: severe hyperkalemia in a geriatric patient receiving standard doses of trimethoprim-sulfamethoxazole

A case is reported of a 96-year-old woman with congestive heart failure, hypertension, and chronic obstructive pulmonary disease who presented with altered mental status and severe hyperkalemia, a serum potassium 9.3 meq/L, and electrocardiograph changes. The patient was discharged 1 week prior, with a normal serum potassium, receiving trimethoprim-sulfamethoxazole for urinary tract infection and pneumonia. Serum potassium measurements returned to normal after discontinuation of the drug. Other causes of hyperkalemia were ruled out. Mild hyperkalemia due to trimethoprim-sulfamethoxazole was first reported in 1983 in a 69-year-old woman in whom leukemia with leukopenia developed. In literature to date, mild hyperkalemia in younger geriatric patients has been described. Trimethoprim is thought to act by inhibiting amiloride sensitive sodium channels in the distal nephron and impairing renal potassium secretion in a dose dependent manner. The authors report the case, review the literature, and discuss age-related reduction in renal function as a possible etiology.

HIV medicine: drug side effects and interactions

The drugs used in HIV medicine often have toxic side effects; additionally, the risk of drug interactions is high because of the frequent necessity to prescribe multiple drugs. This article covers common or important drug side effects and interactions.

[Pneumocystis carinii pneumonia in AIDS: retrospective analysis of 80 documented cases (1985-1993)]

Eighty initial episodes of HIV-associated Pneumocystis carinii pneumonia (PCP) diagnosed at Bordeaux hospital between 1985 and 1993 are reported (57 were men and 23 women). PCP revealed HIV infection in 29 patients (36%). Others cases were patients with poor medical follow up (10%), with a CD4+ lymphocyte count above 200/mm3 at last follow-up (9%), non compliant with PCP prophylaxis (9%), or using aerolized pentamidine (AP+) (20%). The main clinical symptoms were fever (90%), dyspnea (68%), non productive (63%) and productive (17%) cough. Radiographic infiltrates were purely interstitial (59%), acinar and interstitial (25%), purely acinar (5%) and absent (11%). Thirty-eight percent of AP+ had upper lobe preferential involvement and 13% a pleural effusion. In all cases, Pneumocystis carinii was detected in bronchoalveolar lavage. Extrapulmonary localizations of pneumocystosis were noticed (eye, liver, spleen, ascitis) in two AP+. Mean CD4+ count was 54/mm3 in patients not having received aerolized pentamidine (AP-) and 22/mm3 in AP+. P24 antigenemia was positive in 53% (AP-) and 88% (AP+). PaO2 LDH and albuminemia were similar in both groups. Antimicrobial therapy (Cotrimoxazole in 91% of the cases) was combined with corticosteroids in 45% and mechanic ventilation in 19%. After 30 days of follow-up, 17 deaths were observed (21%) and 14 attributed to PCP: mortality was worse in AP+ (31%) than in AP- (19%). The main conclusions of our study are the followings: HIV related PCP is still in 1995 frequent and severe; atypical features should not rule out diagnosis; preventive measures are neither sufficient nor efficient. PCP remains in 1995 a priority in HIV related public health and therapeutical research.

Metabolism of dapsone to its hydroxylamine by CYP2E1 in vitro and in vivo

Dapsone toxicity is putatively initiated by formation of a hydroxylamine metabolite by cytochromes P450. In human liver microsomes, the kinetics of P450-catalyzed N-oxidation of dapsone were biphasic, with the Michaelis-Menten constants of 0.14 +/- 0.05 and 0.004 +/- 0.003 mmol/L and the respective maximum velocities of 1.3 +/- 0.1 and 0.13 +/- 0.04 nmol/mg protein/min (mean +/- SEM). Troleandomycin (40 mumol/L) inhibited hydroxylamine formation at 100 mumol/L dapsone by 50%; diethyldithiocarbamate (150 mumol/L) and tolbutamide (400 mumol/L) inhibited at 5 mumol/L dapsone by 50% and 20%, respectively, suggesting that the low-affinity isozyme is CYP3A4 and the high-affinity isozymes are 2E1 and 2C. Disulfiram, 500 mg, 18 hours before a 100 mg oral dose of dapsone in healthy volunteers, diminished area under the hydroxylamine plasma concentration-time curve by 65%, apparent formation clearance of the hydroxylamine by 71%, and clearance of dapsone by 26%. Disulfiram produced a 78% lower concentration of methemoglobin 8 hours after dapsone.

Ability of primary care physicians to diagnose and manage Pneumocystis carinii pneumonia

This study assesses the ability of primary care physicians to diagnose and manage Pneumocystis carinii pneumonia (PCP) in a standardized patient (SP) with unidentified HIV infection. One hundred thirty-four primary care physicians from five Northwest states saw an SP with unidentified HIV infection who presented with symptoms, chest radiograph, and arterial blood gas results classic for PCP. Seventy-seven percent of the physicians included PCP in their differential diagnoses and 71% identified the SP's HIV risk. However, only a minority of the physicians indicated that they would initiate an appropriate diagnostic evaluation or appropriate therapy: 47% ordered a diagnostic test for PCP, 31% initiated an antibiotic appropriate for PCP, and 12% initiated an adequate dose of trimethoprim - sulfamethoxazole. Only 6% of the physicians initiated adjunctive prednisone therapy, even though prednisone was indicated because of the blood gas result. These findings suggest significant delay in diagnosis and treatment had these physicians been treating an actual patient with PCP.

Therapeutic progress. IV: Treatment and prophylaxis of Pneumocystis carinii infection

Co-trimoxazole presently remains the first choice for prophylaxis and treatment of Pneumocystis carinii infections. The high incidence of adverse reactions experienced by patients taking co-trimoxazole has led to a number of trials comparing it with other antipneumocystis agents. Adjuvant therapy with corticosteroids may benefit patients with severe P. carinii pneumonia. This paper reviews the standard treatments for P. carinii pneumonia, some of the newer agents such as atovaquone, recently licensed in the U.K., and a variety of novel agents being assessed for treatment and prophylaxis. Current recommendations may change over the new few years.

Urinary recovery and kinetics of sulphamethoxazole and its metabolites in HIV-seropositive patients and healthy volunteers after a single oral dose of sulphamethoxazole

1. The urinary excretion of sulphamethoxazole and its metabolites was compared between healthy volunteers and HIV-seropositive patients in order to get a better understanding of why HIV seropositives are more predisposed to idiosyncratic toxicity of sulphonamides. 2. A single 800 mg oral dose of sulphamethoxazole was administered to seven healthy volunteers and seven asymptomatic HIV seropositives without previous use of sulphonamides. 3. Urine was collected for 4 days and drug analysis was by h.p.l.c. 4. No difference was observed between seropositive and seronegative individuals in the urinary recovery of sulphamethoxazole, N4-acetyl-, 5-hydroxy-, N4-acetyl-5-hydroxy-sulphamethoxazole and the N1-glucuronide conjugate. However the recovery of the hydroxylamine metabolite of sulphamethoxazole was significantly lower in the HIV seropositives (0.50 +/- 0.51 vs 2.23 +/- 0.85%; 95% CI on the difference, -0.90 to -2.55; P = 0.0006). 5. Sulphamethoxazole hydroxylamine may be a factor in the susceptibility of HIV infected individuals to sulphonamides.

Combinations of sulphonamides with diaminopyrimidines: how, when and why?

Co-trimoxazole is still widely used for indications where trimethoprim alone is equally effective. The pharmacological rationale of the combination of trimethoprim and sulphamethoxazole involves synergistic action of the two drugs. This is true only from a laboratory point of view; several considerations have led to the conclusion that the synergism between the two components is of only in vivo marginal importance in determining the clinical efficacy of co-trimoxazole. This is due to a greater tissue affinity of trimethoprim compared to that of sulphamethoxazole and, therefore, to the different tissue concentration ratios obtained in vitro and in vivo. Another claim sustaining the combination is the prevention of developing resistance to trimethoprim; however, there is no substantial clinical evidence to support this claim. It does seem likely that trimethoprim has protected against the emergence of that sulphonamide resistance. This slight benefit is outweighed by the disadvantages of the combination, mainly consisting of the occurrence of adverse events due to the sulphonamide moiety. Consequently, the incidence and severity of the adverse events seen with co-trimoxazole should be reduced by using trimethoprim alone. There are only a few cases where co-trimoxazole is better than trimethoprim: toxoplasmosis, brucellosis, nocardiosis, chancroid and pneumonia due to Pneumocystis carinii. For the other and many common infections, scientific rationale, economic and clinical reasons dictate that trimethoprim is superior to co-trimoxazole.

Hyperkalemia and high-dose trimethoprim/sulfamethoxazole

Evidence from the literature strongly supports that high doses of TMP, as used in the treatment of PCP in AIDS patients, have the propensity to cause hyperkalemia by inhibiting sodium channels in the distal nephron, thereby impairing potassium secretion. The mechanism of TMP-induced hyperkalemia is believed to be similar to that of triamterene and amiloride because of the structural similarity of these agents. It is also possible that declining renal function, which is a natural progression of HIV disease, may contribute to the hyperkalemia seen in this patient population. In addition, patients with AIDS also may exhibit a defect in adrenal function, potentiating the hyperkalemic effect of TMP therapy. Therefore, it is crucial for clinicians to monitor closely the serum potassium concentration in this patient population, especially during therapy with high doses of TMP.

Pharmacokinetics of trimethoprim-sulfamethoxazole in critically ill and non-critically ill AIDS patients

Current dosage regimens of trimethoprim-sulfamethoxazole used to treat Pneumocystis carinii pneumonia in AIDS patients have been based on data from healthy subjects or patients without AIDS. The clearance and absorption characteristics of the drugs may potentially be different between patients with and without AIDS. This study was conducted to assess the pharmacokinetics of trimethoprim-sulfamethoxazole in critically ill and non-critically ill AIDS patients treated for P. carinii pneumonia. Patients received trimethoprim at 15 mg/kg of body weight and sulfamethoxazole at 75 mg/kg of body weight daily intravenously in three to four divided doses and were switched to the oral route when the regimen was tolerated. Serum samples for determination of drug concentrations were obtained over 12 h after intravenous and oral dosing. The pharmacokinetics of trimethoprim and sulfamethoxazole were compared in eight critically ill versus nine non-critically ill male patients and were as follows, respectively: clearance, 1.88 +/- 0.44 versus 1.73 +/- 0.64 ml/min/kg for trimethoprim and 0.40 +/- 0.12 versus 0.34 +/- 0.11 ml/min/kg for sulfamethoxazole; volume of distribution, 1.6 +/- 0.5 versus 1.5 +/- 0.5 liters/kg for trimethoprim and 0.5 +/- 0.3 versus 0.4 +/- 0.1 liters/kg for sulfamethoxazole; and half-life, 10.9 +/- 7.4 versus 11.3 +/- 4.0 h for trimethoprim, and 15.5 +/- 9.5 versus 14.3 +/- 4.7 h for sulfamethoxazole. No significant differences (P > 0.05) were observed between patient groups, although there was wide intersubject variability. Absorption appeared to be similar between the critically ill and non-critically patients: bioavailability was 97.5% +/- 22.4% versus 101.8% +/- 22.7% for trimethoprim and 86.2% +/- 17.9% versus 99.1% +/- 20.5% for sulfamethoxazole, respectively. Because of the similar pharmacokinetics of trimethoprim-sulfamethoxazole in critically ill and non-critically ill AIDS patients, the two groups of patients may receive similar dosages. Dosage adjustment does not appear to be required when switching from the intravenous to the oral route.

Pneumonia in patients with HIV infection

The epidemiologic shift in HIV-infected populations from homosexual men to intravenous drug users and their sexual partners, together with the wide application of antipneumocystis prophylaxis and a better understanding of the broad range of HIV-associated illnesses, has changed our concept of the spectrum of lung infections that occur in patients with HIV infection. Bacterial pneumonia, not PCP, is the most common lower respiratory infection. Newer therapies of mild-to-moderate PCP increase the treatment options. The worldwide increase in tuberculosis cases is attributable to coinfection with HIV, and multidrug-resistant tuberculosis is now a serious threat, especially in the inner cities. Fungal pneumonias occur with increased frequency in patients with HIV infection, depending on the geographic factors and the severity of immunodeficiency.

Activity of epiroprim (Ro 11-8958), a dihydrofolate reductase inhibitor, alone and in combination with dapsone against Toxoplasma gondii

We examined the effect of epiroprim (Ro 11-8958), a dihydrofolate reductase inhibitor, alone and in combination with dapsone, against Toxoplasma gondii. In vitro, the anti-T. gondii effects of epiroprim and dapsone were observed at nanogram-per-milliliter levels when a 72-h uracil assay and an infection rate of one parasite per 120 macrophages were used. In combination, these drugs exerted a synergistic effect that, however, was only parasitostatic. In a model of acute infection, mice were infected intraperitoneally with 10(4) parasites of the RH strain of T. gondii and were treated for 14 days by gavage (therapy divided into two daily dosages), starting 24 h after infection. Used alone, dapsone and epiroprim, each at a dose of 50 mg/kg of body weight per day, protected 10 and 0% of the mice, respectively. When these drugs were administered simultaneously, a 100% survival rate was observed. Pyrimethamine-sulfadiazine (4 and 250 mg/kg/day, respectively) protected 100% of the mice. A 3-week therapy of chronically infected mice with either epiroprim (50 mg/kg/day), dapsone (50 mg/kg/day), or pyrimethamine (15 mg/kg/day) reduced the numbers of T. gondii cysts and the inflammation in their brains. A combination of epiroprim and dapsone, both at 50 mg/kg/day, further reduced the number of brain cysts in comparison with the number after the corresponding monotherapies. Epiroprim may have a role in the prophylaxis or therapy of human toxoplasmosis, especially when combined with other drugs active against T. gondii, such as dapsone.

Atovaquone: A Review with Emphasis on its Role in the Treatment of Pneumocystis Carinii Pneumonia

Objective:

To discuss the mechanism of action, in vitro and in vivo activity, pharmacokinetics, clinical trials, adverse effects, drug interactions, and dosage guidelines of atovaquone.

Data Sources:

Pertinent literature published since 1988 was identified via a MEDLINE search. Published proceedings of selected conferences were also used.

Study Selection:

All basic science, microbiologic, and pharmacokinetic articles were evaluated. Since only limited data regarding atovaquone are available in the literature, all clinical trials involving the use of atovaquone in the treatment of Pneumocystis carinii pneumonia were reviewed.

Data Synthesis:

Atovaquone is an antiprotozoal agent that was recently approved for the treatment of mild to moderate P. carinii pneumonia (PCP) in patients who are intolerant of trimethoprim/sulfamethoxazole (TMP/SMX). The exact mechanism of action of atovaquone against P. carinii has not been determined. The drug has in vitro and in vivo activity against P. carinii, Toxoplasma gondii, and Plasmodium species. The bioavailability of oral atovaquone is highly variable. The drug must be administered with food to enhance absorption. In a double-blind comparative trial in AIDS patients with mild to moderate PCP, those who were treated with atovaquone had a significantly higher mortality rate than those treated with TMP/SMX. More patients who received TMP/SMX experienced adverse effects that resulted in discontinuation of therapy.

Conclusions:

Because of concerns of increased mortality in atovaquone recipients, the drug should be reserved for the treatment of mild to moderate PCP in patients who are unable to tolerate TMP/SMX and trimethoprim-dapsone.

The acquired immune deficiency syndrome: an overview for the emergency physician, Part 1

The acquired immune deficiency syndrome (AIDS) was recognized as a distinct entity in 1981. It began as a medical curiosity affecting only several dozen individuals in a restricted segment of the U.S. population. In the 12 years since its description, AIDS has become a pandemic affecting tens of millions with cases reported from all major countries. The illness is caused by a retrovirus, termed human immunodeficiency virus (HIV). It is a blood-borne disease with sexual, parenteral, and perinatal modes of transmission. Infection with the virus can be determined by a number of serologic techniques as well as viral culture. The pathophysiology of illness is incompletely understood, but is in large part related to destruction of helper, CD4 lymphocytes. This results in immune dysfunction and the development of a variety of opportunistic infections and malignancies. A great deal has been learned over the last decade, with important advances in treatment. Zidovudine (AZT) remains the most important agent in slowing progression of the disease and has resulted in prolonging survival. All organ systems can be affected by HIV, and many clinical manifestations are protein. Fever, weight loss, and diarrhea are often encountered general symptoms. The skin is frequently involved, with Kaposi's Sarcoma the most common malignancy and a variety of fungi and viruses the most frequent cause of infection. The lung is involved in the majority of patients, with Pneumocystis Carinii (PCP) and mycobacteria emerging as the most important pathogens. A variety of treatments have demonstrated efficacy for PCP. The risk of PCP is related to the decay in CD4 lymphocytes so that prophylactic treatment is recommended when CD4 counts fall below 200. Mycobacterial infection with multiresistant organisms has complicated the management of these infections and poses new risks to health care workers. Part 1 of this two-part series on AIDS discusses the pathophysiology and clinical expression, epidemiology, laboratory testing, and the general clinical manifestations of AIDS, as well as dermatologic, pulmonary, and cardiac symptoms. Part 2 will discuss the gastrointestinal, neurologic, and ocular symptoms, as well as the treatment and management of the AIDS patient.