Foscarnet-induced severe hypomagnesemia and other electrolyte disorders

Gene-nutrient interactions that impact magnesium homeostasis increase risk for neural tube defects in mice exposed to dolutegravir

In 2018, data from a surveillance study in Botswana evaluating adverse birth outcomes raised concerns that women on antiretroviral therapy (ART) containing dolutegravir (DTG) may be at increased risk for neural tube defects (NTDs). The mechanism of action for DTG involves chelation of Mg2+ ions in the active site of the viral integrase. Plasma Mg2+ homeostasis is maintained primarily through dietary intake and reabsorption in the kidneys. Inadequate dietary Mg2+ intake over several months results in slow depletion of plasma Mg2+ and chronic latent hypomagnesemia, a condition prevalent in women of reproductive age worldwide. Mg2+ is critical for normal embryonic development and neural tube closure. We hypothesized that DTG therapy might slowly deplete plasma Mg2+ and reduce the amount available to the embryo, and that mice with pre-existing hypomagnesemia due to genetic variation and/or dietary Mg2+ insufficiency at the time of conception and initiation of DTG treatment would be at increased risk for NTDs. We used two different approaches to test our hypothesis: 1) we selected mouse strains that had inherently different basal plasma Mg2+ levels and 2) placed mice on diets with different concentrations of Mg2+. Plasma and urine Mg2+ were determined prior to timed mating. Pregnant mice were treated daily with vehicle or DTG beginning on the day of conception and embryos examined for NTDs on gestational day 9.5. Plasma DTG was measured for pharmacokinetic analysis. Our results demonstrate that hypomagnesemia prior to conception, due to genetic variation and/or insufficient dietary Mg2+ intake, increases the risk for NTDs in mice exposed to DTG. We also analyzed whole-exome sequencing data from inbred mouse strains and identified 9 predicted deleterious missense variants in Fam111a that were unique to the LM/Bc strain. Human FAM111A variants are associated with hypomagnesemia and renal Mg2+ wasting. The LM/Bc strain exhibits this same phenotype and was the strain most susceptible to DTG-NTDs. Our results suggest that monitoring plasma Mg2+ levels in patients on ART regimens that include DTG, identifying other risk factors that impact Mg2+ homeostasis, and correcting deficiencies in this micronutrient might provide an effective strategy for mitigating NTD risk.

Hypomagnesemia in Patients With Cancer: The Forgotten Ion

Magnesium is crucial for various cellular and enzymatic processes, yet it often is overlooked or underappreciated. Hypomagnesemia, a deficiency of magnesium in the blood, is a frequent problem in cancer patients and can lead to severe symptoms and morbidity. In this review, we provide an in-depth analysis of the physiology and regulation of magnesium, and signs and symptoms of hypomagnesemia in cancer patients. We also examine the causes and mechanisms of magnesium imbalances in cancer patients, specifically focusing on cancer-specific therapies that can lead to hypomagnesemia. Finally, we provide updates on the management of hypomagnesemia, including oral and parenteral supplementation, as well as the role of drugs in cases that are resistant to treatment. This review aims to raise awareness among health care providers caring for cancer patients about the significance of monitoring magnesium levels in cancer patients and function as a guide. Future clinical studies should focus on magnesium monitoring, its impact on cancer progression, and its potential for preventing acute kidney injury.

An overview of diagnosis and management of drug-induced hypomagnesemia

Magnesium (Mg) is commonly addressed as the "forgotten ion" in medicine. Nonetheless, hypomagnesemia should be suspected in clinical practice in patients with relevant symptomatology and also be considered a predisposing factor for the development of other electrolyte disturbances. Furthermore, chronic hypomagnesemia has been associated with diabetes mellitus and cardiovascular disease. Hypomagnesemia as a consequence of drug therapy is relatively common, with the list of drugs inducing low serum Mg levels expanding. Culprit medications linked to hypomagnesemia include antibiotics (e.g. aminoglycosides, amphotericin B), diuretics, antineoplastic drugs (cisplatin and cetuximab), calcineurin inhibitors, and proton pump inhibitors. In recent years, the mechanisms of drug-induced hypomagnesemia have been unraveled through the discovery of key Mg transporters in the gut and kidney. This narrative review of available literature focuses on the pathogenetic mechanisms underlying drug-induced hypomagnesemia in order to increase the insight of clinicians toward early diagnosis and effective management.

Relationship between renal dysfunction and electrolyte abnormalities in hematopoietic stem cell transplant patients treated with foscarnet

This study aimed to investigate the relationship between renal dysfunction and electrolyte abnormalities, which are adverse events of foscarnet used for cytomegalovirus infection. Of the Ninety hematopoietic stem cell transplantation patients, 32 who met the selection criteria were enrolled in this retrospective study. The study patients were divided into two groups according to whether they developed renal dysfunction. The incidences of hypocalcemia, hypokalemia, and hypomagnesemia with an increase of grade 2 or higher in the renal dysfunction group were 45.5%, 18.2%, and 27.3%, respectively. Additionally, in the renal dysfunction group, a significant correlation was observed between creatinine and calcium (r = -0.458, p = 0.0244) and between creatinine and potassium (r = -0.520, p = 0.0092). This study shows that renal dysfunction and electrolyte abnormalities may be closely related in HSCT patients receiving foscarnet; thus, it is a report that may contribute to the safety of continuous foscarnet treatment.

Magnesium in man: implications for health and disease

Magnesium (Mg(2+)) is an essential ion to the human body, playing an instrumental role in supporting and sustaining health and life. As the second most abundant intracellular cation after potassium, it is involved in over 600 enzymatic reactions including energy metabolism and protein synthesis. Although Mg(2+) availability has been proven to be disturbed during several clinical situations, serum Mg(2+) values are not generally determined in patients. This review aims to provide an overview of the function of Mg(2+) in human health and disease. In short, Mg(2+) plays an important physiological role particularly in the brain, heart, and skeletal muscles. Moreover, Mg(2+) supplementation has been shown to be beneficial in treatment of, among others, preeclampsia, migraine, depression, coronary artery disease, and asthma. Over the last decade, several hereditary forms of hypomagnesemia have been deciphered, including mutations in transient receptor potential melastatin type 6 (TRPM6), claudin 16, and cyclin M2 (CNNM2). Recently, mutations in Mg(2+) transporter 1 (MagT1) were linked to T-cell deficiency underlining the important role of Mg(2+) in cell viability. Moreover, hypomagnesemia can be the consequence of the use of certain types of drugs, such as diuretics, epidermal growth factor receptor inhibitors, calcineurin inhibitors, and proton pump inhibitors. This review provides an extensive and comprehensive overview of Mg(2+) research over the last few decades, focusing on the regulation of Mg(2+) homeostasis in the intestine, kidney, and bone and disturbances which may result in hypomagnesemia.

Drug-induced impairment of renal function

Pharmaceutical agents provide diagnostic and therapeutic utility that are central to patient care. However, all agents also carry adverse drug effect profiles. While most of these are clinically insignificant, some drugs may cause unacceptable toxicity that impacts negatively on patient morbidity and mortality. Recognizing adverse effects is important for administering appropriate drug doses, instituting preventive strategies, and withdrawing the offending agent due to toxicity. In the present article, we will review those drugs that are associated with impaired renal function. By focusing on pharmaceutical agents that are currently in clinical practice, we will provide an overview of nephrotoxic drugs that a treating physician is most likely to encounter. In doing so, we will summarize risk factors for nephrotoxicity, describe clinical manifestations, and address preventive and treatment strategies.

Hypomagnesemia: a clinical perspective

Although magnesium is involved in a wide spectrum of vital functions in normal human physiology, the significance of hypomagnesemia and necessity for its treatment are under-recognized and underappreciated in clinical practice. In the current review, we first present an overview of the clinical significance of hypomagnesemia and normal magnesium metabolism, with a focus on renal magnesium handling. Subsequently, we review the literature for both congenital and acquired hypomagnesemic conditions that affect the various steps in normal magnesium metabolism. Finally, we present an approach to the routine evaluation and suggested management of hypomagnesemia.

Magnesium homeostasis and hypomagnesemia in children with malignancy

Hypomagnesemia is not uncommon among children with malignancies. It is especially seen in association with certain medications and can be further complicated by the presence of diarrhea and malnutrition. Severe hypomagnesemia may cause disturbances in the neuromuscular and cardiovascular systems. All patients with hypomagnesemia should be supplemented with the mineral, and urgent treatment is indicated when serum magnesium decreases below 1.0 mg/dl, a level under which symptoms may develop. This review addresses the essentials of magnesium physiology, and pathophysiology of hypomagnesemia, its etiologies, clinical manifestations and ways to treat it, with an emphasis on the child with hematologic/oncologic disorders.

Drug-induced life-threatening potassium disturbances detected by a pharmacovigilance program from laboratory signals

PURPOSE

Detection and reporting of drug-induced life-threatening potassium disturbances and the study of associated factors under a Pharmacovigilance Program using Laboratory Signals at a Hospital (PPLSH) during a 2-year period.

METHODS

All serum potassium levels <2 mmol/l or >7 mmol/l detected at admission to the hospital, including those of patients who died in the emergency ward or during hospitalization, were monitored prospectively from January 2009 through to December 2010. The incidence rate of each etiology of potassium disturbances was calculated. Factors associated with drug-induced potassium disturbances were detected using a multiple logistic regression model.

RESULTS

The incidence of true life-threatening drug-induced hyper- and hypokalemia events was 3 and 4.32 (Poisson 95 % confidence interval 1.62-10.24), respectively, per 10,000 admissions. Of the severe potassium disturbances, 32.3 % were drug-induced, and 23 % were lethal. We identified previously undescribed pharmacological causes of hyperkalemia (risedronate, doxazosin) and hypokalemia (acyclovir, teicoplanin, cefepime, meropenem, dexketoprofen colistimethate). Significant predictor factors associated with drug-induced hyperkalemia were the use of polypharmacy (>5 drugs), age (>74 years), sex (female) and kidney disease (glomerular filtration rate <60 ml/min) with the presence of ≥4 comorbid conditions. The only predictor of drug-induced hypokalemia was the use of >5 drugs. The triggering factor associated with drug-induced hyperkalemia and hypokalemia was azotemia and hypoalbuminemia, respectively.

CONCLUSIONS

Drug-induced life-threatening potassium disturbances remain a relevant problem. Potential strategies for prevention are to avoid polypharmacy, early discontinuation of treatment of drugs causing hyperkalemia or nephrotoxicity in cases of various clinical situations (cardiac descompensation, infection, hypovolemia) or obstructive causes, and insistence on albumin control during hospitalization.

Drug-induced nutrient deficiencies

Good clinical care extends beyond mere diagnosis and treatment of disease to appreciation that nutrient deficiencies can be the price of effective drug therapy. The major risk factors for developing drug-induced nutrient deficiencies are lack of awareness by the prescribing physician and long duration of drug therapy. The field of pharmacogenomics has potential to improve clinical care by detecting patients at risk for complications from drug therapy. Further improvements in patient safety rely on physicians voluntarily reporting serious suspected adverse drug reactions.

Drug-induced hypomagnesaemia : scope and management

Nearly 50 medications have been implicated as inducing hypomagnesaemia, sometimes based on insufficient data regarding clinical significance and frequency of occurrence. In fact, clinical effects attributed to hypomagnaesemia have been reported in only 17 of these drugs. A considerable amount of literature relating to individual drugs has been published, yet a comprehensive overview of this issue is not available and the hypomagnesaemic effect of a drug could be either overemphasised or under-rated. In addition, there are neither guidelines regarding treatment, prevention and monitoring of drug-induced hypomagnesaemia nor agreement as to what serum level of magnesium may actually be defined as 'hypomagnesaemia'. By compiling data from published papers, electronic databases, textbooks and product information leaflets, we attempted to assess the clinical significance of hypomagnesaemia induced by each drug. A practical approach for managing drug-induced hypomagnesaemia, incorporating both published literature and personal experience of the physician, is proposed. When drugs classified as inducing 'significant' hypomagnesaemia (cisplatin, amphotericin B, ciclosporin) are administered, routine magnesium monitoring is warranted, preventive treatment should be considered and treatment of hypomagnesaemia should be initiated with or without overt clinical manifestations. In drugs belonging to the 'potentially significant' category, among which are amikacin, gentamicin, laxatives, pentamidine, tobramycin, tacrolimus and carboplatin, magnesium monitoring is justified when either of the following occurs: clinical manifestations are apparent; persistent hypokalaemia, hypocalcaemia or alkalosis are present; other precipitating factors for hypomagnesaemia coexist; or treatment is with more than one potentially hypomagnesaemic drug. No preventive treatment is required and treatment should be initiated only if hypomagnesaemia is accompanied by symptoms or clinically significant relevant laboratory findings. In those drugs whose hypomagnesaemic effect is labelled as 'questionable', including furosemide and hydrochlorothiazide, routine monitoring and treatment are not required.

Alkylglycerol prodrugs of phosphonoformate are potent in vitro inhibitors of nucleoside-resistant human immunodeficiency virus type 1 and select for resistance mutations that suppress zidovudine resistance

Phosphonoformate (foscarnet; PFA) is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), but its use for the treatment of HIV-1 infection is limited by toxicity and the lack of an orally bioavailable formulation. Alkylglycerol-conjugated prodrugs of PFA (1-O-octadecyl-sn-glycero-3-PFA [B-PFA]) having sn-2 substituents of hydrogen (deoxybatyl-PFA [DB-PFA]), methyl (MB-PFA), or ethyl (EB-PFA) are more-potent inhibitors of wild-type HIV-1 in vitro than unmodified PFA and are orally bioavailable in mice. We have evaluated the activities of these compounds against a panel of nucleoside-resistant HIV-1 variants and have characterized the resistant variants that emerge following in vitro selection with the prodrugs. Except for an HIV-1 variant encoding the K65R mutation in RT that exhibited 3.3- to 8.2-fold resistance, the nucleoside-resistant viruses included in the panel were sensitive to the PFA prodrugs (<3-fold increase in 50% inhibitory concentration), including multinucleoside-resistant variants encoding the Q151M complex of mutations or the T69S[SA] insert. Viruses resistant to the PFA prodrugs (>10-fold) were selected in vitro after 15 or more serial passages of HIV-1 in MT-2 cells in escalating prodrug concentrations. Mutations detected in the resistant viruses were S117T, F160Y, and L214F (DB-PFA); M164I and L214F (MB-PFA); and W88G and L214F (EB-PFA). The S117T, F160Y, and M164I mutations have not been previously identified. Generation of recombinant viruses encoding the single and double mutations confirmed their roles in prodrug resistance, including 214F, which generally increased the level of resistance. When introduced into a zidovudine (AZT)-resistant background (67N 70R 215F 219Q), the W88G, S117T, F160Y, and M164I mutations reversed AZT resistance. This suppression of AZT resistance is consistent with the effects of other foscarnet resistance mutations that reduce ATP-dependent removal of AZT monophosphate from terminated template primers. The favorable activity and resistance profiles of these PFA prodrugs warrant their further evaluation as clinical candidates.

A double-blind placebo-controlled crossover trial of intravenous magnesium sulfate for foscarnet-induced ionized hypocalcemia and hypomagnesemia in patients with AIDS and cytomegalovirus infection

Foscarnet (trisodium phosphonoformate hexahydrate) is an antiviral agent used to treat cytomegalovirus disease in immunocompromised patients. One common side effect is acute ionized hypocalcemia and hypomagnesemia following intravenous administration. Foscarnet-induced ionized hypomagnesemia might contribute to ionized hypocalcemia by impairing excretion of preformed parathyroid hormone (PTH) or by producing target organ resistance. Prevention of ionized hypomagnesemia following foscarnet administration could blunt the development of ionized hypocalcemia. To determine whether intravenous magnesium ameliorates the decline in ionized calcium and/or magnesium following foscarnet infusions, MgSO(4) at doses of 1, 2, and 3 g was administered in a double-blind, placebo-controlled, randomized, crossover trial to 12 patients with AIDS and cytomegalovirus disease. Overall, increasing doses of MgSO(4) reduced or eliminated foscarnet-induced acute ionized hypomagnesemia. Supplementation, however, had no discernible effect on foscarnet-induced ionized hypocalcemia despite significant increases in serum PTH levels. No dose-related, clinically significant adverse events were found, suggesting that intravenous supplementation with up to 3 g of MgSO(4) was safe in this chronically ill population. Since parenteral MgSO(4) did not alter foscarnet-induced ionized hypocalcemia or symptoms associated with foscarnet, routine intravenous supplementation for patients with normal serum magnesium levels is not recommended during treatment with foscarnet.

Foscarnet-induced electrolyte abnormalities in a bone marrow transplant patient receiving parenteral nutrition

Cytomegalovirus (CMV) is a serious complication of immunosuppressed patients receiving bone marrow transplantation. Foscarnet, a pyrophosphate analog, has been used in the treatment of CMV infections. Renal impairment and electrolyte abnormalities are potential adverse reactions associated with the use of foscarnet. We report a case of significant electrolyte changes after initiation of foscarnet in a bone marrow transplant patient receiving parenteral nutrition.

Magnesium in disease: a review with special emphasis on the serum ionized magnesium

This review deals with the six main clinical situations related to magnesium or one of its fractions, including ionized magnesium: renal disease, hypertension, pre-eclampsia, diabetes mellitus, cardiac disease, and the administration of therapeutic drugs. Issues addressed are the physiological role of magnesium, eventual changes in its levels, and how these best can be monitored. In renal disease mostly moderate hypermagnesemia is seen; measuring ionized magnesium offers minimal advantage. In hypertension magnesium might be lowered but its measurement does not seem relevant. In the prediction of severe pre-eclampsia, elevated ionized magnesium concentration may play a role, but no unequivocal picture emerges. Low magnesium in blood may be cause for, or consequence of, diabetes mellitus. No special fraction clearly indicates magnesium deficiency leading to insulin resistance. Cardiac diseases are related to diminished magnesium levels. During myocardial infarction, serum magnesium drops. Total magnesium concentration in cardiac cells can be predicted from levels in sublingual or skeletal muscle cells. Most therapeutic drugs (diuretics, chemotherapeutics, immunosuppressive agents, antibiotics) cause hypomagnesemia due to increased urinary loss. It is concluded that most of the clinical situations studied show hypomagnesemia due to renal loss, with exception of renal disease. Keeping in mind that only 1% of the total body magnesium pool is extracellular, no simple measurement of the real intracellular situation has emerged; measuring ionized magnesium in serum has little added value at present.

Comparative tolerability of therapies for cytomegalovirus retinitis

Cytomegalovirus (CMV) retinitis is a potentially sight-threatening complication of advanced HIV infection. The acute infection can be controlled with one of several therapies, including intravenous ganciclovir, foscarnet or cidofovir, slow release ganciclovir intraocular implants or serial intraocular injections of ganciclovir or foscarnet. The initial induction course of therapy is typically followed by lifelong maintenance therapy. In addition to the aforementioned treatments, oral ganciclovir and intravitreal fomivirsen injections are other options for maintenance therapy. The choice of agent must take into consideration factors such as comparative short and long term toxicity of the agents, route of administration and the possible need for indwelling catheters, administration time, cost and protection afforded against systemic dissemination of CMV infection. Possible drug interactions and additive toxicities of other agents needed for the management of the underlying HIV infection must also be taken into consideration. These factors can affect the tolerability of therapy as well as the quality of life of the patient. Relapse or progression of CMV retinitis may be caused by either inadequate drug concentrations at the site of the infection or by drug resistance. This may necessitate either an increase in drug dosage, a change in route of administration or a change to an alternative agent. All of these approaches can increase the risk of toxicity of the therapy. With the initiation of highly active antiretroviral therapy and partial reconstitution of the immune system, some patients have been able to successfully discontinue anti-CMV maintenance therapy, thereby decreasing long term drug toxicity. Determination of the patient predictors of success of this approach is an active area of research.

Renal excretion and pharmacokinetics of foscarnet in HIV sero-positive patients: effect of probenecid pretreatment

AIMS

The present study was undertaken to test whether the anti-viral agent foscarnet undergoes significant tubular secretion, by using probenecid, an inhibitor of the organic acid secretory pathway in the proximal segment of the nephron.

METHODS

The pharmacokinetics and renal excretion of foscarnet (90 mg kg-1 infused over 2 h) have been investigated, in the absence and presence of probenecid pretreatment (1 g twice daily for 3 days) in a group of 10 HIV seropositive patients.

RESULTS

Mean (+/-s.d.) peak plasma concentrations were 904 +/- 65 microM (foscarnet) and 862 +/- 97 microM (foscarnet+probenecid) whilst the plasma AUC values were 3326 +/- 451 microM h and 3133 +/- 476 microM h respectively. Terminal elimination half-life remained unchanged at 5.6 +/- 0.7 h and the respective volumes of distribution at steady state were 23 +/- 31 (foscarnet) and 25 +/- 31 (foscarnet+probenecid). Mean total body clearance was 110 +/- 17 ml min-1 (foscarnet) and 113 +/- 13 ml min-1 (foscarnet+probenecid) and the corresponding renal clearances of foscarnet were 102 +/- 5 ml min-1 and 105 +/- 5 ml min-1 respectively. There were no significant differences in the total amount of foscarnet excreted by the kidney with 95 +/- 5% (foscarnet) and 91 +/- 6% (foscarnet+probenecid) of the intravenous dose excreted within 24 h. Glomerular filtration rates at 109 +/- 12 ml min-1 (foscarnet) and 100 +/- 13 ml min-1 (foscarnet+probenecid) and respective creatinine clearances at 120 +/- 15 and 119 +/- 10 ml min-1 remained unchanged throughout the study.

CONCLUSIONS

The study shows that foscarnet is not transported via the probenecid-sensitive organic acid secretory pathway in the proximal tubule; the renal elimination of foscarnet is via glomerular filtration.

Foscarnet alters antidiuretic hormone-mediated transport

Therapy with foscarnet is associated with acute renal failure. Prior studies have emphasized foscarnet's proximal tubular toxicity, but there have been isolated reports of foscarnet-induced nephrogenic diabetes insipidus. As a phosphate analog, foscarnet is a competitive inhibitor of NaPO4 cotransport. However, foscarnet's effect on antidiuretic hormone (ADH)-induced transport has not been previously investigated. We studied foscarnet's modulation of transport in the toad urinary bladder. Foscarnet at 10 microM to 10 mM did not alter basal water or urea flux. Urea transport induced by a maximal dose of ADH (24 mIU/ml) was inhibited by 0.1 to 5.0 mM foscarnet. In tissues challenged with 0.5 to 1.0 mIU of ADH per ml, 1.0 to 10 mM foscarnet increased water flow but did not alter urea flux. Foscarnet also increased water flow induced by 1.0 to 10 microM forskolin. In tissues pretreated with 10 microM naproxen, foscarnet did not alter water flow induced by 0.5 to 1.0 mIU of ADH per ml or forskolin. These results indicate that foscarnet stimulates water flow induced by 0.5 to 1.0 mIU of ADH per ml at a site proximal to that of the generation of cyclic AMP and inhibits urea flux induced by a maximal dose of ADH at a separate site. In humans, foscarnet nephrotoxicity is likely not limited to the proximal nephron, but extends to the collecting duct. Patients receiving foscarnet should be closely monitored for disorders of urinary concentration.

Neurologic sequelae associated with foscarnet therapy

OBJECTIVE

To report three cases of possible foscarnet-induced neurologic sequelae.

CASE SUMMARY

We report two cases of seizures and one case of hand cramping and finger paresthesia after starting foscarnet therapy with no evidence of predisposing risk factors, such as serum laboratory abnormalities, renal dysfunction, or known central nervous system (CNS) involvement. All three patients had stable laboratory values during therapy and when the neurologic adverse effects occurred. All patients were receiving appropriate dosages of foscarnet.

DISCUSSION

The incidence of seizures in AIDS patients was reviewed. A history of CNS lesions, infections, and/or AIDS per se may increase the risk of a neurologic adverse effect while receiving foscarnet therapy. Acute ionized hypocalcemia may cause these neurologic adverse effects. Ionized hypocalcemia is transitory, is related to the rate of foscarnet infusion, and may not be reflected as a change in total serum calcium concentration.

CONCLUSIONS

Foscarnet probably contributed to the neurologic adverse effects reported here. Foscarnet may need to be administered at a slower rate than is recommended by the manufacturer. Electrolytes must be monitored closely; however, a neurologic adverse effect may not be foreseen.

Foscarnet. A reappraisal of its antiviral activity, pharmacokinetic properties and therapeutic use in immunocompromised patients with viral infections

The DNA polymerase of human herpes viruses, including cytomegalovirus (CMV), and the reverse transcriptase of human immunodeficiency virus (HIV) are selectively inhibited in vitro by the pyrophosphate analogue foscarnet. Inhibition is reversible on withdrawal of foscarnet and additive or synergistic effects have been demonstrated in vitro with other antiviral drugs, including ganciclovir and zidovudine. Foscarnet appears to have negligible effects on host enzymes and cells. Complete or partial clinical resolution of ocular symptoms is obtained in more than 89% of patients with acquired immunodeficiency syndrome (AIDS) and CMV retinitis during foscarnet induction therapy, but relapse occurs soon after ceasing treatment. Maintenance treatment given daily can extend the period of remission considerably. Foscarnet and ganciclovir monotherapy had similar efficacy in the treatment of CMV retinitis in patients with AIDS in several studies, and have been used concomitantly in immunocompromised patients with recalcitrant CMV infections. In 1 trial, patients receiving foscarnet survived for significantly longer than those receiving ganciclovir. Foscarnet has been used successfully in the treatment of limited numbers of immunocompromised patients with CMV-associated gastrointestinal (improvement in over 67% of patients) and other infections. Aciclovir-resistant herpes simplex infections in immunocompromised patients have also been treated successfully with foscarnet. Almost 90% of a foscarnet dose is excreted in the urine. Reversible nephrotoxicity is common during foscarnet therapy, but may be reduced by dosage adjustment and adequate hydration. Anaemia, nausea and vomiting, disturbances in electrolyte levels and genital ulceration have also been associated with administration of the drug. The different tolerability profiles of foscarnet and zidovudine facilitate the use of these agents in combination in patients with AIDS and CMV infection; whereas ganciclovir, like zidovudine, is associated with dose-limiting haematological toxicity. The apparent survival benefits seen in these patients when receiving foscarnet and zidovudine (possibly linked to synergy between zidovudine and foscarnet and/or the inherent anti-HIV activity of foscarnet), appear to offer potentially important advantages for foscarnet over ganciclovir in the treatment of selected patients with AIDS and CMV infections.

Concurrent use of foscarnet and ciprofloxacin may increase the propensity for seizures

OBJECTIVE

To report a possible interaction between foscarnet and ciprofloxacin in two patients with AIDS, cytomegalovirus (CMV) retinitis, and disseminated Mycobacterium avium complex (MAC) infection and to review the available literature related to foscarnet-associated seizures.

DATA SOURCE

Case report information was obtained from Medical Service Daily Rounds during the patients' hospitalization and from the patients' medical records. Computerized (MEDLINE) and manual (Index Medicus) search methods were used to obtain English-language literature published between 1980 and 1993.

DATA SYNTHESIS

Foscarnet is a synthetic antiviral agent with activity against herpesviruses and HIV. The incidence of seizures with foscarnet infusion is high, ranging from 13 to 15 percent. Predisposing factors such as renal impairment, electrolyte and metabolic abnormalities, and underlying neurologic disorders have been associated with seizures during foscarnet therapy. We describe two patients with AIDS who developed generalized tonic-clonic seizures while receiving foscarnet and ciprofloxacin for the treatment of CMV retinitis and disseminated MAC infection, respectively. Neither of the patients had any of the aforementioned risk factors for foscarnet-associated seizures.

CONCLUSIONS

Concurrent administration of ciprofloxacin, a known epileptogenic agent, and foscarnet may predispose patients to the development of seizures.