Neurological outcomes after traumatic cardiopulmonary arrest: a systematic review

Background

Despite appropriate care, most patients do not survive traumatic cardiac arrest, and many survivors suffer from permanent neurological disability. The prevalence of non-dismal neurological outcomes remains unclear.

Objectives

The aim of the current review is to summarize and assess the quality of reporting of the neurological outcomes in traumatic cardiac arrest survivors.

Data sources

A systematic review of Embase, Medline, PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and ProQuest databases was performed from inception of the database to July 2020.

Study eligibility criteria

Observational cohort studies that reported neurological outcomes of patients surviving traumatic cardiac arrest were included.

Participants and interventions

Patients who were resuscitated following traumatic cardiac arrest.

Study appraisal and synthesis methods

The quality of the included studies was assessed using ROBINS-I (Risk of Bias in Non-Randomized Studies - of Interventions) for observational studies.

Results

From 4295 retrieved studies, 40 were included (n=23 644 patients). The survival rate was 9.2% (n=2168 patients). Neurological status was primarily assessed at discharge. Overall, 45.8% of the survivors had good or moderate neurological recovery, 29.0% had severe neurological disability or suffered a vegetative state, and 25.2% had missing neurological outcomes. Seventeen studies qualitatively described neurological outcomes based on patient disposition and 23 studies used standardized outcome scales. 28 studies had a serious risk of bias and 12 had moderate risk of bias.

Limitations

The existing literature is characterized by inadequate outcome reporting and a high risk of bias, which limit our ability to prognosticate in this patient population.

Conclusions or implications of key findings

Good and moderate neurological recoveries are frequently reported in patients who survive traumatic cardiac arrest. Prospective studies focused on quality of survivorship in traumatic arrest are urgently needed.

Level of evidence

Systematic review, level IV.

PROSPERO registration number

CRD42020198482.

Vitamin D Supplementation Is Associated with a Reduction in Self-Reported Falls among Older Adults with Previous Fall History – Feasibility Study

Background: Vitamin D insufficiency contributes to muscle weakness and a higher risk of falls in older adults. Objectives: This study explored the impact of vitamin D supplementation on self-reported falls and physical function in older adults with low vitamin D levels and a recent fall history. Materials and Methods: Twenty-five older adults ≥ 70 years with two or more falls during the past year, low vitamin D blood levels (≥10 ng/ml and < 30 ng/mL), and slow gait speed (1.2 m/s) participated in a 6-month vitamin D supplementation (800 IU/day) study. A modified version of the Morse Fall Scale questionnaire was used to assess frequency of falls over one-year prior to study enrollment. Functional outcomes (short physical performance battery, handgrip strength, gait Timed Up and Go, and six-minute walk), and vitamin D levels were assessed at baseline and 6-month follow-up. Results: Based on diaries and pill counts, participants were generally adherent to the intervention (6 of 7 days per week). Supplementation with 800 IU/day of vitamin D for 6 months increased blood vitamin D levels from 23.25±4.8 ng/ml to 29.13±6.9 ng/ml (p<0.001). Self-reported number of falls decreased from an average of 3.76 ± 2.2 falls in one-year to 0.76 ± 1.4 falls (p <0.0001) over the 6-month intervention. No changes in functional outcome measures were observed. Conclusions: Vitamin D supplementation at the currently recommended dose of 800 IU/day increased blood vitamin D levels and reduced frequency of falls in older adults with low vitamin D levels and a recent fall history.

Scientific Impact and Clinical Influence: Identifying Landmark Studies in Burns

Although many reviews describe significant advances in burn care, no studies have yet examined why these papers had such profound impact. Our objective was to identify the most highly cited, as well as the most clinically influential studies in burns, and describe their characteristics, to inform future research in the field. Web of Science was searched using keywords related to burns to identify the 100 most-cited burns papers. Study design, year and journal of publication, and subject of the paper were recorded. A mixed-methods approach was used to identify papers in burn research leading to change in clinical practice. Characteristics of these papers were compared with identify any factors predictive of future citations or clinical influence. The 100 highly cited papers were cited between 159 and 907 times. There was no correlation between total citations and journal impact factor, year of publication, or subject area. Level of evidence did not predict future citations or influence, but may be influenced by evolving research standards. Of 23 clinically influential studies, 6 were not among 100 most-cited. Using papers only from the 100 most-cited list was not sufficient to identify leading researchers in burns. Citation analysis is a beneficial, however not alone sufficient to identify landmark papers, particularly for multidisciplinary fields such as burns.

Didanosine

The evaluation and development of didanosine as a therapy for HIV-infection has demonstrated that results of cell-culture studies are only approximate predictors of clinical effects. Whereas the antiviral activity of didanosine is achieved in cell culture at concentrations much higher than those of zidovudine, the two drugs appear to achieve similar effects on markers of HIV-infection at similar clinical doses. The effect of the differing intracellular-half-life of the respective nucleoside triphosphates on the clinical effects is unknown. Similarly, preclinical toxicology studies, while suggesting a low potential for didanosine-induced haematological toxicities, did not predict the findings of peripheral neuropathy and pancreatitis in clinical studies. Thus, the results of controlled clinical studies are required in order to more fully define the therapeutic and safety profile of didanosine.

Radiation doses from fluoroscopically guided cardiac catheterization procedures in children and young adults in the United Kingdom: a multicentre study

OBJECTIVE

To gather data on radiation doses from fluoroscopically guided cardiac catheterization procedures in patients aged under 22 years at multiple centres and over a prolonged period in the UK. To evaluate and explain variation in doses. To estimate patient-specific organ doses and allow for possible future epidemiological analysis of associated cancer risks.

METHODS

Patient-specific data including kerma area product and screening times from 10,257 procedures carried out on 7726 patients at 3 UK hospitals from 1994 until 2013 were collected. Organ doses were estimated from these data using a dedicated dosimetry system based on Monte Carlo computer simulations.

RESULTS

Radiation doses from these procedures have fallen significantly over the past two decades. The organs receiving the highest doses per procedure were the lungs (median across whole cohort, 20.5 mSv), heart (19.7 mSv) and breasts (13.1 mSv). Median cumulative doses, taking into account multiple procedures, were 23.2, 22.2 and 16.7 mSv for these organs, respectively. Bone marrow doses were relatively low (median per procedure, 3.2 mSv; cumulative, 3.6 mSv).

CONCLUSION

Most modern cardiac catheterizations in children are moderately low-dose procedures. Technological advances appear to be the single most important factor in the fall in doses. Patients undergoing heart transplants undergo the most procedures. An epidemiological assessment of cancer risks following these procedures may be possible, especially using older data when doses were higher.

ADVANCES IN KNOWLEDGE

This is the first large-scale, patient-specific assessment of organ doses from these procedures in a young population.

Measures of participation outcomes related to hand use for 2- to 12-year-old children with disabilities: a systematic review

Many interventions have been used to improve children's hand-related impairments or hand skill performance in functional activities so as to promote life participation. There is thus a need to have suitable instruments assessing children's participation in life situations that specifically require hand use in order to support and evaluate such interventions. This systematic review investigated the availability of potential instruments that can be used to assess children's participation specifically in life situations requiring hand use. Clinical utility and evidence for psychometric properties were also sourced. Database searches initially identified measures that were used to evaluate participation of children aged 2-12 years, involved self- or proxy report or interview administration and had generic application for a range of disabilities/diagnoses. These measures were further evaluated to determine if they fulfilled the above inclusion criteria and contained at least 60% of the items involving hand use. Further searches for psychometric evidence were undertaken for the eligible measures. Fourteen measures were identified and nine met the inclusion criteria. However, none of these measures, except for the Children Helping Out: Responsibilities, Expectations, and Supports (CHORES), contained all items related to hand use. Most of the included measures had limited psychometric properties. Only the Children's Assessment of Participation and Enjoyment/Preferences for Activities of Children (CAPE/PAC), the School Function Assessment-Participation section (SFA-P) and the Children Participation Questionnaire (CPQ) revealed sufficient evidence of validity and reliability. The findings suggest a need for adapting existing participation measures or developing new ones that specifically assess participation in life situations requiring hand use to support interventions.

Aspiration in the context of upper gastrointestinal endoscopy

BACKGROUND

Pulmonary aspiration is a life-threatening complication of upper gastrointestinal endoscopy, the incidence of which has not been determined. Endoscopy-related aspiration has not been studied in procedures in which patients swallow a radiolabelled potential aspirate immediately before endoscopy and undergo nuclear scanning postprocedure.

METHODS

A pilot study was conducted in which 200 MBq of nonabsorbable technetium-99m phytate in 10 mL of water was administered orally to 50 patients who were about to undergo endoscopy. Gamma camera images were obtained to ensure that there had been no aspiration before endoscopy. After endoscopy, a repeat scan was performed. Fluid aspirated through the endoscope was also collected and analyzed for radioactivity using a hand-held radiation monitor.

RESULTS

No evidence of pulmonary aspiration was found in any of the patients studied. The mean estimated percentage of the initially administered radioactivity aspirated through the endoscope was 2.66% (range 0% to 10.3%).

CONCLUSION

The present pilot study confirms earlier observations that clinically significant aspiration in the context of upper gastrointestinal endoscopy is uncommon. The incidence of aspiration may, however, be different in acutely bleeding patients undergoing endoscopy. For logistic reasons, this group could not be studied.

Comparison of atazanavir with lopinavir/ritonavir in patients with prior protease inhibitor failure: a randomized multinational trial

OBJECTIVES

To compare change from baseline in HIV RNA and fasting low-density lipoprotein (LDL) cholesterol levels in protease inhibitor (PI)-experienced patients receiving unboosted atazanavir 400 mg once daily versus lopinavir 400 mg boosted with ritonavir 100 mg twice daily, with two nucleoside reverse transcriptase inhibitors (NRTIs). Secondary objectives included virologic response, CD4 cell count changes, other lipid changes, safety, and tolerability.

METHODS

Randomized, open-label, multinational, 48-week study in patients with one PI-regimen failure, HIV RNA > or = 1000 copies/mL, and CD4 count > or = 50 cells/mm3.

RESULTS

Three hundred patients were randomized; 290 treated (144 atazanavir, 146 lopinavir/ritonavir). Lopinavir/ritonavir resulted in a significantly greater reduction in HIV RNA than unboosted atazanavir (-2.02 vs -1.59 log10 copies/mL, p < 0.001) at week 48. Secondary efficacy endpoints also favored lopinavir/ritonavir; the differences in efficacy between regimens were also observed in secondary analyses comparing those subjects who were susceptible and those subjects who were resistant to their respective PIs at baseline. However, both regimens were equally effective in subjects who had no baseline NRTI mutations. From baseline to week 48, atazanavir resulted in either no change or decreases in fasting LDL cholesterol, total cholesterol, and fasting triglycerides (-6%, -2%, and +1%), whereas lopinavir/ritonavir resulted in increases (+3%, +12%, and +53%) (p < 0.05, all between-treatment comparisons). Fewer patients were administered lipid-lowering therapy in the atazanavir arm (6% vs 20% for lopinavir/ritonavir). Both regimens were safe and well tolerated.

CONCLUSIONS

While both treatments demonstrated good antiviral efficacy, relatively greater antiviral suppression was observed with lopinavir/ritonavir. In those patients with no NRTI mutations at baseline, both regimens demonstrated comparable virologic suppression. Atazanavir-treated patients demonstrated a superior lipid profile and required less frequent lipid-lowering treatment.

Text and illustration: the digitisation of a medieval manuscript

This paper considers the choice of the medieval Aberdeen Bestiary as the first project in Aberdeen University Library's digitisation programme, and discusses some of the unusual features of the manuscript itself. Attention is given to the content and depth of the accompanying commentaries, and particular notice is paid to the nature and extent of the textual apparatus (translation and transcription). The factors influencing the choice of (a) PhotoCD as the image capture method, and (b) JPEG as the image format for transmission of the page images across the World Wide Web are examined. The importance of the Web design to the effectiveness of the overall resource is emphasised.

Virological and immunological responses to once-daily dosing of didanosine in combination with stavudine. AI454-143 Team

OBJECTIVE

To compare the antiviral activity of once-daily didanosine (ddI) and twice-daily ddI in combination with stavudine (d4T).

DESIGN

Randomized, double-blind, multicenter study.

SETTING

Twenty-one sites in the United States.

PATIENTS

Eighty-seven antiretroviral-naive, HIV-1-infected adults with baseline plasma HIV RNA counts of > or = 10,000 copies/ml and CD4 cell counts of > or = 100 cells/mm3 started study therapy.

INTERVENTIONS

Patients received once-daily ddI or twice-daily ddI, each combined with twice-daily d4T.

MAIN OUTCOME MEASURES

Plasma HIV-1 RNA levels, CD4 cell counts, and adverse events were regularly monitored. The primary efficacy analysis used was the time-averaged difference (TAD) between treatment regimens in change from baseline plasma HIV-1 RNA levels over the first 12 weeks of therapy.

RESULTS

At week 12, median log10 HIV-1 RNA changes were -1.83 log10 copies/ml in the once-daily ddI/d4T group and -1.80 log10 copies/ml in the twice-daily ddI/d4T group, and 18 out of 44 patients (41%) and 17 out of 43 patients (40%), respectively, had HIV-1 RNA levels below 400 copies/ml. Similar results were seen at week 24. The TAD between the two treatment groups (once-daily ddI/d4T minus twice-daily ddI/d4T) in change from baseline plasma HIV RNA levels over the first 12 weeks was 0.14 log10 copies/ml (95% CI: -0.11, 0.40). At week 12, subjects averaged an increase in CD4 cell count of over 140 cells/mm3. The TAD between the two treatment groups in change from baseline CD4 cell counts over the first 12 weeks was 2 cells/mm3 (95% CI: -40, 45).

CONCLUSION

Once-daily ddI plus d4T and twice-daily ddI plus d4T were similarly effective in reducing plasma HIV-1 RNA levels and increasing CD4 cell counts over 12-24 weeks of therapy.

Limitations of magnetic resonance imaging in measurement of hepatic iron

To evaluate the usefulness of magnetic resonance imaging for the quantitative determination of hepatic iron, we examined 43 patients with thalassemia major and assessed the influence of pathologic changes in the liver on the precision of estimates of the hepatic iron concentration. Tissue signal intensities were measured from magnetic resonance T1-weighted images derived from gradient-echo (GE) pulse sequences and the ratio of the signal intensity of liver to muscle calculated. By excluding patients (n = 9) having a signal intensity ratio (SIR) less than or equal to 0.2, a linear relationship with hepatic iron was found and subsequent analyses were limited to these 34 patients. In 27 patients with hepatic fibrosis, an overall correlation of -0.848 was found between hepatic iron and SIR. By contrast, in the seven patients with no fibrosis, the correlation coefficient (-0.993) was significantly greater (P < .0001). Despite the differences in correlation, the regression line between hepatic iron and SIR for the patients with no fibrosis did not differ significantly with respect to either slope or intercept from that of the patients with fibrosis. Thus, the presence of fibrosis did not seem to affect the pattern of the relationship between hepatic iron and the SIR, but rather to increase the variability of the relationship. Clinically, the presence of fibrosis makes estimates of hepatic iron derived from magnetic resonance imaging so variable as to be of little practical use in the management of transfusional iron overload.

A phase-I study of the safety, pharmacokinetics, and antiviral activity of combination didanosine and ribavirin in patients with HIV-1 disease. AIDS Clinical Trials Group 231 Protocol Team

A phase-I study was conducted to examine the safety, pharmacokinetics, and activity of combination 2',3'-dideoxyinosine (ddI) and ribavirin against human immunodeficiency virus type 1 (HIV-1)-positive individuals with CD4+ cell counts of < or = 500/microliter. Nineteen patients were enrolled into the study in which ddI monotherapy (200 mg p.o.b.i.d.) was administered for the first 4 weeks, followed by the coadministration of ribavirin (600 mg p.o.q.d.) and ddI (200 mg p.o.b.i.d.) for 8 or 20 additional weeks. The combination regimen was safe and well tolerated. Three patients did not complete 12 weeks of the study because of adverse events or voluntary withdrawal. The pharmacokinetic studies performed at weeks 4, 6, and 12 on specimens collected from the 15 individuals who completed 12 weeks of therapy revealed no pharmacokinetic interaction between ddI and ribavirin. A significant decline from baseline in HIV-1 titer as measured by quantitative HIV-1 culture was detected both during the ddI-monotherapy phase (week 4, p < 0.001) and during the combination-therapy ddI + ribavirin phase (week 12, p < 0.001); the median drop observed was 0.90 log10 at week 4 and 0.92 log10 at week 12. While the addition of ribavirin did not result in further reductions in viremia in the following weeks on study treatment, 13 (81%) of the 16 patients had at least a -0.5 log10 change in viral titer at week 12. The median decline in plasma viral RNA was 0.68 log10 at week 4(p < 0.001) and 0.67 log10 at week 12 (p = 0.005). CD4+ cell counts increased above baseline significantly during the ddI-monotherapy phase of the study (p = 0.0038). The median increase was +26 cells/mm3 at week 4 and +11 cells/mm3 at week 12; for patients who remained on treatment through 24 weeks, the median CD4+ cell count increase was +10 cells/mm3. The L74V ddI resistance-conferring HIV-I reverse-transcriptase mutation emerged in 53% of the patients. Patients with non-syncytium-inducing HIV variants demonstrated greater responses to treatment with larger decreases in virus load and greater increases in CD4+ cell count. Our results reveal that the combination of ddI and ribavirin in HIV-positive patients is safe, well tolerated, without adverse pharmacologic interaction, and associated with significant and sustained declines in virus load over 12 weeks of therapy.

Prognostic value of plasma human immunodeficiency virus type 1 (HIV-1) RNA levels in patients with advanced HIV-1 disease and with little or no prior zidovudine therapy. AIDS Clinical Trials Group Protocol 116A/116B/117 Team

The association of plasma human immunodeficiency virus type 1 (HIV-1) RNA level at study entry and over time with clinical progression was evaluated in 187 patients from AIDS Clinical Trials Group protocol 116A who had little or no prior zidovudine treatment. Three-fold-higher HIV-1 RNA levels at study entry and 3-fold increases by week 8 were associated with progression (relative hazard [RH], 1.67; 95% confidence limits [CL], 1.20, 2.32; and RH, 1.45; CL, 1.02, 2.05, respectively). Having 3-fold-higher CD4 cell count at entry was independently associated with a 52% reduction in risk for progression (adjusted RH, 0.48; CL, 0.33, 0.70). When stratified by length of prior zidovudine therapy, RNA level was predictive in drug-naive patients (adjusted RH, 1.87; CL, 1.23, 2.85) but not predictive in patients with up to 16 weeks of prior therapy (adjusted RH, 1.11; CL, 0.70, 1.76). Analysis suggests that the acquisition of mutations at HIV-1 reverse transcriptase codons 215 and 74 is associated with subsequent increases in HIV-1 RNA level (relative risk, 7.00; CL, 0.86, 56.90).

Pilot Study of Didanosine in Patients with HIV Dementia

In a pilot open-labeled study 10 subjects with AIDS dementia complex (ADC) were treated with didanosine. Only half of the subjects were able to complete the trial as a result of side effects. Five subjects exhibited improved performance on neuropsychological testing, but the mean change in performance in this small group was not statistically significant. The study suggests that this drug may have some value in ADC patients unable to tolerate other therapies, but that further study is needed to establish this firmly.

Longitudinal analysis of responses to oral didanosine therapy following zidovudine therapy in advanced infection with human immunodeficiency virus

The effect on immunologic and virological parameters of up to 24 weeks of therapy with didanosine at daily oral doses of < or = 12.5 mg/(kg.d) was studied retrospectively in 69 patients with advanced disease due to human immunodeficiency virus--i.e., AIDS or advanced AIDS-related complex--who had previously been treated with zidovudine. Patients entered the study with a low CD4 cell count (median, 39/microL) and with evidence of an ongoing depression of bone marrow function. Didanosine therapy was associated with a significant increase in CD4 counts and a prolonged decrease in serum levels of p24 antigen relative to baseline. These changes were more pronounced in the population with baseline CD4 counts of > or = 100/microL. A beneficial effect of didanosine therapy on hematologic parameters was observed in these patients, with increases during therapy of hemoglobin levels as well as white blood cell, granulocyte, and platelet counts. These responses were maximal at weeks 16-20. Further investigations are needed to establish the clinical correlates of these observations.

Long-term follow-up of didanosine administered orally twice daily to patients with advanced human immunodeficiency virus infection and hematologic intolerance of zidovudine

This phase 1 trial was conducted to evaluate the safety and tolerance of didanosine (ddI) in subjects with AIDS or AIDS-related complex (ARC) who previously had demonstrated hematologic intolerance of zidovudine. Thirty subjects, 21 with AIDS and nine with ARC, were enrolled. Initially, didanosine was administered orally twice daily for a total daily dose of either 750 mg or 1,500 mg. Subsequently, the dosage for those receiving 1,500 mg/d was reduced to a maximum of 750 mg/d (375 mg twice daily) when data from this and other phase 1 studies showed that the dosage of 1,500 mg/d (750 mg twice daily) was associated with an unacceptable risk of developing neuropathy. The subjects were studied for 46 weeks (mean time; range, 7-122 weeks). The dose-limiting toxic effect observed was peripheral neuropathy, which occurred in eight patients. Other significant toxic effects included pancreatitis in three patients and xerostomia in eleven. In general, didanosine was well tolerated from a hematologic standpoint by the majority of patients during prolonged administration.

Effect of iron chelation therapy on recovery from deep coma in children with cerebral malaria

BACKGROUND

Cerebral malaria is a severe complication of Plasmodium falciparum infection in children, with a mortality rate of 15 to 50 percent despite antimalarial therapy.

METHODS

To determine whether combining iron chelation with quinine therapy speeds the recovery of consciousness, we conducted a randomized, double-blind, placebo-controlled trial of the iron chelator deferoxamine in 83 Zambian children with cerebral malaria. To be enrolled, patients had to be less than six years old, have P. falciparum parasitemia, have normal cerebrospinal fluid without evidence of bacterial infection, and be in a coma from which they could not be aroused. Deferoxamine (100 mg per kilogram of body weight per day, infused intravenously for 72 hours) or placebo was added to standard therapy with quinine and sulfadoxine-pyrimethamine. The time to the recovery of full consciousness, time to parasite clearance, and mortality were examined with Cox proportional-hazards regression analysis.

RESULTS

The rate of recovery of full consciousness among the 42 patients given deferoxamine was 1.3 times that among the 41 given placebo (95 percent confidence interval, 0.7 to 2.3); the median time to recovery was 20.2 hours in the deferoxamine group and 43.1 hours in the placebo group (P = 0.38). Among 50 patients with deep coma, the rate of recovery of full consciousness was increased 2.2-fold with deferoxamine (95 percent confidence interval, 1.1 to 4.7), decreasing the median recovery time from 68.2 to 24.1 hours (P = 0.03). Among 69 patients for whom data on parasite clearance were available, the rate of clearance with deferoxamine was 2.0 times that with placebo (95 percent confidence interval, 1.2 to 3.6). Among all 83 patients, mortality was 17 percent in the deferoxamine group and 22 percent in the placebo group (P = 0.52).

CONCLUSIONS

Iron chelation therapy may hasten the clearance of parasitemia and enhance recovery from deep coma in cerebral malaria.

Population pharmacokinetic analysis of didanosine (2',3'-dideoxyinosine) plasma concentrations obtained in phase I clinical trials in patients with AIDS or AIDS-related complex

Plasma didanosine concentration data from 36 patients receiving once-a-day therapy and from 33 patients receiving twice-a-day therapy were subject to population pharmacokinetic analysis with the computer program NONMEM. Once- or twice-a-day regimens of didanosine were administered intravenously (i.v.) (dose: 0.8-33 mg/kg) during the first 2 weeks of therapy, and orally (dose: 1.6-66 mg/kg) for the remaining 4 weeks of therapy. Plasma pharmacokinetics were determined after the first and last (steady-state) i.v. and oral doses. Population pharmacokinetic parameters for the combined i.v. and oral steady-state data were (mean [%CV]): systemic clearance, CL, 0.70 (5.2) L/h/kg; central compartment volume, Vc, 0.18 (32) L/kg; steady-state distribution volume, Vdss, 0.84 (6.8) L/kg; first-order absorption rate constant, Ka, 1.3 (9.5) hr-1; and bioavailable fraction, F, 0.34 (8.5). Interindividual variability (omega) was (%CV) 22.3 and 71.0 for CL and Vc, respectively. Intraindividual (residual) variability (sigma) in plasma concentrations (%CV) was 50.2. Body weight, sex, and age did not account for the variability in either CL or Vc, and the use of alternate pharmacokinetic models did not reduce the value of intraindividual variability. Population parameters for the combined i.v. and oral first-dose data were generally similar to those for the steady-state data. The parameters can be used to design dosing regimens in patients using the Bayesian feedback approach.

Phase I study of 2'-3'-dideoxyinosine administered orally twice daily to patients with AIDS or AIDS-related complex and hematologic intolerance to zidovudine

PURPOSE

To evaluate the safety and hematologic tolerance of 2'-3'-dideoxyinosine (didanosine, ddI) in subjects with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex and prior hematologic intolerance to zidovudine.

PATIENTS AND METHODS

A Phase I trial with two dose groups at a single-center, university-affiliated hospital ambulatory care center. Of 30 subjects enrolled, 21 had AIDS and nine had AIDS-related complex. All had CD4 lymphocyte counts less than 0.2 x 10(9)/L at entry. Didanosine was administered orally twice daily at a total daily dose of 750 mg or 1,500 mg for 12 weeks. Subjects who completed the 12-week study continued to receive ddI at the lower dose. All subjects were monitored for toxicity. Virologic and immunologic response markers were also measured.

RESULTS

For the group as a whole, there was no significant decrease in mean hemoglobin level or leukocyte or platelet counts. The dose-limiting toxicity was peripheral neuropathy. Other significant toxicities included pancreatitis and hypocalcemia. Uric acid elevations were common but were without clinical consequence. A sustained decrease in serum p24 antigen of at least 50% was noted in 42% of subjects who were p24 antigen-positive at entry. The mean CD4 lymphocyte count showed an initial increase that was not sustained over the 12-week study. All subjects remained anergic to skin testing.

CONCLUSIONS

Didanosine is well tolerated hematologically in some patients with prior significant hematologic intolerance to zidovudine. The toxicity profile for ddI differs from that of zidovudine and includes peripheral neuropathy and pancreatitis. Changes in CD4 lymphocyte number and HIV p24 antigen levels in some patients suggest antiviral activity of ddI in this population.

Pharmacokinetics of didanosine in patients with acquired immunodeficiency syndrome or acquired immunodeficiency syndrome-related complex

The pharmacokinetics of didanosine (2',3'-dideoxyinosine) after intravenous and oral administration were evaluated in an open, escalating-dose phase I study in patients with acquired immunodeficiency syndrome (AIDS) or severe AIDS-related complex. Didanosine was administered twice a day for 2 weeks as an intravenous infusion of 60 minutes duration at doses ranging from 0.4 to 16.5 mg/kg, followed by 4 weeks of oral treatment at twice the intravenous dose. Serial blood and urine samples were obtained on the first and final day of intravenous administration and after the first oral dose, as well as at steady state. Didanosine demonstrated linear pharmacokinetic behavior over the dose ranges of 0.4 to 16.5 mg/kg intravenously and 0.8 to 10.2 mg/kg orally. There was no indication of significant changes in pharmacokinetic parameters with repeated administration. The apparent elimination half-life after oral administration was approximately 1.4 hour. Renal clearance values exceeded the glomerular filtration rate, indicating that active tubular secretion of didanosine occurs. Bioavailability of didanosine when administered as a solution with an antacid was approximately 43% for doses from 0.8 to 10.2 mg/kg in patients with AIDS and advanced AIDS-related complex. Bioavailability of didanosine from the citrate-phosphate-buffered solution, the formulation currently used in phase II and expanded access studies, was comparable to the formulation used in the phase I trials.

Treatment of AIDS and AIDS-related complex with 2',3'-dideoxyinosine given once daily

In a phase I dosage-finding trial, 2',3'-dideoxyinosine (didanosine; ddI) was administered once daily to 36 patients with AIDS or AIDS-related complex for up to 65 weeks (mean, 32.1 weeks) at six dosage levels. Thirteen of 18 patients previously treated with zidovudine had developed hematologic intolerance. The maximal tolerated dosage of ddI was 12 mg/(kg.d); dose-limiting toxicities were pancreatitis and peripheral neuropathy. Other toxicities included elevation in hepatic transaminase levels, rash, cardiac conduction abnormality, and asymptomatic hyperuricemia. Eighty-six percent of patients who completed 6 weeks of treatment showed improvement in constitutional symptoms and significant weight gain. In patients treated with ddI, the mean number of CD4+ lymphocytes increased from 124/mm3 at baseline to 199/mm3 at 24 weeks (P = .0027) and the mean leukocyte count, total lymphocyte count, and hemoglobin level showed increases (all P less than .01) after 12 weeks. Serum levels of viral p24 antigen decreased greater than or equal to 50% in 14 of 19 assessable patients. No differences between the responses of patients previously treated with zidovudine and those of zidovudine-naive patients were observed. These results indicate that ddI has significant antiretroviral activity in vivo and a toxicity profile different from that of zidovudine.

Overview of phase I trials of 2',3'-dideoxyinosine (ddI) conducted on adult patients

Ninety-two adult patients with AIDS or severe AIDS-related complex were treated with 2',3'-dideoxyinosine (didanosine; ddI) at dosages ranging from 0.8 to 66.0 mg/(kg.d) for at least 6 weeks in phase I trials. Potentially beneficial changes in weight (40% of patients), clinical signs or symptoms (40% of patients), CD4+ cell counts (25% of patients), and serum levels of HIV p24 antigen (50% of antigen-positive patients) were reported. Response rates tended to be higher among patients with AIDS-related complex and among those who had not received prior zidovudine therapy. A major response (improvement in at least one clinical parameter and in at least one laboratory marker) occurred in 29% of patients, and rates of major response tended to be higher in patients receiving higher dosages. The primary dose-limiting toxicity observed was peripheral neuropathy, which was observed with increasing frequency in patients receiving greater than 20 mg/(kg.d). Of the other adverse effects, pancreatitis was possibly dose-dependent and hyperuricemia (without clinical gout) occurred only at high doses. Dosages of 250 mg and 375 mg of ddI twice daily will be used in extended phase II/III studies.

2',3'-Dideoxyinosine in patients with AIDS or AIDS-related complex

Twenty-one patients with AIDS or AIDS-related complex (ARC) received 2',3'-dideoxyinosine (didanosine; ddI) intravenously and then orally (initial dosages of 0.4 mg/kg and 0.8 mg/kg every 12 hours, respectively) for 6-44 weeks in an escalating-dose study. The major dose-limiting effects were peripheral neuropathy (three patients) and pancreatitis (two patients), which were observed at dosages greater than or equal to 20 mg/(kg.d). Hyperuricemia occurred at greater than or equal to 30 mg/(kg.d). No hematologic toxicity developed except for possible sporadic thrombocytopenia (two patients). Significant decreases in serum levels of p24 antigen and increases in CD4+ and CD8+ lymphocytes were noted at 2, 6, and 10-20 weeks and over a wide range of dosages, including the lowest given. Most patients had an increased feeling of well-being and/or a weight gain of greater than or equal to 2 kg at 6 weeks. For this population, ddI has promise as a therapeutic agent, thus warranting further study of this agent in controlled clinical trials.

Once-daily administration of 2',3'-dideoxyinosine (ddI) in patients with the acquired immunodeficiency syndrome or AIDS-related complex. Results of a Phase I trial

We conducted a Phase I open-label trial of 2',3'-dideoxyinosine (ddI) for the treatment of the acquired immunodeficiency syndrome (AIDS) and severe AIDS-related complex. A single daily dose of ddI was administered orally to 34 patients (17 with AIDS and 17 with AIDS-related complex) for a median of 12 weeks (range, 2 to 56). We studied six dose levels from 1.6 to 30.4 mg per kilogram of body weight per day. Of the 17 patients previously treated with zidovudine, 13 had had hematologic side effects. The maximal tolerated dose of oral ddI was estimated to be 20.4 mg per kilogram per day. Pancreatitis and peripheral neuropathy were the major dose-limiting toxic effects. Other toxic effects included elevations in hepatic transaminase levels, abnormalities in cardiac conduction, rash, and asymptomatic elevations in serum urate levels and the creatine kinase fraction from skeletal muscle. Treatment with ddI was associated with an increase in the mean number of CD4 lymphocytes from 125 per cubic millimeter at base line to 182 per cubic millimeter after 10 weeks (P = 0.005). There were also increases after 12 weeks in the mean total lymphocyte count (from 0.8 to 1.2 x 10(9) per liter) and the mean hemoglobin level (from 12.9 to 14.1 g per deciliter) (both P less than 0.01). The amount of human immunodeficiency virus p24 antigen decreased by more than 50 percent in 14 of 19 patients with detectable antigen. No differences in response were observed between patients previously treated with zidovudine and those never treated with the drug. We conclude that ddI has antiretroviral activity in patients with AIDS or AIDS-related complex and that the toxicity of ddI differs from that of zidovudine. However, controlled trials are necessary to evaluate the efficacy of ddI.

2',3'-dideoxyinosine (ddI) in patients with the acquired immunodeficiency syndrome or AIDS-related complex. A phase I trial

2',3'-Dideoxyinosine (ddI) is a purine analogue that after intracellular metabolic conversion suppresses the replication of the human immunodeficiency virus (HIV). We conducted a Phase I dose-escalation study of ddI in 17 patients with the acquired immunodeficiency syndrome (AIDS) and 20 patients with AIDS-related complex. The drug was administered twice daily over a dose range of 0.4 to 66 mg per kilogram of body weight per day for 2 to 44 weeks. The maximal tolerated oral dose of ddI was estimated to be 12 mg per kilogram per day. The major dose-limiting toxic effects were a painful peripheral neuropathy (in eight patients) and pancreatitis (in five). Asymptomatic elevations of the serum aminotransferase levels (in 13 patients) and the serum urate level (in 10) were also noted, but there was no dose-related hematologic toxicity. At the maximal tolerated dose, the peak plasma levels of ddI were 6.3 to 9.6 mumol per liter 0.6 to 1 hour after oral administration; the mean plasma half-life was 1.5 hours. The administration of ddI was associated with statistically significant decreases in serum level of p24 antigen and increases in the numbers of CD4 cells at 2, 6, 10, and 20 weeks. These changes were seen at all dose levels studied. Either a clinical improvement or a weight gain of greater than or equal to 2 kg was observed in 25 of 34 patients at six weeks. We conclude that ddI is a promising therapeutic agent in patients with AIDS or AIDS-related complex. Its efficacy is currently being evaluated in large-scale, controlled clinical trials.

Synthesis and antiviral activity of various 3'-azido, 3'-amino, 2',3'-unsaturated, and 2',3'-dideoxy analogues of pyrimidine deoxyribonucleosides against retroviruses

Various 3'-azido, 3'-amino, 2',3'-unsaturated, 2',3'-dideoxy, and 5-substituted analogues of pyrimidine deoxyribonucleosides have been prepared and tested against Moloney-murine leukemia virus (M-MULV), a mammalian T-lymphotropic retrovirus in vitro. Among these compounds, the 3'-azido analogues of thymidine, 2'-deoxy-5-bromouridine, and 2'-deoxy-5-iodouridine, the 2',3'-unsaturated analogue of thymidine and and 2'-deoxycytidine, and 2',3'-dideoxycytidine were found to be most active, with ED50 values of 0.02, 1.5, 3.0, 2.5, 3.7, and 4.0 microM, respectively. These active compounds were nontoxic to the host SC-1 cells up to 100 microM concentration. The 3'-azido analogues of thymidine and 2'-deoxy-5-bromouridine were also tested in vitro against HTLV-III/LAV/AAV ("AIDS" virus) and found to be significantly active, with ED50 values of 0.23 and 2.3 microM, respectively. The structure-activity relationships are discussed.

Immediate diagnostic criteria for bacterial infection of ascitic fluid. Evaluation of ascitic fluid polymorphonuclear leukocyte count, pH, and lactate concentration, alone and in combination

We prospectively evaluated the ascitic fluid (AF) polymorphonuclear cell (PMN) count, pH, and lactate concentration in single ascitic fluids from 60 patients to determine their relative predictive values for the immediate diagnosis of ascitic fluid infection. Nine of the 60 ascitic fluids were malignant. Of the remaining 51 samples, nine from cirrhotic patients were infected. The mean AF pH, lactate concentration, and PMN count in the infected group were 7.20 +/- 0.19, 80 +/- 51 mg/dl, and 18,199 +/- 19,650 cells/mm3, respectively, and all were significantly different from the corresponding values in noninfected ascites. Mean arterial blood-ascitic fluid (B-AF) pH and lactate gradients in the infected group were 0.23 +/- 0.17 and -46 +/- 31 mg/dl, respectively, and were significantly different from the corresponding values in noninfected ascites (p less than 0.05). Significant differences were not found between infected and malignant ascites, except for the AF PMN count (p less than 0.001). In cirrhosis with ascites, an AF pH less than or equal to 7.34 was the most specific single test (100%) and had the highest diagnostic accuracy (98%). In the larger group of patients with ascites of diverse etiology, a B-AF pH gradient greater than or equal to 0.10 or an AF PMN count greater than or equal to 500 cells/mm3 were the single tests with the highest diagnostic accuracy (92%). Combining an AF PMN count greater than 500 cells/mm3 with any of the other diagnostic criteria increased the specificity and diagnostic accuracy (up to 98%) compared to the best single criterion. Although our data support the use of a number of different combinations of AF measurements for the immediate diagnosis of infection, the simplest and most readily obtainable measurements are the pH and PMN count. Therefore, in the clinical setting we recommend the use of either an AF pH less than or equal to 7.34 or a B-AF pH gradient greater than or equal to 0.10 in combination with an AF PMN count greater than 500 cells/mm3 to obtain the highest degree of accuracy in the immediate diagnosis of ascitic fluid infection.

Drug resistance patterns of herpes simplex virus isolates from patients treated with acyclovir

A decrease in the in vitro sensitivity to acyclovir (ACV) was observed in successive isolates of herpes simplex virus type 1 from three immunocompromised patients during intravenous therapy with this drug. The ACV-resistant isolate from patient 1 was cross-resistant to dihydroxypropoxymethylguanine and bromovinyldeoxyuridine, but still susceptible to three fluoro-substituted pyrimidines, 2'-fluoro-5-iodo-1-beta-D-arabinofuranosylcytosine (FIAC), 2'-fluoro-5-iodo-1-beta-D-arabinofuranosyluracil (FIAU), and 2'-fluoro-5-iodo-1-beta-D-arabinofuranosylthymine (FMAU). The thymidine kinase (TK) from the resistant isolate showed a 50-fold or greater reduction in affinity for thymidine, FIAU, FMAU, and ACV, but the total enzyme activity was similar to that of the sensitive isolate. The ACV-resistant isolate from patient 2 was also resistant to dihydroxypropoxymethylguanine, bromovinyldeoxyuridine, and the fluoro-substituted compounds; TK activity for this isolate was less than 1% of the patient's pretherapy isolate. An isolate obtained during a subsequent recurrence in patient 2 was susceptible to ACV and the other TK-dependent agents. The ACV-resistant isolate from patient 3 was partially resistant to FIAC and FIAU but still susceptible to FMAU; the viral TK had a 10-fold-lower affinity for ACV, FIAU, and FMAU than did the sensitive pretherapy isolate, while the level of TK activity detected was reduced to 6%. In none of the isolates studied was a change in sensitivity to phosphonoformic acid observed. Compared with the corresponding pretherapy ACV-sensitive isolates, there was a 30-fold decrease in neurovirulence for mice of the two drug-resistant isolates with diminished levels of thymidine-phosphorylating activity and no change in virulence for the third isolate. These findings indicate that mixed patterns of drug-resistance to TK-dependent antiviral compounds can occur in clinical isolates, resulting from changes in either the amount or the affinity of viral TK activity.

Frequency and significance of acyclovir-resistant herpes simplex virus isolated from marrow transplant patients receiving multiple courses of treatment with acyclovir

The sensitivity to acyclovir of virus isolates from 52 consecutive marrow transplant patients who received acyclovir for herpes simplex virus infections was studied in vitro. The median sensitivity of viruses obtained during first, second, third, and fourth recurrences was similar, and the median duration of virus positivity (three days) was the same for first and second treatment courses. However, acyclovir-resistant virus was recovered from one of 52 patients (1.9%) during the initial treatment course and from two of 22 patients (9.1%) treated for second recurrences. All three strains had reduced thymidine kinase activity. None caused severe infection. Three other patients remained virus-positive during treatment despite the isolation of acyclovir-sensitive virus. Although continuing surveillance is necessary, these data may suggest that acyclovir-resistant virus will not be the cause of significant clinical illness among immunosuppressed patients. In addition, not all instances of "resistance," defined by the persistence of virus during treatment, will be caused by virus strains that are resistant to acyclovir in vitro.

A colorimetric assay for the measurement of the sensitivity of herpes simplex viruses to antiviral agents

A quantitative colorimetric method for measuring the inhibition of viral cytopathic effects has been adapted to the assay of antiviral compounds. Drug-treated, virus-infected cultures in microtiter plates were stained with the vital dye neutral red and the amount of dye incorporated was determined in a multichannel spectrophotometer. The technique required smaller volumes of reagents, was more easily automated than the standard plaque reduction assay and had good reproducibility. Standard conditions of 30 infectious units of challenge virus and 72-h incubation were judged to be optimal. Median inhibitory concentrations (ID50) for a number of compounds were approximately tenfold higher in the dye-uptake assay compared with the plaque reduction assay, possibly related to the higher multiplicity of infection required to give the desired level of cytopathic effect in the microtiter method.

In vitro sensitivity to acyclovir in genital herpes simplex viruses from acyclovir-treated patients

Genital isolates of herpes simplex virus (HSV) from patients given acyclovir or placebo were tested in vitro for sensitivity to acyclovir. Isolates obtained before therapy were sensitive to acyclovir concentrations of 0.01-19 micrograms/ml, with 86 of 97 isolates inhibited by less than 1 microgram/ml. Before therapy, six patients had isolates of HSV type 2 with ID50 values (concentrations of drug reducing viral cytopathic effect by 50%) of greater than 3 micrograms/ml. Plaque purification revealed mixed populations of virus; some clones were associated with high and some with low rates of acyclovir phosphorylation. Sensitivity to acyclovir decreased in isolates obtained after therapy from four of 25 patients given acyclovir and three of 30 patients given placebo. The occurrence of this change with similar frequency in the two groups suggests that factors other than the use of acyclovir influence the in vitro sensitivity of clinical HSV isolates to this agent. In one patient in whom an acyclovir-resistant, thymidine kinase-negative strain of HSV type 2 emerged during therapy, infection subsequently recurred. The isolate responsible for the recurrence was sensitive to acyclovir and had a high level of acyclovir-phosphorylating activity.

Virus resistance in clinical practice

The sensitivity to acyclovir of more than 800 herpes simplex virus (HSV) isolates from over 300 patients were tested by the dye-uptake method. While a broad spectrum of sensitivity was found, approximately 90% of the isolates were inhibited by less than 1 mg/l of acyclovir. Therapy usually did not significantly alter the sensitivity of HSV isolates except in a few severely immunocompromised patients in whom resistant viruses produced asymptomatic or indolent infections. The sensitivity of viruses isolated during subsequent recurrences was similar to that of the originally infecting virus, regardless of therapy. The requirement of convenient and standardized methods of virus sensitivity testing is emphasized so that additional data can be accumulated to allow more precise correlations between in-vitro virus sensitivity and clinical response to acyclovir therapy.

Pathogenicity of acyclovir-resistant herpes simplex virus type 1 from an immunodeficient child

Sequential isolates of herpes simplex virus type 1 (HSV-1) from a child with severe combined immunodeficiency were examined for sensitivity to acyclovir. Early intravenous courses of acyclovir resulted in dramatic clinical improvement and were associated with the isolation of sensitive strains of HSV-1 (ID50[dose inhibiting 50% of control plaques], 0.010-0.106 microgram/ml), whereas later recurrences following intravenous, oral, and ophthalmic therapy were characterized by low-grade chronic lesions (ID50, 1.04-9.43 microgram/ml) that were unresponsive to acyclovir despite serum levels of up to 10.45 microgram/ml. Diminished sensitivity was associated with reduced viral thymidine kinase activity, and linked resistance with idoxuridine was detected in the isolates from the patient's eye. Intracerebral and cutaneous snout inoculation of a resistant isolate into BALB/c, hairless, and athymic nude mice revealed a 100- to 1,000-fold decrease in virulence as compared with an early sensitive isolate. Acyclovir-resistant HSV-1 can emerge in certain clinical settings but may be associated with diminished virulence.

Spectrum of sensitivity of acyclovir of herpes simplex virus clinical isolates

HSV-1 and HSV-2 clinical isolates were tested for their in vitro sensitivity to acyclovir. The median ID50 for 32 genital HSV-2 isolates was 0.215 micrograms/ml and this was not significantly higher than a median value of 0.125 micrograms/ml for 28 oral HSV-1 isolates (p = 0.08). A wider range of ID50s was observed with the HSV-2 isolates compared with the HSV-1 isolates. The concentration of drug required to inhibit virus replication by 90 and 99 percent was approximately 10- and 100-fold greater than that producing 50 percent inhibition.

Disease and latency characteristics of clinical herpes virus isolated after acyclovir therapy

Herpes simplex virus (HSV) type 1 from a bone marrow transplant recipient and HSV type 2 from a patient with genital herpes infection were examined for sensitivity to acyclovir after both patients received therapy with the drug. A 38- and 83-fold shift in sensitivity was detected in association with a marked decrease in viral thymidine kinase activity in isolates from both patients. The resistant HSV-1 isolate was approximately 900 times less neurovirulent to Balb/C mice but had similar cutaneous virulence in hairless mice compared with the patient's sensitive strain. In contrast, there was no difference in pathogenicity between the sensitive and resistant HSV-2 isolates. Latency was detected in the trigeminal ganglia of mice after snout inoculation with both the sensitive and resistant HSV-1 isolates. The ganglion isolate from the resistant HSV-inoculated mouse was found to be sensitive to acyclovir, implying a selection for or reversion of the sensitive phenotype. No trigeminal ganglion latency was detected after inoculation with either HSV-2 isolate. Resistance to acyclovir can arise during therapy as a result of diminished viral thymidine kinase activity but does not appear to be associated with increased virulence.

Intravenous acyclovir to treat mucocutaneous herpes simplex virus infection after marrow transplantation: a double-blind trial

Acyclovir, a new antiviral agent, was compared to a placebo in a randomized double-blind trial of treatment for culture-proven herpes simplex virus infection after marrow transplantation. Patients received either intravenous acyclovir at 750 mg/m2 body surface area per day or a placebo for 7 days. Thirteen of 17 patients given acyclovir had a beneficial response as compared with two of 17 given the placebo (p less than 0.01). The duration of positive cultures was shorter among acyclovir recipients (3 versus 17 days, p less than 0.00005). Also shorter were the median days to resolution of pain (10 versus 16 days, p = 0.03), to crusting of lesions (7 versus 14 days, p = 0.01), and to total healing (14 versus 28 days, p = 0.03). No acyclovir toxicity was observed. Recurrent infection was common. Acyclovir provided significant antiviral and clinical efficacy without toxicity in highly immunosuppressed patients but had no effect on virus latency.

Acyclovir for chronic mucocutaneous herpes simplex virus infection in immunosuppressed patients

Over 25 episodes of severe chronic and recurrent mucocutaneous herpes simplex virus infections in five immunodeficient patients were successfully treated with intravenous or oral acyclovir treatment. Acyclovir was shown to inhibit viral shedding rapidly, to be well tolerated, and to permit the complete healing of lesions. As expected, a course of acyclovir did not prevent later recurrences of the herpes virus infections. However, symptomatic recurrences were successfully suppressed during long (up to 65-day) courses of oral acyclovir.

Isolation and characterisation of resistant Herpes simplex virus after acyclovir therapy

Sensitivity of herpes simplex virus isolates to acyclovir became reduced in two bone-marrow transplant patients treated for established mucocutaneous infections. These isolates were thymidine-kinase-deficient mutants and were isolated within a week of discontinuation of a 1 week course of acyclovir therapy. The herpetic lesions in both patients continued to heal despite continued shedding of these viruses. Further studies and experience with this new class of antiviral agents are needed to determine the extent to which emergence of less sensitive virus will present clinical difficulties and to formulate treatment regimens that will minimise the emergence of such mutants.

Myoglobin depletion in childhood iron deficiency

Serum concentrations of myoglobin are significantly lower in iron-deficient than in non-iron-deficient children. In the iron-deficient subjects there is a correlation between haemoglobin concentration and serum myoglobin suggesting that the synthesis of both haem compounds is affected in parallel. No abnormality of serum myoglobin concentration was found in adults with iron deficiency anaemia.

Macrophage dependency of in vitro B cell response to influenza virus antigens

Specific B cell responses to influenza viruses were induced by in vitro stimulation of spleen cells from normal or influenza-immune mice with inactivated influenza virus. Both primary and secondary responses to A/Pt Chalmers/73 (A/Pt Ch/73) and A/New Jersey/76 (A/NJ/76) viruses were detected in a hemolytic plaque assay, with peak numbers of specific plaque-forming cells (PFC) present after 4 days of incubation. Depletion of macrophages from BALB/c spleen cell suspensions by treatment with either carrageenan or carbonyl iron markedly reduced the primary and secondary B cell responses to influenza virus. The responses could be restored by reconstitution with either BALB/c or CBA/J macrophages. Specificity of the antibody response was demonstrated in cross-reaction experiments with A/Pt Ch/73 and A/NJ/76 viruses. Evidence of recall to A/NJ/76 virus was, however, found in A/NJ/76-immune spleen cells stimulated in vitro with A/Pt Ch/73 virus. Greatest in vitro stimulation of A/Pt Ch/73-immune spleen cells was produced with inactivated whole A/Pt Ch/73 virus preparations; specific responses were low or absent after stimulation with preparations of partially disrupted virus vaccine, a mixture of purified hemagglutinin (HA) and neuraminidase antigens or soluble hemagglutinin containing similar amounts of viral HA antigen. This lack of response to A/Pt Ch/73 HA could not be overcome with A/NJ/76 whole virus together with purified A/Pt Ch/73 HA.