Once-weekly Injections Research Articles

Benefit-Risk Assessment of Exenatide in the Therapy of Type 2 Diabetes Mellitus

Exenatide is the first incretin mimetic, introduced into type 2 diabetes mellitus therapy in 2005, with first approval in the US. It is a glucagon-like peptide-1 (GLP-1) receptor agonist that can be used for treatment by twice-daily injection. A long-acting release formulation for once-weekly injection is in clinical development. Clinical studies and postmarketing experience with exenatide have shown a significant and sustained reduction in glycosylated haemoglobin (HbA(1c)) by approximately 1% together with other gylcaemic parameters without an intrinsic risk for hypoglycaemias, and a reduction in bodyweight by 5.3 kg in 82 weeks. Blood pressure and lipids are also favourably affected, but hard cardiovascular endpoints are not yet available. Animal studies show an improvement of beta-cell function and an increase in beta-cell mass after exenatide treatment. The most frequent adverse events associated with exenatide therapy are nausea and antibody formation (both approximately 40%). Nausea, mostly mild and transient, was responsible for a 6% dropout rate in clinical studies. A recent review on the association of acute pancreatitis with exenatide treatment showed no increased risk (relative risk 1.0; 95% CI 0.6, 1.7). This review gives a benefit-risk assessment of exenatide.

Application of Adult-Learning Principles to Patient Instructions: A Usability Study for an Exenatide Once-Weekly Injection Device

M ore than 23 million individuals in the United States have diabetes, and ∼ 90% of those have type 2 diabetes. An important aspect of successful disease management for type 2 diabetes is effective use of the numerous pharmacological interventions that are available to target the metabolic defects contributing to the underlying pathology.1 After lifestyle modification and metformin, clinicians may consider many factors when selecting additional therapies. These include efficacy, safety, side effects, treatment complexity (i.e., dosing, administration, and convenience), unique patient characteristics (e.g., physical and cognitive capabilities, understanding of disease, comorbidities, and self-care involvement), and cost. Importantly, patients' ability to initiate and continue using a prescribed therapy is heavily dependent on the education they receive about the disease and its recommended treatments.2 Self-management education is an integral component of diabetes care and is emphasized in the American Diabetes Association's Standards of Medical Care in Diabetes3 and in the Chronic Care Model.4,5 Data support the positive impact of self-management education on quality of life, glycemic control, and psychological factors.6–9 Furthermore, self-management education raises patient awareness of the impact of poor disease management on the occurrence of disease-related complications, premature mortality, and morbidity.10 However, few patients are actually educated by trained professionals or have access to diabetes education training programs.11–14 Often, patients must rely on sources such as the Internet, lay and promotional materials, and peers to supplement the education received from providers who must balance patient needs with severe time and resource constraints.15 In addition, individual characteristics such as language, literacy, vision, comprehension of the need for a therapy, and willingness to try alternatives to managing the disease will influence understanding and subsequent use of any prescribed therapy.16,17 These education challenges also apply …

Five years experience of pegylated interferon (PEG-IFN) plus Ribavirin (RBV) therapy in chronic hepatitis C

Introduction: PEG-IFN combined with RBV is currently regarded as the best antiviral treatment for chronic hepatitis C (CHC). Aim: To survey our experience with this treatment modality between 2004 and 2009. Patients and methods: The pts were treated for 12 months with once-weekly injections of PEG-IFN combined with 1.0–1.2g RBV daily. To date, 222 pts were enrolled in this course of therapy and the 6 months follow-up period. One hundred and fifty-five (70%) had not participated in previous IFN treatment (88 women, 67 men, age range (17–65 years, mean: 46.8 +/- 9.7), bodyweight 40–120kg (mean: 75.4 +/- 15.0). Sixty-seven (30%) had taken part in various previous treatment modalities, which had proved unsuccessful, e.g. IFN monotherapy, PEG-IFN monotherapy, standard IFN + RBV therapy or PEG-IFN + RBV therapy (36 women, 31 men, age range (23–63 years, mean: 46.8 +/- 9.7), bodyweight 40–120kg (mean: 75.4 +/- 15.0). Of the 155 treatment-naive pts, 115 (74.2%) completed the course of therapy, while 40 (25.8%) dropped out because of the “stopping rule“ (25), the spontaneous cessation of therapy (3) or various adverse events (12), such as septic infections, photosensitivity, hyperthyroidism, psychiatric disorders or cytopenias. Results: Among the treatment-naive 155 pts, 69 pts (44.5%) displayed a sustained virological response (SVR). On the other hand, there was a SVR in only 15 of the 67 previously unsuccessfully treated pts (22.4%). A PEG-IFN dose reduction was necessary in 19 treatment-naive pts because of neutropenia or thrombopenia, and a RBV dose reduction was needed in 44 treatment-naive pts because of anemia, as compared with 4 and 11, respectively, in the previously unsuccessfully treated group. Conclusions: This survey of our data demonstrates that this treatment modality with PEG-IFN + RBV may be effective in around half of treatment-naive CHC pts and in a somewhat smaller proportion of previously unsuccessfully treated CHC pts. The side-effects are mostly tolerable. An RBV dose reduction was necessary more often than in the case of PEG-IFN.

Exenatide once weekly for the treatment of type 2 diabetes

Exenatide is the first glucagon-like peptide-1 (GLP-1) receptor agonist approved for the treatment of type 2 diabetes mellitus (T2DM). Exenatide lowers blood glucose through multiple mechanisms, including enhancement of glucose-dependent insulin secretion, suppression of excess glucagon secretion, reduction of food intake and slowing of gastric emptying. The current formulation of exenatide requires twice-daily dosing (exenatide BID), and an extended-release formulation of exenatide is now in development for use as a once-weekly injection (exenatide QW). The purpose of this report is to review the most current clinical data on the development of exenatide QW for the treatment of T2DM. In clinical trials, exenatide QW significantly improved glycemic control, resulted in patient weight loss, and was well tolerated in patients with T2DM. In a head-to-head clinical trial, exenatide QW caused greater improvements in glycemic control and was better tolerated than exenatide BID. Given the rapidly increasing prevalence of diabetes and obesity worldwide, exenatide QW is a promising development candidate for the treatment of T2DM.

Low‐dose etanercept therapy in moderate to severe psoriasis in Korean

Etanercept is a fully humanized soluble tumor necrosis factor (TNF)-alpha receptor that competitively inhibits the interaction of TNF-alpha with cell-surface receptors. It was approved as monotherapy for psoriasis in the USA in 2004, but in Korea, no clinical reports on its use for psoriasis are available. We performed a retrospective analysis of 26 moderate-to-severe psoriasis patients who had been treated with etanercept. Patients received twice-weekly injections of 25 mg etanercept s.c. for at least 4 weeks. When the patients achieved a 50% reduction of the psoriasis area severity index (PASI 50) they received once-weekly injections, then biweekly injections were provided for maintenance. Patients were evaluated biweekly by clinical photographs and PASI scoring. Treatment efficacy was as follows. A PASI 75 was achieved in 14 patients (54%) and the mean number of injections before achieving a PASI 75 was 10 +/- 7.5. Patients whose initial PASI was less than 10 (iPASI < 10) showed an earlier response (2.6 +/- 1.3 weeks) and a higher PASI 75 rate (63%), than with iPASI > or = 10 (6.9 +/- 4.5 weeks, 50%). Eight patients (31%) received additional phototherapy or systemic therapy because of insufficient responses or for faster improvements and they were excluded in the efficacy evaluation. Adverse events were observed in eight patients (31%), but were not serious. This is the first report on the effectiveness of low-dose etanercept regimen on Asian psoriasis patients. Results in this study showed that low-dose etanercept therapy is effective for moderate-to-severe Asian psoriasis patients, and it may be a valuable treatment option even for relatively moderate psoriasis patients not responsive to conventional treatment. In addition, the medical cost was relatively low compared to that of the standard regimen for white patients.

Extended Prophylaxis of Venous Thromboembolism with Idraparinux

The extended use of vitamin K antagonists for prophylaxis against venous thromboembolism is often constrained by risk-benefit limitations and inconvenience. We evaluated the efficacy and safety of a 6-month extension of prophylaxis against recurrent venous thromboembolism with idraparinux in patients who had initially received 6 months of prophylaxis with an anticoagulant. We randomly assigned patients who had completed 6 months of prophylaxis with idraparinux or a vitamin K antagonist and in whom extended anticoagulation was warranted to receive once-weekly injections of 2.5 mg of idraparinux or placebo for 6 months without monitoring. The primary efficacy and safety outcomes were recurrent venous thromboembolism and major bleeding. Of 1215 patients, 6 of 594 (1.0%) in the idraparinux group and 23 of 621 (3.7%) in the placebo group had recurrent venous thromboembolism (P=0.002). Major bleeding occurred in 11 patients (1.9%) in the idraparinux group and in none in the placebo group (P<0.001). Of these 11 episodes, 3 were fatal intracranial hemorrhages. As compared with patients whose initial treatment was a vitamin K antagonist, patients whose initial treatment was idraparinux who were assigned to 6 months in the placebo group had a lower incidence of recurrent thromboembolism (0.7% vs. 5.9%); patients who received 6 additional months of idraparinux therapy had a higher incidence of major bleeding (3.1% vs. 0.9%). During a 6-month extension of thromboprophylaxis, idraparinux was effective in preventing recurrent thromboembolism but was associated with an increased risk of a major hemorrhage. (ClinicalTrials.gov number, NCT00071279 [ClinicalTrials.gov].).

Pegylated interferon (PEG-IFN) plus ribavirin (RBV) therapy in chronic hepatitis C: a single-center experience

Introduction: PEG-IFN combined with RBV is currently regarded as the best antiviral treatment for chronic hepatitis C (CHC). Aim: To survey our experience with this treatment modality. Patients and methods: The pts were treated for one year with once-weekly injections of PEG-IFN combined with 1.0–1.2g RBV daily. To date 111 of them have completed the course of therapy and the follow up period. Ninety-six had not participated in previous IFN treatment, 2 were relapsers to IFN monotherapy, 1 was a relapser to PEG-IFN monotherapy, and 12 had relapsed following previous standard IFN + RBV therapy. Results: Among the treatment-naive pts 79 pts (82%) gave an early virological response (EVR), and 58 of them displayed a negative HCV RNA test at the end of therapy, while 42 pts (44%) showed a sustained virological response (SVR). On the other hand, only 2 of 15 for a previous therapy relapse pts (13%) displayed an SVR. A PEG-IFN dose reduction was necessary in 20 pts because of neutropenia or thrombopenia. An RBV dose reduction was needed in 34 pts because of anemia. A thyroid dysfunction appeared in 8 pts but required no changes in the dosing of PEG-IFN or RBV. Conclusions: The data show that this treatment modality with PEG-IFN may be effective in about one-half of treatment-naive CHC pts. The side effects are mostly tolerable, and an RBV dose reduction was necessary more often than that of PEG-IFN.

Influence of Antiinflammatory Drugs (Methylprednisolone and Diclofenac Sodium) on Experimental Pleurodesis Induced by Silver Nitrate or Talc

To determine whether the administration of antiinflammatory drugs interferes with experimental pleurodesis induced by silver nitrate or talc. Two groups of 30 white New Zealand rabbits were scheduled to receive an intrapleural injection of 0.5% silver nitrate or 400 mg/kg of talc. Each group was further classified into three subgroups (10 animals each), which received the following: (subgroup 1) the sclerosing agent only, (subgroup 2) the sclerosing agent plus 1 mg/kg of methylprednisolone, and (subgroup 3) the sclerosing agent plus 1.1 mg/kg of diclofenac sodium. The antiinflammatory agents were administered IM 24 h before the sclerosing agent and daily during the first week, followed by once-weekly injections until death at 28 days. At this time, the pleural cavity was macroscopically evaluated, and samples of pleura and lungs were collected for further microscopic examination. The degree of pleural adhesions was higher after silver nitrate administration (p = 0.019). No reduction in the adhesions was observed after administering antiinflammatory drugs to this group (p > 0.05). Conversely, the adhesion score was significantly reduced after administration of both prednisolone (p = 0.028) and diclofenac (p = 0.032) to the animals that received talc. Administration of the antiinflammatory agents did not influence microscopic pleural or lung changes induced by silver nitrate or talc. These results show that the sustained systemic administration of antiinflammatory agents (steroidal or nonsteroidal) reduces the degree of pleural adhesions in animals with talc-induced pleurodesis but does not affect silver nitrate-induced pleurodesis. Extrapolation of these results to humans suggests that the use of antiinflammatory drugs should be avoided in patients with talc-induced pleurodesis and that appropriate clinical studies with silver nitrate should be conducted in patients chronically treated with these antiinflammatory agents.

Pegylated Arginine Deiminase Treatment of Patients With Metastatic Melanoma: Results From Phase I and II Studies

Individuals with metastatic melanoma have a poor prognosis. Many human melanomas are auxotrophic for arginine, and arginine is not an essential amino acid in humans. We hypothesized that this auxotrophy may be therapeutically exploited. A novel amino acid-degrading enzyme (arginine deiminase) conjugated to polyethylene glycol (ADI-SS PEG 20,000 mw) was used to lower plasma arginine in individuals with metastatic melanoma. Two cohort dose-escalation studies were performed. A phase I study in the United States enrolled 15 patients, and a phase I to II study in Italy enrolled 24 patients. The Italian patients also received two subsequent cycles of treatment, each consisting of four once-weekly injections of 160 U/m2. The goals of these studies were to determine pharmacokinetics (PK), pharmacodynamics (PD), safety, and the antitumor activity of ADI-SS PEG 20,000 mw. PK and PD studies indicated that a dose of 160 U/m2 lowered plasma arginine from a resting level of approximately 130 micromol/L to less than 2 micromol/L for at least 7 days; nitric oxide levels also were lowered. There were no grade 3 or 4 toxicities directly attributable to the drug. Six of 24 phase I to II patients responded to treatment (five partial responses and one complete response; 25% response rate) and also had prolonged survival. CONCLUSION Elimination of all detectable plasma arginine in patients with metastatic melanoma was well tolerated and may be effective in the treatment of this cancer. Further testing of ADI-SS PEG 20,000 mw in a larger population of individuals with metastatic melanoma is warranted.

Cutaneous necrosis after injection of polyethylene glycol–modified interferon alfa

Pegylated interferon alfa-2b is a formulation of recombinant human interferon conjugated with polyethylene glycol. Compared with standard interferon alfa injections, this preparation has a longer half-life allowing for once-weekly injections and superior antiviral efficacy in the treatment of hepatitis C when used in combination with ribavirin. Cutaneous side effects caused by interferon are well known. Cutaneous necrosis as a result of interferon alfa is an infrequent complication with unknown pathogenesis, in which a cutaneous local immune-mediated inflammatory process might be involved. We report 5 patients (3 patients with chronic hepatitis C treated with pegylated interferon alfa-2b in association with oral ribavirin and two patients with chronic myelocytic leukemia) who developed local cutaneous reactions at sites of injection after the administration of weekly subcutaneous injections of pegylated interferon alfa-2b at different doses. The ulcers slowly healed with local therapy, but two patients required dose modification of the pegylated interferon alfa-2b and one patient required treatment withdrawal. We review the literature on previously reported cases of cutaneous necrosis after injection of standard interferon alfa or pegylated interferon alfa-2b and discuss the different pathophysiologic mechanisms that might be involved.

Relations between dose magnitude, subject sensitivity, and the development of tolerance to cocaine-induced behavioral disruptions in pigeons

Keypecking by 12 pigeons, maintained by a fixed-ratio 30 schedule of food presentation, was decreased in rate by acute pre-session injections of cocaine in a dose-dependent manner, with larger doses producing more disruption. A constant dose of cocaine was then injected prior to every session for 40 days. Some subjects received a relatively small dose, some received a medium-sized dose, and others received a large dose. Subsequently, dose-effects were reassessed via once-weekly probe injections, with every other session continuing to be preceded by injection of the daily dose of cocaine. Then a different dose of cocaine was administered daily for 40 more days, after which the dose-effect function was redetermined in like manner. In general, tolerance to cocaine-induced response-rate reductions was most likely to develop when (a) the repeatedly-administered dose of cocaine was relatively small (even without acute effect on keypecking) and (b) the subject's keypecking was disrupted by smaller doses of cocaine in the initial dose-effect assessment. Tolerance was generally observed as a shift in the dose-effect function that, in several cases, could be eliminated by increasing the magnitude of the daily administered dose. In addition, every subject's rate of keypecking following saline injections was lowered after daily exposure to cocaine. These results (a) are partially consistent with the reinforcement-loss account of tolerance to cocaine-induced behavioral disruptions, and (b) support previous observations of withdrawal symptoms following cessation of extended exposure to cocaine.

Prophylactic and corrective action of the polyethylene oxide polyox WSR-301 in rats with experimental lipoidosis

Two once-weekly intravenous injections of the polyethylene oxide Polyox WSR-301 (yielding a blood concentration of the order of 5×10−6 g/ml) led to a 38% decrease in the area occupied by sudanophilic lesions in the aortic arch of rats fed an atherogenic diet for two weeks. Perfusion under constant pressure of the formalin-fixed vascular system in the posterior part of the body with physiological saline and then with polyethylene oxide (10−5 g/ml) was without effect in normal rats and in those with mild lipoidosis, but reduced hydrodynamic vascular resistance by 9–14.5% in rats with pronounced lipoidosis. Intravenous injection of polyethylene oxide into anesthetized rats with pronounced lipoidosis in doses that were subthreshold for normal rats (blood concentrations of the polymer were of the order of 10−7 g/ml) caused a 20% decrease in the total peripheral resistance to blood flow, with a 17–20% rise of the blood flow rate in the carotid artery.

Long-term sensitization to the behavioral effects of naltrexone is associated with regionally specific changes in the number of μ and δ opioid receptors in rat brain

Enhanced sensitivity to some of the behavioral effects of the opioid antagonist naltrexone (NTX) develops following once-weekly injections of cumulative doses of the drug. Rats treated with this regimen of NTX injections show enhanced sensitivity to the operant response rate decreasing effects of NTX and NTX-induced salivation. The enhanced sensitivity is long-lasting and appears to be produced through conditioning processes. We have conducted saturation binding assays to assess possible changes in the number and affinity of mu and delta opioid receptors in cortical, midbrain and hindbrain membrane preparations from Long-Evans rats treated once weekly for 8 weeks with cumulative doses of the drug (1, 3, 10, 30 and 100 mg/kg). 3H-DAMGO (0.5-21 nM) and 3H-pCl-DPDPE (0.04-4 nM) were used to characterize mu and delta receptors, respectively. NTX treatment had no effect on 3H-DAMGO binding in cortex, but decreased binding in midbrain and increased binding in hindbrain relative to saline-treated controls. Saturation analyses revealed that these differences reflected changes in the number, but not the affinity of mu receptors. NTX treatment also increased the amount of 3H-pCl-DPDPE bound to delta receptors in midbrain and hindbrain, but not in cortex. Again, these changes were due to changes in the number of receptors. Thus, chronic NTX differentially affects the number of mu and delta opioid receptors in various brain regions.

Situational specificity of tolerance to decreased operant responding by cocaine

Responding of rats was maintained in three different environmental situations each day. Interruption of a photobeam was maintained under a shock avoidance schedule in the first session, lever pressing was maintained under a 5-min fixed-interval (FI) schedule of food presentation in a second session, and nose-key pressing was maintained undera 30-response fixed-ratio (FR) schedule of food presentation in a third session. After receiving once-weekly injections of cocaine (3–17 mg/kg) prior to each of the sessions, animals received daily administration of 13 mg/kg after responding in the third daily session for four weeks, before responding in the third session for four weeks, before responding in the daily session for four weeks, and then before responding in the first daily session for four weeks. Tolerance that developed in the environment that was coincident with the pharmacological actions of cocaine did not extend to operants in other environmental situations. Instead, tolerance to the behavioral effects of cocaine was specific to particular stimulus conditions associated with drug administration, indicating that the expression of tolerance depended on both pharmacologic action as well as concurrently operating behavioral processes.

The influence of NSAIDs on morphology of articular cartilage.

A large number of experimental data have given evidence that many NSAIDs can inhibit the synthetic processes of connective tissue in-vitro and ex-vivo. During the past 18 years we have investigated the in-vivo effect of antirheumatic drugs on knee joint cartilage using rats and hens. Single or once-weekly intraarticular injections of salicylates, indomethacin, phenylbutazone, naproxen, ibuprofen, clofezone, fufenamic acid, niflumic acid, or dexamethasone induced morphological alterations in the joint cartilage and subchondral bone, which were demonstrable by means of histology, stereoelectron-microscopy, biochemistry and X-ray. The cartilage of these laboratory animals had a faster turnover compared to man, and the degenerative and destructive processes occurred within 8-12 weeks and were identical or very similar to osteoarthritis in man. In contrast to the general opinion that all NSAIDs possess more or less the same pharmacological properties, the influence of these drugs on articular cartilage was, surprisingly, quite different. In our animal experiments we found that comparable doses between NSAIDs, such as fenbufen, ketoprofen, diclofenac, and tiaprofenic acid, did not induce any degenerative processes in cartilage and subchondral bone in-vivo. A documentation of our radiographical, macroscopical and histomorphological results demonstrated the pronounced differences between NSAIDs on joint tissue. Our experimental data suggested that in the pharmacotherapy of osteoarthritis a specific selection of NSAIDs between those with catabolic and those with non-catabolic characteristics in regard to connective tissue metabolism was important and beneficial.

The area postrema in deoxycorticosterone-salt hypertension in rats.

Ablation of the area postrema in rats prevents sustained hypertension during angiotensin II infusion and after unilateral renal artery constriction (two-kidney, one clip hypertension). The current experiment was performed to determine whether an intact area postrema is required for hypertension development in a low renin model of experimental hypertension in rats. In 11 rats, the area postrema was destroyed using electrical current; the extent and specificity of each lesion was confirmed later by blind histological analysis. In 12 rats, sham operations were performed. All rats were uninephrectomized and drank saline. During once-weekly injections of deoxycorticosterone pivalate (5 mg/wk) for 4 weeks, sham-operated rats (n = 10) showed a significant increase in mean arterial pressure (Days 6-28) and saline intake (Days 12-28), but no significant increase in sodium or water retention. Deoxycorticosterone-treated rats with area postrema ablation (n = 9) exhibited no change in arterial pressure, sodium retention, or water retention, but a significant increase in saline intake (Days 17-28). Plasma renin activity was equally suppressed in both groups of rats. The depressor response to ganglion blockade with hexamethonium (20 mg/kg i.v.) was significantly increased during the 2nd, 3rd, and 4th weeks of steroid treatment in sham-operated, but not area postrema-ablated, rats. Four rats (2 sham-operated; 2 ablated) showed no change in any variable over 28 days in the absence of steroid treatment. It is concluded that the area postrema may be important in some non-angiotensin-dependent forms of experimental hypertension, possibly by affecting neurogenic control mechanisms.

Removal of Polymeric Plutonium by DTPA Directed into Cells by Liposome Encapsulation

DTPA (diethylenetriaminepentaacetic acid) encapsulated within lipid spherules (liposomes) removes more plutonium (Pu) from the liver and femurs of mice injected with polymeric Pu than conventional nonencapsulated DTPA. A single intravenous injection, 3 days after Pu injection, of 100 mg/kg of the calcium trisodium salt of DTPA encapsulated in liposomes made with phosphatidylcholine and cholesterol (3:1) reduced the Pu in liver to 43-51% of the control level at 10 days, compared to 60% after injection of nonencapsulated DTPA. It reduced the Pu in the femurs to 60.4-62.5% of the control level, compared to 83-113%. Liposomal DTPA was equally effective when given intraperitoneally, or when stored for 3 days before use. Liposomal DTPA at doses as low as 25 mg/kg was not significantly less effective than a higher dose of 100 mg/kg. Four once-weekly injections of liposomal DTPA continued to give improved removal of Pu compared to conventional DTPA. When given 24 days after Pu, liposomal DTPA had a greater advant...

Radioimmunoassay of human plasma retinol-binding protein.

A radioimmunoassay for human plasma retinol-binding protein (RBP) has been developed utilizing a double antibody precipitation technique. RBP was purified 1500- to 2000-fold by procedures described previously. A specific anti-human RBP antiserum was prepared in rabbits by three once-weekly injections of purified RBP emulsified with Freund's adjuvant. RBP was iodinated with (131)I and the RBP-(131)I was purified by gel filtration on Sephadex G-100 after complex formation with human plasma prealbumin. The RBP-(131)I was completely (> 95%) immunoprecipitable in the presence of an excess of specific antiserum, it was not (< 5%) immunoprecipitable in the absence of specific antiserum, and it could be completely displaced from antibody by excess unlabeled RBP. The standard curve obtained in the immunoassay with normal plasma was identical to that with pure RBP. Duplicate samples differed from their mean by 5 +/-5% (+/-SD). There was a quantitative recovery of pure RBP added in varying amounts to normal plasma. The immunoassay accurately measured RBP in amounts of 10-100 ng per assay tube. There was no significant difference in the immunoreactivity of apo-RBP as compared to holo-RBP. The mean plasma values (+/-SEM) for a group of 76 normal subjects were 47.2 +/-1.6 mug/ml for males and 41.6 +/-1.6 mug/ml for females. Plasma RBP levels were markedly depressed (15 +/-2.3 mug/ml) in 14 patients with acute viral hepatitis. There was a highly significant correlation between the plasma levels of RBP and of vitamin A in both normal subjects and patients with hepatitis. In all subjects plasma RBP was generally saturated with retinol. The data suggest that under normal circumstances RBP circulates almost exclusively as the holoprotein.