CSF concentrations of famotidine

Effect of famotidine on cognitive and behavioral dysfunctions induced in post-COVID-19 infection: A randomized, double-blind, and placebo-controlled study

OBJECTIVES

This is an investigation of the efficacy and safety of famotidine, a selective histamine H2 receptor antagonist, on improvement of cognitive impairment, depression and anxiety symptoms developing post-COVID-19, in a 12-week, randomized controlled trial.

METHODS

A total of 50 patients with a confirmed diagnosis of COVID-19 and a score ≤ 23 on the Mini-Mental State Examination (MMSE) test or a score ≤ 22 on the Montreal Cognitive Assessment (MoCA) were randomly assigned to either the famotidine (40 mg twice daily) or the placebo group. Changes in MMSE scores at weeks 6 and 12 were the primary outcome, while changes in other scales were the secondary outcomes. Participants and evaluators were blinded.

RESULTS

At weeks 6 and 12, patients in the famotidine group had significantly higher MMSE scores (p = 0.014, p < 0.001, respectively). Regarding the MoCA scale, the famotidine group had a significantly higher score at weeks 6 and 12 (p = 0.001, p < 0.001, respectively). Considering the HAM-D scale (Hamilton Depression Rating Scale), at weeks 6 and 12, the famotidine group experienced a larger reduction (p = 0.009, p = 0.02, respectively). Additionally, comparison of the HAM-A scale scores (Hamilton Anxiety Rating Scale) at weeks 6 and 12 showed a statistically significant larger reduction in the famotidine group (p = 0.04, p = 0.02, respectively). The two groups did not differ in the frequency of adverse effects.

CONCLUSION

Our study supports safety and efficacy of famotidine in treating cognitive impairment, depression and anxiety symptoms induced by COVID-19.

TRIAL REGISTRATION

This trial was registered at the Iranian registry of clinical trials (IRCT: www.irct.ir; registration number: IRCT20090117001556N138).

Famotidine activates the vagus nerve inflammatory reflex to attenuate cytokine storm

BACKGROUND

Severe COVID-19 is characterized by pro-inflammatory cytokine release syndrome (cytokine storm) which causes high morbidity and mortality. Recent observational and clinical studies suggest famotidine, a histamine 2 receptor (H2R) antagonist widely used to treat gastroesophageal reflux disease, attenuates the clinical course of COVID-19. Because evidence is lacking for a direct antiviral activity of famotidine, a proposed mechanism of action is blocking the effects of histamine released by mast cells. Here we hypothesized that famotidine activates the inflammatory reflex, a brain-integrated vagus nerve mechanism which inhibits inflammation via alpha 7 nicotinic acetylcholine receptor (α7nAChR) signal transduction, to prevent cytokine storm.

METHODS

The potential anti-inflammatory effects of famotidine and other H2R antagonists were assessed in mice exposed to lipopolysaccharide (LPS)-induced cytokine storm. As the inflammatory reflex is integrated and can be stimulated in the brain, and H2R antagonists penetrate the blood brain barrier poorly, famotidine was administered by intracerebroventricular (ICV) or intraperitoneal (IP) routes.

RESULTS

Famotidine administered IP significantly reduced serum and splenic LPS-stimulated tumor necrosis factor (TNF) and IL-6 concentrations, significantly improving survival. The effects of ICV famotidine were significantly more potent as compared to the peripheral route. Mice lacking mast cells by genetic deletion also responded to famotidine, indicating the anti-inflammatory effects are not mast cell-dependent. Either bilateral sub-diaphragmatic vagotomy or genetic knock-out of α7nAChR abolished the anti-inflammatory effects of famotidine, indicating the inflammatory reflex as famotidine's mechanism of action. While the structurally similar H2R antagonist tiotidine displayed equivalent anti-inflammatory activity, the H2R antagonists cimetidine or ranitidine were ineffective even at very high dosages.

CONCLUSIONS

These observations reveal a previously unidentified vagus nerve-dependent anti-inflammatory effect of famotidine in the setting of cytokine storm which is not replicated by high dosages of other H2R antagonists in clinical use. Because famotidine is more potent when administered intrathecally, these findings are also consistent with a primarily central nervous system mechanism of action.

Famotidine activates the vagus nerve inflammatory reflex to attenuate cytokine storm

Background. Severe COVID-19 is characterized by pro-inflammatory cytokine release syndrome (cytokine storm) which causes high morbidity and mortality. Recent observational and clinical studies suggest famotidine, a histamine 2 receptor (H2R) antagonist widely used to treat gastroesophageal reflux disease , attenuates the clinical course of COVID-19. Because evidence is lacking for a direct antiviral activity of famotidine, a proposed mechanism of action is blocking the effects of histamine released by mast cells. Here we hypothesized that famotidine activates the inflammatory reflex, a brain-integrated vagus nerve mechanism which inhibits inflammation via alpha 7 nicotinic acetylcholine receptor ( α7nAChR ) signal transduction, to prevent cytokine storm. Methods. The potential anti-inflammatory effects of famotidine and other H2R antagonists was assessed in mice exposed to lipopolysaccharide (LPS)-induced cytokine storm. As the inflammatory reflex is integrated and can be stimulated in the brain, and H2R antagonists penetrate the blood brain barrier poorly, famotidine was administered by intracerebroventricular (ICV) or intraperitoneal (IP) routes. Results. Famotidine administered IP significantly reduced serum and splenic LPS-stimulated tumor necrosis factor α and interleukin-6 concentrations, significantly improving survival. The effects of ICV famotidine were significantly more potent as compared to the peripheral route. Mice lacking mast cells by genetic deletion also responded to famotidine, indicating the anti-inflammatory effects are not mast cell dependent. Either bilateral sub-diaphragmatic vagotomy or genetic knock-out of α7nAChR abolished the anti-inflammatory effects of famotidine, indicating the inflammatory reflex as famotidine's mechanism of action. While the structurally similar H2R antagonist tiotidine displayed equivalent anti-inflammatory activity, the H2R antagonists cimetidine or ranitidine were ineffective even at very high dosages. Conclusions. These observations reveal a previously unidentified vagus nerve-dependent anti-inflammatory effect of famotidine in the setting of cytokine storm which is not replicated by high dosages of other H2R antagonists in clinical use. Because famotidine is more potent when administered intrathecally, these findings are also consistent with a primarily central nervous system mechanism of action.

Central histaminergic signalling, neural excitability and epilepsy

Epilepsy is a common neurological disorder characterized by repeated and spontaneous epileptic seizures and is not well controlled by current medication. Traditional theory suggests that epilepsy results from an imbalance of excitatory glutamate neurons and inhibitory GABAergic neurons. However, new evidence from clinical and preclinical research suggests that histamine in the CNS plays an important role in the modulation of neural excitability and in the pathogenesis of epilepsy. Many histamine receptor ligands have achieved curative effects in animal epilepsy models, among which the histamine H₃ receptor antagonist pitolisant has shown anti-epileptic effects in clinical trials. Recent studies, therefore, have focused on the potential action of histamine receptors to control and treat epilepsy. In this review, we summarize the findings from animal and clinical epilepsy research on the role of brain histamine and its receptors. We also identify current gaps in the research and suggest where further studies are most needed.

Histamine receptors, agonists, and antagonists in health and disease

Histamine in the brain is produced by a group of tuberomamillary neurons in the posterior hypothalamus and a limited number of mast cells in different parts of the brain. Four G-protein-coupled receptors mediate the effects of histamine. Two of these receptors, H3 and H4 receptors, are high-affinity receptors in the brain and immune system, respectively. The two classic histamine receptors, H1 receptor and H2 receptor, are well known as drug targets for allergy and gastric ulcer, respectively. These receptors have lower affinity for histamine than the more recently discovered H3 and H4 receptors. The H1 and H2 receptors are important postsynaptic receptors in the brain, and they mediate many of the central effects of histamine on, e.g., alertness and wakefulness. H3 receptor is a pre- and postsynaptic receptor, which regulates release of histamine and several other neurotransmitters, including serotonin, GABA, and glutamate. H4 receptor is found in cerebral blood vessels and microglia, but its expression in neurons is not yet well established. Pitolisant, a H3 receptor antagonist, is used to treat narcolepsy and hypersomnia. H1 receptor antagonists have been used to treat insomnia, but its use requires precautions due to potential side effects. H2 receptor antagonists have shown efficacy in treatment of schizophrenia, but they are not in widespread clinical use. H4 receptor ligands may in the future be tested for neuroimmunological disorders and potentially neurodegenerative disorders in which inflammation plays a role, but clinical tests have not yet been initiated.

A randomized clinical trial of histamine 2 receptor antagonism in treatment-resistant schizophrenia

Histamine has important functions as regulator of several other key neurotransmitters. Patients with schizophrenia have lower histamine H1 receptor levels. Since a case report in 1990 of an effect of the H2 antagonist famotidine on negative symptoms in schizophrenia, some open-label trials have been performed, but no randomized controlled trial. Recently, it was shown that clozapine is a full inverse agonist at the H2 receptor. We performed a researcher-initiated, academically financed, double-blind, placebo-controlled, parallel-group, randomized trial with the histamine H2 antagonist famotidine in treatment-resistant schizophrenia. Thirty subjects with schizophrenia were randomized to have either famotidine (100 mg twice daily, n = 16) or placebo (n = 14) orally, added to their normal treatment regimen for 4 weeks. They were followed up weekly with the Scale for the Assessment of Negative Symptoms (SANS), the PANSS (Positive and Negative Syndrome Scale), and Clinical Global Impression (CGI) Scale. In the famotidine group, the SANS score was reduced by 5.3 (SD, 13.1) points, whereas in the placebo group the SANS score was virtually unchanged (mean change, +0.2 [SD, 9.5]). The difference did not reach statistical significance (P = 0.134) in Mann-Whitney U analysis. However, the PANSS Total score and the General subscore as well as the CGI showed significantly (P < 0.05) greater change in the famotidine group than in the placebo group. No significant adverse effects were observed. This is the first placebo-controlled, randomized clinical trial showing a beneficial effect of histamine H2 antagonism in schizophrenia. H2 receptor antagonism may provide a new alternative for the treatment of schizophrenia.

Histamine metabolites in cerebrospinal fluid of patients with chronic schizophrenia: their relationships to levels of other aminergic transmitters and ratings of symptoms

Levels of the histamine metabolites, tele-methylhistamine (t-MH) and tele-methylimidazoleacetic acid (t-MIAA), and metabolites of other aminergic transmitters and of norepinephrine were measured in cerebrospinal fluid of 36 inpatients with chronic schizophrenia and eight controls. The mean t-MH level from controls was nearly identical to the levels seen previously in healthy volunteers. Compared with controls, the mean level of t-MH in the schizophrenic patients was 2.6-fold higher (p = 0.006); 21 of the patients had levels exceeding the range of controls. There was no significant difference (p > 0.05) in levels of other analytes, although the levels of t-MH correlated significantly with those of t-MIAA, homovanillic acid, 3,4-dihydroxyphenylacetic acid, norepinephrine, 3-methoxy-4-hydroxyphenylglycol and 5-hydroxyindoleacetic acid. The difference in levels of t-MH were not attributable to medication, since those taking (n = 10) or withdrawn from (n = 26) neuroleptic drugs had nearly the same mean levels of t-MH; each group had higher levels than controls (ANOVA: p < 0.05). Patients with or without tardive dyskinesia showed no significant differences in means of any analyte. Only levels of t-MH among those with schizophrenia correlated with positive symptom scores on the Psychiatric Symptom Assessment Scale (rs = 0.45, p < 0.02). The elevated levels of t-MH in cerebrospinal fluid, which represent histamine that was released and metabolized, suggest increased central histaminergic activity in patients with chronic schizophrenia.

Famotidine as an adjunct treatment of resistant schizophrenia

Some patients suffering from schizophrenia fail to respond to or tolerate adequate doses of available antipsychotic medications. Thus, innovative pharmacotherapeutic approaches, such as augmentation strategies, play an important role in the management of these treatment-resistant patients. A recent case report suggested that the administration of famotidine to a patient suffering from schizophrenia with peptic ulcer disease was associated with improvement in the deficit symptoms of schizophrenia. Famotidine is a potent highly selective H2 receptor antagonist which crosses the blood-brain barrier. Impressed by this finding, famotidine was prescribed to some of our treatment-resistant patients suffering from schizophrenia who demonstrated significant deficit symptoms of schizophrenia. The subjects were 12 (eight male, four female) treatment-resistant psychotic patients whose antipsychotic medications were augmented with famotidine in an open trial. They ranged in age from 21 to 48 years with a mean age of 32.75 years. Seven of the 12 subjects made significant improvement resulting in discharge from hospital. Paranoid disturbances as well as absence of comorbid substance use were predictors of good response to famotidine augmentation of the antipsychotic medications. The results implied that H2 receptor activity in the brain might play a role in the pathogenesis of deficit syndromes in schizophrenia. Further studies of this strategy are recommended, since it may open a window of understanding of the negative (deficit) syndrome and its treatment.

Clinical pharmacokinetics of famotidine

Famotidine is a potent histamine H2-receptor antagonist widely used in the treatment and prevention of peptic ulcer disease. After intravenous administration the plasma famotidine concentration-time profile exhibits a biexponential decay, with a distribution half-life of about 0.18 to 0.5h and an elimination half-life of about 2 to 4h. The volume of distribution of the drug at steady-state ranges from 1.0 to 1.3 L/kg; plasma protein binding is low (15 to 22%). Famotidine is 70% eliminated unchanged into urine after intravenous administration. The total body and renal clearances of famotidine correlate significantly with creatinine clearance. Because its renal clearance (15 L/h) far exceeds the glomerular filtration rate, famotidine is considered to be eliminated not only via glomerular filtration but also via renal tubular secretion. Since its clearance is reduced in patients with renal insufficiency and in elderly patients, the maintenance dosage should be reduced in these patient groups. Removal of famotidine by any of the currently employed blood purification procedures (haemodialysis, peritoneal dialysis and haemofiltration) does not occur to a clinically significant degree. Liver cirrhosis does not appear to affect the disposition of famotidine unless severe renal insufficiency coexists. After oral administration, peak plasma concentrations are attained within 2 to 4h; the oral bioavailability ranges from 40 to 50%, due mainly to incomplete absorption. The oral absorption of the drug is dose-independent within a range of 5 to 40 mg. There are 3 formulations available (tablet, capsule and suspension), which appear to be bioequivalent. Coadministration of potent antacids reduces the oral absorption of famotidine by 20 to 30%. On a weight-to-weight basis, the antisecretory effect of famotidine is about 20 and 7.5 times more potent than those of cimetidine and ranitidine, respectively. Plasma famotidine concentrations correlate with its antisecretory effect: values of about 13 and 20 micrograms/L produce a 50% reduction in the gastrin-stimulated gastric acid secretion and a fasting intragastric pH of greater than 4, respectively. Available data suggest that famotidine interacts neither with the hepatic oxidative drug metabolism nor with the tubular secretion of other commonly used therapeutic agents. However, further studies are required to evaluate a full spectrum of its drug interaction potential.

Pharmacokinetic and pharmacodynamic properties of histamine H2-receptor antagonists. Relationship between intrinsic potency and effective plasma concentrations

Histamine H2-receptor antagonists are a unique class of compounds. Pharmacologically they are characterised as a family by their ability to inhibit the secretion of gastric acid, and kinetically they are classified as a family by their similarity in absorption, distribution and elimination. All the H2-receptor antagonists exhibit classical competitive drug-receptor interactions, with Schild slope parameters not significantly different from unity. Comparison of the values of the negative logarithm of the molar concentration of antagonist in the presence of which the potency of the agonist is reduced 2-fold (PA2) indicates that famotidine is about 20 to 50 times more potent than cimetidine and 6 to 10 times more potent than ranitidine. To date, famotidine is the most potent among marketed H2-receptor antagonists. Oral absorption of all the H2-receptor antagonists under clinical investigation is fairly rapid. Peak plasma concentrations are usually attained within 1 to 3h after the dose, but a second peak after oral administration has been observed with cimetidine, ranitidine, famotidine, ramixotidine and etintidine. The mean oral bioavailability for the H2-antagonists ranges from 50 to 70%. Reports on the plasma profiles after intravenous administration are available only for cimetidine, ranitidine, famotidine and nizatidine: plasma concentrations of all 4 decline in a biexponential manner. All of the H2-antagonists are eliminated quite rapidly, with a terminal half-life of 1 to 3h and a total body clearance of 24 to 48 L/h. Elimination is mainly attributable to renal excretion, with renal clearances ranging from 13.8 to 30 L/h. As the values for renal clearance greatly exceed the glomerular filtration rate (6 to 7.2 L/h), it is apparent that renal tubular secretion plays an important role. There is a simple, direct correlation between plasma concentrations of H2-receptor antagonists and the inhibition of gastric acid secretion. This implies a rapid equilibration between drug concentration in plasma and at the site of action, and a reversible drug-receptor interaction. Success in correlating the plasma concentration of H2-receptor antagonists and their pharmacological effects stems from reliable and precise measurement of both items. Despite the heterogeneous nature of data sources, 50% inhibitory concentration (IC50) values for cimetidine, ranitidine, famotidine, nizatidine, etintidine and roxatidine obtained in vitro appear to be in good agreement with those determined in vivo. These results suggest that at an early stage of development of an H2-receptor antagonist, IC50 determined from in vitro studies may be useful as a first approximation to predict the clinically effective concentration of the new agent.

Clinical pharmacokinetics of drugs used in the treatment of gastrointestinal diseases (Part II)

Part I of this article, which appeared in the previous issue of the Journal, covered the following agents: histamine H2-receptor antagonists (cimetidine, ranitidine, famotidine, nizatidine); muscarinic-M1-receptor antagonists (pirenzepine); proton pump inhibitors (omeprazole); site-protective agents (colloidal bismuth subcitrate, sucralfate); antacids and prostaglandin analogues; antiemetics and prokinetics (metoclopramide, domperidone, cisapride); and antispasmodics. In Part II, we consider the anti-inflammatory salicylates, nonspecific antidiarrhoeal agents, laxatives and cathartics.

Famotidine. An updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in peptic ulcer disease and other allied diseases

Famotidine is a highly selective histamine H2-receptor antagonist. In healthy volunteers and patients with acid hypersecretory disease it is approximately 20 to 50 times more potent at inhibiting gastric acid secretion than cimetidine and 8 times more potent than ranitidine on a weight basis. As shown in placebo-controlled trials, famotidine is effective in healing both duodenal and gastric ulcers. Famotidine 20mg twice daily or 40mg at bedtime achieves healing rates and symptom relief similar or superior to those achieved by cimetidine 800mg daily or ranitidine 300mg daily in patients with peptic ulcer disease. Results of 1 placebo-controlled study suggest that famotidine prevents recurrence of duodenal ulcer, but comparative trials are needed to establish its relative efficacy in maintenance therapy. The few non-comparative trials conducted to date also suggest that famotidine 10 to 20mg twice daily may be effective in the treatment of gastritis and reflux gastro-oesophagitis. In comparative trials, famotidine was similar in efficacy to cimetidine in the treatment of upper gastrointestinal bleeding and to ranitidine in the prevention of pulmonary aspiration of acid. In patients with Zollinger-Ellison syndrome, the potency and long duration of action of famotidine may confer an advantage over other H2-receptor antagonists--in individualised doses (mean 0.33 g/day) famotidine successfully controlled acid secretion for up to 72 months in 1 study of such patients. Accumulated clinical evidence confirms that famotidine is very well tolerated and is free of the antiandrogenic effects infrequently reported with cimetidine. Moreover, famotidine is not associated with altered hepatic metabolism of drugs. Thus, famotidine is an effective, well-tolerated alternative to cimetidine and ranitidine. Famotidine is also promising as maintenance therapy for preventing recurrence of duodenal ulcer and as initial or maintenance treatment of gastric hypersecretory disorders, but further clinical experience, particularly in the long term, is needed to define the relative efficacy and tolerability of famotidine in these indications.

A comparison of the cholinergic activity of selected H2-antagonists and sulfoxide metabolites

Famotidine and selected H2-antagonists were evaluated with respect to toxicity and selected pharmacological activities. When administered intraperitoneally to mice at a dose equivalent to 10 times their respective H2-antagonist ED50 values, no deaths were observed. Similarly, no alteration in brain ACh concentrations or overt pharmacological effects were noted. However, at 400 mg/kg, ranitidine produced 89% lethality, followed by cimetidine (11%) and famotidine. Only cimetidine and famotidine at this dose significantly elevated brain acetylcholine levels. These results do not correlate with the in vitro data, where ORF-17578 and ranitidine were the most potent entities with respect to acetylcholinesterase inhibition (approximately 1-2 X 10(-6) M), followed by nizatidine greater than cimetidine greater than famotidine. The sulfoxide metabolites of ranitidine and cimetidine were approximately one-tenth as potent as their parent compounds with respect to inhibition of acetylcholinesterase. Direct muscarinic stimulation or potentiation of acetylcholine-induced contraction in ileal tissue was not observed for any of the H2-antagonists.

Newer H2-receptor antagonists. Clinical pharmacokinetics and drug interaction potential

Since H2-receptor antagonists are widely and successfully used in the treatment of peptic ulcer, several alternatives to the standard agents cimetidine and ranitidine have been developed. Promising 'new' candidates might be famotidine and nizatidine. For proper selection of the appropriate drug, its pharmacokinetic properties and interaction potential should be known. All 'old' and 'new' H2-receptor blockers are eliminated relatively rapidly (t 1/2 ranges from 1.5 to 4 hours), mainly by the renal route (glomerular filtration and tubular secretion). They exhibit a linear disposition and their distribution is similar. Absorption is most complete for nizatidine, whereas famotidine demonstrates the lowest effective plasma concentrations. Since etintidine shares the same imidazole ring structure as cimetidine, it can also impair oxidative drug metabolism in the liver. In this respect, the non-interacting famotidine and nizatidine (like ranitidine) offer a definite advantage. Based on their very similar pharmacokinetic and interaction profiles, these 2 H2-receptor antagonists might be regarded as alternatives to the older drugs in this group, and at least some economic benefits might result from the competition they will provide.