A clinically relevant review of tizanidine hydrochloride dose relationships to pharmacokinetics, drug safety and effectiveness in healthy subjects and patients

Maximal Tizanidine withdrawal managed with dexmedetomidine: a vital intervention

Tizanidine withdrawal is a rare and complex phenomenon characterized by a surge in adrenergic activity upon abrupt discontinuation of the drug. We present a unique case of a 41-year-old male with multiple comorbidities who self-administered an exceptionally high daily dose of Tizanidine, leading to severe withdrawal symptoms. This case report highlights the challenges in managing such cases. The patient, with a history of myofascial pain syndrome, hypertension, anxiety, and depression, experienced distressing symptoms, including tachycardia, rebound hypertension, neuropsychiatric manifestations, and involuntary muscle movements. Unlike previous cases, our patient required the addition of dexmedetomidine in conjunction with benzodiazepines for symptom management. Reintroduction of Tizanidine, carefully controlled and tapered, led to stabilization of hemodynamics and cessation of involuntary movements. This case underscores the importance of individualized treatment and vigilant monitoring when dealing with Tizanidine withdrawal, particularly at elevated daily doses.

Tizanidine Toxicity From Ciprofloxacin: A Cautionary Tale

Tizanidine is an alpha-2 adrenergic agonist used commonly by medical professionals to treat patients' chronic spasticity, muscle spasms, and neuralgia usually associated with myofascial components. This medication is also used very frequently in detoxification centers on patients treated for analgesic withdrawal, especially those who are suffering from rebound headaches due to the discontinuation of analgesics. Tizanidine is metabolized in the human body by the cytochrome P450 CYP1A2. On the other hand, ciprofloxacin is a common antibiotic belonging to the class of fluoroquinolones and is used to treat various infections. Ciprofloxacin inhibits the bacterial DNA-gyrase enzyme resulting in the destruction of the organism. Ciprofloxacin is also an inhibitor of the cytochrome P450 CYP1A2. Even though these two medications show obvious interaction still, however, both these medications are often prescribed together, and their interactions/contraindications are often overlooked by many physicians and other providers. We hereby describe the case report of the interaction between tizanidine and ciprofloxacin, along with the adverse outcome related to the concomitant use of these two drugs.

Understanding Inter-individual Variability in the Drug Interaction of a Highly Extracted CYP1A2 Substrate Tizanidine: Application of a Permeability-limited Multi-compartment Liver Model in a Population Based PBPK Framework

Tizanidine, a centrally acting skeletal muscle relaxant, is predominantly metabolised by CYP1A2 and undergoes extensive hepatic first-pass metabolism following oral administration. As a highly extracted drug, the systemic exposure to tizanidine exhibits considerable inter-individual variability and is altered substantially when co-administered with CYP1A2 inhibitors or inducers. The aim of the current study was to compare the performance of a permeability-limited multi-compartment liver (PerMCL) model, which operates as an approximation of the dispersion model (DM), and the well-stirred model (WSM) for predicting tizanidine DDIs. Physiologically-based pharmacokinetic (PBPK) models were developed for tizanidine, incorporating the PerMCL model and the WSM, respectively, to simulate the interaction of tizanidine with a range of CYP1A2 inhibitors and inducers. While the WSM showed a tendency to under-predict the fold change of tizanidine AUC (AUC ratio) in the presence of perpetrators, the use of PerMCL model increased precision (absolute average-fold error: 1.32 - 1.42 versus 1.58) and decreased bias (average-fold error: 0.97 - 1.25 versus 0.63) for the predictions of mean AUC ratios as compared to the WSM. The PerMCL model captured the observed range of individual AUC ratios of tizanidine as well as the correlation between individual AUC ratios and CYP1A2 activities without interactions, whereas the WSM was not able to capture these. The results demonstrate the advantage of using the PerMCL model over the WSM in predicting the magnitude and inter-individual variability of DDIs for a highly extracted sensitive substrate tizanidine. Significance Statement This study demonstrates the advantages of the permeability-limited multi-compartment liver (PerMCL) model, which operates as an approximation of the dispersion model (DM), in mitigating the tendency of the well-stirred model (WSM) to under-predict the magnitude and variability of DDIs of a highly extracted CYP1A2 substrate tizanidine when it is administered with CYP1A2 inhibitors or inducers. The PBPK modelling approach described herein is valuable to the understanding of drug interactions of highly extracted substrates and the source of its inter-individual variability.

Coadministration of tizanidine and ciprofloxacin: a retrospective analysis of the WHO pharmacovigilance database

PURPOSE

Tizanidine, an alpha-adrenergic substance with antinociceptive and antihypertensive effects, is extensively metabolized via cytochrome P450 (CYP) 1A2. Therefore, coadministration with potent CYP1A2 inhibitors, such as ciprofloxacin, is contraindicated. However, both drugs are broadly utilized in various countries. Their concomitant use bears an inherent high risk for clinically significant symptoms, especially in multimorbid patients experiencing polypharmacy. This study aims to investigate the impact of coadministration of tizanidine and ciprofloxacin using real-world pharmacovigilance data and to raise awareness of this potentially underestimated safety issue.

METHODS

We conducted a retrospective study including Individual Case Safety Reports (ICSR) registered until March 1, 2017, in the World Health Organization (WHO) global database. Demographic data, drug administration information, the course of the adverse drug reaction (ADR), its severity, and outcomes were analyzed for cases reporting ciprofloxacin comedication.

RESULTS

In 91 (2.0%) of the identified 4192 worldwide ICSR on tizanidine, coadministration of ciprofloxacin was reported. Most of the patients were female (n = 59, 64.8%) with a median age of 54 years (range 13-85 years). The countries contributing most reports were the USA (n = 54, 59.3%) and Switzerland (n = 16, 17.6%). ADRs reported most often affected the nervous system and the cardiac function, especially with large tizanidine doses or drugs with CNS and cardiovascular depressant effects. In two cases, a fatal outcome was reported.

CONCLUSION

Despite the existing formal contraindication, the concomitant use of tizanidine and ciprofloxacin can be observed in real-world clinical practice. Reactions mainly affected the central nervous and the cardiovascular system resulting in potentially severe adverse effects. The concomitant use of tizanidine and ciprofloxacin should absolutely be avoided.

Managing Multiple Myeloma in the Face of Drug-Induced Adverse Drug Reaction

Drug-induced liver injury has been reported to cause up to 10% of adverse drug reactions in the United States. Risk factors for druginduced liver injury include female gender, older age, interacting medications and drugs that are metabolized by the liver. This case report describes a patient who was newly initiated on tizanidine, an alpha2 adrenergic agonist used for muscle spasm and musculoskeletal pain, and bortezomib, a proteasome inhibitor used for multiple myeloma. Both medications are metabolized by cytochrome P450 isoenzyme 1A2. The medications were suspected of causing acute hepatitis based on the timing of their initiation and evidence to suggest that they can cause acute hepatitis. The Naranjo adverse drug reaction scale was scored as possible. In addition, the drugs' blood levels may have been increased by acyclovir and hydralazine, both inhibitors of cytochrome P450 isoenzyme 1A2. A dilemma for the team was how to best manage bortezomib. It is part of first line treatment for multiple myeloma when combined with lenalidomide and dexamethasone. Other proteasome inhibitors are available for multiple myeloma treatment. When starting chemotherapy, it is important to be aware of medications that cause a rise in liver enzymes, potential drug interactions, and how best to manage the clinical consequences.

Physiologically based pharmacokinetic modeling of altered tizanidine systemic exposure by CYP1A2 modulation: Impact of drug-drug interactions and cigarette consumption

Tizanidine is an alpha2-adrenergic agonist, used to treat spasticity associated with multiple sclerosis and spinal injury. Tizanidine is primarily metabolized by CYP1A2 and is considered a sensitive index substrate for this enzyme. The physiologically based pharmacokinetic (PBPK) modeling platform Simcyp® was used to evaluate the impact of CYP1A2 modulation on tizanidine exposure through drug-drug interactions (DDIs) and host-dependent habits (cigarette smoking). A PBPK model was developed to predict tizanidine disposition in healthy volunteers following oral administration. The model was verified based on agreement between model-simulated and clinically observed systemic exposure metrics (C_max, AUC). The model was then used to carry-out DDI simulations to predict alterations in tizanidine systemic exposure when co-administered with various CYP1A2 perpetrators including competitive inhibitors (fluvoxamine, ciprofloxacin), a mechanism-based inhibitor (rofecoxib), and an inducer (rifampin). Additional simulations were performed to evaluate the impact of cigarette smoking on systemic exposure. Under each scenario, the PBPK model was able to capture the observed fold changes in tizanidine C_max and AUC of tizanidine when coadministered with CYP1A2 inhibitors or inducers. These results add to the available research findings in the literature on PBPK predictions of drug-drug interactions and illustrate the potential application in drug development, specifically to support product labeling.

CYP2B6 Genotype-Dependent Inhibition of CYP1A2 and Induction of CYP2A6 by the Antiretroviral Drug Efavirenz in Healthy Volunteers

We investigated the effect of efavirenz on the activities of cytochrome P450 (CYP)1A2, CYP2A6, xanthine oxidase (XO), and N-acetyltransferase 2 (NAT2), using caffeine as a probe. A single 150 mg oral dose of caffeine was administered to healthy volunteers (n = 58) on two separate occasions; with a single 600 mg oral dose of efavirenz and after treatment with 600 mg/day efavirenz for 17 days. Caffeine and its metabolites in plasma and urine were quantified using liquid chromatography/tandem-mass spectrometry. DNA was genotyped for CYP2B6*4 (785A>G), CYP2B6*9 (516G>T), and CYP2B6*18 (983T>C) alleles using TaqMan assays. Relative to single-dose efavirenz treatment, multiple doses of efavirenz decreased CYP1A2 (by 38%) and increased CYP2A6 (by 85%) activities (P < 0.05); XO and NAT2 activities were unaffected. CYP2B6*6*6 genotype was associated with lower CYP1A2 activity following both single and multiple doses of efavirenz. No similar association was noted for CYP2A6 activity. This is the first report showing that efavirenz reduces hepatic CYP1A2 and suggesting chronic efavirenz exposure likely enhances the elimination of CYP2A6 substrates. This is also the first to report the extent of efavirenz-CYP1A2 interaction may be efavirenz exposure-dependent and CYP2B6 genotype-dependent.

Analysis of Drug-Drug Interactions in Swiss Claims Data Using Tizanidine and Ciprofloxacin as a Prototypical Contraindicated Combination

BACKGROUND

Potential drug-drug interactions (pDDIs) are described in various case reports, but few studies have evaluated the impact of specific combinations on a population level.

OBJECTIVE

To analyze the type and frequency of multiple contraindicated (X-pDDIs) and major interactions (D-pDDIs) and to subsequently assess the impact of the particular combination of tizanidine and ciprofloxacin on outpatient physician visits and hospitalizations.

METHODS

Anonymized Swiss claims data from 524 797 patients in 2014-2015 were analyzed. First, frequencies of X- and D-pDDIs were calculated. Next, a retrospective cohort study was conducted among patients prescribed tizanidine and ciprofloxacin (exposed, n = 199) or tizanidine and other antibiotics (unexposed, n = 960). Hospitalizations and outpatient physician visits within 7, 14, and 30 days after initiation of antibiotic therapy were evaluated using multiple binary logistic regression and multiple linear regression.

RESULTS

The relative frequencies of X- and D-pDDIs were 0.4% and 6.65%, respectively. In the cohort study, significant associations between exposure to tizanidine and ciprofloxacin and outpatient physician visits were identified for 14 and 30 days (odds ratio [OR] = 1.61 [95% CI = 1.17-2.24], P = 0.004, and OR = 1.59 [95% CI = 1.1-2.34], P = 0.016). A trend for increased risk of hospitalization was found for all evaluated time periods (OR = 1.68 [95% CI = 0.84-3.17], OR = 1.52 [95% CI = 0.63-3.33], and OR = 2.19 [95% CI = 0.88-5.02]). Conclusion and Relevance: The interaction between tizanidine and ciprofloxacin is not only relevant for individual patients, but also at the population level. Further investigation of the impact of other clinically relevant DDIs is necessary to improve patient safety and reduce avoidable health care utilization.

Management of Tizanidine Withdrawal Syndrome: A Case Report

Most drugs that act on the central nervous system (CNS) require dose titration to avoid withdrawal syndrome. Tizanidine withdrawal syndrome is caused by adrenergic discharge due to its α₂-agonist mechanism and is characterized by hypertension, reflex tachycardia, hypertonicity, and anxiety. Although tizanidine withdrawal syndrome is mentioned as a potential side effect of cessation, it is not common and there have been few reports. We present the case of a 31-year-old woman with tizanidine withdrawal syndrome after discontinuing medication prescribed for a muscle contracture (tizanidine). She showed high adrenergic activity with nausea, vomiting, generalized tremor, dysthermia, hypertension, and tachycardia. Symptoms were reversed and successful reweaning was achieved by restarting tizanidine followed by slow downward titration. Withdrawal syndrome should be considered when drugs targeting the CNS are suddenly stopped. Weaning regimens should be closely monitored for acute withdrawal reactions.

Long-term myocardial toxicity in a patient with tizanidine and etizolam overdose

Tizanidine hydrochloride, α2-receptor stimulant, is a central muscle relaxant. Etizolam is a benzodiazepine-based anti-anxiety agent. Both drugs are widely used for the treatment of a variety of muscle pain and frequently used together in Japan. We experienced a case of complicating prolonged myocardial dysfunction in a 56-year-old woman. Six hours after overdose of 48 mg tizanidine and 24 mg etizolam, she showed sinus bradycardia and peripheral vascular resistance decreasing shock. At that time new ST-T depressions were recognized in electrocardiography (ECG); however, structural heart diseases were interpreted as negative by other examinations. Intravenous norepinephrine infusion was useful to maintain the hemodynamic stability. ECG reversed to normal findings on day 14; however, the cardiac nuclear medicine studies on day 30 showed severe fatty metabolic disorder and sympathetic denervation. Non-sustained ventricular tachycardia was detected. Complete recovery of the myocardium damage required one year. For one mechanism, it was suggested that over-stimulation of α2-receptor by tizanidine inhibited the norepinephrine secretion and reuptake at pre-synaptic surface of adipose cell and cardiac sympathetic nerve. We want to suggest that the cardiologist should consider the risk of fatal arrhythmia and long-term myocardium toxicity as the poisoning of the central muscle relaxant and benzodiazepine agent. <Learning objective: We experienced a case of complicating prolonged myocardial dysfunction in a 56-year-old woman. Six hours after overdose of 48 mg tizanidine and 24 mg etizolam, she showed sinus bradycardia and peripheral vascular resistance decreasing shock. The cardiac nuclear medicine studies on day 30 showed severe fatty metabolic disorder and sympathetic denervation. Non-sustained ventricular tachycardia was detected. Complete recovery of the myocardium damage required one year.>.

Limitations and obstacles of the spontaneous adverse drugs reactions reporting: Two "challenging" case reports

Introduction:

Nowadays, based on several epidemiological data, iatrogenic disease is an emerging public health problem, especially in industrialized countries. Adverse drugs reactions (ADRs) are extremely common and, therefore, clinically, socially, and economically worthy of attention. Spontaneous reporting system for suspected ADRs represents the cornerstone of the pharmacovigilance, because it allows rapid detection of potential alarm signals related to drugs use. However, spontaneous reporting system shows several limitations, which are mainly related to under-reporting. In this paper, we describe two particular case reports, which emphasize some reasons of under-reporting and other common criticisms of spontaneous reporting systems.

Materials and Methods:

We performed a computer-aided search of Medline, PubMed, Embase, Cochrane library databases, national and international databases of suspected ADRs reports in order to identify previous published case reports and spontaneous reports about the ADRs reviewed in this paper, and to examine the role of suspected drugs in the pathogenesis of the described adverse reactions.

Results:

First, we reported a case of tizanidine-induced hemorrhagic cystitis. In the second case report, we presented an episode of asthma exacerbation after taking bimatoprost. Through the review of these two cases, we highlighted some common criticisms of spontaneous reporting systems: under-reporting and false causality attribution.

Discussion and Conclusion:

Healthcare workers sometimes do not report ADRs because it is challenging to establish with certainty the causal relationship between drug and adverse reaction; however, according to a key principle of pharmacovigilance, it is always better to report even a suspicion to generate an alarm in the interest of protecting public health.

Tizanidine (Zanaflex): a muscle relaxant that may prolong the QT interval by blocking IKr

BACKGROUND

Tizanidine (Zanaflex) is a centrally acting imidazoline muscle relaxant that is structurally similar to clonidine (α(2)-adrenergic agonist) but not to other myorelaxants such as baclofen or benzodiazepines. Interestingly, cardiac arrhythmias and QT interval prolongation have been reported with tizanidine.

OBJECTIVE

To evaluate the effects of tizanidine on cardiac ventricular repolarization.

METHODS

(1) Whole-cell patch-clamp experiments: HERG- or KCNQ1+KCNE1-transfected cells were exposed to tizanidine 0.1-100 µmol/L (n = 29 cells, total) to assess drug effect on the rapid (I(Kr)) and slow (I(Ks)) components of the delayed rectifier potassium current. (2) Langendorff retroperfusion experiments: isolated hearts from male Hartley guinea pigs (n = 6) were exposed to tizanidine 1 µmol/L to assess drug-induced prolongation of monophasic action potential duration measured at 90% repolarization (MAPD(90)). (3) In vivo wireless cardiac telemetry experiments: guinea pigs (n = 6) implanted with radio transmitters were injected a single intraperitoneal (ip) dose of tizanidine 0.25 mg/kg and 24 hours electrocardiography (ECG) recordings were made.

RESULTS

(1) Patch-clamp experiments revealed an estimated IC(50) for tizanidine on I(Kr) above 100 µmol/L. Moreover, tizanidine 1 µmol/L had hardly any effect on I(Ks) (5.23% ± 4.54% inhibition, n = 5 cells). (2) While pacing the hearts at stimulation cycle lengths of 200 or 250 ms, tizanidine 1 µmol/L prolonged MAPD(90) by 8.22 ± 2.03 (6.7%) and 11.70 ± 3.08 ms (8.5%), respectively (both P < .05 vs baseline). (3) Tizanidine 0.25 mg/kg ip caused a maximal 11.93 ± 1.49 ms prolongation of corrected QT interval (QTc), 90 minutes after injection.

CONCLUSION

Tizanidine prolongs the QT interval by blocking I(Kr). Patients could be at risk of cardiac proarrhythmia during impaired drug elimination, such as in case of CYP1A2 inhibition during drug interactions.

Hypotension and bradycardia associated with concomitant tizanidine and lisinopril therapy

PURPOSE

A case of severe bradycardia and hypotension associated with concomitant tizanidine and lisinopril therapy is reported.

SUMMARY

An 85-year-old man with a chief complaint of profound weakness was admitted to the hospital with a blood pressure reading of 60/32 mm Hg and a heart rate of 37 beats/min. His medical history included type 2 diabetes mellitus, congestive heart failure, gastroesophageal reflux disease, chronic obstructive pulmonary disease, osteoarthritis, restless leg syndrome, benign prostatic hyperplasia, generalized anxiety disorder with depression, and severe chronic back pain for which he was receiving treatment at a pain clinic. Two days before hospital admission, he had been seen at the pain clinic and started on ti-zanidine. Additional medications included acetaminophen, chlorpromazine, citalopram, finasteride, lidocaine patch, lisinopril, metformin, pramipexole, omeprazole, simvastatin, theophylline, diclofenac topical gel, hydrocodone-acetaminophen, and ondansetron. After taking three doses of the newly prescribed tizanidine, he developed severe hypotension and bradycardia. Notable laboratory test values included a serum creatinine concentration of 1.90 mg/dL, a blood urea nitrogen concentration of 21 mg/dL, a serum potassium concentration of 5.5 meq/L, and a serum sodium concentration of 128 meq/L. Upon admission, tizanidine, lisinopril, theophylline, omeprazole, and simvastatin were withheld, and i.v. fluids were administered. The patient's vital signs began to gradually improve. Within 24 hours, the patient's blood pressure and heart rate had improved, as had the previously abnormal laboratory test values. Tizanidine was discontinued, and all of his other preadmission medications were restarted at discharge.

CONCLUSION

The addition of tizanidine in a patient receiving long-term treatment with lisinopril was associated with severe hypotension and bradycardia.

Pharmacokinetic variability of long-acting stimulants in the treatment of children and adults with attention-deficit hyperactivity disorder

Methylphenidate- and amfetamine-based stimulants are first-line pharmacotherapies for attention-deficit hyperactivity disorder, a common neurobehavioural disorder in children and adults. A number of long-acting stimulant formulations have been developed with the aim of providing once-daily dosing, employing various means to extend duration of action, including a transdermal delivery system, an osmotic-release oral system, capsules with a mixture of immediate- and delayed-release beads, and prodrug technology. Coefficients of variance of pharmacokinetic measures can estimate the levels of pharmacokinetic variability based on the measurable variance between different individuals receiving the same dose of stimulant (interindividual variability) and within the same individual over multiple administrations (intraindividual variability). Differences in formulation clearly impact pharmacokinetic profiles. Many medications exhibit wide interindividual variability in clinical response. Stimulants with low levels of inter- and intraindividual variability may be better suited to provide consistent levels of medication to patients. The pharmacokinetic profile of stimulants using pH-dependent bead technology can vary depending on food consumption or concomitant administration of medications that alter gastric pH. While delivery of methylphenidate with the transdermal delivery system would be unaffected by gastrointestinal factors, intersubject variability is nonetheless substantial. Unlike the beaded formulations and, to some extent (when considering total exposure) the osmotic-release formulation, systemic exposure to amfetamine with the prodrug stimulant lisdexamfetamine dimesylate appears largely unaffected by such factors, likely owing to its dependence on systemic enzymatic cleavage of the precursor molecule, which occurs primarily in the blood involving red blood cells. The high capacity but as yet unidentified enzymatic system for conversion of lisdexamfetamine dimesylate may contribute to its consistent pharmacokinetic profile. The reasons underlying observed differential responses to stimulants are likely to be multifactorial, including pharmacodynamic factors. While the use of stimulants with low inter- and intrapatient pharmacokinetic variability does not obviate the need to titrate stimulant doses, stimulants with low intraindividual variation in pharmacokinetic parameters may reduce the likelihood of patients falling into subtherapeutic drug concentrations or reaching drug concentrations at which the risk of adverse events increases. As such, clinicians are urged both to adjust stimulant doses based on therapeutic response and the risk for adverse events and to monitor patients for potential causes of pharmacokinetic variability.

Relative bioavailability of tizanidine hydrochloride capsule formulation compared with capsule contents administered in applesauce: a single-dose, open-label, randomized, two-way, crossover study in fasted healthy adult subjects

BACKGROUND

The alpha2-adrenergic agonist tizanidine has been reported to have a narrow therapeutic index. A multiparticulate capsule formulation of tizanidine has been developed in an attempt to improve patient tolerability.

OBJECTIVE

This study assessed bioequivalence between a single, intact, 6-mg capsule of tizanidine and the capsule contents sprinkled in applesauce in fasted healthy subjects.

METHODS

Healthy male and female subjects aged 18 to 45 years completed 2 treatment periods: one with a tizanidine 6-mg capsule administered intact and the other with capsule contents sprinkled in applesauce. The 2 treatment periods had a 6-day washout period between administrations. Plasma tizanidine concentrations were determined for blood samples collected over 24 hours after administration. All treatment-emergent adverse events were recorded and graded by intensity and relationship to the study drug (not, improbable, possible, probable, definite) by the attending physician based on his or her clinical impression.

RESULTS

A total of 19 men and 9 women (mean age, 26 years) completed the trial. Geometric mean natural logarithm-transformed AUC values (AUC(0-infinity) [AUC to infinity] and AUC(0-t) [AUC to the last measurable time point]) and C(max) ratios were significantly (P <or= 0.035) increased to 1.14 (90% CI, 105.47%-127.01%), 1.16 (90% CI, 106.80%-130.53%), and 1.17 (90% CI, 103.95%-133.66%), respectively, when the contents were sprinkled, with 90% CIs laying outside the 0.80 to 1.25 ratio established by regulatory authorities for bioequivalence. A total of 31 adverse events were reported by 17 of the 28 subjects (61%), including 15 subjects (54%) with the intact capsule reporting 18 events and 11 subjects (39%) with the sprinkled contents reporting 13 events. No serious adverse events or deaths were reported, and no subjects were discontinued due to adverse events.

CONCLUSIONS

The contents of the tizanidine capsule sprinkled in applesauce were not bioequivalent to the intact 6-mg capsule in these fasted healthy volunteers. Therefore, if switching from the intact capsule to the capsule contents mixed in applesauce, monitoring for adverse events is recommended; in this situation, dose adjustment could be necessary.