Pharmacokinetics, Safety, and Tolerability of Intramuscular Ziprasidone in Healthy Volunteers

Little has been published regarding the pharmacokinetics of the intramuscular (IM) formulation of Ziprasidone. The authors report results from 2 early phase I studies in healthy volunteers: a trial of single 5-, 10-, or 20-mg IM doses of ziprasidone in 24 subjects and an open-label 3-way crossover trial of 5-mg intravenous (IV), 5-mg IM, and 20-mg oral ziprasidone in 12 subjects. Absorption of IM ziprasidone was rapid (Tmax < 1 hour). The IM pharmacokinetic profile was consistent between studies and linear, with dose-related increases in exposure observed. The mean IM elimination t(1/2) was short and approximately 2.5 hours. The mean bioavailability for the 5-mg IM ziprasidone dose was approximately 100%. Adverse events were generally mild to moderate, and no subjects were discontinued from the study. No significant effects on renal function or other laboratory values were noted. These results support the use of IM ziprasidone in treating acutely agitated patients with schizophrenia.

The effect of food on the absorption of oral ziprasidone

Oral ziprasidone bioavailability is increased when taken with food. Here we describe two pharmacokinetic studies to quantify the impact of food on ziprasidone absorption in healthy volunteers. The first, an open-label, six-way crossover study, investigated ziprasidone absorption in eight healthy men. Subjects received oral ziprasidone (20, 40, and 80 mg) after an 8-hour fast or immediately following a US Food and Drug Administration standard meal (50% fat). In this study, area under the serum concentration- time curve (AUC) was greater in fed than in fasting states at each dose (20 mg, +48%; 40 mg, +87%; 80 mg, +101%). Under fasting conditions, increases in AUC and maximum drug concentration (Cmax) were less than dose-proportional; under fed conditions, they were dose-proportional. The second, an open-label, randomized, three-way crossover study, explored the impact of dietary fat on ziprasidone absorption in 14 healthy subjects. Subjects received ziprasidone (40 mg) under three conditions: fasting, with a high-fat meal (60% fat), and with a moderate-fat (30% fat) meal. AUC and Cmax under fed conditions increased by 104% and 84% (60%-fat meal) and 79% and 98% (30%-fat meal) , respectively, relative to the fasting state. There was no clear difference in ziprasidone bioavailability between the fed groups, suggesting that meal fat content is not a major determinant of bioavailability. Less pharmacokinetic variability was observed in the fed state, suggesting more consistent absorption of ziprasidone. These results demonstrate that administration of ziprasidone with food is crucial to ensure optimal, reliable dose-dependent bioavailability and thus predictable symptom control and tolerability.

Single-dose pharmacokinetics and safety of ziprasidone in children and adolescents

OBJECTIVE

The purpose of this study was to provide single-dose pharmacokinetic, safety, and tolerability data for ziprasidone in youths with tic disorder, for comparison to adult studies to discern whether ziprasidone pediatric dosing could be modeled from adult data.

METHOD

A single-dose, open-label study of ziprasidone was conducted in youths (ages 7-16 years) with Tourette's disorder or chronic tic disorder. Dosing of ziprasidone oral suspension (40 mg/mL) was weight adjusted: >60 kg, 20 mg (group 1, n = 8); 31 to 60 kg, 10 mg (group 2, n = 8); and 16 to 30 kg, 5 mg (group 3, n = 8). Patients were assessed for serum ziprasidone concentration, safety, tolerability, and electrocardiogram pre- and postdose.

RESULTS

Twenty-four patients were evaluated for safety and tolerability, and 23 were evaluated for pharmacokinetics. Regression analysis of AUC(0-infinity) and Cmax values versus weight-normalized dose showed linear, dose-related changes in ziprasidone exposure. Ziprasidone was well tolerated with frequent, although transient, somnolence. No clinically significant change from baseline was observed in Bazett's or Fridericia's corrected QT(c) interval, and change in QT(c) interval was not related to serum ziprasidone concentration.

CONCLUSIONS

Oral ziprasidone exhibited linear pharmacokinetics and dose-related exposure in youths with Tourette's disorder or chronic tic disorder, which are comparable to adult data. A single dose of ziprasidone was well tolerated without clinically significant effects on electrocardiograms collected around the time of maximum serum concentration.

A randomized evaluation of the effects of six antipsychotic agents on QTc, in the absence and presence of metabolic inhibition

Many drugs have been associated with QTc prolongation and, in some cases, this is augmented by concomitant administration with metabolic inhibitors. The effects of 6 antipsychotics on the QTc interval at and around the time of estimated peak plasma/serum concentrations in the absence and presence of metabolic inhibition were characterized in a prospective, randomized study in which patients with psychotic disorders reached steady-state on either haloperidol 15 mg/d (n = 27), thioridazine 300 mg/d (n = 30), ziprasidone 160 mg/d (n = 31), quetiapine 750 mg/d (n = 27), olanzapine 20 mg/d (n = 24), or risperidone 6-8 mg/d increased to 16 mg/d (n = 25/20). Electrocardiograms (ECGs) were done at estimated Cmax at steady-state on both antipsychotic monotherapy and after concomitant administration of appropriate cytochrome P-450 (CYP450) inhibitor(s). Mean QTc intervals did not exceed 500 milliseconds in any patient taking any of the antipsychotics studied, in the absence or presence of metabolic inhibition. The mean QTc interval change was greatest in the thioridazine group, both in the presence and absence of metabolic inhibition. The presence of metabolic inhibition did not significantly augment QTc prolongation associated with any agent. Each of the antipsychotics studied was associated with measurable QTc prolongation at steady-state peak plasma concentrations, which was not augmented by metabolic inhibition. The theoretical risk of cardiotoxicity associated with QTc prolongation should be balanced against the substantial clinical benefits associated with atypical antipsychotics and the likelihood of other toxicities.

Pharmacodynamics of ziprasidone in children and adolescents: impact on dopamine transmission

OBJECTIVE

Ziprasidone is an atypical antipsychotic with a high ratio of 5-HT(2A) to D(2) receptor antagonism. It is also an agonist at 5-HT(1A), which has been shown in rats to increase dopamine in prefrontal cortex. The objective of this study was to probe the dopamine agonist and antagonist pharmacodynamic properties of ziprasidone in youth.

METHOD

A single-dose, open-label study was conducted in 24 youths, 7 to 16 years of age, with Tourette syndrome or chronic tic disorder. Ziprasidone oral suspension (40 mg/mL) was given to achieve 0.2 to 0.3 mg/kg. Patients were subsequently assessed for serum ziprasidone, serum prolactin, and eye blink rates.

RESULTS

Serum ziprasidone peaked 4 hours postdose. Prolactin (baseline mean 7.2 ng/mL, 95% confidence interval [CI] 5.2-9.2) peaked at 4 hours (mean 27.5 ng/mL, 95% CI 22.6-32.3). Eyeblink rates per 5 minutes (baseline mean 60, 95% CI 42-79) peaked at 6 hours (mean 74, 95% CI 52-96).

CONCLUSIONS

Ziprasidone acutely blocks dopamine transmission, as indicated by increased prolactin levels, and, in a delayed fashion, appears to stimulate dopaminergic transmission, as indicated by the increase in spontaneous eye blinks. The mechanism of dopaminergic stimulation is presumed to be indirect, via 5-HT(1A) agonism.

Ziprasidone metabolism, aldehyde oxidase, and clinical implications

Ziprasidone (Geodon, Zeldox), a recently approved atypical antipsychotic agent for the treatment of schizophrenia, undergoes extensive metabolism in humans with very little (<5%) of the dose excreted as unchanged drug. Two enzyme systems have been implicated in ziprasidone metabolism: the cytosolic enzyme, aldehyde oxidase, catalyzes the predominant reductive pathway, and cytochrome P4503A4 (CYP3A4) is responsible for two alternative oxidation pathways. The involvement of two competing pathways in ziprasidone metabolism greatly reduces the potential for pharmacokinetic interactions between ziprasidone and other drugs. Because CYP3A4 only mediates one third of ziprasidone metabolism, the likelihood of interactions between ziprasidone and CYP3A4 inhibitors/ substrates is low. Furthermore, aldehyde oxidase activity does not appear to be altered when drugs or xenobiotics are coadministered. Aldehyde oxidase, a molybdenum-containing enzyme, catalyzes the oxidation of N-heterocyclic drugs such as famciclovir and zaleplon, in addition to reducing some agents such as zonisamide. Both reactions can occur simultaneously. Although in vitro inhibitors of aldehyde oxidase have been identified, there are no reported clinical interactions with aldehyde oxidase inhibitors or inducers. There is no evidence of genetic polymorphism in aldehyde oxidase, and thus it not surprising that ziprasidone exposure demonstrates unimodality in humans. Aldehyde oxidase is unrelated to the similarly named enzyme aldehyde dehydrogenase, which is predominantly responsible for the oxidation of acetaldehyde during ethanol metabolism. Consequently, it is unlikely that there would be any pharmacokinetic interaction between ethanol and ziprasidone.

The anxiolytic effect of the novel antipsychotic ziprasidone compared with diazepam in subjects anxious before dental surgery

The novel atypical antipsychotic ziprasidone has a pharmacologic profile notable for potent agonism of serotonin (5-HT)1A receptors, antagonism at 5-HT1D receptors, and reuptake inhibition of norepinephrine. 5-HT1A receptor agonism, in particular, suggests anxiolytic activity, and ziprasidone has shown preliminary efficacy in treating the symptoms of anxiety associated with psychotic disorders. In this study, the anxiolytic efficacy of ziprasidone was evaluated in nonpsychotic subjects who were anxious before undergoing minor dental surgery. We compared a single oral dose of 20 mg ziprasidone (N = 30) with that of 10 mg diazepam (N = 30) and placebo (N = 30) in a randomized, parallel-group, double-blind study. The peak anxiolytic effect of ziprasidone compared with that of placebo was similar to that of diazepam but had a later onset. At 3 hours postdose, the anxiolytic effect of ziprasidone was significantly greater than that of placebo (p < 0.05) and somewhat greater than that of diazepam. Diazepam showed a significantly greater anxiolytic effect than placebo at 1 hour (p < 0.05) but not at 3 hours. The sedative effect of ziprasidone was never greater than that of placebo, whereas that of diazepam was significantly greater than that of placebo 1 to 1.5 hours postdose. Ziprasidone was generally well tolerated. Only one patient reported treatment-related adverse events (nausea and vomiting) and, unlike diazepam, ziprasidone did not cause reductions in blood pressure. Dystonia, extrapyramidal syndrome, akathisia, and postural hypotension were not seen with ziprasidone. Thus, ziprasidone may possess anxiolytic effects in addition to its antipsychotic properties.

The effect of carbamazepine on the steady-state pharmacokinetics of ziprasidone in healthy volunteers

AIMS

To evaluate the effect of steady-state carbamazepine administration on the steady-state pharmacokinetics of ziprasidone in healthy young adults, in an open, randomised, parallel-group study.

METHODS

Twenty-five subjects were randomized to one of two treatment groups. Group 1 received 20 mg ziprasidone twice daily on days 1 and 2, and a single dose on day 3. A single 100 mg dose of carbamazepine was given once daily on days 5 and 6 and twice daily on days 7 and 8, followed by 200 mg twice daily until day 28 and on the morning only on day 29. Ziprasidone 20 mg was also administered twice daily on days 26 and 27 and in the morning only on day 28. Group 2 received the same treatment regimen with carbamazepine replaced by placebo. Pharmacokinetic data were obtained on days 3 and 28.

RESULTS

Nine subjects in group 1 and 10 in group 2 completed all three treatment periods (ziprasidone, carbamazepine or placebo; and ziprasidone plus carbamazepine or placebo). Carbamazepine administration to group 1 was associated with modest reductions in ziprasidone exposure, with mean decreases in ziprasidone AUC(0,12 h) and Cmax values of 36% and 27%, respectively, on day 28 compared with day 3 (P<0.03). The mean differences between day 28 and day 3 ziprasidone AUC(0,12 h) and Cmax values were also statistically significantly greater in the carbamazepine group than in the placebo group. The mean half-life of ziprasidone decreased by 1 h from day 3 to day 28 in the subjects receiving carbamazepine, compared with virtually no change in the placebo group. All adverse events were mild or moderate in severity and there were no serious adverse events, or clinically significant changes in ECGs and vital signs throughout the study.

CONCLUSIONS

Induction of CYP3A4 with carbamazepine led to a modest reduction (<36%) in steady-state exposure to ziprasidone that is believed to be clinically insignificant.

Single- and multiple-dose pharmacokinetics of ziprasidone under non-fasting conditions in healthy male volunteers

AIMS

To evaluate the pharmacokinetics and tolerability of single and multiple oral doses of ziprasidone in healthy male volunteers, and to determine the influence of ziprasidone on serum prolactin levels.

METHODS

Single and multiple doses of ziprasidone were given orally (as two divided daily doses), at fixed dosages of 10 and 40 mg day(-1), and using titrated regimens of 40-80 and 40-120 mg day(-1), for 14 days. All dosages were taken immediately after food. The study adopted a randomized, double-blind, placebo-controlled design. Prolactin response, sedative properties, tolerability, and extrapyramidal symptoms were also investigated.

RESULTS

Steady-state exposure to ziprasidone was attained after 1 day of dosing. Mean Cmax and AUC(0,12 h) increased with increasing dose, with apparent dose-proportionality between the 20 and 60 mg dose levels. Trough-to-peak ratios at steady state ranged from 2 to 5. Accumulation ratios for the fixed-dose regimens were 1.49 and 1.48 at the 5 and 20 mg dose levels, respectively. Ziprasidone was associated with transient prolactin elevation but levels of prolactin returned to baseline within the dosing interval at steady state. There was a marginal, transient increase in serum prolactin levels which was not dose-related at the 80 and 120 mg day(-1) doses, and which was noted to attenuate with chronic dosing. Ziprasidone was generally well tolerated. The most frequent side-effect was mild or moderate headache. A minority of patients suffered first-dose postural hypotension. Ziprasidone was also associated with a mild sedative effect that became less pronounced as treatment continued. There were no drug-related changes in electrocardiogram or clinical laboratory variables that were of clinical importance.

CONCLUSIONS

Ziprasidone is characterized by a predictable pharmacokinetic profile resulting in symptoms that reflect its pharmacological action.

Identification of the major human liver cytochrome P450 isoform(s) responsible for the formation of the primary metabolites of ziprasidone and prediction of possible drug interactions

AIMS

To identify the cytochrome P450 (CYP) isoform(s) responsible for the formation of the primary metabolite of ziprasidone (ziprasidone sulphoxide), to determine the kinetics of its formation and to predict possible drug interactions by investigating CYP isoform inhibition in an in vitro study.

METHODS

In vitro metabolism of [14C]-ziprasidone was studied using human liver microsomes. The metabolites were identified using mass spectrometry. The kinetics of metabolite formation were determined using [14C]-ziprasidone (10-200 microM) over 5 min, and Km and Vmax were estimated from Lineweaver-Burk plots. IC50 values for the inhibition of specific probe substrates for CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4, by ziprasidone, risperidone and 9-hydroxyrisperidone were also determined using human liver microsomes from three subjects. Mean Ki values were calculated.

RESULTS

Three CYP-mediated metabolites - ziprasidone sulphoxide, ziprasidone sulphone and oxindole acetic acid - were identified. The apparent Km and Vmax values for the formation of the major metabolite, ziprasidone sulphoxide (measured as the sum of sulphoxide and sulphone) were 235 microM and 1.14 nmol mg(-1) protein min(-1), respectively. Isoform-selective inhibitors and recombinant enzymes indicated that CYP3A4 is responsible for the formation of ziprasidone metabolites. Ziprasidone was not a substrate for the other isoforms studied. Similar in vitro inhibition of CYP2D6 (Ki 6.9-16 microM) and CYP3A4 (Ki 64-80 microM) was obtained with ziprasidone, risperidone and 9-hydroxyrisperidone. The in vivo free drug concentrations associated with clinically effective doses of ziprasidone are at least 1500-fold lower than the mean Ki for either CYP2D6 inhibition or CYP3A4 inhibition.

CONCLUSIONS

Ziprasidone is predominantly metabolized by CYP3A4 in human liver microsomes and is not expected to mediate drug interactions with coadministered CYP substrates, at clinically effective doses.

The effects of ketoconazole on ziprasidone pharmacokinetics--a placebo-controlled crossover study in healthy volunteers

AIMS

To assess the effects of multiple oral doses of ketoconazole on the single-dose pharmacokinetics of oral ziprasidone HCl.

METHODS

This was a 14-day, open-label, randomized, crossover study in 14 healthy subjects aged 18-31 years. Group 1 received oral ketoconazole 400 mg once daily for 6 days, followed by a 2 day wash-out period and 6 days of placebo administration. Group 2 received placebo followed by ketoconazole. Single oral doses of ziprasidone HCl 40 mg were administered on days 5 and 13 in both groups. Ziprasidone pharmacokinetic parameters were compared between placebo and ketoconazole administration periods.

RESULTS

Co-administration of ziprasidone with ketoconazole was associated with a modest increase in ziprasidone exposure; mean ziprasidone AUC(0,infinity) increased by 33%, from 899 ng ml(-1) h with placebo to 1199 ng ml(-1) h with ketoconazole. Mean Cmax increased by 34%, from 89 ng ml(-1) to 119 ng ml(-1), respectively. The treatment effect on both of these parameters was statistically significant (P<0.02). Most adverse events were of mild intensity. There were no serious adverse events, laboratory abnormalities, abnormal ECGs, or clinically significant alterations in vital signs throughout the study.

CONCLUSIONS

The concurrent administration of ketoconazole and ziprasidone led to modest, statistically significant increases in ziprasidone exposure, although the changes seen were not considered clinically relevant. This suggests that other inhibitors of CYP3A4 are unlikely to significantly affect the pharmacokinetics of ziprasidone.

Bioavailability studies of drugs with nonlinear pharmacokinetics: II. Absolute bioavailability of intravenous phenytoin prodrug at therapeutic phenytoin serum concentrations determined by double-stable isotope technique

Measurement of the absolute bioavailability of phenytoin (PHT) derived from test doses of phenytoin prodrug (PPD) at therapeutic PHT serum concentrations is complicated by two problems: 1) the area under the serum concentration versus time curve (AUC) produced by a given size of test dose will vary directly with background PHT serum concentration due to the nonlinear pharmacokinetic properties of PHT; 2) PPD is more water soluble than PHT, making renal excretion of PPD more likely. The authors describe a double-stable isotope method that obviates these two problems. Using only six subjects, the authors were able to demonstrate bioequivalence of PHT derived from intravenous PPD with intravenous PHT by current FDA standards for AUC ratio of test/reference formulation (90% confidence intervals between 0.80 and 1.20; ratio > or = 0.80 in > or = 80% of subjects; statistical power to detect a difference of 0.20 with a probability of 0.80).

Pharmacokinetics and dynamics of furosemide in the newborn piglet

Furosemide was administered as either an i.v. bolus (6 mg/kg) or primed continuous infusion (4 mg/kg/hr) with quantitative fluid replacement to 10 3-day-old and 9 18-day old piglets. Total and unbound plasma as well as urinary furosemide concentrations were measured for up to 6 hr and drug disposition and renal sodium excretory dynamics were compared at the two ages. The plasma clearance of furosemide was concentration-independent over the range studied (0.1-10 mg/l). Steady-state volume of distribution and unbound fraction of furosemide in plasma were both considerably higher in the younger piglets (618 +/- 320 vs. 201 +/- 71 ml/kg, p less than .01 and 0.22 +/- 0.08 vs. 0.06 +/- 0.02 ml/kg, p less than .001, respectively) while unbound secretory clearance was several-fold lower in this age group (49.2 +/- 23 vs. 107 +/- 55 ml/min/kg, P less than .01). A log-logistic equation was fitted to sigmoidal plots of sodium excretion rate vs. log furosemide excretion rate. While basal response and slope parameters did not differ significantly, maximal response and stimulus required for half-maximal response were both reduced in the younger piglets (0.70 +/- 0.24 vs. 1.18 +/- 0.30 mmol/min and 0.06 +/- 0.04 vs. 0.14 +/- 0.06 mumol/min, respectively, P less than 0.05). Thus, younger piglets were more sensitive to the natriuretic effects of the drug. While term piglets were useful for studying the maturation of protein binding and renal drug excretory processes for furosemide, drug disposition was not comparable to that in human premature infants because of the higher secretory capability of the piglet.

Renal response to furosemide in very low birth weight infants during chronic administration

Renal response to furosemide following initial and chronic doses was investigated in premature infants with bronchopulmonary dysplasia. Seven infants (mean birth weight = 890 +/- 216 g, mean gestational age at birth = 27.7 +/- 2.6 weeks, mean postnatal age at the start of diuretic therapy = 2.7 +/- 0.9 weeks) were studied. Twelve-hour urine collections were performed after the initial dose, and following chronic doses after 1 week and 3 weeks of therapy. Volume of each urine sample was measured and concentrations of furosemide, sodium and creatinine determined. Linear dose-response relationships were found between the logarithm of the urinary furosemide excretion rate and diuretic/natriuretic response (urine output and urinary sodium excretion rate). The furosemide excretion rate required to achieve midrange diuretic and natriuretic responses was significantly greater during chronic dosing than following initial doses, indicating a decrease in renal responsiveness to drug with sustained use. Increasing postconceptional age was associated with a decrease in initial responsiveness to furosemide. These data demonstrate that in premature infants renal sensitivity to furosemide decreases with chronic use as well as with increasing postconceptional age at the start of therapy. The decrease in renal sensitivity to drug with chronic use is of much greater magnitude, and appears to represent renal compensation for drug-induced diuresis and natriuresis.

Furosemide pharmacokinetics in very low birth weight infants

The pharmacokinetics of furosemide were studied longitudinally during long-term administration in 10 very low birth weight infants with bronchopulmonary dysplasia. Mean birth weight of the infants was 829 +/- 217 g, mean gestational age at birth was 26.6 +/- 2.9 weeks, and mean postnatal age at the start of therapy was 2.4 +/- 1.0 weeks. Serial determinations of furosemide pharmacokinetic parameters were performed during 2 weeks to 3 months of long-term therapy. Plasma half-life was prolonged in infants less than 31 weeks postconceptional age (gestational + postnatal age), frequently exceeding 24 hours. All infants less than 29 weeks postconceptional age whose dosing schedule was once every 12 hours accumulated furosemide to potentially ototoxic levels. Furosemide renal clearance increased and plasma half-life decreased in association with increasing postconceptional age. Furosemide secretory clearance was very low in patients less than 31 weeks postconceptional age, resulting in a reliance on glomerular filtration to deliver drug to its main site of action within the lumen of the loop of Henle. Thus elevated plasma levels may be required to ensure adequate luminal delivery and adequate diuresis in these infants with low secretory clearance. Nevertheless, the current dosing schedule (once every 12 hours) of furosemide should be modified to once every 24 hours in infants of low postconceptional age to avoid possible toxic effects.

Model for gradient formation in polycrystalline germanium-silicon alloy GRIN crystals via Czochralski crystal growing

A mathematical model has been developed which describes the silicon composition gradient produced in germanium-silicon alloy GRIN crystals formed via Czochralski crystal growing. This model is based on the naturally occurring segregation effect of silicon in germanium. The refractive index of the alloy is described in terms of its relation to the band gap energy, which is itself dependent on the silicon composition. A relationship between refractive index and silicon composition of the alloy is derived.

Measurement of the refractive-index profile in polycrystalline germanium-silicon alloy GRIN crystals

The refractive index as a function of spatial coordinate in three Czochralski grown germanium-silicon alloy GRIN crystals has been measured using ac interferometric techniques. The interferometer is capable of high phase resolution and is computer controlled for real-time data processing. The measured refractive-index profiles were compared to theoretical profiles which were calculated from a model based on the segregation effect of silicon in germanium.

Gradient-index eyepiece design

A study of gradient-index eyepieces was conducted. The general performance of homogeneous eyepieces having two and three elements was examined. Axial gradients were introduced into the eyepieces in an attempt to increase the half-fields of view to 25 degrees and extend the eye reliefs to 12 mm. The homogeneous eyepieces examined were of the Huygenian, Ramsden, and Kellner configurations. These eyepieces were scaled to the specifications of f/13, 21.4-mm focal length, and magnifying power of 10X. These classic systems were optimized to produce two- and three-element homogeneous eyepieces to determine how homogeneous systems could perform with the extended eye relief and larger field of view. Axial gradient eyepieces having two and three elements were designed to the same specifications. The balance of third-order aberrations, color, and distortion was maintained or improved compared to the homogeneous systems.. The additional degrees of freedom associated with the gradient made it possible to extend the eye relief and increase the field of view of these eyepieces.