CLINICAL PHARMACOLOGY
Mechanism Of Action
Sotalol has both beta-adrenoreceptor blocking (Vaughan Williams
Class II) and cardiac action potential duration prolongation (Vaughan Williams
Class III) antiarrhythmic properties. Sotalol hydrochloride is a racemic
mixture of two isomers, both of which have similar Class III antiarrhythmic
effects, while the l-isomer is responsible for virtually all of the
beta-blocking activity. The beta-blocking effect of sotalol is
non-cardioselective, half maximal at an oral dose of about 80 mg/day and
maximal at doses between 320 and 640 mg/day. Sotalol does not have partial
agonist or membrane stabilizing activity. Although significant beta-blockade
occurs at oral doses as low as 25 mg, significant Class III effects are seen
only at daily doses of 160 mg and above.
In children, a Class III electrophysiological effect can
be seen at daily doses of 210 mg/m² body surface area (BSA). A reduction of the
resting heart rate due to the beta-blocking effect of sotalol is observed at
daily doses ≥ 90 mg/m² in children.
Pharmacodynamics
Electrophysiology
Sotalol prolongs the plateau phase of the cardiac action
potential in the isolated myocyte, as well as in isolated tissue preparations
of ventricular or atrial muscle (Class III activity). In intact animals it
slows heart rate, decreases AV nodal conduction and increases the refractory
periods of atrial and ventricular muscle and conduction tissue.
In man, the Class II (beta-blockade) electrophysiological
effects of sotalol are manifested by increased sinus cycle length (slowed heart
rate), decreased AV nodal conduction and increased AV nodal refractoriness. The
Class III electrophysiological effects in man include prolongation of the
atrial and ventricular monophasic action potentials, and effective refractory
period prolongation of atrial muscle, ventricular muscle, and atrio-ventricular
accessory pathways (where present) in both the anterograde and retrograde
directions. With oral doses of 160 to 640 mg/day, the surface ECG shows
dose-related mean increases of 40-100 msec in QT and 10-40 msec in QTc. In a
study of patients with atrial fibrillation/flutter (AFIB/AFL) receiving three
different oral doses of sotalol given q12h (or q24h in patients with a reduced
creatinine clearance), mean increases in QT intervals measured from 12-lead
ECGs of 25 msec, 40 msec and 54 msec were found in the 80 mg, 120 mg, and 160
mg dose groups, respectively [see WARNINGS AND PRECAUTIONS]. No
significant alteration in QRS interval was observed.
In a small study (n=25) of patients with implanted
defibrillators treated concurrently with sotalol, the average defibrillatory
threshold was 6 joules (range 2-15 joules) compared to a mean of 16 joules for
a non-randomized comparative group primarily receiving amiodarone.
In a dose-response trial comparing three dose levels of sotalol,
80 mg, 120 mg, and 160 mg with placebo given every 12 hours (or every 24 hours
in patients with a reduced renal creatinine clearance) for the prevention of
recurrence of symptomatic atrial fibrillation (AFIB)/flutter (AFL), the mean
ventricular rate during recurrence of AFIB/AFL was 125, 107, 110 and 99
beats/min in the placebo, 80 mg, 120 mg and 160 mg dose groups, respectively
(p < 0.017 for each sotalol dose group versus placebo). In another placebo
controlled trial in which sotalol was titrated to a dose between 160 and 320
mg/day in patients with chronic AFIB, the mean ventricular rate during
recurrence of AFIB was 107 and 84 beats/min in the placebo and sotalol groups,
respectively (p < 0.001).
Twenty-five children in an unblinded, multicenter trial
with supraventricular (SVT) and/or ventricular (VT) tachyarrhythmias, aged
between 3 days and 12 years (mostly neonates and infants), received an
ascending titration regimen with daily doses of 30, 90 and 210 mg/m² with
dosing every 8 hours for a total of 9 doses. During steady-state, the
respective average increases above baseline of the QTc interval, in msec (%),
were 2(+1%), 14(+4%) and 29(+7%) msec at the 3 dose levels. The respective mean
maximum increases above baseline of the QTc interval, in msec (%), were
23(+6%), 36(+9%) and 55(+14%) msec at the 3 dose levels. The steady-state
percent increases in the RR interval were 3, 9 and 12%. The smallest children
(BSA < 0.33m²) showed a tendency for larger Class III effects (ΔQTc) and
an increased frequency of prolongations of the QTc interval as compared with
the larger children (BSA ≥ 0.33m²). The beta-blocking effects also tended
to be greater in the smaller children (BSA < 0.33m²). Both the Class III and
beta-blocking effects of sotalol were linearly related with the plasma
concentrations.
Hemodynamics
In a study of systemic hemodynamic function measured
invasively in 12 patients with a mean LV ejection fraction of 37% and
ventricular tachycardia (9 sustained and 3 non-sustained), a median dose of 160
mg twice daily of sotalol produced a 28% reduction in heart rate and a 24%
decrease in cardiac index at 2 hours post-dosing at steady-state. Concurrently,
systemic vascular resistance and stroke volume showed non-significant increases
of 25% and 8%, respectively. Pulmonary capillary wedge pressure increased
significantly from 6.4 mmHg to 11.8 mmHg in the 11 patients who completed the
study. One patient was discontinued because of worsening congestive heart
failure. Mean arterial pressure, mean pulmonary artery pressure and stroke work
index did not significantly change. Exercise and isoproterenol induced
tachycardia are antagonized by sotalol, and total peripheral resistance
increases by a small amount.
In hypertensive patients, sotalol produces significant
reductions in both systolic and diastolic blood pressures. Although sotalol is
usually well-tolerated hemodynamically, in patients with marginal cardiac
compensation, deterioration in cardiac performance may occur [see WARNINGS
AND PRECAUTIONS].
Pharmacokinetics
In healthy subjects, the oral bioavailability of sotalol
is 90-100%. After oral administration, peak plasma concentrations are reached
in 2.5 to 4 hours, and steady-state plasma concentrations are attained within
2-3 days (i.e., after 5-6 doses when administered twice daily). Over the oral
dosage range 160-640 mg/day sotalol displays dose proportionality with respect
to plasma concentrations. Distribution occurs to a central (plasma) and to a
peripheral compartment, with a mean elimination half-life of 12 hours. Dosing
every 12 hours results in trough plasma concentrations, which are approximately
one-half of those at peak.
Sotalol does not bind to plasma proteins and is not
metabolized. Sotalol shows very little intersubject variability in plasma
levels. The pharmacokinetics of the d and l enantiomers of sotalol are
essentially identical. Sotalol crosses the blood brain barrier poorly.
Excretion is predominantly via the kidney in the unchanged form, and therefore
lower doses are necessary in conditions of renal impairment [see DOSAGE AND
ADMINISTRATION]. Age per se does not significantly alter the
pharmacokinetics of sotalol, but impaired renal function in geriatric patients
can increase the terminal elimination half-life, resulting in increased drug
accumulation. The absorption of sotalol was reduced by approximately 20%
compared to fasting when it was administered with a standard meal. Since
sotalol is not subject to first-pass metabolism, patients with hepatic
impairment show no alteration in clearance of sotalol.
The combined analysis of two unblinded, multicenter
trials (a single dose and a multiple dose study) with 59 children, aged between
3 days and 12 years, showed the pharmacokinetics of sotalol to be first order.
A daily dose of 30 mg/m² of sotalol was administered in the single dose study
and daily doses of 30, 90 and 210 mg/m² were administered every 8 hours in the
multi-dose study. After rapid absorption with peak levels occurring on average
between 2-3 hours following administration, sotalol was eliminated with a mean
half-life of 9.5 hours. Steady-state was reached after 1-2 days. The average
peak to trough concentration ratio was 2. BSA was the most important covariate
and more relevant than age for the pharmacokinetics of sotalol. The smallest
children (BSA < 0.33m²) exhibited a greater drug exposure (+59%) than the
larger children who showed a uniform drug concentration profile. The
intersubject variation for oral clearance was 22%.
Clinical Studies
Clinical Studies In Ventricular Arrhythmias
Oral sotalol has been studied in life-threatening and
less severe arrhythmias. In patients with frequent premature ventricular
complexes (VPC), sotalol was significantly superior to placebo in reducing
VPCs, paired VPCs and non-sustained ventricular tachycardia (NSVT); the
response was dose-related through 640 mg/day with 80-85% of patients having at
least a 75% reduction of VPCs. Sotalol was also superior, at the doses
evaluated, to propranolol (40-80 mg TID) and similar to quinidine (200-400 mg
QID) in reducing VPCs. In patients with life threatening arrhythmias [sustained
ventricular tachycardia/fibrillation (VT/VF)], sotalol was studied acutely [by
suppression of programmed electrical stimulation (PES) induced VT and by
suppression of Holter monitor evidence of sustained VT] and, in acute
responders, chronically.
In a double-blind, randomized comparison of sotalol and
procainamide given intravenously (total of 2 mg/kg sotalol vs. 19 mg/kg of
procainamide over 90 minutes), sotalol suppressed PES induction in 30% of
patients vs. 20% for procainamide (p=0.2).
In a randomized clinical trial [Electrophysiologic Study
Versus Electrocardiographic Monitoring (ESVEM) Trial] comparing choice of
antiarrhythmic therapy by PES suppression vs. Holter monitor selection (in each
case followed by treadmill exercise testing) in patients with a history of
sustained VT/VF who were also inducible by PES, the effectiveness acutely and
chronically of sotalol hydrochloride was compared with 6 other drugs
(procainamide, quinidine, mexiletine, propafenone, and imipramine). Overall
response, limited to first randomized drug, was 39% for sotalol and 30% for the
pooled other drugs. Acute response rate for first drug randomized using
suppression of PES induction was 36% for sotalol vs. a mean of 13% for the
other drugs. Using the Holter monitoring endpoint (complete suppression of
sustained VT, 90% suppression of NSVT, 80% suppression of VPC pairs, and at
least 70% suppression of VPCs), sotalol yielded 41% response vs. 45% for the
other drugs combined. Among responders placed on long-term therapy identified
acutely as effective (by either PES or Holter), sotalol, when compared to the
pool of other drugs, had the lowest two-year mortality (13% vs. 22%), the
lowest two-year VT recurrence rate (30% vs. 60%), and the lowest withdrawal
rate (38% vs. about 7580%). The most commonly used doses of sotalol
hydrochloride in this trial were 320480 mg/day (66% of patients), with 16%
receiving 240 mg/day or less and 18% receiving 640 mg or more. It cannot be
determined, however, in the absence of a controlled comparison of sotalol vs.
no pharmacologic treatment (e.g., in patients with implanted defibrillators)
whether sotalol response causes improved survival or identifies a population
with a good prognosis.
Clinical Studies In Supra-Ventricular Arrhythmias
Sotalol has been studied in patients with symptomatic
AFIB/AFL in two principal studies, one in patients with primarily paroxysmal
AFIB/AFL, the other in patients with primarily chronic AFIB.
In one study, a U.S. multicenter, randomized,
placebo-controlled, double-blind, dose-response trial of patients with
symptomatic primarily paroxysmal AFIB/AFL, three fixed dose levels of sotalol
hydrochloride (80 mg, 120 mg and 160 mg) twice daily and placebo were compared
in 253 patients. In patients with reduced creatinine clearance (40-60 mL/min)
the same doses were given once daily. Patients were not randomized for the
following reasons: QT > 450 msec; creatinine clearance < 40 mL/min; intolerance
to beta-blockers; bradycardia-tachycardia syndrome in the absence of an
implanted pacemaker; AFIB/AFL was asymptomatic or was associated with syncope,
embolic CVA or TIA; acute myocardial infarction within the previous 2 months;
congestive heart failure; bronchial asthma or other contraindications to
beta-blocker therapy; receiving potassium losing diuretics without potassium
replacement or without concurrent use of ACE-inhibitors; uncorrected
hypokalemia (serum potassium < 3.5 meq/L) or hypomagnesemia (serum magnesium
< 1.5 meq/L); received chronic oral amiodarone therapy for > 1 month within
previous 12 weeks; congenital or acquired long QT syndromes; history of Torsade
de Pointes with other antiarrhythmic agents which increase the duration of
ventricular repolarization; sinus rate < 50 bpm during waking hours; unstable
angina pectoris; receiving treatment with other drugs that prolong the QT
interval; and AFIB/AFL associated with the Wolff-Parkinson-White (WPW)
syndrome. If the QT interval increased to ≥ 520 msec (or JT ≥ 430
msec if QRS > 100 msec) the drug was discontinued. The patient population in
this trial was 64% male, and the mean age was 62 years. No structural heart
disease was present in 43% of the patients. Doses were administered once daily
in 20% of the patients because of reduced creatinine clearance.
Sotalol was shown to prolong the time to the first
symptomatic, ECG-documented recurrence of AFIB/AFL, as well as to reduce the
risk of such recurrence at both 6 and 12 months. The 120 mg dose was more
effective than 80 mg, but 160 mg did not appear to have an added benefit. Note
that these doses were given twice or once daily, depending on renal function.
The results are shown in Figure 2, Table 5 and Table 6.
Figure 2: Study 1 – Time to First ECG-Documented
Recurrence of Symptomatic AFIB/AFL Since Randomization
Table 5: Study 1 – Patient Status at 12 Months
|
Placebo |
Sotalol Dose |
80 mg |
120 mg |
160 mg |
Randomized |
69 |
59 |
63 |
62 |
On treatment in NSR at 12 months without recurrencea |
23% |
22% |
29% |
23% |
Recurrenceab |
67% |
58% |
49% |
42% |
D/C for AEs |
6% |
12% |
18% |
29% |
a Symptomatic AFIB/AFL
b Efficacy endpoint of Study 1; study treatment stopped.
Note that columns do not add up to 100% due to discontinuations (D/C) for
“other” reasons. |
Table 6: Study 1 – Median Time to Recurrence of
Symptomatic AFIB/AFL and Relative Risk (vs. Placebo) at 12 Months
|
Placebo |
Oral Sotalol Dose |
80 mg |
120 mg |
160 mg |
p-value vs. placebo |
|
p=0.32 5 |
p=0.01 8 |
p=0.02 9 |
Relative Risk (RR) to placebo |
|
0.81 |
0.59 |
0.59 |
Median time to recurren ce (days) |
27 |
106 |
229 |
175 |
Discontinuation because of adverse events was dose
related.
In a second multicenter, randomized, placebo-controlled,
double-blind study of 6 months duration in 232 patients with chronic AFIB, oral
sotalol was titrated over a dose range from 80 mg/day to 320 mg/day. The
patient population of this trial was 70% male with a mean age of 65 years.
Structural heart disease was present in 49% of the patients. All patients had
chronic AFIB for > 2 weeks but < 1 year at entry with a mean duration of
4.1 months. Patients were excluded if they had significant electrolyte
imbalance, QTc > 460 msec, QRS > 140 msec, any degree of AV block or
functioning pacemaker, uncompensated cardiac failure, asthma, significant renal
disease (estimated creatinine clearance < 50 mL/min), heart rate < 50 bpm,
myocardial infarction or open heart surgery in past 2 months, unstable angina,
infective endocarditis, active pericarditis or myocarditis, ≥ 3 DC
cardioversions in the past, medications that prolonged QT interval, and
previous amiodarone treatment. After successful cardioversion patients were
randomized to receive placebo (n=114) or sotalol (n=118), at a starting dose of
80 mg twice daily. If the initial dose was not tolerated it was decreased to 80
mg once daily, but if it was tolerated it was increased to 160 mg twice daily.
During the maintenance period 67% of treated patients received a dose of 160 mg
twice daily, and the remainder received doses of 80 mg once daily (17%) and 80
mg twice daily (16%).
Tables 7 and 8 show the results of the trial. There was a
longer time to ECG-documented recurrence of AFIB and a reduced risk of
recurrence at 6 months compared to placebo.
Table 7: Study 2 – Patient Status at 6 Months
Randomized |
Oral Sotalol |
Placebo |
118 |
114 |
On treatment in NSR at 6 months without recurrencea |
45% |
29% |
Recurrenceab |
49% |
67% |
D/C for AEs |
6% |
3% |
Death |
|
1% |
a Symptomatic or asymptomatic AFIB/AFL
b Efficacy endpoint of Study 2; study treatment |
Table 8: Study 2 – Median Time to Recurrence of
Symptomatic AFIB/AFL/Death and Relative Risk (vs. Placebo) at 6 Months
p-value vs. placebo |
Oral Sotalol |
Placebo |
p=0.002 |
|
Relative Risk (RR) to placebo |
0.55 |
|
Median time to recurrence (days) |
> 180 |
44 |
Figure 3: Study 2 – Time to First ECG-Documented
Recurrence of Symptomatic AFIB/AFL/Death Since Randomization
Clinical Studies In Patients With Myocardial Infarction
In a multicenter double-blind randomized study, the
effect of sotalol 320 mg once daily was compared with that of placebo in 1456
patients (randomized 3:2, sotalol to placebo) surviving an acute myocardial
infarction (MI). Treatment was started 5-14 days after infarction. Patients
were followed for 12 months. The mortality rate was 7.3% in the sotalol group
and 8.9% in the placebo group, not a statistically significant difference.
Although the results do not show evidence of a benefit of sotalol in this
population, they do not show an added risk in post MI patients receiving
sotalol. There was, however, a suggestion of an early (i.e., first 10 days)
excess mortality (3% on sotalol vs. 2% on placebo).
In a second small trial (n=17 randomized to sotalol)
where sotalol was administered at high doses (e.g., 320 mg twice daily) to
high-risk postinfarction patients (ejection fraction < 40% and either > 10
VPC/hr or VT on Holter), there were 4 fatalities and 3 serious
hemodynamic/electrical adverse events within two weeks of initiating sotalol.