4.4       Special warnings and precautions for use

 

The physician should not prescribe clarithromycin I.V. to pregnant women without carefully weighing the benefits against risk, particularly during the first three months of pregnancy.

 

Clarithromycin is principally excreted by the liver and kidney. Caution should be exercised in administering this antibiotic to patients with impaired hepatic and renal function or those concomitantly receiving potentially hepatotoxic drugs.

 

Attention should be paid to the possibility of cross-resistance between clarithromycin and other macrolide drugs, as well as lincomycin and clindamycin.

 

Prolonged or repeated use of clarithromycin may result in overgrowth of non-susceptible bacteria.   If super-infection occurs, clarithromycin should be discontinued and appropriate therapy instituted.

 

There have been post-marketing reports of colchicine toxicity with concomitant use of clarithromycin and colchicine, especially in the elderly, some of which occurred in patients with renal insufficiency. Deaths have been reported in some such patients (see section 4.5).

 

Pseudomembranous colitis has been reported with nearly all antibacterial agents, including macrolides, and may range in severity from mild to life-threatening. Clostridium difficile associated diarrhoea (CDAD) has been reported with use of nearly all antibacterial agents including clarithromycin, and may range in severity from mild diarrhoea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon, which may lead to overgrowth of C. difficile.

 

CDAD must be considered in all patients who present with diarrhoea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.

 

Exacerbation of symptoms of myasthenia gravis has been reported in patients receiving clarithromycin therapy.

 

4.5       Interaction with other medicinal products and other forms of interaction

 

 

The use of the following drugs is strictly contraindicated due to the potential for severe drug interaction effects:

 

Elevated cisapride levels have been reported in patients receiving clarithromycin and cisapride concomitantly. This may result in QT prolongation and cardiac arrhythmias including ventricular tachycardia, ventricular fibrillation and torsades de pointes. Similar effects have been observed in patients, taking clarithromycin and pimozide concomitantly (see section 4.3, Contraindications).

 

Macrolides have been reported to alter the metabolism of terfenadine resulting in increased levels of terfenadine which has occasionally been associated with cardiac arrhythmias, such as QT prolongation, ventricular tachycardia, ventricular fibrillation and torsades de pointes (see section 4.3, Contraindications). In one study in 14 healthy volunteers, the concomitant administration of clarithromycin (tablets) and terfenadine resulted in a 2 to 3-fold increase in the serum level of the acid metabolite of terfenadine and in prolongation of the QT interval which did not lead to any clinically detectable effect.  Similar effects have been observed with concomitant administration of astemizole and other macrolides.

 

Ergotamine/dihydroergotamine

Post-marketing reports indicate that co-administration of clarithromycin with ergotamine or dihydroergotamine has been associated with acute ergot toxicity characterized by vasospasm, and ischemia of the extremities and other tissues including the central nervous system. Concomitant administration of clarithromycin and these medicinal products is contraindicated (see section 4.3, Contraindications).

Effects of Other Medicinal Products on Clarithromycin

The following drugs are known or suspected to affect circulating concentrations of clarithromycin; clarithromycin dosage adjustment or consideration of alternative treatments may be required.

Efavirenz, nevirapine, rifampicin, rifabutin and rifapentine

Strong inducers of the cytochrome P450 metabolism system such as efavirenz, nevirapine, rifampicin, rifabutin, and rifapentine may accelerate the metabolism of clarithromycin and thus lower the plasma levels of clarithromycin, while increasing those of 14-(R)-hydroxy-cvlarithromycin (14-OH-clarithromycin), a metabolite that is also microbiologically active. Since the microbiological activities of clarithromycin and 14-OH-clarithromycin are different for different bacteria, the intended therapeutic effect could be impaired during concomitant administration of clarithromycin and enzyme inducers.

Fluconazole

Concomitant administration of fluconazole 200 mg daily and clarithromycin 500 mg twice daily to 21 healthy volunteers led to increases in the mean steady-state minimum clarithromycin concentration (Cmin) and area under the curve (AUC) of 33% and 18% respectively. Steady state concentrations of the active metabolite 14-OH-clarithromycin were not significantly affected by concomitant administration of fluconazole. No clarithromycin dose adjustment is necessary.

 

Ritonavir

A pharmacokinetic study demonstrated that the concomitant administration of ritonavir 200 mg every eight hours and clarithromycin 500 mg every 12 hours resulted in a marked inhibition of the metabolism of clarithromycin. The clarithromycin Cmax increased by 31%, Cmin increased 182% and AUC increased by 77% with concomitant administration of ritonavir. An essentially complete inhibition of the formation of 14-OH-clarithromycin was noted. Because of the large therapeutic window for clarithromycin, no dosage reduction should be necessary in patients with normal renal function. However, for patients with renal impairment, the following dosage adjustments should be considered: For patients with CL_CR 30 to 60 mL/min the dose of clarithromycin should be reduced by 50%. For patients with CL_CR <30 mL/min the dose of clarithromycin should be decreased by 75%. Doses of clarithromycin greater than 1 gm/day should not be coadministered with ritonavir.

 

Effect of Clarithromycin on Other Medicinal Products

 

Antiarrhythmics

There have been postmarketed reports of torsade de points occurring with the concurrent use of clarithromycin and quinidine or disopyramide. Electrocardiograms should be monitored for QTc prolongation during co-administration of clarithromycin with these drugs. Serum levels of these medications should be monitored during clarithromycin therapy.

 

CY3A4-based interactions

Co-administration of clarithromycin, known to inhibit CYP3A, and a drug primarily metabolized by CYP3A may be associated with elevations in drug concentrations that could increase or prolong both therapeutic and adverse effects of the concomitant drug. Clarithromycin should be used with caution in patients receiving treatment with other drugs known to be CYP3A enzyme substrates, especially if the CYP3A substrate has a narrow safety margin (e.g., carbamazepine) and/or the substrate is extensively metabolized by this enzyme. Dosage adjustments may be considered, and when possible, serum concentrations of drugs primarily metabolized by CYP3A should be monitored closely in patients concurrently receiving clarithromycin.

 

The following drugs or drug classes are known or suspected to be metabolized by the same CYP3A isozyme: alprazolam, astemizole, carbamazepine, cilostazol, cisapride, cyclosporine, disopyramide, ergot alkaloids, lovastatin, methylprednisolone, midazolam, omeprazole, oral anticoagulants (e.g. warfarin), pimozide, quinidine, rifabutin, sildenafil, simvastatin, tacrolimus, terfenadine, triazolam and vinblastine. Drugs interacting by similar mechanisms through other isozymes within the cytochrome P450 system include phenytoin, theophylline and valproate.

 

HMG-CoA Reductase Inhibitors

As with other macrolides, clarithromycin has been reported to increase concentrations of HMG-CoA reductase inhibitors (e.g., lovastatin and simvastatin). Rare reports of rhabdomyolysis have been reported in patients taking these drugs concomitantly.

 

Omeprazole

Clarithromycin (500 mg every 8 hours) was given in combination with omeprazole (40 mg daily) to healthy adult subjects. The steady-state plasma concentrations of omeprazole were increased (C_max, AUC_0-24, and t_1/2 increased by 30%, 89%, and 34%, respectively), by the concomitant administration of clarithromycin. The mean 24-hour gastric pH value was 5.2 when omeprazole was administered alone and 5.7 when omeprazole was co-administered with clarithromycin.

 

Oral anticoagulants

Spontaneous reports in the post-marketing period suggest that concomitant administration of clarithromycin and oral anticoagulants may potentiate the effects of the oral anticoagulants. Prothrombin times should be carefully monitored while patients are receiving clarithromycin and oral anticoagulants simultaneously.

 

Sildenafil, tadalafil and vardenafil

Each of these phosphodiesterase inhibitors is metabolized, at least in part, by CYP3A, and CYP3A may be inhibited by concomitantly administered clarithromycin. Co-administration of clarithromycin with sildenafil, tadalafil or vardenafil would likely result in increased phosphodiesterase inhibitor exposure. Reduction of sildenafil, tadalafil and vardenafil dosages should be considered when these drugs are co-administered with clarithromycin.

 

Theophylline, carbamazepine

       Results of clinical studies indicate that there was a modest but statistically significant (p≤ 0.05) increase of circulating theophylline or carbamazepine levels when either of these drugs were administered concomitantly with clarithromycin.

 

       Tolterodine

The primary route of metabolism for tolterodine is via the 2D6 isoform of cytochrome P450 (CYP2D6). However, in a subset of the population devoid of CYP2D6, the identified pathway of metabolism is via CYP3A. In this population subset, inhibition of CYP3A results in significantly higher serum concentrations of tolterodine. A reduction in tolterodine dosage may be necessary in the presence of CYP3A inhibitors, such as clarithromycin in the CYP2D6 poor metabolizer population.

 

Triazolobenzodiazepines (e.g., alprazolam, midazolam, triazolam)

When midazolam was co-administered with clarithromycin tablets (500 mg twice daily), midazolam AUC was increased 2.7-fold after intravenous administration of midazolam and 7-fold after oral administration. Concomitant administration of oral midazolam and clarithromycin should be avoided. If intravenous midazolam is co-administered with clarithromycin, the patient must be closely monitored to allow dose adjustment. The same precautions should also apply to other benzodiazepines that are metabolized by CYP3A, including triazolam and alprazolam. For benzodiazepines which are not dependent on CYP3A for their elimination (temazepam, nitrazepam, lorazepam), a clinically important interaction with clarithromycin is unlikely.

 

There have been post-marketing reports of drug interactions and central nervous system (CNS) effects (e.g., somnolence and confusion) with the concomitant use of clarithromycin and triazolam. Monitoring the patient for increased CNS pharmacological effects is suggested.

 

Other drug interactions

Colchicine

Colchicine is a substrate for both CYP3A and the efflux transporter, P-glycoprotein (Pgp). Clarithromycin and other macrolides are known to inhibit CYP3A and Pgp. When clarithromycin and colchicine are administered together, inhibition of Pgp and/or CYP3A by clarithromycin may lead to increased exposure to colchicine. Patients should be monitored for clinical symptoms of colchicine toxicity (see section 4.4 Warnings and Precautions).

 

Digoxin

Digoxin is thought to be a substrate for the efflux transporter, P-glycoprotein (Pgp). Clarithromycin is known to inhibit Pgp. When clarithromycin and digoxin are administered together, inhibition of Pgp by clarithromycin may lead to increased exposure to digoxin. Elevated digoxin serum concentrations in patients receiving clarithromycin and digoxin concomitantly have also been reported in post marketing surveillance. Some patients have shown clinical signs consistent with digoxin toxicity, including potentially fatal arrhythmias. Serum digoxin concentrations should be carefully monitored while patients are receiving digoxin and clarithromycin simultaneously.

 

Zidovudine

       Simultaneous oral administration of clarithromycin tablets and zidovudine to HIV-infected adult patients may result in decreased steady-state zidovudine concentrations. Because clarithromycin appears to interfere with the absorption of simultaneously administered oral zidovudine, this interaction can be largely avoided by staggering the doses of clarithromycin and zidovudine. This interaction does not appear to occur in paediatric HIV-infected patients taking clarithromycin suspension with zidovudine or dideoxyinosine.

 

       Bi-directional drug interactions

       Atazanavir

Both clarithromycin and atazanavir are substrates and inhibitors of CYP3A, and there is evidence of a bi-directional drug interaction. Co-administration of clarithromycin (500 mg twice daily) with atazanavir (400 mg once daily) resulted in a 2-fold increase in exposure to clarithromycin and a 70% decrease in exposure to 14-OH-clarithromycin, with a 28% increase in the AUC of atazanavir. Because of the large therapeutic window for clarithromycin, no dosage reduction should be necessary in patients with normal renal function. For patients with moderate renal function (creatinine clearance 30 to 60 mL/min), the dose of clarithromycin should be decreased by 50%. For patients with creatinine clearance <30 mL/min, the dose of clarithromycin should be decreased by 75% using an appropriate clarithromycin formulation. Doses of clarithromycin greater than 1000 mg per day should not be co-administered with protease inhibitors.

 

Itraconazole

Both clarithromycin and itraconazole are substrates and inhibitors of CYP3A, leading to a bidirectional drug interaction. Clarithromycin may increase the plasma levels of itraconazole, while itraconazole may increase the plasma levels of clarithromycin. Patients taking itraconazole and clarithromycin concomitantly should be monitored closely for signs or symptoms of increased or prolonged pharmacologic effect.

 

Saquinavir

            Both clarithromycin and saquinavir are substrates and inhibitors of CYP3A, and there is evidence of a bi-directional drug interaction. Concomitant administration of clarithromycin (500 mg bid) and saquinavir (soft gelatin capsules, 1200 mg tid) to 12 healthy volunteers resulted in steady-state AUC and C_max values of saquinavir which were 177% and 187% higher than those seen with saquinavir alone. Clarithromycin AUC and Cmax values were approximately 40% higher than those seen with clarithromycin alone. No dose adjustment is required when the two drugs are co-administered for a limited time at the doses/formulations studied. Observations from drug interaction studies using the soft gelatin capsule formulation may not be representative of the effects seen using the saquinavir hard gelatin capsule. Observations from drug interaction studies performed with saquinavir alone may not be representative of the effects seen with saquinavir/ritonavir therapy. When saquinavir is co-administered with ritonavir, consideration should be given to the potential effects of ritonavir on clarithromycin (see section 4.4 Warnings and Precautions). Observations from drug interaction studies performed with saquinavir alone may not be representative of the effects seen with the combination therapy of saquinavir and ritonavir, therefore when this combination therapy is co-administered with clarithromycin consideration should be given to the potential effects of ritonavir on clarithromycin (see Section 4.5-Ritonavir).

 

 

Verapamil

Hypotension, bradyarrhythmias and lactic acidosis have been observed in patients taking clarithromycin and verapamil concomitantly.

 

No clinically relevant studies addressing physical compatability of clarithromycin with other intravenous admixtures have been performed at this time.

4.8       Undesirable effects

 

Table 1 displays adverse events reported in patients administered clarithromycin I.V.during clinical studies as well as events seen with oral formulation. Adverse events are displayed by body system and frequency (common ≥ 1/100, < 1/10).

 

Table 1.

Adverse Events Reported in Clinical Studies

System Organ Class	Frequency	Adverse Events
Nervous system disorders	Common	headache taste perversion
Gastrointestinal disorders	Common	diarrhoea nausea abdominal pain dyspepsia vomiting
General disorders and administration site conditions*	Common	injection site inflammation tenderness phlebitis pain
Investigations	Common	hepatic enzyme increased

* specific to calrithromycin I.V.

 

Post Marketing Experience

 

Clarithromycin is marketed in several different formulations. Table 2 is a compilation of adverse reactions for all formulations including clarithromycin I.V. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Patient exposure is estimated to be greater than 1 billion patient treatment days for clarithromycin.

 

Table 2

Adverse Reactions from Post-Marketing Surveillance

 

System Organ Class	Adverse Reaction
Infections and infestations	oral candidiasis
Blood and lymphatic system disorders	leukopaenia thrombocytopaenia
Immune System disorders	anaphylactic reaction hypersensitivity
Metabolism and nutrition disorders1	hypoglycaemia
Psychiatric disorders	psychotic disorder hallucination
	disorientation
	confusional state
	depersonalization depression anxiety insomnia abnormal dreams
Nervous system disorders	Convulsion dizziness ageusia anosmia dysgeusia parosmia
Ear and labyrinth disorders	deafness vertigo tinnitus
Cardiac disorders2	torsade de pointes electrocardiogram QT prolonged ventricular tachycardia
Gastrointestinal disorders	pancreatitis acute glossitis stomatitis tongue discoloration tooth discoloration
Hepatobiliary disorders3	hepatic failure hepatitis hepatitis cholestatic jaundice cholestatic jaundice hepatocellular hepatic function abnormal
Skin and subcutaneous tissue disorders	Stevens-Johnson syndrome toxic epidermal necrolysis urticaria rash
Musculoskeletal and connective tissue disorders	myalgia
Renal and urinary disorders	nephritis interstitial
Investigations	blood creatinine increase hepatic enzyme increased
1 There have been rare reports of hypoglycaemia, some of which have occurred in patients on concomitant oral hypoglycaemic agents or insulin. 2 As with other macrolides, QT prolongation, ventricular tachycardia, and torsades de pointes have rarely been reported with clarithromycin. 3 In very rare instances, hepatic failure with fatal outcome has been reported and generally has been associated with serious underlying diseases and/or concomitant medications.

 

There have been post-marketing reports of colchicine toxicity with concomitant use of clarithromycin and colchicine, especially in the elderly, some of which occurred in patients with renal insufficiency. Deaths have been reported in some such patients (see sections 4.4 Warnings and Precautions and 4.5 Interaction with other medicinal products and other forms of interactions).

Adverse events in immunocompromised patients:  Although there are currently no data regarding use of clarithromycin I.V. in this patient population, data are available regarding the use of oral clarithromycin in HIV-infected patients.

 

In AIDS and other immunocompromised patients treated with the higher doses of clarithromycin over long periods of time for mycobacterial infections, it was often difficult to distinguish adverse events possibly associated with clarithromycin administration from underlying signs of HIV disease or intercurrent illness.  

 

In adult patients, the most frequently reported adverse events by patients treated with total daily doses of 1000 mg of clarithromycin were: nausea, vomiting, taste perversion, abdominal pain, diarrhoea, rash, flatulence, headache, constipation, hearing disturbance, SGOT and SGPT elevations.  Additional low-frequency events included dyspnoea, insomnia and dry mouth.  The incidences were comparable for patients treated with 1000mg and 2000mg, but were generally about 3 to 4 times as frequent for those patients who received total daily doses of 4000mg of clarithromycin.    

 

In these immuncompromised patients evaluations of laboratory values were made by analysing those values outside the seriously abnormal level (i.e. the extreme high or low limit) for the specified test.  On the basis of these criteria, about 2% to 3% of those patients who received 1000mg or 2000mg of clarithromycin daily had seriously abnormal elevated levels of SGOT and SGPT, and abnormally low white blood cell and platelet counts.  A lower percentage of patients in these two dosage groups also had elevated Blood Urea Nitrogen (BUN) levels.  Slightly higher incidences of abnormal values were noted for patients who received 4000mg daily for all parameters except WBC.

5.1       Pharmacodynamic properties

 

Clarithromycin is a semi-synthetic derivative of erythromycin A.  It exerts its antibacterial action by binding to the 50s ribosomal sub-unit of susceptible bacteria and suppresses protein synthesis.  Clarithromycin demonstrates excellent in vitro activity against standard strains of clinical isolates.  It is highly potent against a wide variety of aerobic and anaerobic gram positive and negative organisms.  The minimum inhibitory concentrations (MICs) of clarithromycin are generally two-fold lower than the MICs of erythromycin.

 

The 14-(R)-hydroxy metabolite of clarithromycin, formed in man by first pass metabolism also has anti-microbial activity.  The MICs of this metabolite are equal to or two-fold higher than the MICs of the parent compound except for H. influenzae where the 14-hydroxy metabolite is two-fold more active than the parent compound.

 

Klacid IV for Infusion is usually active against the following organisms in vitro. Please see below for table of MIC breakpoints.

 

Gram-positive Bacteria:  Staphylococcus aureus (methicillin susceptible); Streptococcus pyogenes (Group A beta-haemolytic streptococci); alpha-haemolytic streptococcus (viridans group); Streptococcus (Diplococcus) pneumoniae; Streptococcus agalactiae; Listeria monocytogenes.

 

Gram-negative Bacteria:  Haemophilus influenzae, Haemophilus parainfluenzae, Moraxella (Branhamella) catarrhalis, Neisseria gonorrhoeae; Legionella pneumophila, Bordetella pertussis, Helicobacter pylori; Campylobacter jejuni.

 

Mycoplasma:  Mycoplasma pneumoniae; Ureaplasma urealyticum.

 

Other Organisms:  Chlamydia trachomatis; Mycobacterium avium; Mycobacterium leprae; Chlamydia pneumoniae.

 

Anaerobes:  Macrolide-susceptible Bacteriodes fragilis; Clostridium perfringens; Peptococcus species; Peptostreptococcus species; Propionibacterium acnes.

 

Clarithromycin has bactericidal activity against several bacterial strains.  These organisms include H. influenzae, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Morazella (Brahamella) catarrhalis, Neisseria gonorrhoeae, Helicobacter pylori and Campylobacter spp.

 

The activity of clarithromycin against H. pylori is greater at neutral pH than at acid pH.

 

Breakpoints

The following breakpoints for clarithromycin, separating susceptible organisms from resistant organisms, have been established by the European Committee for Antimicrobial Susceptibility Testing (EUCAST).

Breakpoints (MIC, μg/ml)
Microorganism	Susceptible (£)	Resistant (>)
Streptococcus spp.	0.25 mg/ml	0.5 mg/ml
Staphylococcus spp.	1 mg/ml	2 mg/ml
Haemophilus spp.	1 mg/ml	32 mg/ml
Moraxella catarrhalis	0.25 mg/ml	0.5 mg/ml
Clarithromycin is used for the eradication of H. pylori; minimum inhibitory concentration (MIC) ≤ 0.25 mg/ml which has been established as the susceptible breakpoint by the Clinical and Laboratory Standards Institute (CLSI).