- Generic Name: penicillin g benzathine
- Dosage Forms: n.a.
- Other Brand Names: Bicillin L-A
What is Penicillin G Benzathine/Procaine/Potassium/Sodium?
Treatment of native vertebral osteomyelitis or prosthetic joint infections caused by susceptible β-hemolytic streptococci (penicillin G potassium or sodium).
Treatment of native vertebral osteomyelitis or prosthetic joint infections caused by susceptible Enterococcus (penicillin G potassium or sodium); used with or without an aminoglycoside.
Treatment of native vertebral osteomyelitis or prosthetic joint infections caused by susceptible Cutibacterium acnes (formerly Propionibacterium acnes) (penicillin G potassium or sodium).
Endocarditis
Treatment of native valve endocarditis or endocarditis involving prosthetic valve or other prosthetic material caused by certain susceptible gram-positive bacteria (penicillin G potassium or sodium).
Treatment of endocarditis caused by susceptible Streptococcus pyogenes (group A β-hemolytic streptococci; GAS), other β-hemolytic streptococci (including groups C, H, G, L, and M), or S. pneumoniae. AHA states IV penicillin G is a reasonable regimen for treatment of endocarditis caused by susceptible S. pyogenes, S. agalactiae (group B streptococci; GBS), groups C and G streptococci, and highly penicillin-susceptible S. pneumoniae (penicillin MIC ≤0.1 mcg/mL); consider concomitant use of gentamicin for endocarditis caused by streptococci groups B, C, or G.
Treatment of endocarditis caused by viridans group streptococci or nonenterococcal group D streptococci, including S. gallolyticus (formerly S. bovis). AHA states IV penicillin G (with or without gentamicin) is a regimen of choice for such infections caused by highly penicillin-susceptible strains (penicillin MIC ≤0.12 mcg/mL); use IV penicillin G in conjunction with gentamicin if strains are relatively resistant to penicillin G (penicillin MIC >0.12 mcg/mL but <0.5 mcg/mL).
Treatment of endocarditis caused by viridans group streptococci, Abiotrophia defectiva, or Granulicatella with penicillin MIC ≥0.5 mcg/mL. AHA states IV penicillin G in conjunction with gentamicin is a reasonable regimen for such infections.
Treatment of endocarditis caused by Enterococcus faecalis, E. faecium, or other enterococci susceptible to penicillin G and gentamicin. AHA states IV penicillin G in conjunction with gentamicin is a regimen of choice for such infections; streptomycin can be substituted for gentamicin if enterococci are susceptible to penicillin and streptomycin, but resistant to gentamicin.
Has been used for treatment of endocarditis caused by nonpenicillinase-producing staphylococci. AHA states that IV penicillin G may be considered for treatment of endocarditis caused by penicillin-susceptible S. aureus or coagulase-negative staphylococci in pediatric patients; penicillin G not included in current AHA recommendations for treatment of staphylococcal endocarditis in adults.
AHA recommends that treatment of endocarditis be managed in consultation with an infectious disease expert, especially when endocarditis is caused by S. pneumoniae, β-hemolytic streptococci, staphylococci, or enterococci.
Consult current guidelines from AHA for additional information on management of endocarditis.
Meningitis and Other CNS Infections
Treatment of meningitis caused by certain susceptible gram-positive or gram-negative bacteria (penicillin G potassium or sodium).
Treatment of meningitis caused by susceptible Listeria monocytogenes; used alone or in conjunction with an aminoglycoside.
Treatment of meningitis caused by susceptible Neisseria meningitidis. A drug of choice for penicillin-susceptible strains.
Treatment of meningitis caused by susceptible S. agalactiae (group B streptococci; GBS). Consider concomitant use of an aminoglycoside.
Treatment of meningitis caused by susceptible S. pyogenes or other β-hemolytic streptococci, including groups C, H, G, L and M.
Treatment of meningitis or ventriculitis caused by susceptible S. pneumoniae (penicillin MIC <0.1 mcg/mL). Consider that S. pneumoniae with intermediate resistance or complete resistance to penicillin G reported with increasing frequency.
Treatment of healthcare-associated ventriculitis and meningitis caused by susceptible Cutibacterium acnes (formerly Propionibacterium acnes) (penicillin G potassium or sodium).
Has been used for treatment of meningitis caused by susceptible nonpenicillinase-producing Staphylococcus (penicillin G potassium or sodium).
Pharyngitis and Tonsillitis
Treatment of pharyngitis and tonsillitis caused by S. pyogenes (group A β-hemolytic streptococci; GAS) and prevention of initial attacks (primary prevention) of rheumatic fever (penicillin G benzathine).
AAP, IDSA, and AHA recommend a penicillin regimen (i.e., 10 days of oral penicillin V or oral amoxicillin or single dose of IM penicillin G benzathine) as treatment of choice for S. pyogenes pharyngitis and tonsillitis; other anti-infectives (narrow-spectrum oral cephalosporins, oral macrolides, oral clindamycin) recommended as alternatives in penicillin-allergic patients.
If signs and symptoms of pharyngitis recur shortly after initial treatment and presence of S. pyogenes documented, retreatment with original or alternative anti-infective recommended. Alternative regimens recommended for retreatment include a narrow-spectrum oral cephalosporin, oral clindamycin, oral fixed combination of amoxicillin and clavulanate, oral macrolide, or IM penicillin G benzathine.
Consider that multiple, recurrent episodes of symptomatic pharyngitis within several months to years may indicate the patient is a long-term pharyngeal carrier of S. pyogenes experiencing repeated episodes of nonstreptococcal (e.g., viral) pharyngitis.
Treatment not usually recommended for asymptomatic chronic pharyngeal carriers of S. pyogenes. Eradication of the carrier state may be desirable in certain situations (e.g., community outbreak of acute rheumatic fever, acute poststreptococcal glomerulonephritis, or invasive S. pyogenes infections; outbreak of S. pyogenes pharyngitis in a closed or partially closed community; multiple episodes of documented symptomatic S. pyogenes pharyngitis occurring within a family for many weeks despite appropriate treatment; personal or family history of acute rheumatic fever). In such situations, recommended regimens include oral clindamycin, oral fixed combination of amoxicillin and clavulanate, or oral rifampin used in conjunction with either IM penicillin G benzathine or oral penicillin V.
Respiratory Tract Infections
Treatment of mild to moderate upper respiratory tract infections caused by susceptible S. pyogenes (group A β-hemolytic streptococci; GAS) (penicillin G benzathine).
Treatment of moderately severe to severe upper respiratory tract infections caused by susceptible S. pyogenes (penicillin G procaine, fixed combination of penicillin G benzathine and penicillin G procaine).
Treatment of serious respiratory tract infections (e.g., pneumonia, empyema) caused by susceptible S. pyogenes or other β-hemolytic streptococci (including groups C, H, G, L, and M) (penicillin G potassium or sodium).
Treatment of moderately severe respiratory tract infections (pneumonia) caused by susceptible S. pneumoniae (penicillin G procaine, fixed combination of penicillin G benzathine and penicillin G procaine).
Treatment of respiratory tract infections, including community-acquired pneumonia (CAP), caused by susceptible streptococci, including S. pneumoniae (penicillin G potassium or sodium). Consider that S. pneumoniae with resistance to penicillin G reported with increasing frequency. A drug of choice if CAP caused by penicillin-susceptible S. pneumoniae (MIC ≤2 mcg/mL). IDSA states parenteral penicillin G may be used for empiric treatment of CAP in infants or school-aged children fully immunized against invasive pneumococcal and Haemophilus influenzae type b (Hib) disease if local epidemiologic data for S. pneumoniae do not show substantial high-level penicillin resistance; other anti-infectives recommended for empiric treatment of CAP in adults and other infants and children.
Treatment of serious respiratory tract infections (e.g., pneumonia, empyema) caused by susceptible nonpenicillinase-producing staphylococci (penicillin G potassium or sodium).
Septicemia
Treatment of septicemia caused by susceptible S. pyogenes, other β-hemolytic streptococci (including groups C, H, G, L, and M), S. pneumoniae, or nonpenicillinase-producing staphylococci (penicillin G potassium or sodium).
Skin and Skin Structure Infections
Treatment of moderately severe to severe skin and skin structure infections caused by susceptible S. pyogenes (penicillin G procaine, fixed combination of penicillin G benzathine and penicillin G procaine).
Treatment of necrotizing infections of the skin, fascia, and muscle caused by susceptible S. pyogenes (penicillin G potassium or sodium). IDSA recommends IV penicillin G in conjunction with IV clindamycin for treatment of documented S. pyogenes necrotizing fasciitis.
Treatment of moderately severe to severe skin and skin structure infections caused by susceptible staphylococci (penicillin G procaine). Because of high incidence of resistant strains, perform in vitro culture and susceptibility testing when treating suspected staphylococcal infections.
Treatment of myonecrosis and gas gangrene caused by Clostridium perfringens or other clostridium (penicillin G potassium or sodium).
Actinomycosis
Treatment of actinomycosis (penicillin G potassium or sodium).
IV penicillin G is a drug of choice for all forms of actinomycosis, including respiratory (pulmonary, bronchial, laryngeal), abdominal, genitourinary, CNS, and cervicofacial infections.
Anthrax
Inhalational anthrax (postexposure) to reduce the incidence or progression of disease following suspected or confirmed exposure to aerosolized Bacillus anthracis spores (penicillin G procaine). Ciprofloxacin or doxycycline are initial drugs of choice for prophylaxis following suspected or confirmed exposure to aerosolized anthrax spores, including exposures that occur in the context of biologic warfare or bioterrorism. If penicillin susceptibility confirmed, consideration can be given to changing prophylaxis to a penicillin (oral amoxicillin or penicillin V) in infants and children, pregnant or lactating women, or when drugs of choice not tolerated or not available; oral amoxicillin may be preferred, especially in infants and children.
Treatment of mild, uncomplicated cutaneous anthrax caused by susceptible B. anthracis that occurs as the result of naturally occurring or endemic exposure to anthrax (penicillin G procaine). If cutaneous anthrax occurs in the context of biologic warfare or bioterrorism, initial drugs of choice are ciprofloxacin and doxycycline. If penicillin susceptibility confirmed, consideration can be given to changing to a penicillin (oral amoxicillin or penicillin V) in infants and children, pregnant or lactating women, or when drugs of choice not tolerated or not available; oral amoxicillin may be preferred, especially in infants and children.
Treatment of anthrax (inhalational, GI, or meningitis) caused by penicillin-susceptible B. anthracis that occurs as the result of natural or endemic exposures to anthrax (penicillin G potassium or sodium).
Alternative for use in multiple-drug parenteral regimens for initial treatment of systemic anthrax (inhalational, GI, meningitis, cutaneous anthrax with systemic involvement, lesions on the head or neck, or extensive edema) caused by penicillin-susceptible B. anthracis that occurs in the context of biologic warfare or bioterrorism (penicillin G potassium or sodium).
Clostridium Infections
Treatment of myonecrosis and gas gangrene caused by Clostridium perfringens or other clostridium (penicillin G potassium or sodium). IV penicillin G is a drug of choice; some experts recommend concomitant use of IV clindamycin. Anti-infectives are an adjunct to debridement and excision of the infected area.
Adjunct to tetanus immune globulin (TIG) in management of tetanus caused by C. tetani (penicillin G potassium or sodium). Anti-infectives cannot neutralize toxin already formed and cannot eradicate C. tetani spores, which may revert to toxin-producing vegetative forms. Role of anti-infectives in treatment of tetanus unclear; if anti-infective used for adjunctive treatment, metronidazole usually preferred.
Adjunct in management of botulism (penicillin G potassium or sodium). Botulism immune globulin IV (BIG-IV) is standard of care for infant botulism and anti-infectives not indicated unless clearly necessary for a concurrent infection. Botulism antitoxin (not commercially available in US, but may be available from CDC) is recommended treatment for other forms of botulism (e.g., foodborne and wound botulism) and for botulism that occurs in the context of biologic warfare or bioterrorism. Although role of anti-infectives in management of wound botulism unclear, penicillin G potassium or sodium has been used as adjunct to antitoxin and surgical debridement in wound botulism, including when antitoxin could not be administered.
Diphtheria
Adjunct to diphtheria antitoxin (not commercially available in US, but may be available from CDC) for treatment of diphtheria caused by Corynebacterium diphtheriae (penicillin G procaine, penicillin G potassium or sodium). Anti-infectives are not a substitute for diphtheria antitoxin. If a penicillin used for adjunctive treatment of diphtheria, CDC recommends IM penicillin G procaine. Patients usually no longer contagious 48 hours after initiation of anti-infective treatment. Confirm eradication of C. diphtheriae 24 hours after completion of treatment by 2 consecutive negative cultures taken 24 hours apart. Because diphtheria infection may not confer immunity, initiate or complete immunization with a preparation containing diphtheria toxoid adsorbed during convalescence.
Prevention of diphtheria in asymptomatic, household or close contacts of patients with respiratory or cutaneous diphtheria (penicillin G benzathine). If a penicillin used for prevention of diphtheria in contacts, CDC and AAP recommend IM penicillin G benzathine. Prompt initiation of prophylaxis indicated in all household or other close contacts of individuals with suspected or proven diphtheria, regardless of vaccination status of exposed individual. An immediate dose of age-appropriate preparation containing diphtheria toxoid adsorbed also indicated in contacts if inadequately immunized against diphtheria, immunization status unknown, or last booster dose received ≥5 years previously.
Elimination of diphtheria carrier state in identified carriers of toxigenic C. diphtheriae (penicillin G benzathine, penicillin G procaine). If a penicillin used to eliminate diphtheria carrier state, CDC and AAP recommend IM penicillin G benzathine. Obtain follow-up cultures ≥2 weeks after treatment of diphtheria carriers; if cultures positive, give a 10-day course of oral erythromycin and obtain additional follow-up cultures.
Erysipelothrix rhusiopathiae Infections
Treatment of erysipeloid caused by Erysipelothrix rhusiopathiae (penicillin G procaine).
Treatment of Erysipelothrix endocarditis (penicillin G potassium or sodium).
Fusobacterium Infections
Treatment of moderately severe infections of the oropharynx caused by Fusobacterium, including Vincent’s gingivitis and pharyngitis (penicillin G procaine).
Treatment of severe Fusobacterium infections of the oropharynx (including acute necrotizing ulcerative gingivitis [Vincent’s infection], trench mouth, Fusobacterium gingivitis or pharyngitis), lower respiratory tract, or genital area (penicillin G potassium or sodium). Not recommended for empiric treatment of such infections; although penicillin G may be effective against Fusobacterium, other organisms may also be involved (e.g., Bacteroides fragilis, Prevotella, Porphyromonas) that usually are resistant to the drug.
Leptospirosis
Treatment of severe leptospirosis (penicillin G potassium or sodium).
Leptospiral infections often result in asymptomatic or subclinical illness that is self-limited; however, severe, life-threatening infections can occur. Initiate anti-infective therapy as soon as possible after symptom onset; benefits of anti-infectives uncertain, especially if initiated in patients with late and/or severe disease.
Listeria Infections
Treatment of serious infections caused by susceptible L. monocytogenes (e.g., infections during pregnancy, granulomatosis infantiseptica, septicemia, meningitis, endocarditis, pneumonia) (penicillin G potassium or sodium). Ampicillin used alone or in conjunction with gentamicin or streptomycin generally considered treatment of choice for invasive infections caused by L. monocytogenes.
Lyme Disease
Treatment of early Lyme disease in patients with acute neurologic disease manifested as meningitis or radiculopathy (penicillin G potassium or sodium). Alternative to IV ceftriaxone.
Treatment of late Lyme disease in patients with recurrent Lyme arthritis and objective evidence of neurologic disease (penicillin G potassium or sodium). Alternative to IV ceftriaxone.
Treatment of late neurologic Lyme disease affecting central or peripheral nervous system (penicillin G potassium or sodium). Alternative to IV ceftriaxone.
Neisseria Infections
Treatment of serious infections caused by susceptible N. meningitidis (e.g., meningococcal sepsis, meningitis, pneumonia, arthritis) (penicillin G potassium or sodium). A drug of choice for most invasive meningococcal infections.
May not eliminate nasopharyngeal carriage of N. meningitidis. Chemoprophylaxis with ceftriaxone, ciprofloxacin, or rifampin usually recommended to eradicate nasopharyngeal carriage of N. meningitidis after treatment of invasive disease and prior to hospital discharge.
Do not use for treatment of gonorrhea. Was used in the past for infections caused by penicillin-susceptible N. gonorrhoeae (penicillin G potassium or sodium). Penicillins no longer recommended by CDC or others for gonococcal infections (high incidence of penicillinase-producing strains of N. gonorrhoeae).
Pasteurella Infections
Treatment of serious infections caused by Pasteurella multocida, including bacteremia and meningitis (penicillin G potassium or sodium). A drug of choice for local infections, septicemia, osteomyelitis, endocarditis, or other serious infections.
Rat-bite Fever
Treatment of rat-bite fever caused by susceptible Streptobacillus moniliformis (erythema arthriticum epidemicum, Haverhill fever) or Spirillum minus (sodoku) (penicillin G procaine, penicillin G potassium or sodium).
IV penicillin G usually drug of choice. Concomitant aminoglycoside (streptomycin or gentamicin) may be indicated for initial treatment of S. moniliformis endocarditis.
Syphilis
Treatment of syphilis (penicillin G benzathine, penicillin G procaine, penicillin G potassium or sodium).
CDC and other experts state IM penicillin G benzathine is drug of choice for treatment of primary syphilis (i.e., ulcer or chancre at infection site), secondary syphilis (i.e., manifestations that include, but are not limited to, rash, mucocutaneous lesions, and lymphadenopathy), and tertiary syphilis (i.e., cardiac syphilis, gummatous lesions, tabes dorsalis, and general paresis) in adults, adolescents, and children.
IM penicillin G benzathine also drug of choice for treatment of latent syphilis (i.e., detected by serologic testing but lacking clinical manifestations), including both early latent syphilis (latent syphilis acquired within the preceding year) and late latent syphilis (i.e., all other cases of latent syphilis or syphilis of unknown duration) in all age groups.
For treatment of neurosyphilis and otic or ocular syphilis, CDC and other experts state IV penicillin G potassium or sodium is drug of choice; IM penicillin G procaine (with oral probenecid) is an alternative if compliance can be ensured.
For treatment of congenital syphilis, CDC recommends IV penicillin G potassium or sodium or IM penicillin G procaine in neonates with proven or highly probable congenital syphilis (i.e., abnormal physical examination consistent with congenital syphilis, serum quantitative nontreponemal serologic titer fourfold higher than the mother's titer, or positive darkfield test or polymerase chain reaction [PCR] of lesions or body fluids). IV penicillin G potassium or sodium, IM penicillin G procaine, or IM penicillin G benzathine recommended in neonates with possible congenital syphilis (i.e., normal physical examination and serum quantitative nontreponemal serologic titer no more than fourfold higher than the mother's titer and the mother received a recommended treatment regimen less than 4 weeks before delivery; the mother was not treated or was inadequately treated, including treatment with erythromycin or any regimen not included in CDC recommendations; or there is no documentation that the mother received treatment).
CDC states that syphilis diagnosed in infants and children ≥1 month of age should be managed by a pediatric infectious disease specialist.
HIV-infected neonates with congenital syphilis and HIV-infected children, adolescents, and adults with neurosyphilis or any stage of syphilis: Use same treatment regimens recommended for those without HIV infection. Because serologic nonresponse and neurologic complications may be more frequent in HIV-infected individuals, close follow-up is essential in those coinfected with syphilis and HIV. In addition, careful neurologic examinations indicated in all coinfected patients.
Infant or child with congenital syphilis and known or suspected penicillin hypersensitivity: No proven alternatives to penicillin G; CDC recommends desensitization and treatment with appropriate penicillin G preparation.
Nonpregnant patient with primary, secondary, or latent syphilis and penicillin hypersensitivity: Can consider certain alternatives to penicillin G (e.g., doxycycline, tetracycline); if compliance with alternatives or follow-up cannot be ensured, CDC recommends desensitization and treatment with IM penicillin G benzathine.
Nonpregnant patient with neurosyphilis and penicillin hypersensitivity: No proven alternatives to penicillin G, but can consider ceftriaxone in certain circumstances; if compliance with alternatives or follow-up cannot be ensured, CDC recommends desensitization and treatment with appropriate penicillin G preparation.
Pregnant woman with any stage of syphilis and penicillin hypersensitivity: No proven alternatives to penicillin G; CDC recommends desensitization and treatment with appropriate penicillin G preparation.
Do not use a fixed combination of penicillin G benzathine and penicillin G procaine (Bicillin C-R, Bicillin C-R 900/300) for treatment of any form of syphilis; inadvertent use of a fixed combination may not provide the sustained serum concentrations of penicillin G required for syphilis treatment and could increase risk of treatment failure and neurosyphilis, especially in HIV-infected patients.
Whipple's Disease
Treatment of Whipple’s disease caused by Tropheryma whipplei.
Optimal regimens for treatment of Whipple’s disease not identified; relapses may occur, even after adequate and long-term anti-infective treatment. Some clinicians recommend an initial parenteral regimen (e.g., ceftriaxone, penicillin G with or without streptomycin) followed by a long-term regimen of oral co-trimoxazole.
Yaws, Pinta, and Bejel
Treatment of yaws (T. pertenue), pinta (T. carateum), and bejel (T. pallidum var. endemic syphilis) (penicillin G benzathine, penicillin G procaine). Drugs of choice.
Do not use fixed combinations of penicillin G benzathine and penicillin G procaine (Bicillin C-R, Bicillin C-R 900/300) for treatment of yaws, pinta, and bejel.
Prevention of Perinatal Group B Streptococcal Disease
Prevention of early-onset neonatal group B streptococcal (GBS) disease (penicillin G potassium or sodium).
Intrapartum anti-infective prophylaxis to prevent early-onset neonatal GBS disease is indicated in women identified as GBS carriers during routine prenatal GBS screening performed at 35–37 weeks of gestation during the current pregnancy, in women with GBS bacteriuria identified at any time during current pregnancy, and in those with a previous infant diagnosed with invasive GBS disease. In those with unknown GBS status at onset of labor, intrapartum anti-infective prophylaxis indicated in those with delivery at <37 weeks of gestation, amniotic membrane rupture for ≥18 hours, or intrapartum temperature of ≥38°C.
When intrapartum anti-infective prophylaxis indicated in the mother for prevention of GBS in the neonate, initiate at onset of labor or rupture of membranes. If cesarean delivery performed before onset of labor in a woman with intact amniotic membranes, anti-infective prophylaxis not usually indicated, regardless of GBS colonization status of the woman or gestational age.
IV penicillin G is drug of choice and IV ampicillin is preferred alternative. Penicillin G has a narrower spectrum of activity and is less likely to select for antibiotic-resistant organisms.
Regardless of whether the mother received anti-infective prophylaxis, initiate appropriate diagnostic evaluations and anti-infective therapy in the neonate if signs or symptoms of active infection develop.
Consult most recent CDC and AAP guidelines for additional information on prevention of perinatal GBS disease.
Prevention of Rheumatic Fever Recurrence
Prevention of recurrent attacks of rheumatic fever (secondary prophylaxis) in individuals who have had a previous attack of rheumatic fever (penicillin G benzathine).
IM penicillin G benzathine generally considered drug of choice for secondary prophylaxis of rheumatic fever because it ensures compliance; alternatives include oral penicillin V or oral sulfadiazine.
AHA and AAP recommend long-term (continuous) prophylaxis following treatment of documented acute rheumatic fever (even if manifested solely by Sydenham chorea) and in those with evidence of rheumatic heart disease (even after prosthetic valve replacement).
Initiate prophylaxis as soon as rheumatic fever or rheumatic heart disease diagnosed, although patients with acute rheumatic fever should first receive usually recommended anti-infective treatment for S. pyogenes (group A β-hemolytic streptococci; GAS) pharyngitis and tonsillitis.
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor 
Penicillin G Benzathine/Procaine/Potassium/Sodium - Zerlor