NexGard for Dogs Dosage Calculator and Safety Guide

NexGard – Monthly Flea + Tick Chew

NexGard (afoxolaner) is a flavored monthly chewable manufactured by Boehringer Ingelheim. It’s one of the most popular flea/tick preventives in the USA. Active ingredient is an isoxazoline-class insecticide/acaricide.

How NexGard Works

Fleas and ticks must bite the dog to be killed – drug is absorbed through bloodstream from the chew and circulates throughout. Onset:

• Fleas killed within 8 hours
• Ticks killed within 24-48 hours
• 35-day duration per chew

Kills:

• Adult fleas
• Brown dog tick (Rhipicephalus sanguineus)
• American dog tick (Dermacentor variabilis)
• Lone star tick (Amblyomma americanum)
• Black-legged tick (Ixodes scapularis) – Lyme vector
• Gulf Coast tick

Off-label uses:

• Sarcoptic mange (scabies) – often single curative dose
• Demodicosis (Demodex mites)

Questions This Calculator Answers

• “Which NexGard size do I buy?” – Weight-based size selection
• “Is NexGard safe?” – Yes with caveats – FDA isoxazoline warning for seizure-prone dogs
• “How often do I give NexGard?” – Monthly (every 30 days)
• “How fast does NexGard work?” – Fleas 8 hours; ticks 24-48 hours
• “Is NexGard safe for puppies?” – Approved 8+ weeks AND 4+ lb (1.8+ kg)
• “Can NexGard be given with heartworm meds?” – Yes; NexGard does NOT prevent heartworm
• “Does NexGard work for mange?” – Yes (off-label) – single curative dose for sarcoptes

Size Chart by Weight

⚠ FDA Isoxazoline Neurologic Warning

In 2018 (updated 2021), the FDA issued a warning about the isoxazoline class (NexGard, Bravecto, Simparica, Credelio) for potential neurologic adverse events:

• Muscle tremors
• Ataxia
• Seizures

Most dogs tolerate isoxazolines well, but use cautiously in dogs with:

• History of epilepsy
• Unexplained seizures
• Neurologic disease

Alternatives for seizure-history dogs:

• Topical Frontline Plus (fipronil + S-methoprene) + Seresto collar for ticks
• Advantage II (imidacloprid) – fleas only
• Capstar (nitenpyram) – oral, fleas only, 24-hour duration

Most dogs benefit > risk for flea/tick prevention.

Side Effects

MDR1 Breed Safety

NexGard is SAFE in MDR1-sensitive breeds (Collie, Australian Shepherd, Sheltie, Border Collie, Old English Sheepdog, Long-haired Whippet, German Shepherd, English Shepherd).

Unlike high-dose ivermectin, isoxazolines do not cross the blood-brain barrier significantly, so the MDR1 transporter defect doesn’t apply.

Contraindications

• ❌ Under 8 weeks of age
• ❌ Under 4 lb (1.8 kg)
• ⚠ Seizure history – use cautiously
• ⚠ Pregnant/lactating – safety not established
• ⚠ Liver disease – monitoring

Administration Tips

• Give monthly – same date each month
• Can give with or without food (food improves palatability)
• Chewable beef-flavored tablet – most dogs eat readily
• Verify swallowed
• If vomits within 2 hours – repeat dose
• If vomits after 2 hours – dose typically retained

NexGard Does NOT Prevent Heartworm

NexGard kills fleas and ticks only. Pair with monthly heartworm preventive:

• Heartgard Plus (ivermectin + pyrantel)
• Interceptor Plus (milbemycin + praziquantel)
• Sentinel Spectrum
• Trifexis

Or use combination products:

• NexGard Spectra – NexGard + milbemycin (heartworm) – same brand
• Simparica Trio – sarolaner + moxidectin (heartworm) + pyrantel

Cost

• Per chew: $18-45 USA
• Annual: $200-450
• Vet prescription required
• Compare prices: Chewy, Petco, 1-800-PetMeds, vet office

Conclusion

NexGard is an effective monthly flea/tick chew with broad species coverage and a generally good safety profile. FDA isoxazoline warning means seizure-prone dogs may need alternatives. MDR1-safe in herding breeds. Doesn’t cover heartworm – pair with heartworm preventive or use NexGard Spectra combination.

Frequently Asked Questions

Is NexGard safe for dogs?

GENERALLY YES with caveats. NexGard (afoxolaner) has FDA approval and millions of doses given. SIDE EFFECT PROFILE: mild and uncommon – vomiting ~4%, dry skin ~3%, diarrhea ~3%, lethargy ~1.5%. SERIOUS RARE: neurologic events (tremors, ataxia, seizures) – FDA WARNED 2018 + UPDATED 2021 about ISOXAZOLINE class (NexGard, Bravecto, Simparica, Credelio). USE CAUTIOUSLY if dog has: epilepsy/seizure history, unexplained collapse episodes, neurologic disease. ALTERNATIVES for seizure-prone dogs: Frontline Plus (fipronil topical) + Seresto collar; Advantage II (imidacloprid); Capstar (nitenpyram). MDR1 SAFE – unlike ivermectin, isoxazolines don’t cross blood-brain barrier so Collie/Aussie/Sheltie/herding breeds safe. APPROVED 8+ weeks AND 4+ lb (1.8 kg minimum weight). Most dogs benefit from flea/tick protection – real disease prevention (Lyme, ehrlichiosis, anaplasmosis, flea allergy) outweighs rare adverse effects. DISCUSS with vet if any neurologic concerns; topical alternatives often acceptable.

How fast does NexGard work?

FLEAS killed within 8 HOURS of administration. TICKS killed within 24-48 HOURS. Onset is fast because afoxolaner is absorbed rapidly into bloodstream after the chew is eaten. NEW INFESTATIONS – existing fleas die quickly but eggs in environment continue hatching for 1-3 months; results in apparent flea persistence even with good prevention; ENVIRONMENT TREATMENT (vacuuming, washing bedding hot, possibly area spray) speeds resolution. DURATION 35 DAYS – typically given monthly for continuous coverage. PROTECTION begins immediately with first dose; no loading dose needed. COMPARISON to topical: NexGard faster than topical Frontline Plus (which kills fleas within 12 hours, ticks within 48 hours); slightly faster than Simparica (3-8 hours fleas). FOR HEAVY INFESTATION – combine NexGard with environment treatment + treating ALL pets in household + considering Capstar (nitenpyram) as adjunct for rapid initial kill (24-hour duration).

Can NexGard cause seizures?

RARELY but documented. FDA issued WARNING in September 2018 (updated August 2021) about NEUROLOGIC ADVERSE EVENTS in ISOXAZOLINE class drugs (NexGard, Bravecto, Simparica, Credelio). REPORTED SIGNS: muscle tremors, ataxia (uncoordinated movement), seizures – typically within hours of dose, occasionally days. NEUROLOGIC adverse event RATE – difficult to determine exact frequency; estimated under 1% but underreporting likely. RISK FACTORS: dogs with EPILEPSY or seizure history are at HIGHER RISK; sometimes first seizure occurs at standard dose in previously healthy dog. WHAT TO DO if your dog has seizure post-NexGard: 1) CONTACT vet/emergency vet immediately; 2) REPORT to FDA via online portal; 3) DON’T RE-DOSE; 4) Switch to non-isoxazoline alternative. ALTERNATIVES: Topical FRONTLINE PLUS (fipronil) + SERESTO collar for ticks (long-lasting); ADVANTAGE II (imidacloprid) for fleas only. RISK-BENEFIT – majority of dogs tolerate isoxazolines well; flea/tick-borne diseases (Lyme, ehrlichiosis, Rocky Mountain Spotted Fever) cause SIGNIFICANT morbidity/mortality. DISCUSS with vet your dog’s specific risk factors. NOT all neurologic events are isoxazoline-related – underlying epilepsy may be coincidental; vet can help assess timing/causation.

Does NexGard treat sarcoptic mange?

YES – effective OFF-LABEL use, often SINGLE CURATIVE DOSE. SARCOPTIC MANGE (Sarcoptes scabiei) is itchy zoonotic mite infection. ISOXAZOLINES (NexGard afoxolaner, Bravecto fluralaner, Simparica sarolaner, Credelio lotilaner) revolutionized scabies treatment. PROTOCOL: 1) SINGLE DOSE at standard flea/tick dose; 2) MAY repeat in 30 days if needed; 3) Often CURATIVE with one dose; 4) RESOLUTION 1-2 weeks typically. ALSO works for DEMODICOSIS (Demodex canis – generalized adult demodex). ADVANTAGES over historical treatments: 1) No ivermectin (MDR1 breeds excluded historically); 2) ORAL not weekly lime sulfur dips; 3) Convenient single dose; 4) High efficacy. SARCOPTES TREATMENT MUST also include: 1) WASH BEDDING hot; 2) VACUUM thoroughly; 3) TREAT all in-contact dogs; 4) Wildlife exposure (foxes especially) source – may not always be eliminable; 5) Steroids may be needed for severe itch initially. STILL VET-PRESCRIBED – though widely available, sarcoptic mange diagnosis (skin scrape often negative due to mite location, sometimes empirical treatment), zoonotic risk to humans, and need for whole-household management mean vet involvement essential. ENORMOUS QUALITY OF LIFE improvement when scabies resolved – severely itchy dogs return to comfort within 1-2 weeks.

How much does NexGard cost?

USA pricing varies by size and source: 1) ORANGE (4-10 lb) USD 18-28 per chew; 2) BLUE (10.1-24 lb) USD 22-32 per chew; 3) PURPLE (24.1-60 lb) USD 25-38 per chew; 4) RED (60.1-121 lb) USD 30-45 per chew. PURCHASE OPTIONS: 1) VET OFFICE typically HIGHEST PRICE; 2) ONLINE PHARMACIES (Chewy, 1-800-PetMeds, Petco, Amazon Pharmacy) typically 20-40% cheaper; 3) BULK BUYING (6+ months) per-chew price drops; 4) GENERIC AFOXOLANER not available; 5) FRESHPET COUPONS/REBATES available on manufacturer site $20-30 rebate annually. ANNUAL COST: $200-500 depending on dog size + purchase channel. COMPARE TO ALTERNATIVES: 1) BRAVECTO ($60-90 every 3 months = $240-360/year); 2) SIMPARICA TRIO ($30-45/month combo with heartworm = $360-540/year but eliminates separate heartworm prevention cost); 3) FRONTLINE PLUS topical ($15-20/month = $180-240/year); 4) SERESTO COLLAR ($55-75 every 8 months = $80-115/year – cheaper but slower kill); 5) HEARTGARD ($75-110/6 months heartworm only). COMBO PRODUCT VALUE – if buying NexGard separately + heartworm prevention separately = $300-450 + $100-200 heartworm = $400-650/year; SIMPARICA TRIO combination = $360-540/year. RX REQUIREMENT – vet must approve before purchase; online pharmacies will request vet info; some vets do bundled annual visit + heartworm test + prevention prescription. ANNUAL HEARTWORM TEST required for most pharmacies/vets to renew prescription.

What’s the difference between NexGard and NexGard Spectra?

NEXGARD = afoxolaner ONLY (flea + tick coverage). NEXGARD SPECTRA = afoxolaner + MILBEMYCIN OXIME (flea + tick + heartworm + intestinal worms). NEXGARD: kills adult fleas, kills 5 tick species; monthly chew; does NOT prevent heartworm; does NOT treat intestinal worms (roundworm, hookworm, whipworm). NEXGARD SPECTRA: includes everything NexGard does PLUS HEARTWORM PREVENTION (milbemycin oxime kills heartworm larvae L3/L4 stages) PLUS INTESTINAL WORMS (roundworm Toxocara canis, hookworm Ancylostoma caninum, whipworm Trichuris vulpis). WHICH TO CHOOSE: 1) NEXGARD alone – if using SEPARATE heartworm prevention (Heartgard, Interceptor, Trifexis) and don’t need intestinal worm coverage; 2) NEXGARD SPECTRA – if want SINGLE MONTHLY PRODUCT covering flea + tick + heartworm + intestinal worms; 3) ALTERNATIVE COMBO: Simparica Trio (sarolaner + moxidectin + pyrantel) – same coverage as NexGard Spectra; brand preference. AVAILABILITY: NexGard Spectra is widely available in EU, UK, Australia, Canada; available in USA. PRICING: NexGard Spectra typically slightly more expensive than NexGard alone, but cheaper than buying NexGard + separate heartworm preventive. CONVENIENCE: single monthly chew vs multiple products. ANNUAL HEARTWORM TEST still required regardless. EFFICACY: equivalent flea/tick efficacy; milbemycin heartworm prevention well-established. MDR1 SAFETY: milbemycin at heartworm prevention doses is safe in MDR1 breeds (high-dose ivermectin different – DON’T confuse). SIDE EFFECTS same as NexGard plus possible mild GI from milbemycin. DECIDE based on overall prevention plan + your dog’s lifestyle (high tick exposure vs heartworm risk area).

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Related Articles & Guides

Read the in-depth PuppaDogs guides that explain the science and clinical context behind this calculator:

• Nexgard® for dogs: Benefits, Dosage, Side Effects, and More

References & Further Reading

The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.

1. Boehringer Ingelheim – NexGard product information.
2. FDA Center for Veterinary Medicine – Animal Drug Safety Communication: FDA Alerts Pet Owners and Veterinarians About Potential for Neurologic Adverse Events Associated with Certain Flea and Tick Products (2018, updated 2021).
3. Beugnet F et al. Efficacy of afoxolaner (NexGard) against fleas and ticks – field studies.
4. Letendre L et al. Pharmacokinetics of afoxolaner in dogs.
5. Beugnet F et al. Efficacy of afoxolaner in the treatment of sarcoptic mange. Parasites & Vectors 2016.
6. Becskei C et al. Efficacy of NexGard against demodicosis in dogs.
7. Mealey KL. MDR1 gene mutations in dogs – drugs of concern.
8. Plumb DC. Plumb’s Veterinary Drug Handbook – afoxolaner.
9. Companion Animal Parasite Council (CAPC) – flea and tick guidelines.
10. European Scientific Counsel Companion Animal Parasites (ESCCAP).
11. Maddison JE et al. Small Animal Clinical Pharmacology – antiparasitics chapter.
12. PuppaDogs. Heartworm Risk & Prevention Calculator, Mites/Demodex/Sarcoptes Workup Calculator, Tick-Borne Disease Pre-Test Calculator. puppadogs.com.

Suyash Dhoot